6 Mechanical Components
6.1
6.2
6.3
6.4
6.5
6.6
6.7
Crane Cab Inspection and Repair Guidelines
6.1.1
Introduction and Purpose
6.1.2
Frequency
6.1.3
Structural components
6.1.4
Fasteners
6.1.5
Open Cabs
6.1.6
Enclosed Cabs
Bumpers
6.2.1
Introduction
6.2.2
Frequency of Inspection & Maintenance
6.2.3
Visual External Checks
6.2.4
Corrosive Environments
6.2.5
Protective Bellows or Boots
6.2.6
Bumper Alignment
6.2.7
Bumper Failure
6.2.8
Compressed Gas Return Spring
6.2.9
Mechanical Return Spring
6.2.10 Typical Mounting Arrangements
6.2.11 Other Bumper Types
6.2.12 Other Considerations
Bearings
6.3.1
Introduction
6.3.2
Precautions for Proper Handling of Bearings
6.3.3
Bearing Cleaning
6.3.4
Mounting
6.3.5
Inspection and Evaluation of Bearings
6.3.6
Operational Stress
6.3.7
Maintenance
Crane Wheel Assembly Inspection and Repair Guidelines
6.4.1
Introduction and Purpose
6.4.2
Scope
6.4.3
Inspection
6.4.4
Tread Diameter Inspection
6.4.5
Flange Inspection
6.4.6
Weld Repair Comments and Risks
6.4.7
Axle Inspection
6.4.8
Related Hardware
Crane Rail Inspection and Corrective Action Guidelines
6.5.1
Introduction
6.5.2
Scope
6.5.3
Qualifications and Responsibilities of Inspectors
6.5.4
Crane Rail Inspection – Summary of OSHA Regulations
6.5.5
Rail Irregularities, Corrective Actions and Field Identification
6.5.6
References
Crane Rail Clips, Rail Pad, Splices
6.6.1
Introduction
6.6.2
Frequency of Inspection & Maintenance
6.6.3
General Condition of Rail Clips
6.6.4
Splice Joints
6.6.5
Rail Center
6.6.6
Rail on Concrete
Hook Inspections
6.7.1
Introduction
6.7.2
References Referenced documents for Hook Information in this section
6.7.3
Nomenclature
6.7.4
Inspection Methodology
6.7.5
Remedies and Repairs
6.7.6
Recommendations
6.7.7
Exclusions
6.8
Gearbox Inspection and Repair Guidelines
6.8.1
Purpose
6.8.2
Scope
6.8.3
Inspection while in Service
6.8.4
Inspection and Repair upon Removal from Service
6.8.5
Gearbox Upgrade Considerations
6.9
Worm and Worm Gear Replacement
6.9.1
Purpose of this Worm Gear Section
6.9.2
Overview
6.9.3
Worm Gearing Operating Under Normal Conditions
6.10 Wire Rope
6.10.1 Introduction
6.10.2 Working Load and Design Factor
6.10.3 Wire Rope Usage
6.10.4 Lubrication and Inspection
6.10.5 When Removed From Service
6.10.6 Potential Problems
6.10.7 A Wire Rope is a Machine
6.10.8 Wire Rope Inspection
6.10.9 Fittings
6.10.10 Removal Criteria - All removal criteria are based on the use of steel sheave
6.10.11 Maintenance
6.11 Sheave Wheel Inspection and Repair Guidelines
6.11.1 Introduction and Purpose
6.11.2 Scope
6.11.3 Inspection
6.11.4 Groove Inspection
6.11.5 Bore Inspection
6.11.6 Hub Face Inspection
6.11.7 Related Hardware
6.11.8 Reference Sources
6.12 Rope Drum Inspection and Repair Guidelines
6.12.1 Introduction and Purpose
6.12.2 Scope
6.12.3 Inspection
6.12.4 Groove Inspection
6.12.5 Gear Seat Inspection
6.12.6 Bearing Seat Inspection
6.12.7 Oil / Grease Seal Journal Inspection
6.12.8 Rope Clamps
6.12.9 Related Hardware
6.12.10 Reference Sources
6.13 Fabricated Spreader Beams
6.13.1 Purpose
6.13.2 Scope
6.13.3 Nomenclature for Spreader Beam
6.13.4 The Inspection of the Spreader Beam
6.13.5 Inspection Frequency
6.14 Lubrication Section
6.14.1 Purpose
6.14.2 Grease
6.14.3
6.14.4
6.14.5
6.14.6
6.14.7
Oils
Gearing in High Temperature Environments
Open Gearing
Crane Wheel Flanges
Wire Rope
6. Mechanical Components
6.1. Crane Cab Inspection and Repair Guidelines
6.1.1. Introduction and Purpose
6.1.1.1.
The cab is the most common place where human and machine interface. It is also one of
the most identifiable components for safety and operating efficiency. This purpose of this
section is to identify and correct items that have direct impact on the safety of the operator and
personnel in the environs of the crane as well as its functionality.
6.1.2. Frequency
6.1.2.1.
Crane Operator should inspect the cab prior to the start of his shift. Any irregularities or
concerns should be noted to the proper plant personnel.
6.1.2.2.
General Inspections should be quarterly or as necessary by a qualified inspector
6.1.3. Structural components
6.1.3.1.
Connections of the cab to the structure, access platforms, handrails and gates as well as
all items fastened to the cab.
6.1.3.2.
Structure
6.1.3.2.1.
Visually examine the cab supports on both the crane and cab side of the
connection. Note: special attention should be paid to any item affecting the integrity of the
connection. Most specifically – examine areas around welds, cut-outs, bends, corners and
fasteners. Additional areas of concern are intersections of the cab walls to the floor and roof
as well as the access platform, all handrails, gates and guarding.
6.1.3.2.2.
Common Failure Modes
6.1.3.2.2.1. Fatigue cracks emulating from drilled holes, cut-outs and heat affected metal
adjacent to welds.
6.1.3.2.2.2. Metal loss through corrosion.
6.1.3.2.2.3. Damaged, bent or distorted components resulting from collisions with other
objects (fixed or moving).
6.1.3.2.3.
Remedies and Repairs
6.1.3.2.3.1. Fatigue cracks.
6.1.3.2.3.1.1. Remove all dirt and paint around the crack with a sander and wire brush.
6.1.3.2.3.1.2. Thoroughly examine the affected area. If the area where the crack is
discovered is critical to the safety of the operator or personnel and machinery.
Additional NDT through dye penetrant, magnetic particle or ultra-sonic is
recommended.
6.1.3.2.3.1.3. Clean out and taper the crack walls with a grinder to permit full weld
penetration. Preheat repair and cool the welded crack in accordance with
recommended AWS D14.1 methods. Repaint.
6.1.3.2.3.2. Metal loss through corrosion.
6.1.3.2.3.2.1. Remove the corroded metal with a grinder. If the corrosion is extensive and
more than surface rust – it may be necessary to completely remove the affected
section along with a margin of solid base metal. Determine if the affected area is in
tension, compression or has significant contribution to the integrity of the structure. If
metal loss is more than surface rust, the metal loss must be considered and the
strength of remaining section must be calculated. If the affected area is critical to the
structural integrity of the cab, qualified personnel shall be consulted in establishing
the repair procedure. Replace and/or reinforce the affected section in accordance
with AWS D14.1 recommended procedures. Repaint.
6.1.3.2.3.3. Damaged, bent or distorted components
6.1.3.2.3.3.1. If damage is moderate and not in a critical area such as a slightly bent
hand, it may be acceptable to heat the affected area and bend it back into shape. If
the area is either extensive or in an area critical to structural integrity it should be
reviewed by a qualified person. Consideration may be given to reinforcing or
replacing damaged area or component. All heating and welding should be done in
accordance with AWS recommendations.
6.1.3.2.4.
Exclusions
6.1.3.2.4.1. It is never acceptable to simply patch a piece of metal over a fatigue crack,
corrosion or damaged area. Placement of a patch plate may be part of a solution but
should be only implemented after being considered by a qualified person.
6.1.4. Fasteners
6.1.4.1.
Visually examine all structural fasteners and holes on above, part of and below the cab
connection. Special attention should be paid to the bolt, nut and bolt holes.
6.1.4.2.
Common Failure Modes
6.1.4.2.1.
Bolts and nuts may loosen from vibration.
6.1.4.2.2.
Bolts and nuts may wear if the connection is active.
6.1.4.2.3.
Bolts may elongate or fail due to overstress, bending or a combination of factors.
6.1.4.2.4.
If bolts are elongated, broken or corroded bolt-holes should be examined and
measured for distortion.
6.1.4.2.5.
If bolts or nuts are loose, they should be removed if possible and the bolt-hole
inspected for distortion.
6.1.4.3.
Remedies and Repairs
6.1.4.3.1.
Loose bolts and nuts should be tightened with a torque wrench in accordance with
the original manufacturer’s specification or the appropriate values set forth in the American
Institute of Steel Construction, Research Council on Structural Connections, ASTM
specification.
6.1.4.3.2.
Elongated, corroded and broken bolts must be replaced immediately. In these
cases, bolt size and properties should be reviewed by a qualified person.
6.1.4.3.3.
Worn bolts and the associated holes should be reviewed. If bolts and the holes are
distorted, or worn two courses of action may be taken. The hole may be re-drilled enlarged
and a larger bolt inserted or a reinforcement plate added and drilled for the appropriate size
holes.
6.1.4.3.4.
If the bolt and the associated hole are corroded, the area should be assessed and a
plan to reinforce the area considered by a qualified person.
6.1.4.4.
Exclusions
6.1.4.4.1.
It is never acceptable to tighten distorted, worn corroded or bent fasteners.
Fasteners in these conditions may have lost significant strength and represent a hidden
potential for catastrophic failure.
6.1.5. Open cabs
6.1.5.1.
Railings, gates, hinges, latches and guarding should be in good working condition and
comply with applicable codes. If not, components should be replaced as necessary.
6.1.6. Enclosed cabs
6.1.6.1.
Door hinges and latches should be in good working condition and comply with applicable
codes. If not, components should be replaced as necessary.
6.1.6.2.
Windows
6.1.6.2.1.
If the cab glass is cracked, chipped or has reduced visibility, it shall be replaced with
glass appropriate to the operating environment
6.1.6.3.
Frame, hinges and tracks should be in good working condition. If not, components
should be replaced as necessary.
6.1.6.4.
Interior
6.1.6.4.1.
The Operator should ensure that the overhead light and switch are functioning
properly
6.1.6.4.2.
6.1.6.5.
Ventilation and Climate Control
6.1.6.5.1.
6.1.6.6.
Floor condition should be kept clean and in good condition by the operator.
Operator should ensure that the system is functioning properly.
Operator chair
6.1.6.6.1.
The operator should maintain the condition of the chair to ensure a safe,
comfortable operating environment.
6.1.6.6.2.
6.2. Bumpers
6.2.1. Introduction
If the chair does not function properly, the chair should be repaired or replaced.
6.2.1.1.
For the purposes of this discussion, the words “Buffer”, “Bumper” and “Shock Absorber”
are interchangeable to mean a device to absorb and/or dissipate the energy generated by a
crane or trolley impact with another object. That other object could be an end stop, another
crane, trolley, or some other device designed as part of a crane runway system. The definition
for bumpers, as applied by OSHA can be found cited in 29CFR1910.179(a)(23).
6.2.1.2.
OSHA requires bumpers on cranes and trolleys in most conditions, as cited in
29CFR1910.179(e)(2) and 29CFR1910.179(e)(3).
6.2.1.3.
The following information pertains primarily to hydraulic-type bumpers used on crane
bridges or trolleys. Other types of bumpers are discussed at the end of this section.
6.2.2. Frequency of Inspection & Maintenance
6.2.2.1.
The amount of attention that a hydraulic crane bridge or trolley bumper requires largely
depends upon the working conditions in which the bumper is operating. Regardless, the
bumper should be inspected along with the other crane components as part of the periodic
inspections required by OSHA. Inspection and maintenance of a crane bumper typically occur
at the same time. Because of dirty conditions in steel mills, the bumper should be swept or
brushed to remove collected contaminants, such as metal scale or mill dust prior to inspection to
allow for good visibility of the individual components. Wipe the plunger or cylinder area clean to
protect the bumper seals from damage due to material ingress during impact.
6.2.3. Visual External Checks
6.2.3.1.
The first external items that should be verified as present are the required safety cables
or chains, and the bumper impact heads. Safety cables should be intact and securely fastened
to the bumper, as they are required by OSHA to secure the bumper components from falling
from the crane in the event of a damaging impact. Bumper heads should be securely fastened
and free from major metal loss from impact. Mounting bolts or hardware should be present,
undamaged and tightly secured. Welds should be visually checked for evident cracks.
6.2.3.2.
The following Table 6.2.3 is a suggested matrix for bumper visual inspection:
CHECK
(a) Extension of the plunger when free
compared to design dimension.
ACTION (if faulty)
Proceed with service/maintenance or remove
bumper for attention.
(b) Mounting brackets for cracks.
Repair or replace the bumper.
(c) Mounting bolts for tightness.
Retighten or replace bolts.
(d) If applicable, Bumper head fastening for
integrity.
Retighten or replace head bolts.
(e) Safety Cable/Chain for presence and
secure attachment.
(f) Check bellows or protective boot for rips or
holes in the material.
(g) Check for oil leaks beneath bumper.
Repair attachment or replace.
Replace bellows or boot.
Remove bumper for service/maintenance.
Table 6.2.3 – Bumper Visual Inspection Matrix
6.2.4. Corrosive Environments
6.2.4.1.
Where bumpers are operating in corrosive environments, such as pickle lines or outdoor
dockside installations, airborne corrosive particles in the atmosphere can be deposited on the
bumper and in time cause corrosion of the plunger or cylinder. In such environments it is
recommended that particular care be taken in the inspection and maintenance of the plungers
or cylinders. This moving part of the bumper should be frequently cleaned to remove any
corrosive or abrasive deposits, and then coated with a film of mineral oil or another corrosive
inhibitor.
6.2.5. Protective Bellows or Boots
6.2.5.1.
In some environments it is likely that a type of bellows or boot has been fitted to protect
the plunger from accumulated debris. These protective covers should be removed at regular
service intervals and the plunger wiped clean as above to prevent contaminants from being
collected and drawn into the bumper. The boot or bellows material should be checked for
damage and replaced, if needed. Particulates that have collected in the bellows should be
dumped or blown out.
6.2.6. Bumper Alignment
6.2.6.1.
The bumper should also be inspected for alignment with its opposing striking surface, be
that another bumper, end stop or end truck, etc. The support structures and mounting hardware
should also be visually checked for cracks, corrosion or other forms of damage. Any
deficiencies should be noted on the inspection record for repair or replacement by a qualified
maintenance person.
6.2.7. Bumper Failure
6.2.7.1.
Outside of obvious mechanical damage, the two primary reasons for bumper failure are
oil leaking from the bumper due to internal seal wear or degradation, or the failure of the internal
return spring, often either a mechanical coil spring or gas under pressure. Many bumpers can
be rebuilt by the original manufacturer, and sometimes all that is needed is seal replacement
and the re-filling of the oil and pressurized gas. Prior to disassembly of the bumper, the original
manufacturer of the bumper should be consulted. A hydraulic bumper should be disassemblied
by qualified personnel only. Hydraulic bumpers contain internal energy sources such as
pressurized fluids or compressed springs which must be properly handled during disassembly.
6.2.7.2.
Bumpers are designed and installed in pairs. If a bumper requires replacement, it
should be matched with its pair (i.e. replaced in kind). If a bumper has failed in service and
replaced, its pair and the surrounding structure of the crane and runway area should be
inspected prior to the crane returning to service.
6.2.8. Compressed Gas Return Spring
6.2.8.1.
Referring to Figure 6.2.8, if the bumper is leaking either oil or gas, it generally means
that the seals have worn out and should be replaced by removing the bumper and rebuilding it
in a qualified shop, including changing the seals. Because the return spring is compressed air
or gas, any failure of the bumper should be visually noticeable because the plunger will not
return to the ready position (full projection, see Figure 6.2.10.1 or 6.2.10.2) after the impacting
force is removed.
6.2.8.2.
A thorough internal inspection should also be completed while the bumper is
disassembled to determine if any other components have failed. The bumper should then be
refilled with fluid and the gas spring should be recharged according to the manufacturer’s
specifications.
Figure 6.2.8
6.2.9. Mechanical Return Spring
6.2.9.1.
Referring to Figure 6.2.9, if the bumper has a mechanical return spring, the spring itself
is typically not visible without disassembling the bumper. This can be deceptive because, even
though all of the fluid may have leaked out, the internal coil spring can often reset the bumper
plunger or cartridge once the impacting force is removed. This may give the false impression
that the bumper is functioning properly. An “operational check” of a mechanical spring-return
bumper must be performed. The test impact should be performed while the bumper is installed
on the crane (or runway), and should be done by running the crane or trolley at the slowest
possible speed, in case the bumper is not fully operational. A hard stop without a change in the
deceleration rate after bumper impact would indicate bumper failure. (Typically, the crane
operator is aware of a bumper failure first because the stop at the end of travel is more abrupt
than when the bumpers are functioning properly.)
6.2.9.2.
If the bumper is not operational, it should be removed and submitted to an inspection. If
there is any damage to the mechanical return spring, the spring should be replaced or the
bumper discarded.
Figure 6.2.9
1. Seals
2. Piston Rod
3. Fluid Orifice
4. Not used
5. Cylinder
6. Fluid Reservoir
7. Coil Return Spring
6.2.10.
Typical Mounting Arrangements
Figure 6.2.10.1
Figure 6.2.10.2
6.2.11.
Other Bumper Types
6.2.11.1.
Rubber or Polymer Bumpers – solid, polymer bumpers should be replaced if any sort of
damage is found during inspection. These types of bumpers should not be repaired, but should
be replaced in kind.
6.2.11.2.
Wooden Bumpers – Wooden bumpers should be replaced with a bumper that meets the
current standard according to AIST Technical Report No. 6.
6.2.11.3.
Spring Bumpers – Spring type bumpers should be inspected for a broken coil spring or
damaged plunger. A damaged spring bumper should be replaced by an energy-absorbing
bumper according to AIST Technical Report No. 6.
6.2.12.
Other Considerations
6.2.12.1.
Bumpers mounted on end stops should be inspected as part of the crane and not part of
the mill building structure. Even though they may not be mounted to the crane, they are still
subject to the periodic inspections called out by OSHA.
6.3. Bearings
6.3.1. Introduction
6.3.1.1.
Bearings are found in many places on overhead traveling cranes, such as gear boxes,
motors, bottom blocks, pinion shafts, cross shafts and wheel assemblies. Crane bearings are
always heavy duty to stand up to the rigors of lifting heavy loads in mill environments. There
are several categories of bearings, described by function including axial, radial and thrust
bearings. Also there are different types of bearings, usually named for their type of construction
such as ball, cylindrical, needle, tapered and spherical. Plain bearings and split bearings are
also found on older cranes.
6.3.1.2.
For complete information on Bearings and Bearing Practices including detailed images
of bearing failures, refer to the AIST Lubrication Engineers Manual 4th Edition, Section 6 Bearing
Practices.
6.3.1.3.
Examples of reasons why bearings fail:
20%
Unsuitable Lubricant
20%
Solid Contamination
20%
Aged Lubricant
15%
Insufficient Lubricant
10%
Unsuitable Choice of Bearing (design, size, load-carrying capacity)
5%
Consequential Damage
5%
Mounting Faults
5%
Liquid Contamination
<1%
Material and Production Faults
6.3.2. Precautions for Proper Handling of Bearings
6.3.2.1.
Rolling bearings are high precision machine parts and must be handled carefully.
Performance will be affected if they are not handled properly. Precautions to be observed are
as follows:
6.3.2.1.1.
Keep Bearings and Surrounding Area Clean
6.3.2.1.1.1. Dust and dirt, even if invisible to the naked eye, can have harmful effects on
bearings. It is necessary to prevent the entry of dust and dirt by keeping the bearings
and their environment as clean as possible.
6.3.2.1.2.
Careful Handling
6.3.2.1.2.1. Heavy shocks during handling may cause bearings to be scratched or
otherwise damaged possibly resulting in their failure. Excessively strong impacts may
cause brinelling, breaking, or cracking.
6.3.2.1.3.
Use Proper Tools
6.3.2.1.3.1. Always use the proper equipment when handling bearings and avoid general
purpose tools.
6.3.2.1.4.
Prevent Corrosion
6.3.2.1.4.1. Since perspiration on the hands and various other contaminants may cause
corrosion, keep the hands clean when handling bearings. Wear gloves if possible. Pay
attention to rust caused by corrosive gasses.
6.3.3. Bearing Cleaning
6.3.3.1.
When bearings are inspected, appearance should first be recorded and the amount and
condition of the residual lubricant should be checked. After the lubricant has been sampled for
examination, the bearings should be cleaned. In general, light oil or kerosene may be used as a
cleaning solution.
6.3.3.2.
Dismounted bearings should first be given a preliminary cleaning followed by a finishing
rinse. Each bath should have a metal net or rack to support the bearings in the oil without them
touching the sides or bottom of the tank. If the bearings are rotated with foreign matter in them
during preliminary cleaning, the raceways may be damaged. The lubricant and other deposits
should be removed in the oil bath during the initial rough cleaning with a brush or other means.
6.3.3.3.
After the bearing is relatively clean, it is given the finishing rinse. The finishing rinse
should be done carefully with the bearing being rotated while immersed in the rinsing oil. It is
necessary to always keep the rinsing oil clean.
6.3.4. Mounting
6.3.4.1.
It is critical in the mounting and installation process to pay strict attention to the following:
6.3.4.1.1.
Use of proper tools and ovens/induction heaters. Use a sleeve to impact the entire
inner ring face of the ring being press fit. Verify the shaft and housing tolerances. If the fit is
too tight you will create too much preload, and if the fit is too loose, you will create too little
preload, which may allow the shaft to rotate or creep in the bearing. Check for proper
diameters, roundness, and chamfer radius.
6.3.4.1.2.
Avoid misalignment or shaft deflection. This is especially critical in mounting
bearings that have separable components such as cylindrical roller bearings where
successful load bearing and optimal life are established or diminished at installation.
Figure 6.3.4.1
6.3.4.1.3.
Be aware of “radial internal clearance” (Figure 6.3.4.1): It is critical to maintain the
proper R.I.C that was established in the original design. The standard scale in order of
ascending clearance is C2, C0, C3, C4, C5. The proper clearance for the application is
critical in that it allows for the challenges of:
6.3.4.1.3.1. Lubrication: A proper film of lubricant must be established between the rolling
elements. Reducing internal clearance and impeding lubricant flow can lead to
premature failure
6.3.4.1.3.2. Shaft fit: A reduction in the radial internal clearance is inevitable when the
bearing is press fit.
6.3.4.1.3.3. Heat: In normal bearing operation, heat is produced that creates thermal
expansion of the inner and outer rings. This can reduce the internal clearance, which will
reduce the optimal bearing life.
6.3.4.1.4.
The method of mounting rolling bearings strongly affects their accuracy, life, and
performance, so their mounting deserves careful attention. It is recommended that the
handling procedures for bearings be done with respect to the following items:
•
Cleaning the bearings and related parts.
•
Checking the dimensions and finish of related parts.
•
Mounting
•
Inspection after mounting.
•
Supply of lubricants.
6.3.4.1.5.
New bearings should not be unpacked until just prior to mounting. When using
ordinary grease lubrication, the grease should be packed in the bearings without first
cleaning them. Even in the case of ordinary oil lubrication, cleaning the bearings is not
required. However, bearings for instruments or for high speed operation must first be
cleaned with clean filtered oil in order to remove the anti-corrosion agent.
6.3.4.1.6.
After the bearings are cleaned with filtered oil, they should be protected to prevent
corrosion. Pre-lubricated bearings must be used without cleaning. Bearing mounting
methods depend on the bearing and type of fit. As bearings are usually used on rotating
shafts, the inner rings require a tight fit. Bearings with cylindrical bores are usually mounted
by pressing them on the shafts (press fit) or heating them to expand their diameter (shrink
fit). Bearings with tapered bores can be mounted directly on tapered shafts or cylindrical
shafts using tapered sleeves.
6.3.4.1.7.
Besides heating in oil, bearing heaters, which use electromagnetic induction to heat
bearings, are widely used to shrink fit bearings. These heaters use electricity (AC) in a coil
to produce a magnetic field that induces a current inside the bearing that generates heat.
Consequently, without using flames or oil uniform heating in a short time is possible, making
bearing shrink fitting more efficient and cleaner.
6.3.4.1.8.
Bearings are usually mounted in housings with a loose fit. However, in cases where
the outer ring has an interference fit, a press may be used. Bearings can be interferencefitted by cooling them before mounting using dry ice. In this case, a rust preventive
treatment must be applied to the bearing because moisture in the air condenses on its
surface.
6.3.5. Inspection and Evaluation of Bearings
6.3.5.1.
After being thoroughly cleaned, bearings should be examined for the condition of their
raceways and external surfaces, the amount of cage wear, the increase in internal clearance,
and degradation of tolerances. These should be carefully checked, in addition to examination for
possible damage or other abnormalities, in order to determine the possibility for its reuse.
6.3.5.2.
In the case of small non-separable ball bearings, hold the bearing horizontally in one
hand, and then rotate the outer ring to confirm that it turns smoothly.
Separable bearings such as tapered roller bearings may be checked by individually examining
their rolling elements and the outer ring raceway.
6.3.5.3.
Large bearings cannot be rotated manually; however, the rolling elements, raceway
surfaces, cages, and contact surface of the ribs should be carefully examined visually. The
more important a bearing is, the more carefully it should be inspected.
6.3.5.4.
The determination to reuse a bearing should be made only after considering the degree
of bearing wear, the function of the machine, the importance of the bearings in the machine,
operating conditions, and the time until the next inspection. However, if any of the following
defects exist, reuse is impossible and replacement is necessary:
6.3.5.4.1.
Cracks in the inner or outer rings, rolling elements, or cage.
6.3.5.4.2.
Flaking of the raceway or rolling elements, significant smearing of the raceway
surfaces, ribs, or rolling elements.
6.3.5.4.3.
Cage is significantly worn or rivets are loose.
6.3.5.4.4.
Rust or scoring on the raceway surfaces or rolling elements.
6.3.5.4.5.
Significant impact or Brinell traces on the raceway surfaces or rolling elements.
6.3.5.4.6.
Significant evidence of creep on the bore or the periphery of the outer ring.
6.3.5.4.7.
Discoloration by heat is evident.
6.3.5.4.8.
Significant damage to the seals or shields of grease sealed bearings has occurred.
6.3.6. Operational Stress
Sound
Other Indicators
Causes
Hiss
Small Bearings
Raceway, ball or roller surfaces
are rough
Buzz to Roar
Loudness and pitch change with speed
Resonation
Poor Fit
Bearing rings deformed
Vibration of raceways, ball or
rollers Dust/Contamination
Crunch
Felt when bearing is rotated by hand
Scoring of raceways surfaces
Scoring of ball or rollers
Dust/Contamination
Hum
Disappears when power supply is shut
Electromagnetic sound of motor
off
Clatter
Screech/Howl
Noticable at low speeds, continuous at
Bumping in cage pockets due to
high speeds
insufficient lubricant
Occurs mainly on Cylindrical Roller
Large radial clearance. Poor
bearings
lubrication
Sound changes with speed. Goes away
temporarily with lubrication
Squeak
Metal to Metal spalling sound. High pitch
Small clearance
Squeal
Generated irregularly due to grating
Slipping of fitting surfaces
Rustle
Sound quality remains the same even if
Dirt on raceways, ball or rollers
speed changes
surfaces are rough
Continuous at high speeds
Scoring on raceway, balls or
Growl
rollers
Quiet Fizzing or
Generated irregularly on small bearings
popping
Large sound pressure
Bursting sound of bubbles in
grease
Large sound pressure
Rough raceway, roller or ball
surfaces
Raceways, rollers or ball
deformed by wear
Large internal clearance due to
wear
Table 6.3.6 Bearing Failure Modes
6.3.7. Maintenance
6.3.7.1.
Detecting and Correcting Irregularities
6.3.7.1.1.
In order to maintain the original performance of a bearing for as long as possible,
proper maintenance and inspection should be performed. If proper procedures are used,
many bearing problems can be avoided and the reliability, productivity, and operating costs
of the equipment containing the bearings are all improved. It is suggested that periodic
maintenance be done following the procedure specified. This periodic maintenance
encompasses the supervision of operating conditions, the supply or replacement of
lubricants, and regular periodic inspection. Items that should be regularly checked during
operation include bearing noise, vibration, temperature, and lubrication.
6.3.7.1.2.
If an irregularity is found during operation, the cause should be determined and the
proper corrective actions should be taken after referring to Table 6.3.6.
6.3.7.1.3.
If necessary, the bearing should be dismounted and examined in detail. As for the
procedure for dismounting and inspection, refer to Section, Inspection of Bearings.
6.3.7.2.
Bearing Failures and Countermeasures
6.3.7.2.1.
In general, if rolling bearings are used correctly they will survive to their predicted
fatigue life. However, they often fail prematurely due to avoidable mistakes. In contrast to
fatigue life, this premature failure is caused by improper mounting, handling, or lubrication,
entry of foreign matter, or abnormal heat generation.
6.3.7.2.2.
For instance, the causes of rib scoring, as one example of premature failure, may
include insufficient lubrication, use of improper lubricant, faulty lubrication system, entry of
foreign matter, bearing mounting error, excessive deflection of the shaft, or any combination
of these. Thus, it is difficult to determine the real cause of some premature failures.
6.3.7.2.3.
If all the conditions at the time of failure and previous to the time of failure are
known, including the application, the operating conditions, and environment; then by
studying the nature of the failure and its probable causes, the possibility of similar future
failures can be reduced. The most frequent types of bearing failure, along with their causes
and corrective actions, are listed in Table 6.3.7.
Table 6.3.7 - Causes and Countermeasure for Bearing Failures
Type of Failure
Probable Causes
Countermeasure
A loose fit should be used when
Flaking of one-side of the
raceway of radial bearing.
Abnormal axial load.
mounting the outer ring of freeend bearings to allow axial
expansion of the shaft.
Flaking of the raceway in
Out-of-roundness of the
symmetrical pattern.
housing bore.
Correct the faulty housing.
Flaking pattern inclined
relative to the raceway in
radial ball bearings. Flaking
near the edge of the raceway
Flaking
and rolling surfaces in roller
Improper mounting, deflection
of shaft, inadequate tolerances
for shaft and housing.
Use care in mounting and
centering, select a bearing with
a large clearance, and correct
the shaft and housing shoulder.
bearings.
Large shock load during
Use care in mounting and apply
Flaking of raceway with same mounting, rusting while bearing is a rust preventive when machine
spacing as rolling elements.
Premature flaking of raceway
and rolling elements.
Premature flaking of duplex
bearings.
Scoring
Scoring or smearing between
raceway and rolling surfaces.
out of operation for
operation is suspended for a
prolonged period.
long time.
Insufficient clearance, excessive
load, improper lubrication, rust,
etc.
Excessive preload.
Inadequate initial lubrication,
excessively hard grease and high
acceleration when starting.
6.4. Crane Wheel Assembly Inspection and Repair Guidelines
6.4.1. Introduction and Purpose
Select proper fit, bearing
clearance, and lubricant.
Adjust the preload.
Use a softer grease and avoid
rapid acceleration.
Spiral scoring or smearing of
raceway surface of thrust ball
bearing.
Scoring or smearing between
the end face of the rollers
and guide rib.
Raceway rings are not parallel
and excessive speed.
mounting and large axial load.
modify the mounting.
surface cylindricality, improper
sleeve taper, large fillet radius,
development of thermal cracks
and advancement of flaking.
Crack in rolling element.
Broken rib.
Fractured cage.
Indentations in raceway in
same pattern as rolling
elements.
bearing type.
Select proper lubricant and
interference in fitting, poor
Cracks
preload, or select another
Inadequate lubrication, incorrect
Excessive shock load, excessive
Crack in outer or inner ring.
Correct the mounting, apply a
Advancement of flaking, shock
applied to the rib during mounting
or dropped during handling.
Examine the loading conditions,
modify the fit of bearing and
sleeve. The fillet radius must be
smaller than the bearing
chamfer.
Be careful in handling and
mounting.
Abnormal loading of cage due
Reduce the mounting error and
to incorrect mounting and
review the lubricating method
improper lubrication.
and lubricant.
Shock load during mounting or
excessive load when not rotating.
Use care in handling.
Indentations
Indentations in raceway and Foreign matter such as metallic Clean the housing, improve the
rolling elements.
Abnormal
Wear
False brinelling
(phenomenon similar to
brinelling)
chips or sand.
Vibration of the bearing without
rotation during shipment or
rocking motion of small
amplitude.
seals, and use a clean lubricant.
Secure the shaft and housing,
use oil as a lubricant and reduce
vibration by applying a preload.
Fretting
Slight wear of the fitting surface.
Wearing of raceway, rolling
Penetration by foreign matter,
elements, rib, and cage.
incorrect lubrication, and rust.
Creep
Increase interference and apply
oil.
Improve the seals, clean the
housing, and use a clean
lubricant.
Insufficient interference or
Modify the fit or tighten the
insufficient tightening of sleeve.
sleeve
Review the internal clearance
Discoloration and melting of
Seizure
raceway, rolling elements,
and ribs.
and bearing fit, supply an
Insufficient clearance, incorrect
adequate amount of the proper
lubrication, or improper mounting.
lubricant and improve the
mounting method and related
parts.
Install a ground wire to stop the
Electric
Fluting or corrugations.
Burning
Melting due to electric arcing.
flow of electricity or insulate the
beaning.
Use care in storing and avoid
Corrosion
&
Rust
Condensation of water from
Rust and corrosion of fitting
the air, or fretting. Penetration
surfaces and bearing interior.
by corrosive substance
(especially varnish-gas, etc).
high temperature and high
humidity, treatment for rust
prevention is necessary when
operation is stopped for long
time. Selection of varnish and
grease.
6.4.1.1.
The purpose of this chapter is to provide guidelines for the inspection, repair, and
servicing of Crane Wheels and Crane Wheel Assemblies in overhead cranes.
6.4.2. Scope
6.4.2.1.
This chapter applies to Crane Wheels and Crane Wheel Assemblies in overhead cranes
for steel mill service.
6.4.3. Inspection
6.4.3.1.
Inspection of the crane wheel primarily relates to the tread diameter, tread condition, and
the condition of the flanges. Inspection includes both dimensional and nondestructive testing.
6.4.4. Tread Diameter Inspection
6.4.4.1.
A visual inspection should be conducted while the wheel is installed on the crane.
6.4.4.2.
If significant tread grooving is observed, the wheel should be replaced.
6.4.4.3.
If any amount of spalling is observed, the wheel should be replaced.
6.4.4.4.
If displaced metal from flange wear is present on the tread diameter, the wheel should
be replaced.
6.4.4.5.
If a flat spot is found on the tread diameter, the wheel should be replaced. This is also
detected by a noticeable thumping sound (one per revolution) while the wheel is in motion. The
flat spot is caused by sliding the wheel, which leads to localized softening at the slide spot and
an increased wear rate.
Flat spot on tread
diameter
Figure 6.4.4.5 Flat Spot on Crane Wheel Tread
6.4.4.6.
Change the crane wheel when the tread has worn through the case hardness thickness
on 56 HRc hardened wheels.
6.4.4.7.
Change crane wheel when uneven wheel wear is detected in any set of wheels.
6.4.4.8.
Tread Diameters on Drive Wheels need to be matched on mechanically connected drive
arrangements.
6.4.4.9.
Typical mill practices for mechanically connected arrangements are to change drive
wheels in pairs and match straight tread diameters within 0.005” and tapered tread diameters
within 0.020”
6.4.4.10.
AIST TR6 requirements dictate that straight tread bridge drive wheels shall have tread
diameters matched within 0.010” maximum of each other.
6.4.4.11.
All other applications, including tapered tread, shall have bridge and trolley driver wheels
matched within 0.030” diameter maximum of each other.
6.4.5. Flange Inspection
6.4.5.1.
The Crane Wheel should be changed when a flange reaches 50% of its original
thickness
Thin flange as a
result of wear
Displace metal on tread
diameter from flange wear
Figure 6.4.5.1 Flange Wear
6.4.5.2.
As flanges wear, the float (Clearance between the flange and side of the rail) will
increase. Users must evaluate operating conditions to determine if the crane begins to run
skewed.
6.4.5.3.
AIST TR6 identifies the float requirements as follows:
6.4.5.3.1.
Bridge Wheel Float (tapered or straight) 1 7/16” – 1 5/8” based on rail size
6.4.5.3.2.
Trolley Wheel Float (straight) 7/16” – 5/8” based on rail size
6.4.5.4.
The crane wheel should also be changed if any cracks are found at the base of the
flange.
6.4.5.5.
The crane wheel should be changed if any discernible pushing or rolling of the flange off
of the vertical plane is noticed.
Displaced metal on tread
diameter from flange wear
Pushed or rolled flange away
from vertical plane of rim
face
Figure 6.4.5.5 Displaced Metal from Flange
6.4.6. Weld Repair Comments and Risks
6.4.6.1.
Users must understand that crane wheels are manufactured from a variety of steel
chemistries, many of which contain high carbon contents. Welding of high carbon content steel
is very prone to cracking, even under ideal circumstances. Also, all hardened wheels contain a
high internal compressive stress level which is the normal result of the heating and quenching
process. The localized heating of the wheel tread during the welding process alters the stress
profile of the entire wheel. Welding of the tread can lead to tread and flange cracks or even
dramatic fractures as a result of the welding process.
6.4.6.2.
Welding of the tread diameter and flanges of heat treated crane wheels to reconfigure a
used wheel to original size is never recommended and is possibly dangerous. Even if
attempted with the correct supervision and knowledge, and if the welding is successful, the
inadequate interface below the tread diameter surface will likely result in spalling or peeling of
the tread surface when the crane wheel is subjected to vertical loading.
6.4.7. Axle Inspection
6.4.7.1.
If after disassembly, damage is present on the axle, the common decision is to scrap
and replace the axle. This decision is generally economically based, as the repair quickly
becomes more expensive than replacing the axle.
6.4.7.2.
If the axle will be re-used in the new crane wheel assembly, the surface of the axle shall
be tested nondestructively, either with dye penetrant or magnetic particle inspection. Any
cracking or discontinuity found shall be cause for replacement.
6.4.7.3.
If diameters are found to be undersized in the crane wheel position, this diameter can be
built up with chrome plating or metal spray if the undersized condition is not significant. Weld
repair, with a sound procedure, is also possible if the axle material chemistry is known. It is
typically an expensive process compared to the simple replacement of the axle.
6.4.8. Related Hardware
6.4.8.1.
Normal practice is to replace bearings, seals and other hardware during the rebuild of a
crane wheel assembly. The primary exception is if the bearing is of sufficient size to evaluate
for reconditioning. Inspection and determination of bearing reconditioning can be made by the
bearing manufacturer.
6.5. Crane Rail Inspection and Corrective Action Guidelines
6.5.1. Introduction
6.5.1.1.
The crane rail is an integral part and critical asset of the crane system.
6.5.1.2.
The guidelines provided are directed towards educating end users of the importance of
the crane rail in the trolley and bridge rail systems incorporated into the designs of heavy
industrial and steel mill cranes. The goal is to establish a safe and reliable crane system and to
protect the investments in overhead, gantry or semi-gantry cranes.
6.5.1.3.
Irregularities or deficiencies in Crane Rail Systems can be traced to poor quality of
installation or workmanship in the construction or maintenance of the rail system. There are also
many types of stresses that affect the condition of crane rails. These include bending and shear
stress, wheel/rail contact stress, thermal stress, residual stress and dynamic loading effects.
Others can be related to flaws in the rail as it is manufactured. The objective of rail inspection
and follow-up corrective actions is to identify irregularities in a bridge or trolley rail system and
develop corrective actions to remediate the effects and restore the system to a safe and
acceptable operating condition.
6.5.2. Scope
6.5.2.1.
This chapter applies to bridge and trolley rail systems of all types, sizes and sections
used in steel mills, aluminum plants and other heavy material manufacturing or handling
facilities.
6.5.3. Qualifications and Responsibilities of Inspectors
6.5.3.1.
A “Qualified Crane Rail Inspector” (Inspector) is a person possessing a mechanical, civil
or structural engineering degree, or a person having significant and practical crane runway or
rail inspection experience. Individuals must have at least two (2) years of crane rail or runway
inspection, maintenance or construction experience.
6.5.3.2.
The Inspector is responsible to assure that inspections are performed in accordance with
OSHA Regulations, Manufacturer’s Recommendations and/or End User Specifications.
6.5.3.3.
The Inspector is responsible to determine whether the rail conditions observed at the
time of inspection comply with OSHA Regulations, Manufacturer’s Recommendations,
Generally Accepted Industry Best Practices or Customer Specifications.
6.5.3.4.
The Inspector is responsible to report any deviations from the fully compliant condition
established by the standards and regulations.
6.5.3.5.
The Inspector shall perform the visual inspection by walking the runway with adequate
fall protection or in a man-lift which allows for effective rail inspection.
6.5.3.6.
For embedded rail systems such as are found in gantry or semi-gantry cranes, the
Qualified Crane Rail Inspector must possess skills to survey the rails and identify signs of rail
irregularities including changes in rail span, straightness, elevation, excessive movement and
cracked or damaged surfaces of the surrounding materials. (Asphalt, concrete or other filler.)
6.5.3.7.
The Qualified Crane Rail Inspector shall complete an Inspection Report as a written
record. The Report shall be maintained on file by the Inspector or other responsible party and
the end user for a period of three (3) years following completion of the inspection. The report
shall document all observations of rail irregularities, the location of the irregularity, the character
of these irregularities and any corrective actions that are recommended at the time of the
inspection. Corrective actions shall be documented when completed, and maintained with the
inspection report for a period of three (3) years.
6.5.4. Crane Rail Inspection – Summary of OSHA Regulations
6.5.4.1.
All crane rail systems shall be inspected in accordance with OSHA 1910.179 (j), by a
“qualified rail inspector” according to the following provisions.
6.5.4.2.
OSHA 1910.179 (j)(1)(i) Initial inspection. Prior to initial use all new and altered cranes
shall be inspected to insure compliance with the provisions of this section. Bridge and trolley
rails shall comply with this OSHA requirement.
6.5.4.3.
OSHA 1910.179 (j)(1)(ii)(b) Period inspection – 1 to 12 month intervals. Bridge and
trolley rails shall comply with this OSHA requirement.
6.5.4.4.
OSHA 1910.179 (j)(2)(i) All functioning operating mechanisms for maladjustment
interfering with proper operation. This shall include joints, rail clips, rail pad and crane girder
tiebacks, and be completed according to the “periodic” inspection detail of 1 to 12 months.
Bridge and trolley rails shall comply with this OSHA requirement.
6.5.4.5.
OSHA 1910.179 (j)(2)(vi) All functional operating mechanisms for excessive wear of
components. Bridge and trolley rails shall comply with this OSHA requirement.
6.5.4.6.
OSHA 1910.179 (j)(3) Periodic inspection. Complete inspections of the crane shall be
performed at intervals generally defined in paragraph (j)(ii)(b) of this section, depending upon its
activity, severity of service, and environment; or as specifically stated. Any deficiencies such as
listed shall be carefully examined and determination made as to whether they constitute a safety
hazard. Bridge and trolley rails shall comply with this OSHA requirement.
6.5.4.7.
OSHA 1910.179 (j)(3)(i) Deformed, cracked or corroded members. Bridge and trolley
rails shall comply with this OSHA requirement.
6.5.4.8.
OSHA 1910.179 (j)(3)(ii) Loose bolts or rivets. Bridge and trolley rails which are
mechanically joined shall be inspected for these characteristics.
6.5.4.9.
OSHA 1910.179 (j)(3)(iv) Worn, cracked or distorted parts. Bridge and trolley rails which
are mechanically joined, or weld jointed shall be inspected for these characteristics.
6.5.4.10.
OSHA 1910.179 (j)(3)(v) Excessive wear. Bridge and trolley rails shall be inspected for
this characteristic.
6.5.4.11.
OSHA 1910.179 (j)(4)(i) A crane that has been idle for a period of 1 month or more, but
less than 6 months, shall be given an inspection conforming with requirements of paragraph
(j)(2) cited in this section before placing in service. Bridge and trolley rails shall comply with this
OSHA requirement.
6.5.4.12.
OSHA 1910.179 (j)(4)(ii) A crane which has been idle for a period of over 6 months shall
be given a complete inspection conforming with requirements of paragraphs (j)(2) cited in this
section, before placing into service. Bridge and trolley rails shall comply with this OSHA
requirement.
6.5.5. Rail Irregularities, Corrective Actions and Field Identification
6.5.5.1.
Rail irregularities and corrective actions are presented in Table 6.5.5.
6.5.5.2.
Common rail nomenclature and positions of planes through the rail should be used in the
documentation of irregularities in rails as shown in Figures 6.5.5.2.1 & 6.5.5.2.2.
Figure 6.5.5.2.1 Rail Nomenclature
Figure 6.5.5.2.2 Relative Positions of Planes Through a Rail
Figure 6.5.5.2.3
Illustration Showing Wheel-Rail Contact Points
Figure 6.5.5.2.4 Examples of good rail wear pattern down the middle of the rail head
Table 6.5.5
Irregularity/Deficiency Field Identification Guide & Corrective Actions
Irregularity/Deficiency
Figure
Corrective Action
REPAIR
REPLACE
Notes
Loose/Missing Splice Bolts
6
Retighten
Bolts, if needed
Splice Bolt Hole Crack
7
If possible
Splice Joint Section
Minimum 10’ Length
Splice Bolt Hole Fracture
7
Splice Joint Section
“
Cracked Welded Rail Joint
8
Weld Joint Section
“
Broken Welded Rail Joint
9
Weld Joint Section
“
If not repairable
“
Rail Section
“
End/Joint Batter +1/4”
10 &
11
If possible
If possible
Head & Web Separation
12
Broken Rail Base
13
If possible
Rail Section
“
Corrosion
14
Monitor
Rail Section, if severe
“
Wheel Slip/Skid Damage
15
If possible
Rail Section
“
Crushed Head
16
Rail Section
“
Split Head – Vertical
17
Rail Section
“
Split Head – Horizontal
18
Rail Section
“
Split Web
19
Rail Section
“
Flaking
20
Rail Section
“
Metal Flow
21
If severe, section
“
Torch Cut Ends or Holes
22
Rail Section
“
Corrugation
23
If needed
“
Rail Section
“
Rail Section
“
Monitor
Profile Grind
Rail Wear - 90 LB/YD or
less
24
3/8” max. side or head
Rail Wear – Above 90#
1/2” max. side or head
24
NOTE: Because there is presently no North American standard for crane rail wear, some data in Table 6.5.5
above is based on industry best practices and studies of railroad rail wear done by the Federal Railroad
Administration, U.S. Department of Transportation and other sources. The recommendations should be
considered “general” and should be implemented with the help of an industry expert in Crane Rail.
Figure 6.5.5.2.5
6.5.5.3.
Splice Bolt Hole Crack
Alternating Splice Bolt Pattern
6.5.5.3.1.
A progressive fracture originating at a bolt hole. Bolt hole cracks are not visible until
a bolt or joint bar has been removed; unless the irregularity has progressed beyond the
head of the bolt, edge of the washer, edge of the nut or perimeter of the joint bar. The
character is often a hairline condition extending from an edge of the bolt hole. (Figure
6.5.5.3.1)
Figure 6.5.5.3.1
6.5.5.4.
General Appearance of Bolt Hole Cracks
Bolt Hole Fracture
6.5.5.4.1.
A sudden and rapid fracture originating at a bolt hole. The appearance is similar to
what is shown in Figure 6.5.3.3.1, however the initially cracked area becomes completely
separated from the rail section. The entire splice area should be replaced.
6.5.5.5.
Cracked or Broken Weld
6.5.5.5.1.
A complete or partial transverse separation of the head, web and base of the rail in
the area of a weld. (Figures 6.5.5.5.1 & 6.5.5.5.2). Broken joints may first appear as hairline
cracks in an isolated area within the rail joint or completely around the rail. Hairline cracks in
joints should be noted and monitored. If the welded joint is severe or progresses to a
complete separation of the rail joint, it should be replaced completely.
Figure 6.5.5.5.1 General Appearance of Hairline Cracks
Figure 6.5.5.5.2 General Appearance of Welded Joint Crack or Broken Rail
6.5.5.6.
End/Joint Batter
6.5.5.6.1.
End batter is a progressive irregularity influenced by repeated impact loads from
wheels transitioning over mechanically joined rail sections. The initial characteristic of end
batter is a widening of the wheel contact area, combined with a depression developing
across the two adjoined rail ends. Action should be taken if end batter exceeds 1/4”. The
extent of joint batter damage can be measured according to Figure 6.5.5.6.1.2. Related to
end/joint batter is the separation distance of the ends of adjoining rail sections. According to
CMAA Specification #70 and AIST Technical Report #13, rail separation at joints should not
exceed 1/16”. Joints are often damaged as a result of loose splices or excessive horizontal
movement of the rails.
Figure 6.5.5.6.1.1
Photos of Rail Joints With End/Joint Batter
Figure 6.5.6.1.2
6.5.5.7.
End/Joint Batter Measurement
Head and Web Separation
6.5.5.7.1.
A progressive fracture separating the head and web of the rail. This condition can
be recognized in an early stage by wavy lines appearing along the fillet under the rail head.
As the condition progresses, a small crack will appear along the fillet on either side
progressing longitudinally with slight irregular turns upward and downward. In advanced
stages, bleeding cracks will extend downward from the longitudinal separation through the
web and may extend through the base. (Figure 6.5.5.7.1)
Figure 6.5.5.7.1
6.5.5.8.
General Appearance of Head/Web Separation
Broken Rail Base
6.5.5.8.1.
Any break in the base of the rail, Generally, these appear as half-moon
characteristics in the rail base, as shown in Figure 6.5.5.8.1. They can also appear as
transverse irregularities the difference being cracks are present on the base of the rail.
Figure 6.5.5.8.1
6.5.5.9.
General Appearance of Broken Rail Base
Corrosion
6.5.5.9.1.
The process of wearing away due to chemical reactions, mainly oxidation. It occurs
whenever a gas or liquid chemically attacks an exposed surface of the rail. The process is
accelerated by warm temperatures and by acids and salts. Initial corrosion is orange
discoloration on the rail surface. This progresses into a reddish-brown crust that forms on
the surface. The underlying rail steel becomes pitted and progresses into crevices
developing on the surface. Rail base surfaces are most apt to develop corrosion
irregularities in outdoor systems or those exposed to the contributing chemical elements.
The side-head surfaces and bases of embedded rails are also very apt to develop corrosion
conditions. Corrosion can lead to stress cracking of rails. (See Figure 6.5.5.9.1 photos
below.)
Figure 6.5.5.9.1
6.5.5.10.
Photos of Rail Corrosion
Wheel Slip / Skid
6.5.5.10.1. Wheel slip or skid damage refers to a progressive condition caused by frictional
wear of the top of the rail head, from trolley or bridge wheels slipping or skidding on the
surface. (Figure 6.5.5.10.1) The wheel slipping on the rail wears a groove into the top-head
surface. Often, the grooves become deep making it difficult for the wheels to pass over this
area smoothly.
Figure 6.5.5.10.1
6.5.5.11.
Typical Appearance of Wheel Slip / Skid
Crushed Head
6.5.5.11.1. A progressive failure of the rail head. Crushed head conditions are characterized by
the flattening of several inches along the top rail head, usually accompanied by a crushing
downward of the metal, but with no signs of cracking in the junction of the head and the
web. (Figure 6.5.5.11.1)
Figure 6.5.5.11.1
General Appearance of Crushed Rail Head
6.5.5.12.
Vertical Split Head
6.5.5.12.1. A progressive, longitudinal fracture of the rail head perpendicular to the running
surface. Vertical split heads are characterized by either a dark streak on the running
surface, a widening of the rail head for the length of the split, sagging of the side-head
accompanied by a rust streak on the top-head, a hairline crack near the middle of the rail
head and in advance stages a bleeding crack is apparent on the rail surface and in the fillet
at the head-web junction. (Figure 6.5.5.12.1)
Figure 6.5.5.12.1
6.5.5.13.
General Appearance of Vertical Split Head
Horizontal Split Head
6.5.5.13.1. A progressive, horizontal fracture in the rail head parallel to the running surface.
Horizontal split head conditions are characterized by surface metal exhibiting a creased
appearance on the running surface to one side of the rail head, the rail head showing
unusually flowed metal to one side and in advance stages, a protrusion of flowed metal
hanging down or separated from the side of the head. (Figure 6.5.5.13.1)
Figure 6.5.5.13.1
6.5.5.14.
General Appearance of Horizontal Split Rail Head
Split Web
6.5.5.14.1. A progressive fracture through the web in a longitudinal and/or transverse direction.
It appears in the rail as horizontal and/or vertical bleeding cracks in the web. (Figure
6.5.5.14.1)
Figure 6.5.5.14.1
6.5.5.15.
Flaking
General Appearance of Split Web
6.5.5.15.1. A progressive horizontal separation on the running surface where the wheel flange
makes contact with the top corner radius of the rail head. It is characterized by shallow
depressions with irregular edges occurring on the running surface approximately ¼” from
the top-head corner radius. Flaking can also appear as hairline cracks along the running
surface, resembling small slivers. (Figure 6.5.5.15.1)
Figure 6.5.5.15.1
6.5.5.16.
General Appearance of Flaking
Metal Flow
6.5.5.16.1. Metal flow is a deformation of the top-head surface. Vertical wheel loadings
compress the metal causing a bi-directional movement towards the sides of the rail head.
Some metal flow is a normal wear phenomenon. The progression of flow must be monitored
to assess the extension of the flow and the potential for the plastically deformed material to
crack and break away from the side-head areas. (Figure 6.5.5.16.1)
Figure 6.5.5.16.1
6.5.5.17.
General Appearance of Metal Flow
Torch-Cut Rail Ends or Bolt Holes
6.5.5.17.1. Any rail that is cut or otherwise modified (including bolt holes) using an acetylene or
other torch. The appearance in the rail is an irregular, jagged and rough surface texture on
rail ends or bolt holes. (Figure 6.5.5.17.1)
Figure 6.5.5.17.1
6.5.5.18.
General Appearance of Torch Cut Rail
Corrugation
6.5.5.18.1. Corrugation is a progressive surface irregularity influenced by frictional forces upon
the rail head. Corrugation is characterized by depressions (waves) in the running surface,
the severity and unevenness of which vary in relation to an ideal profile. It is often referred
to as a washboard effect. (Figure 6.5.5.18.1)
Figure 6.5.5.18.1
6.5.5.19.
Rail Corrugation Photograph
Rail Wear
6.5.5.19.1. The loss of material from the top running surface and sides of the rail head due to
the repeated passage of wheels. See Figures 6.5.5.19.1 and 6.5.5.19.2. Rail wear appears
initially as a flattening of the top-head profile and gouging or grooving into the side-head
areas. One of the best methods of measuring the amount of rail wear is to compare the
dimensions of a worn section with the dimensions of the rail at the ends of the runway,
which see little or no wheel passes.
Figure 6.5.5.19.1
General Appearance of Vertical Head and Side Wear
Figure 6.5.5.19.2
6.5.5.20.
Photos of Rail Head Wear
Short Rail
6.5.5.20.1. Mechanically spliced Heavy Crane Rails, (CR Sections 104 LB/YD to 175 LB/Y) are
typically provided in lengths of 39’ and 60’. Light rails, (ASCE or T-Rail Sections 20 LB/YD
to 100 LB/YD) are provided in standard lengths of 20’, 30’ and 40’. European Crane Rails, (
Din 536 A-Rails) cannot be mechanically spliced and typically have welded joints or
diagonal splice joints. Per AIST Technical Report #13, rail sections should not be less than
ten (10) feet in length.
6.5.6. References
6.5.6.1.
OSHA Regulations; Overhead and Gantry Cranes 29 CFR 1910.179
www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9830
6.5.6.2.
U.S. Army Technical Manual “Railroad Track Standards” TM5-628 / Air Force AFR 91-44
www.militarynewbie.com/pubs/US%20Army%20%20Railroad%20Track%20Standards%20TM%205-628.pdf
6.5.6.3.
“Rail Defect Manual”; Sperry Rail Service Company. www.sperryrail.com
6.5.6.4.
“Estimation of Rail Wear Limits Based on Rail Strength Investigations” , Federal Railroad
Administration, U.S. Department of Transportation;
www.fra.dot.gov/downloads/research/ord9807.pdf
6.5.6.5.
“Uniform Facilities Criteria – Railroad Track Maintenance & Safety Standards”, U.S.
Department of Defense. www.wbdg.org/ccb/DOD/UFC/ufc_4_860_03.pdf
6.5.6.6.
AIST Technical Report #13, “Guide for the Design and Construction of Mill Buildings” ;
www.aist.org
6.5.6.7.
AIST Technical Report #6, “Specification for Electric Overhead Traveling Cranes for
Steel Mill Service”; www.aist.org
6.5.6.8.
CMAA Specification #70; “Electric Overhead Traveling Cranes”; www.mhia.org
6.6. Crane Rail Clips, Rail Pad, Splices
6.6.1. Introduction
6.6.1.1.
Rail clips, rail pad and associated hardware on a crane runway system are often
neglected unless there is some type of failure. There are some proactive measures that can be
taken to avoid untimely breakdowns associated with these items, and some guidelines to use
for inspecting these components of a crane rail system.
6.6.1.2.
OSHA requires that all components of a crane and runway system are to be inspected
and maintained per the manufacturer’s recommendation, as cited in 29CFR1910.179. This
obviously includes all the components of a rail fastening system.
6.6.1.3.
The following information pertains generally to rail fastening systems of any type, but will
focus on the engineered adjustable rail clip most prevalent on steel mill crane runways and
bridges. These principles can also apply to concrete supported runways such a rails for transfer
cars, manipulators and other equipment that runs on rails in a steel mill.
6.6.1.4.
Other types of rail clips, such as hard-mount, non-adjustable clips are sometimes used
on lower duty cycle applications, such as service cranes and those not as frequently used as
process cranes. J-bolts, also known as hook bolts, are not recommended and will not be
discussed in this work. Similarly, rails should never be welded or permanently and rigidly fixed
to the support structure of any crane runway. Rail should be able to move longitudinally by
either thermal expansion/contraction or forces generated by crane wheel skid or spin. Similar
principles for inspection, maintenance and repair would, however apply to other types of rail
fastening systems.
6.6.2. Frequency of Inspection & Maintenance
6.6.2.1.
The amount of attention that a crane runway requires largely depends upon the working
conditions in which the crane is operating. Regardless, crane runways should be inspected
along with the other crane components as part of the periodic inspections required by OSHA.
Inspections and maintenance of rail fastening systems typically occur simultaneously. Because
of the dirty conditions in steel mills, the runway should be swept or, preferably vacuumed to
remove collected contaminants, such as metal scale or mill dust prior to inspection to allow for
good visibility of the individual components. Most steel mill crane runways are not visible
without prior cleaning.
Figure 6.6.2.1
6.6.3. General Condition of Rail Clips
6.6.3.1.
Presence of Clips and Hardware
6.6.3.1.1.
According to AISC, rail clips should be installed in opposing pairs on center
distances ranging from 24” to 36”. A design engineer should determine the clip spacing
based on factors such as lateral load, duty cycle and whether or not pad is used. Since it is
not likely that an inspector will know the required spacing, attention should be focused on
clip spacing that exceeds 36”. Clips missing from an obviously intended location should be
replaced. Missing bolts or studs, cracked or broken components or severely worn rail clips
should also be replaced.
Figure 6.6.3.1.1
6.6.3.2.
Checking for Tightness
6.6.3.2.1.
Rail clips are designed to hold the rail in close lateral alignment. If clips are missing,
are not properly installed, not correctly adjusted and tightened, have been wrongly specified
or if the forces from the crane are higher than anticipated, it is possible for the clips to be
pushed away from the rail. Thus an inspection should look for any lateral movement of the
rail and any displacement of the rail clips. It is not recommended that the clip nut torque be
checked unless there is movement of the rail. Torque wrenches are not high accuracy tools
and it is possible to find all the clip nuts are seemingly too loose due to an inaccurate torque
wrench. Because most rail clip bolts are structural bolts, A325, Grade 5, A490 or Grade 8,
they will stretch when tightened. If the tightness of rail clip bolts is checked too frequently,
this can lead to premature failure. Often the “hammer test” can be more effective and it will
not stretch the bolts. Rail clip bolts should never be reused once removed either
intentionally or otherwise.
6.6.3.3.
Clip Adjustment
6.6.3.3.1.
When rail clips are properly installed and adjusted, the portion of the rail clip that is
intended to rest against the rail should be in flush contact with the rail flange, foot or
intended section. (See Figure 6.6.3.4.1). Any gap between the clip and the rail should be
corrected. Manufacturer’s installation instructions should always be consulted and followed
when installing or adjusting rail clips.
6.6.3.4.
Nose Compression
6.6.3.4.1.
The purpose of the rubber nose is not to hold the rail down with a vertical clamping
force, but rather to absorb the energy of uplift generated in one clip when a wheel passes an
adjacent clip and deflects the rail and girder in a downward direction. Clips that are not
designed specifically for the rail size used could cause over or under compression when
tightened down. Too much compression could limit rail longitudinal movement and cause
undue stress in the rail between clip pairs and damage the rail clips themselves. The figure
below shows proper nose compression before and after the clip bolts are tightened.
Figure 6.6.3.4.1
6.6.3.5.
Clip Welds
6.6.3.5.1.
Some rail clips are attached to the girders by first welding a fixed base or lower
component to the girder. How that component is welded and the present condition of the
welds is crucial to the proper performance of the clip. The inspection should confirm
adherence to the manufacturer or designer welding specification (see Figure 6.6.3.5.1).
Figure 6.6.3.5.1
6.6.3.6.
Rail Pad
6.6.3.6.1.
On steel girder runways, rail pad is used in continuous sections, butted together
beneath the entire rail length. Pad is used in particular on 171#CR, because 171 is not
crowned at the head and pad is often used to insure alignment between the wheel tread and
rail head.
6.6.3.6.2.
The most important check of a rail pad system is the position of the pad beneath the
rail. If the pad is visible outside of the longitudinal edge of the rail, it is an indication that a
problem exists somewhere in the rail system. Pad movement from beneath the rail can
indicate loose splice joints that allow the ends of the rail to move excessively. The best
solution is to make sure the splices are tight and that there are rail clips located near the rail
seam. (See “Cut Clips at Rail Splices”) Pad movement can also be caused by the rail clip
pairs being spaced too far apart. While the primary function of a rail clip is to restrain the rail
laterally, the clips are integral in holding the pad beneath the rail. If the clip spacing is
correct and sufficient to hold the rail, but does not retain the pad, pad keepers may need to
be installed.
Figure 6.6.3.6.2
6.6.3.7.
Pad Stops
6.6.3.7.1.
If the gap between adjacent girders or at expansion joints is greater than 3/4", pad
stops are recommended. These should be 1/4" thick, U-shaped steel bars, welded at the
ends of the girder. Pad stops should also be considered at the ends of each runway where
excessive longitudinal rail movement relative to the girder or soleplate is expected. A typical
detail is shown below.
Rail
Figure 6.6.3.7.1
6.6.3.8.
Pad Keepers
6.6.3.8.1.
Pad keepers can be as simple as short pieces of bar stock welded to the girder or
soleplate just outside the rail flange edge in between pairs of clips. They act like shear
blocks to limit the lateral movement of the rail pad.
6.6.3.9.
Pad for Trolley Rails
6.6.3.9.1.
Particular attention should be paid to pad beneath the bridge rails that the trolley
runs upon. With box girder designs that feature vertical stiffener plates that run
perpendicular to the rails, stress points can be created by girder deflection against the pad
causing possible cutting of the pad at those points.
6.6.4. Splice Joints
6.6.4.1.
Types of Splices – U.S. Crane Rail and Tee Rail
6.6.4.1.1.
Of the various methods to join rail sections together for a runway, mechanical
splices are more popular on smaller rail sizes, such as ASCE sections, or tee rails and are
used on runways that are lighter duty than process cranes. Of those joints which are
mechanically fastened, most use the splice bar type of plates without any toe, instead of
partial or full toe splices.
6.6.4.1.2.
The term "splice bar" refers to only one type of connector and frequently is confused
with other types. The drawings below provide clarification of the proper term for each type of
connector bar. Angle bars are sometimes called “full-toe joint bars”, and “joint bars” are
sometimes referred to as “short toe” bars. (Figure 6.6.4.1.2)
Splice Bars
Angle Bars
Joint Bars
Figure 6.6.4.1.2
6.6.4.1.3.
U.S. crane rail sizes 104# and above have three drilled holes on the end of each rail
and a six-bolt splice bar pair. Crane rail splice bars are typically around 34” long and weigh
from 60 LB to 70 LB per pair, depending on rail size. They are secured with six (6) sets of
track bolt assemblies, consisting of a bolt, a nut and sometimes a washer. ASCE and tee
rail sections are joined with four (4) bolt assemblies. Drilling of rail ends and punching of
splice plates follow generally accepted industry standard patterns for hole size and spacing.
Note in the figure below that rail splice bolts should be inserted from alternating sides of the
splice to aid in the equal distribution of tightening forces.
Figure 6.6.4.1.3
6.6.4.1.4.
formed.
Splice plates are sometimes referred to as “fish plates” because of the type of splice
Figure 6.6.4.1.4
6.6.4.1.5.
The standard drillings for tee rails and corresponding punching for splice bars
provide for a 1/8" gap between rail ends. Although this construction is satisfactory for
railroad track and light crane service, its use in general crane service may lead to joint
failure. For best service in bolted splices, it is recommended that "tight joints" be stipulated
for all rails for crane service. Rail separation at the joint should not exceed 1/16”.
6.6.4.2.
Splice Bolts
6.6.4.2.1.
While there is no torque requirement specifically for rail splice bolts, standard torque
ratings for bolt size and grade should be followed. One common field technique is to use a
split lock washer and tighten the bolts until the washer flattens out. Splice bolts should be
retightened after 30 days of use, and every 3 months thereafter. Sometimes “Huck” bolts
are used to secure splices.
TRACK BOLT
Figure 6.6.4.2.1.1 Button head Oval Neck Track Bolt with square Nut
Crane Rail Bolt
Figure 6.6.4.2.1.2 Hex Head A-325 Structural Bolt
6.6.4.3.
Types of Splices - DIN or “A” Crane Rail
6.6.4.3.1.
Because the web of DIN rails, such as A55, A100, etc. is very short, there is no
room for splice plates to hold adjacent rail sections together. These rails are most often
joined by welding. On occasion, miter joints, (Figure 6.6.4.3.1.1) or diagonal splices, (Figure
6.6.4.3.1.2), are used and rail clips are placed in tight spacing at the splices.
Figure 6.6.4.3.1.1
Figure 6.6.4.3.1.2
6.6.4.4.
Cut Clips at Rail Splices
6.6.4.4.1.
Cut clips have the entire front face of the rail clip removed so that the clip will fit up
under the hardware of a rail splice. (Figure 6.6.4.4.1.1) They are best installed with a pair of
clips within 3-5 inches of the actual rail seam. (Figure 6.6.4.4.1.2)
Figure 6.6.4.4.1.1
Figure 6.6.4.4.1.2
6.6.5. Rail Center
6.6.5.1.
Rail Centricity
6.6.5.1.1.
Crane rails shall be centered in the middle of the girder directly above the girder
web. This is to prevent excess twisting of the top flange of the girder, which could lead to
cracking at that point.
.
Figure 6.6.5.1.1
6.6.6. Rail on Concrete
6.6.6.1.
For gantry crane, semi-gantry crane and transfer car runways, rails are often either
imbedded in the floor or ground, or mounted on top of soleplates on the ground. The soleplates
support the rail in one of two methods, either discontinuous or continuous. (Figure 6.6.6.1)
Sometimes a hybrid method is used in which the soleplates are intermittent and the space
between them is filled with grout. Most of the above principles apply to this type of rail support
system, and a few additional items should be included in any inspection, maintenance and
repair program.
Figure 6.6.6.1
6.6.6.2.
Grout Beneath Soleplates
6.6.6.2.1.
The additional item to be inspected is the grout under the soleplates. For
discontinuous installations, the grout is formed in pedestals, and for continuous systems the
grout is poured beneath the entire surface of the soleplates. Typically either cement-based
grout or epoxy grout is used as a load-bearing material to help reduce the pressure on the
concrete below. (Figure 6.6.6.2.1) The grout should be free from visible cracks or voids, and
should fill up the entire space beneath whichever soleplate is used. Any cracks or voids
should be filled with the appropriate repair material.
Figure 6.6.6.2.1
6.7. Hook Inspections
6.7.1. Purpose
6.7.1.1.
This document is intended to aid the end user in the understanding, operational
requirements, and inspection items of a hook on a load block assembly for an EOT crane or
lifting device.
6.7.2. References Referenced documents for Hook Information in this section
OSHA 1910.179(h)(4): Recommendations for Inspection Frequencies
OSHA 1910.179(j)(2)(iii): Inspection List
OSHA 1910.179(l)(3)(iii)(a): Defects and Recommendations to Repair Defects
OSHA 1910.179(k)(2): Testing Requirements
ASME B30.10 – Hooks
6.7.3. Nomenclature
6.7.4. Inspection Methodology
6.7.4.1.
Check for obvious cracks, nicks, gouges, or wear that would indicate an inclusion
6.7.4.2.
Check for spalling / lamination / plastic flow in proximity to the saddle.
6.7.4.3.
Check for excessive saddle wear.
6.7.4.4.
Check for twist in the hook.
6.7.4.5.
Check for any distortion of the throat opening.
6.7.4.6.
Ensure the safety latch (if applicable) is in good working order.
6.7.4.7.
A monthly certification record which includes the date of inspection, the signature of the
person who performed the inspection and the serial number, or other identifier, of the hook
inspected shall be maintained.
6.7.5. Remedies and Repairs
6.7.5.1.
Hooks shall be taken out of service until repaired or replaced for any of the following
unless otherwise specified by the manufacturer:
6.7.5.1.1.
Saddle wear exceeding 10% of the original dimension.
6.7.5.1.2.
A bend or twist exceeding 10 deg. from the plane of the unbent hook.
6.7.5.1.3.
An increase in the throat opening exceeding 5%
Figure 6.7.5.1
6.7.5.2.
Cracks, nicks, or gouges shall be repaired by a designated person grinding longitudinally
along the contour of the hook as long as the loss of material does not exceed 10% of the
original dimension.
6.7.5.2.1.
All other repairs shall be performed by the manufacturer or a qualified person.
6.7.5.2.2.
All replacement parts should at least be equal to the manufacturer’s specifications.
6.7.6. Recommendations
6.7.6.1.
Inspection frequency:
6.7.6.1.1.
Non Destructive Testing (NDT) is recommended yearly on all hooks by a qualified
person. Where practical, removal of the entire hook from the block for a complete inspection
is recommended.
6.7.6.1.2.
Operators should perform a daily visual inspection
6.7.6.1.3.
Inspection frequency for each type of service crane
6.7.6.1.3.1. Normal service cranes (service that involves operating at less than 85% of
rated load except for isolated instances) - monthly.
6.7.6.1.3.2. Heavy service cranes (service that involves operating at 85%-100% of rated
load as a regular specified procedure) - weekly to monthly.
6.7.6.1.3.3. Severe service cranes (heavy service coupled with abnormal operating
conditions) - daily to weekly.
6.7.6.2.
Inspection with a certification record includes the date of inspection, the signature of the
person who performed the inspection and the serial number, or other identifier, of the hook
inspected.
6.7.6.2.1.
6.7.6.3.
Inspection Records should be retained per company policy or prevailing authority.
Hooks are never to be painted unless by the manufacturer.
6.7.6.4.
Welding on a hook should never be performed.
6.7.7. Exclusions
6.7.7.1.
This material is intended as reference material only.
6.7.7.2.
Refer to the standards cited above or the manufacturer’s specifications for the
component and its intended use.
6.8. Gearbox Inspection and Repair Guidelines
6.8.1. Purpose
6.8.1.1.
The purpose of this chapter is to provide guidelines for the inspection, repair, and
servicing of gearboxes.
6.8.2. Scope
6.8.2.1.
This chapter applies to gearboxes in overhead cranes for steel mill service.
6.8.3. Inspection while in Service
6.8.3.1.
The most important inspection required is during the installation of the replacement
gearbox.
6.8.3.2.
While the manufacture of the gearbox should have inspected the contact and backlash
in the gearing assembled inside the gearbox, improper assembly of the gearbox on the crane
can change conditions (example: improper shims causing housing to twist). During installation,
apply a contact media (Dykem Blue) to one member of each gear set that can be inspected
during operation. After a short period of use, be sure to inspect the area that was treated to
inspect the contact pattern and be sure to photograph the results.
Figure 6.8.3.2 Full Face Gear Contact
6.8.3.3.
The relationship between the drum pinion and the drum gear is very important and often,
the most difficult to maintain. In most overhead cranes, the drum gear is mounted on the rope
drum. The contact pattern between the drum pinion and drum gear is established when the rope
drum is assembled into the gearbox on the crane, setting the pillow block bearing. It is critical
that the contact pattern be evaluated, centering the contact as best as possible.
6.8.3.4.
Try to avoid mixing your gear sets. Managing the drum pinion and gear is difficult, in
that the gearbox and rope drum are not always changed at the same time. When this occurs,
the set may be made up of a pinion and gear from different manufacturers. The member may
also be new and used, and there can be hardness or quality mismatches.
6.8.3.5.
Periodic inspections of the gearing are a good practice. Initially, inspections can be on
an annual basis, and then modified based on the results observed. Take photos of the gear
condition, date and compare with other readings to determine the extent of change. The photos
below are of a main hoist drum gear over a four (4) year period.
Year 1
Year 3
Year 4
Figure 6.8.3.1.4 Gear Teeth Photos over 4 Year Period
6.8.3.6.
Lubrication analysis is also an excellent means to monitor the condition of the gearbox.
In that most of these applications are “splash” lubrication system, contaminants in the oil is
passing thru the gear mesh.
6.8.3.7.
General inspections that can help extend the service of the gearbox include monitoring
seal performance and the breather.
6.8.3.8.
While vibration monitoring has yet to yield dependable results in monitoring gearbox
performance in overhead cranes, monitoring temperatures at the bearing locations can help
detect a potential problem.
6.8.4. Inspection and Repair upon Removal from Service
6.8.4.1.
Completely disassemble the gearbox and note any unusual findings (contaminants in the
gearbox, unusual wear, signs of heat related damage, etc.).
6.8.4.1.1.
Dimensional and NDT inspection of all gearing and shafts.
6.8.4.1.2.
Reassemble housing, torque the split line bolts to proper levels and inspect bore
sizes and alignment – this is especially important when uneven gear contact patterns are
noted. Housing inspection ideally is performed by a CMM or a horizontal boring mill of
known accuracy.
6.8.4.2.
In the event that the gearing is not performing to expectations or there is a need to
replace the gearing in the gearbox, it is advised that you perform a strength and durability rating
calculations in order to evaluate the gear quality relative to the application. A qualified Gear
Engineer should perform this analysis and make recommendations.
6.8.4.3.
Replace gearing in sets that are properly matched with regard to surface hardness.
Figure 6.8.4.3 Properly Matched Gear Set
6.8.4.4.
Housing bore repairs may require replacement or repair of the gearing. Repairing the
bores of the housing, results in an alignment change. The gearing, which has worn into the
previous condition, must be addressed or they will have a poor contact pattern.
Figure 6.8.4.4 Gear tooth surface reestablished
6.8.4.5.
Replace all bearings and seals.
6.8.4.6.
Document the final contact pattern and backlash results.
6.8.4.7.
Perform a “no load” run test to monitor noise, temperature and vibration. This test should
be for a minimum of four (4) hours for gearboxes that operate in one direction or two (2) hours in
each direction for gearboxes that operate in both directions.
6.8.4.8.
Take action if lubrication is not adequately supplying to the gearing or bearings.
6.8.4.9.
While in storage, rotate the bearings every 3 to 6 months. Store the gearbox in an area
where it is not subject to significant temperature changes, moisture accumulation or vibration. It
is recommended to remove the breather and plug the hole to reduce moisture from entering the
gearbox.
6.8.5. Gearbox Upgrade Considerations
6.8.5.1.
Consider crowning one member of each set to compensate for misalignment or any
deflection experienced in service.
Figure 6.8.5.1 Crowning Gear Teeth
6.8.5.2.
If gearing needs to be replaced, consider the use of higher hardness and/or higher
AGMA quality gearing to significantly extend the life of your gearing.
6.8.5.3.
Address poor performing seals. Consider different types of seals if the seals are in poor
condition or if the box lubrication is obviously contaminated from an external source.
6.8.5.4.
Add inspection ports to the housing if none were incorporated to the original housing
design. This will allow for easier access to visually inspect the gearing.
6.9. Worm and Worm Gear Replacement
6.9.1. Purpose of this Worm Gear Section
6.9.1.1.
What should we look for when inspecting the worm and gear during our shutdown
period?
6.9.1.2.
When should the worm be replaced?
6.9.1.3.
When should the gear be replaced?
6.9.2. Overview
6.9.2.1.
Except for a few special applications, the worms and gears supplied by a reputable
Worm gear manufacturer can be looked upon as a hardened steel worm with a surface
hardness of 56-60RC, accurately ground, operating on a low friction bronze gear, hardness 95120Bhn. By virtue of its sliding action, power is transmitted with a smooth, uninterrupted torque
flow.
6.9.2.2.
The rate of wear should be slight and normally localized on the gear. As a result, the
worm thread contours should remain unchanged throughout the life of the drive. The gear
teeth, even with the presence of wear, are forced by the generating action of the worm, to
maintain their correct profiles. This action maintains the efficiency of the drive through its life.
6.9.3. Worm Gearing Operating Under Normal Conditions
6.9.3.1.
Normal operating conditions assumes that a suitable lubricant is being used, the
lubricant is maintained at the proper level, and that the lubricant is being changed and the unit
flushed out at recommended intervals. It also assumes that the drive is not being subjected to
continuous abnormal loading or shock, and that contamination is not a factor.
6.9.3.2.
One other assumption is that the gear has been correctly adjusted to give optimum
contact with the worm.
6.9.3.3.
The inspection of a worm and gear set in the field revolves around a comparison
between what one expects to see and what one does see, and noting the difference, if any,
between the two. What one expects to see is the BENCHMARK or STANDARD, and unless that
standard is understood, the inspection may fall short of its purpose and could result in costly
repairs and subsequent down time.
6.9.3.4.
When looking directly at the gear tooth flank as shown on the following page, the worm
thread moves across the flank from left to right. With left hand gearing, the worm thread would
move across the flank from right to left.
Figure 6.9.3.4.1 Worm gear tooth terminology.
Figure 6.9.3.4.2 Worm terminology
6.9.3.5.
Inspection of the Gear.
6.9.3.5.1.
Contact Patterns
Figure 6.9.3.5.1.1: No load contact pattern
6.9.3.5.2.
Figure 6.9.3.5.1.2: Full load contact pattern.
Although the gearing may be operating under normal conditions, inspection
of the gear teeth will often reveal a phenomenon that, unless understood, may cause some
panic on the part of the observer. This condition is referred to as PITTING.
Figure 6.9.3.6 Corrective pitting phenomenon
6.9.3.5.3.
Under normal conditions, during the inspection of the gear, we would
expect to see a gear tooth that showed a full contact pattern, and depending upon length of
time in operation, a certain degree of wear, with the possibility of corrective pitting having
occurred, either localized or full face.
6.9.3.5.4.
Photos of Damaged Gears that need replacing:
Figure 6.9.3.8.1: Overloaded gear damage
Figure 6.9.3.8.2 Incorrect contact pattern damage
Figure 6.9.3.8.3 Excessive gear tooth wear
6.9.3.6.
Inspection of the Worm
6.9.3.6.1.
The contact pattern that will be evident on the worm thread flank will be in
the shape of an elongated diamond, as shown on the imaginary unwrapped worm thread.
6.9.3.6.2.
Under normal circumstances, the pattern will be smooth and highly
polished. Depending on the length of time in service, some wear may or may not be
apparent. There should be no wear on the worm threads, if there is then scrap it.
6.9.3.6.3.
Inspection of the worm should include examination of the threads to
determine wear and general condition of the contact surface, and careful examination of the
contact surface for possible cracks. Assuming that conditions are normal, during the
inspection of the worm, we would expect to see a well-defined contact pattern; the surface
being smooth, shiny, polished, and free of cracks.
Figure 6.9.3.6.3.1 Thermal cracking of worm threads
Figure 6.9.3.6.3.2 Thermal cracking and pitting of worm
Figure 6.9.3.6.3.3 Bronze pick-up on worm threads
Figure 6.9.3.6.3.4
6.9.3.7.
Broken worm threads
Errors that are involved in the failures:
6.9.3.7.1.
No attention being paid to the importance of proper gear adjustment
6.9.3.7.2.
Failure to recognize that the reduction in chordal tooth thickness of the gear
teeth was the result of cutting action of the cracks in the worm threads and not wear
6.9.3.7.3.
Incorrect or inadequate lubrication
6.9.3.7.4.
Failure to inspect the Gearing on a regular Maintenance schedule.
6.10. Wire Rope
6.10.1.
Introduction
6.10.1.1.
Wire rope will fail if worn out, overloaded, misused, damaged or improperly maintained.
Even in normal service, wire rope loses strength and work capability over time. Abuse and
misuse increase the rate of loss. It is also important to remember that the minimum breaking
strength (MBS) of wire rope applies only to a new, unused rope. MBS should be considered the
straight line force with both rope ends fixed to prevent rotation, which will actually break a new,
unused rope. The Minimum Breaking Strength of a rope should be considered to be its
maximum working load.
6.10.2.
Working Load and Design Factor
6.10.2.1.
To determine the working load of a wire rope, the minimum or nominal breaking strength
must be reduced by a design factor, (formerly called a Safety Factor). The Design Factor will
vary depending upon the type of machine and installation, and the application. The user must
determine the applicable Design Factor based on how a rope is being used.
6.10.2.2.
For example, a Design Factor of "5" means that the Minimum, or Nominal Breaking
Strength of the wire rope must be divided by five to determine the maximum load that can be
applied to the rope system. Design Factors have been established by DIN, ISO, CEN, OSHA,
ANSI, ASME and similar government and industrial organizations. No wire rope should ever be
installed or used without full knowledge and consideration of the Design Factor for the
application.
6.10.2.3.
The strength of a wire rope increases slightly after the break-in period, but will decrease
over the remainder of time it is in service. When approaching the finite fatigue life, the breaking
strength will sharply decrease. Never evaluate the remaining fatigue life of a wire rope by testing
a portion of a rope to destruction only. An in-depth rope inspection must be part of such
evaluations.
6.10.3.
Wire Rope Usage
6.10.3.1.
Never overload a wire rope. This means never use the rope where the load applied is
greater than the working load determined by dividing the Minimum Breaking Strength of the
rope by the appropriate Design Factor.
6.10.3.2.
Never ‘shock load’ a wire rope. A sudden application of force or load can cause both
visible external damage (e.g. bird-caging) and internal damage. There is no practical way to
estimate the force applied by shock loading a rope. The sudden release of a load can also
damage a wire rope.
6.10.4.
Lubrication & Inspection
6.10.4.1.
Lubricant is applied to the wires and strands of a wire rope when manufactured. This
lubricant is depleted when the rope is in service and should be replaced periodically.
6.10.4.2.
Regular, periodic inspections of the wire rope, and the keeping of permanent records
signed by a qualified person, are required by OSHA and other regulatory bodies for every crane
and hoist rope installation. The purpose of inspection is to determine whether or not a wire rope
may continue to be safely used on that crane. Inspection criteria, including number and location
of broken wires, wear and elongation, have been established by DIN, ISO, CEN, OSHA, ANSI,
ASME and other organizations. If in doubt, replace the rope.
6.10.5.
When Removed From Service
6.10.5.1.
When a wire rope has been removed from crane service because it is no longer suitable,
it must not be re-used on another application.
6.10.5.2.
Every wire rope user should be aware of the fact that each type of fitting attached to a
wire rope has a specific efficiency rating which can reduce the working load of a rope assembly
or rope system, and this must be given due consideration in determining the capacity of a wire
rope system.
6.10.6.
Potential Problems
6.10.6.1.
Some conditions that can lead to problems in a wire rope system include:
6.10.6.1.1. Sheaves that are too small, worn or corrugated can cause damage to wire rope.
6.10.6.1.2. Broken wires mean a loss of strength.
6.10.6.1.3. Kinks permanently damage a wire rope.
6.10.6.1.4. Environmental factors such as corrosive conditions and heat can damage a wire
rope.
6.10.6.1.5. Lack of lubrication can significantly shorten the useful service life of a wire rope.
6.10.6.1.6. Contact with electrical wire and the resulting arcing will damage a wire rope.
6.10.7.
A Wire Rope is a Machine
6.10.7.1.
Wire rope is a machine, by dictionary definition: "An assemblage of parts...that transmit
forces, motion, and energy one to another in some predetermined manner and to some desired
end."
6.10.7.2.
A typical wire rope may contain hundreds of individual wires which are formed and
fabricated to operate at close bearing tolerances one to another. When a wire rope bends, each
of its many wires slides and adjusts in the bend to accommodate the difference in length
between the inside and the outside bend. The sharper bend, the greater movement.
Figure 6.10.7.2 Wire rope bends
6.10.7.3.
Every wire rope has three basic components:
6.10.7.3.1. The wires which form the strands and collectively provide the rope strength;
6.10.7.3.2. The strands, which are helically around the core; and,
6.10.7.3.3. The core, which forms a foundation for the strands.
Figure 6.10.7.3.3 Wire Rope Basic Components
6.10.7.4.
The core of wire rope may be an Independent Wire Rope Core (Steel Core, IWRC, SE,
or CW), which in many cases is actually a rope in itself. This core provides between 10% and
50% (in non-rotating constructions) of the wire rope's strength.
6.10.7.5.
The greatest difference in wire ropes are found in the number of strands, the
construction of strands, the size of the core, and the lay direction of the strand versus the core.
6.10.7.6.
The wires of wire rope are made of high-carbon steel. These carbon steel wires come in
various grades. The term "Grade" is used to designate the strength of the wire rope. Rope wires
are usually made of 1770 N/mm , 1960 N/mm , or 2160 N/mm steel grades [Approximate
equivalents are Improved Plow Steel (IPS), Extra Improved Plow Steel (EIPS) or Extra Extra
Improved Plow Steel (EEIPS)].
6.10.7.7.
One cannot determine the Tensile Grade of a wire rope by its feel or appearance. To
properly evaluate a rope's tensile grade you must obtain the Grade from the supplier.
RRL
Right Regular Lay
LRL
Left Regular Lay
RLL
Right Lang Lay
LLL
Left Lang Lay
Figure 6.10.7.7 Wire Rope Lays
6.10.8.
Wire Rope Inspection
6.10.8.1.
General
6.10.8.1.1. It is essential to maintain a well-planned program of periodic inspections. In most
cases there are statutory and/or regulatory agencies whose requirements must be adhered
to.
6.10.8.1.2. Whether or not such requirements exist in your specific environment, you can be
guided by the suggested procedures that follows.
6.10.8.1.3. Abrasion, Bending and Crushing represent the basics of wire rope abuse, and it is
the primary goal of good inspection practice to discover such conditions with minimum effort.
When any degradation indicates a loss of original rope strength, a decision must be made
quickly to allow the rope to remain in service. Such a decision can only be made by an
experienced inspector. His determination will be based on:
1. Details of the equipment’s operation
2. Frequency of inspeciton
3. Maintenance History
4. Consequences of failure
5. Historical Records of similar equipment
6.10.8.2.
Broken Wires
6.10.8.2.1. Shortly after installation - The occasional premature failure of a single wire may be
found early in the rope life and in most cases it should not constitute a basis for rope
removal. Note the area and watch carefully for any further wire breaks. Remove the broken
ends by bending the wire backwards and forwards. In this way the wire is more likely to
break inside the rope where the ends are left tucked away between the strands. These
infrequent premature wire breaks are not caused by fatigue of the wire material.
Figure 6.10.8.2.1 Premature Wire Breaks
6.10.8.2.2. During wire rope service (Fatigue Breaks) - The rope must be replaced if a certain
number of broken wires are found which indicate that the rope has reached its finite fatigue
life span. Refer to the wire rope manufacturer’s recommendation or to ASME B30.2 for
proper rope replacement criteria.
6.10.8.2.3. Crown Wire Breaks - Under normal operating conditions single wires will break due
to material fatigue on the Crown of a strand. All wire rope removal/retirement criteria are
based on Fatigue wire breaks located at the Crown of a strand. Example: Severe crown
wire breaks on a 10-strand overhead crane wire rope. Crown breaks originate at the outside
of the rope at the contact point between rope and sheave/drum.
Figure 6.10.8.2.3.1 Crown Fatigue Breaks
Figure 6.10.8.2.3.2 Crown wire breaks on a non-rotating wire rope.
6.10.8.2.4. Valley Wire Breaks - Remove wire rope from service if even if you detect a single
valley wire break only. Valley breaks hide internal wire failures at the core or at the contact
between strand and core
Figure 6.10.8.2.4.1 Valley wire breaks on an 8-strand overhead crane wire rope.
Figure 6.10.8.2.4.2 Valley breaks originate inside the rope. Condition of the inner strands of the same rope
as above. The core has completely failed and immanent catastrophic rope failure will be the result.
Figure 6.10.8.2.4.3 A single valley wire break on a 19x7 rotation resistant rope.
Figure 6.10.8.2.4.4 Condition of core under that same single valley break. Note the extreme notching of
individual wire and the countless wire breaks. Such a condition is hidden under just a single (1) valley break.
6.10.8.2.5. Fatigue wire breaks are typically squared off straight across the wire.
Figure 6.10.8.2.5 Fatigue Wire Break
6.10.8.2.6. Tensile wire breaks are characterized by their typical 'cup and cone' appearance.
Figure 6.10.8.2.6.1 Tension Wire Breaks
Figure 6.10.8.2.6.2 On the right and left a typical cut-and-cone break pattern. The wires in the center of the
photo are a combination of fatigue and shear break.
6.10.8.3.
Worn and Abraded Wires
6.10.8.3.1. Wear, due to friction on sheaves, rollers, drums, etc., eventually causes outer wire
abrasion.
6.10.8.3.2. Before any inspection is made, determine what type of wire rope you have in
service. Many of today's wire ropes are 'compacted', 'calibrated', or 'die formed'. This
manufacturing process purposely flattens the outer wires and for an inexperienced inspector
these ropes may appear to be already abraded when indeed they are brand new. If you are
in doubt about what type of rope you are about to inspect, have a look at a section of the
rope which was not subjected to any abrasive work; e.g. like the safety wraps on the drum
or a section just behind the end connection.
6.10.8.3.3. The round outer wires of standard wire rope will become flat on the outside due to
friction when in contact with drums, sheaves, or other abrasive matter like sand or gravel.
This is part of normal service deterioration and in most crane installations relatively even
abrasion will occur. The rope must be replaced, however, if this wear exceeds 1/3 of the
diameter of the wire.
6.10.8.3.4. It is good practice to compare a section of the rope which was NOT subjected to any
bending work (e.g. the safety wraps, or a short section behind the end fitting) to the rope
section to be inspected.
6.10.8.3.5. The same applies when evaluating any possible reduced rope diameter during
service.
6.10.8.3.6. When the surface wires are worn by 1/3 or more of their diameter the rope must be
replaced. Abrasion caused by dragging the rope over a sharp object (steel corner, sharp
plate, abrasive surface etc.) Peening and subsequent wire break caused by high fleet angle
and rope vibration. Rope abrasion caused by normal operating condition on a high cycle
crane. Rope must be retired.
Figure 6.10.8.3.6 Worn Wire Rope
6.10.8.4.
Reduction in Wire Rope Diameter
6.10.8.4.1. As discussed previously on the 'Measuring the rope diameter' page and on the
'Break-In-Period' page, shortly after installation, the wire rope diameter will slightly decrease.
This is normal and is caused by the adjustment of all rope elements when loaded the first
time. To evaluate the diameter reduction, you have to measure the rope when new, and you
also have to measure the rope after the break in period at a specified load. This gives you a
good indication of the magnitude of the initial diameter reduction in your specific application.
The diameter reading you took after the break in period should now become your 'gauge'.
Do not compare the rope diameter you are about to take with the 'catalogue' diameter. It
may give you a false indication, since wire rope may have a plus tolerance of up to 4% to
5% over the 'catalogue' diameter.
6.10.8.4.2. If you detect a further diameter reduction when measuring the rope under the same
load condition as after the break in period, it is often due to excessive abrasion of the
outside wires, loss of core support, internal or external corrosion, inner wire failures, and/or
inner wire abrasion. However, there will always be a normal continuous small decrease in
diameter throughout the rope's service life.
6.10.8.4.3. Core deterioration, when it occurs, is revealed by a more rapid reduction in
diameter, and when observed, it is time for removal.
6.10.8.4.4. Deciding whether or not a rope is safe is not always a simple matter. A number of
different but interrelated conditions must be evaluated. It would be dangerously unwise for
an inspector to declare a rope 'safe' for continued service simply because its diameter had
not reached a certain minimum diameter if, at the same time, other observations led to a
different conclusion.
6.10.8.4.5. Because the removal criteria are much varied for different rope constructions and
types of cores, a table of minimum diameters has been deliberately omitted from this
publication.
Figure 6.10.8.4.5 Measure rope diameter After the Break In Period.
6.10.8.5.
Rope Stretch
6.10.8.5.1. Constructional Stretch - All ropes will stretch to varying degrees when loads are
initially applied. This stretch is known as the 'constructional stretch'.
6.10.8.5.2. This stretch occurs in three phases:
6.10.8.5.2.1.Initial or constructional stretch during the early period (Run-In) of rope service,
caused by the rope adjusting to the operating conditions.
6.10.8.5.2.2.Following the run-in period there is an extended period – the longest part of the
rope’s service life – during which a slight increase in stretch takes place over an
extended time. This results from normal wear, fatigue etc. On a graph this portion would
almost be a horizontal straight line inclined slightly upward from its initial level.
6.10.8.5.2.3.Thereafter, the stretch occurs at a quicker rate. This means that the rope has
reached the point of rapid degradation; a result of prolonged subjection to abrasive wear,
fatigue, and inner undetected wire breaks, etc. This second upturn of the curve is a
warning indicating that the rope should be removed to avoid sudden catastrophic rope
failures.
Figure 6.10.8.5.2.3
6.10.8.6.
Units of Rope Life
Elastic Stretch / Elastic Limit
6.10.8.6.1. Elastic stretch of wire rope occurs as soon as a load is applied. When the load is
released the rope returns to its initial length, hence the term 'elastic' stretch. This stretch is
caused by the elastic deformation of the steel itself (the individual steel wires) and also by the
lay of the rope which could be compared to resemble a coil spring. With other words, the
longer the lay length of a rope becomes, the less elastic stretch it will develop. Elastic stretch
in a wire rope is a desired feature. The ability of a rope to stretch under load means that the
rope is capable to absorb energy; the term here is 'energy absorption capability'.
6.10.8.6.2. In many instances it is not easy to clearly distinguish between (the remains of)
constructional stretch and elastic stretch as they may occur together especially when the rope
is new. The values for Elastic Stretch are dependent on rope construction, lay length and type,
steel material, tensile strength of wires etc. An approximation is o.25% to o.6% at WLL (or
lifting capacity). The E-module varies similarly from about 11 Million to 16 Million LB/inch
6.10.8.6.3. Elastic stretch turns into a 'permanent' stretch when the rope is loaded beyond 55%60% of its breaking strength (or beyond 2-1/2 to 3 times its WLL). At that point the steel
material elongates and deforms permanently and renders the rope inoperable as the individual
wires will have lost much of their mechanical properties to withstand material fatigue.
Figure 6.10.8.6.3
6.10.8.7.
Core Wire Breaks
6.10.8.7.1. The most difficult to detect wire rope deterioration. Core wire breaks are more likely
to appear in 6 & 8-strand and 19x7/19x19 ropes, rather than in multi-strand plastic coated
core wire rope. We have had examples where 8x36 and 19x7 ropes broke showing no
externally visible removal criteria, yet the core was completely broken to pieces. Once the
core breaks, the resultant sudden shock load on the outer strands may cause the rope to fail
in a catastrophic, unpredictable manner.
6.10.8.7.2. Core wire breaks in plastic coated core ropes are not likely to appear due to the
cushioning effect of the plastic layer. Field experience from customer returned plastic coated
core rope revealed no broken core wires without the outer strands having visible wire breaks
in excessive numbers far beyond any removal criteria.
6.10.8.7.3. To inspect the core of a 6- or 8-strand wire rope, the rope must be completely
unloaded. Carefully insert a spike through one or two strands and turn the spike with the
rope lay. If the core is heavily lubricated you need good lighting to see broken wires! You
may also wish to use an air gun to blow excessive lubricant off the core, but be sure to relube the core after your inspection.
6.10.8.7.4. As with any rotation resistant or non-rotating rope we recommend to leave such
internal inspections to the expert as such inspections can permanently damage the rope.
Figure 6.10.8.7.4 Inspection of a 6-strand wire rope
6.10.8.8.
Mechanical Damages - It is nearly impossible to list all variations of mechanical damage
a rope might be subjected to. Therefore, the following list should only be taken as a guideline.
None of these damages are repairable. However, the magnitude of the damages may vary from
a slight cosmetic damage to total destruction of the wire rope. If you are not sure about the
extent of the damage, change the rope, or call us for technical assistance and advice.
Figure 6.10.8.8.1 Bird Cage (6-strand rope) caused by shock loading.
Figure 6.10.8.8.2 Bird Cage (non-rotating rope) caused by worn sheave grooves.
Figure 6.10.8.8.3 Bird Cage forced through a tight sheave.
Figure 6.10.8.8.4 Protruding Core because of shock loading, torque build-up during installation, tight
sheaves, or incorrect rope design.
Figure 6.10.8.8.5 Example of a wire rope which jumped out of the sheave. Note the imprint of the sheave
flange.
Figure 6.10.8.8.6 Wire rope rolled off a sheave
Figure 6.10.8.8.7 Multiple drum winding: Layer-to-Layer Crushing
Figure 6.10.8.8.8 Smooth drum winding: Rubbing between drum wraps
Figure 6.10.8.8.9 Smooth drum winding: Crushing at Crossover Points
Figure 6.10.8.8.10 Example of a rotation resistant wire rope which was forced to run in too tight sheave
grooves. Result is so called 'core popping'.
6.10.8.9.
Kinks - Kinked wire rope due to improper installation procedure.
Figure 6.10.8.9 Kinked wire ropes which have been used. Kinks are pulled tight, caused distortion and
failure.
6.10.8.10. Corrosion
6.10.8.10.1.
Corrosion, while difficult to evaluate, is a more serious cause of degradation
than abrasion. Usually, it signifies a lack of lubrication. Corrosion will often occur internally
before there is any visible external evidence on the rope surface.
6.10.8.10.2.
The plastic protects the core against corrosion and the user does not have to
worry about undetected corrosion which may lead to a sudden and unexpected rope failure.
6.10.8.10.3.
Corrosion of the rope core not only attack the metal wires, but also prevents the
rope's component parts from moving smoothly as it flexes.
6.10.8.10.4.
Severe rusting leads to premature fatigue failure of single wires. When the rope
shows more than one wire failure near a fitting, it should be removed immediately. To
prevent abnormal corrosion, the rope should be kept well lubricated. In situations where
abnormal corrosive action can occur, it may be necessary to use galvanized or stainless
steel wire rope.
6.10.9.
Fittings
6.10.9.1.
Inspect the fittings on your rope and look for wire breaks at the shank of sockets or
sleeves. Inspect the fittings for wear, distortion, cracks, and corrosion. Follow the inspection
criteria of the fitting manufacturer and do not attempt to repair any wire rope fitting yourself.
Watch for missing hook latches and install new ones if necessary. If latches wear out too
rapidly, ask the manufacturer for special Heavy Duty latches which may fit your hook. Some
hook manufacturers offer self-locking and special Gate Latch hooks.
6.10.9.2.
Inspect wire rope at all fittings. Replace fitting if any broken wires are detected.
Figure 6.10.9.2 Wire Rope Fittings
6.10.10. Removal Criteria - All removal criteria are based on the use of steel sheave.
Fault
Possible Cause
Accelerated Wear
Severe abrasion from being dragged over the ground or
obstructions.
Rope not suitable for application.
Poorly aligned sheaves.
Large fleet angle.
Worn sheave with improper groove, size or shape.
Sheaves and rollers have rough wear surface.
Stiff or seized sheave bearings.
High bearing and contact pressures.
Sheaves/drum too small.
Rapid Appearance of Broken Wires
Rope not suitable for application.
Reverse bends.
Sheaves/drums too small.
Overload and shock loads.
Excessive rope vibration.
Kinks that have formed and have been straightened out.
Crushing and flattening of the rope.
Sheave wobble.
Corrosion
Inadequate lubrication.
Improper storage.
Exposure to acids or alkalis.
Kinks
Improper installation.
Improper handling.
Slack rope pulled tight.
Excessive localized Wear
Drum crushing.
Equalizer Sheave.
Vibration.
Stretch
Overload.
Passed normal stretch and approaches failure.
Broken Wires near Fitting
Rope Vibration.
Fittings get pulled too close to sheave or drum.
Sheaves/Drums Wear Out
Material too soft
Pinching, Crushing,
Sheaves grooves too small.
oval Shape
Not following proper installation and maintenance procedure
on multiple layer drums
Rope Unlays
Wrong rope construction.
(Opens up)
Rope end attached to swivel.
Reduction in Diameter
Broken core.
Overload.
Internal wear.
Corrosion.
Bird Cage
Tight Sheaves.
Rope is forced to rotate around its own axis.
Shock loads.
Improper Wedge Socket installation.
Core Protrusion
Shock loading.
Disturbed rope lay.
Rope unlays.
Load spins and rotates rope around its own axis.
Table 6.10.10 Removal Criteria
6.10.11. Maintenance
6.10.11.1. Inspection of Sheaves and Drums
6.10.11.1.1.
Proper maintenance of the equipment on which the ropes operate has an
important bearing on rope life. Worn grooves, poor alignment of sheaves and worn parts
resulting in shock loads and excessive vibration will have a deteriorating effect.
6.10.11.1.2.
Sheaves should be checked periodically for wear in the grooves which may
cause pinching, abrasion, and bird-caging of the rope. If the groove shows signs of rope
imprints the sheave must be replaced or re-machined and re-hardened. The same should
be done on drums showing similar effect.
6.10.11.1.3.
Poor alignment of sheaves will result in rope wear and wear on the sheave
flange. This should be corrected immediately.
6.10.11.1.4.
Excessive wear in the sheave bearings can cause rope fatigue from vibration.
6.10.11.1.5.
Large fleet angles will cause severe abrasion of the rope as it winds onto the
drum.
6.10.11.1.6.
Furthermore, the rope will roll into the sheave groove introducing torque and
twist which may cause high stranding and bird-cages.
6.10.11.2. Dimension of the Groove Radius
6.10.11.2.1.
The very first item to be checked when examining sheaves and drums, is the
condition of the grooves. To check size, contour and amount of wear, a groove gauge is
used.
6.10.11.2.2.
Two types of groove gauges are in general use and it is important to note which
of these is being used. The two differ in their percentage over the Nominal Rope Diameter.
6.10.11.2.3.
For new or re-machined grooves, and for inspection of fitness for new ropes,
the groove gauge should be 1% over the maximum allowable Plus Tolerance of the new
rope; alternately, the sheave groove must measure 1% over the Actual Rope Diameter
intended to be installed.
6.10.11.2.4.
Many groove gauges on the market are so called 'No-Go' gauges and are made
with Nominal plus 1/2 of permissible rope Plus Tolerance. If you use these gauges be sure
that the existing rope is smaller than this gauge. A rope operating in an even slightly
undersized groove, deteriorates faster and may develop bird-cages.
Figure 6.10.11.2.4 .1 Sheave gauges for rope sizes ranging from 8 mm - 32 mm and ¼” to 1 1/2” are
available
Figure 6.10.11.2.4.2 Check bearings for wobble, lubrication & ease of rotation
Figure 6.10.11.2.4.3 Properly matched rope & sheave groove
Figure 6.10.11.2.4.4 Sheave groove too small
Figure 6.10.11.2.4.5 Sheave groove is undercut and new rope will get damaged beyond repair
Figure 6.10.11.2.4.6 A sheave corrugated by the rope's 'print'. This sheave will damage the rope
6.10.11.3. Cut and Slip Procedure
6.10.11.3.1.
On multiple layer drums, wire rope will wear out at the crossover points from
one wrap to the next. At these crossover points, the rope is subjected to severe abrasion
and crushing as it is pushed over the rope 'grooves' and rides across the crown of the layer
beneath. The scrubbing of the rope, can easily be heard.
6.10.11.3.2.
In order to extend the working life, shortening of the rope at the drum anchoring
point of approx. 1/3 of the drum circumference, moves the crossover point to a different
section of the rope. Now, a rope section previously not subjected to wear will take the
workload.
Figure 6.10.11.3.2 Cross-over points at which damage to a rope may occur first
6.10.11.4. Lubrication
6.10.11.4.1.
During fabrication, ropes are lubricated; the kind and amount depending on the
rope's size, type and use, if known. This in-process treatment will provide the finished rope
with ample protection for a reasonable time if it is stored under proper conditions, and in the
early stages of the rope's working life. It must be supplemented, however, at regular
intervals.
6.10.11.4.2.
Re-lubrication of a wire rope is not always a simple task. Apart from lubricant
being messy in itself, old lubricant, dirt and other particles may cover the outside of a rope to
a point were newly applied lubricant will not penetrate the inside of a rope. In these cases it
becomes necessary to either thoroughly clean the rope, or use a high pressure lubrication
device and force new lubricant into the rope.
6.10.11.4.3.
If the wire rope surface is clean, re-lubrication can also be made with spray
cans of specially formulated lubricant which penetrates the inside of a rope.
6.10.11.4.4.
The lubrication procedure and is very much dependent on the length and size
of a rope and on the equipment the rope is installed on. In any case, if a planned program of
regular lubrication is not carried out, the rope will deteriorate more rapidly.
6.10.11.4.5.
Tests have shown that non-lubricated ropes will generate only about 1/3 of the
bending cycles than ropes which are lubricated. Ropes with a plastic coated core have the
advantage that the inner rope is 'permanently lubricated'.
Figure 6.10.11.4.5 Lubricating Wire Rope
6.10.11.5. Unreeling A Wire Rope
6.10.11.5.1.
When removing the rope from the shipping reel or coil, the reel or coil must
rotate as the rope unwinds. Any attempt to unwind a rope from stationary reel or coil will
result in a kinked rope that is ruined beyond repair.
6.10.11.5.2.
The following illustrations demonstrate the right and wrong way of unreeling a
rope.
6.10.11.5.3.
Special care must be taken not to drag the rope over obstacles, over a
deflection shaft, or around corners.
6.10.11.5.4.
Avoid large fleet angles between the shipping reel and the first sheave. The
rope may roll in the sheave causing the rope to un-lay. This is particularly important for all
DoPar, Lang lay, and non-rotating rope constructions.
Figure 6.10.11.5.4 Unreeling wire rope
6.10.11.5.5.
Avoid reeving the rope through small deflection sheaves and avoid changing
the plane from vertical to horizontal direction.
6.10.11.5.6.
If you have to unspool large and heavy wire rope, use a brake to keep a slight
tension on the rope. Never let the rope go slack and form loops.
6.10.11.5.7.
All of these precautions apply to standard 6-strand, 19x7, 19x19, and 34x7 wire
ropes.
6.11. Sheave Wheel Inspection and Repair Guidelines
6.11.1.
Introduction and Purpose
6.11.1.1.
The purpose of this chapter is to provide guidelines for the inspection, repair, and
servicing of wire rope sheaves and sheave block assemblies in overhead cranes.
6.11.2.
Scope
6.11.2.1.
This chapter applies to wire rope sheaves, sheave wheel assemblies, and sheave block
assemblies found on electric overhead traveling cranes for steel mill service.
6.11.2.2.
Crane hooks, hook blocks, side plates and their related components, are beyond the
scope of this guideline.
6.11.3.
Inspection - For proper sheave wheel operation, the two most important areas to be
inspected are the groove area and the bore area. In addition, the hub faces should be inspected for
wear resulting from the accumulation of abrasive dirt and debris between the sheave wheels on the
sheave pin.
6.11.4.
Groove Inspection
6.11.4.1.
The first item requiring inspection on a sheave wheel is the rope groove. The actual root
diameter of the sheave wheel, while important, is not as important as the size and condition of
the groove itself. To check the size, contour, and amount of wear in the groove, a sheave
groove gauge is used. There are two types of sheave groove gauges; (1) Gauges for checking
the size of the grooves of new sheave wheels, or for the inspection of existing sheave wheel
grooves for suitability for use with new wire ropes; and (2) Gauges for checking the amount of
wear in the groove of a used sheave wheel. This second type of gauge is referred to as a
groove wear gauge, or sometimes as a ‘No-Go’ gauge, and will be the type of gauge discussed
here. This groove wear gauge is different than a new groove gauge in that the size indicated on
the gauge is the nominal rope diameter plus 2-1/2% (A ‘new groove’ gauge is nominal rope size
plus 5%). This ‘rope size plus 2-1/2%’ gauge represents the minimum acceptable diameter of a
worn sheave or drum groove. If this gauge does not fit properly, applicable standards
recommend replacement or re-machining of the sheave or drum groove. Fig. 6.11.4.1 and the
accompanying tables have been reproduced from AIST Technical Report #6 and show the
AIST/AISE recommended values for the sheave wheel groove radius for various rope sizes.
Figure 6.11.4.1 from AIST TR #6
Rope
Dia
A
B
C
½
12
11 ½
1¾
9
15
14 3/8
2
11
5
/8
¾
7
/8
1
1 1/8
1¼
1 3/8
1½
18
21
24
27
30
33
36
17 ¼
20 1/8
23
25 7/8
28 ¾
31 5/8
34 ½
D
/32
/32
2¼
13
2½
31
2¾
E
F
½
1
5
1
/8
¾
/32
/32
G
¾
15
/16
1
1 1/8
/8
3
1 5/16
35
1
3
1½
3
39
1 1/8
3
1 11/16
3¼
11
1
1
1 7/8
1 3/8
1
2 1/16
1½
1
2 1/4
3½
3¾
/32
/32
7
/64
/64
/64
/16
¾
13
/16
/64
/64
/64
/16
/16
/16
Table 6.11.4.2 Sheave Wheel Contours – 24:1 Sheave-to-Rope Ratio
Rope
Dia
A
B
C
D
½
15
14 ½
1¾
9
5
/8
18 ¾
18 1/8
2
¾
22 ½
21 ¾
7
/8
26 ¼
1
E
F
G
/32
¾
½
1
11
5
/8
1
15
2¼
13
¾
1
1 1/8
25 3/8
2½
31
7
/8
3
1 5/16
30
29
2¾
35
1
3
1½
1 1/8
33 ¾
32 5/8
3
39
1 1/8
3
1 11/16
1¼
37 ½
36 ¼
3¼
11
1¼
1
1 7/8
/32
/32
/32
/64
/64
/64
/16
/32
/32
/64
/64
/64
/16
/16
1 3/8
41 ¼
39 7/8
3½
1½
45
43 ½
3¾
¾
13
/16
1 3/8
1
2 1/16
1½
1
2 1/4
/16
/16
Table 6.11.4.3 Sheave Wheel Contours – 30:1 Sheave-to-Rope Ratio
6.11.4.2.
Inspection of the sheave groove radius is performed by placing the appropriate groove
wear gauge in the throat of the sheave. A worn rope groove will generally have a smaller radius
than when new due to the abrasive wear of the wire rope in the sheave groove. This wear will
be evident by space, or ‘daylight’ between the wear gauge and the bottom of the sheave
groove. Any sheave with a groove radius smaller than the radius on the appropriate groove
wear gauge (i.e. daylight under the wear gauge) needs to be replaced or re-grooved. Failure to
re-groove or replace sheaves with worn grooves will result in pinching of the wire rope which will
cause damage to the rope through premature rope wear, strand breakage, or high stranding of
the rope. Due to the small amount of hardened material beneath the root diameter of the
sheave, and the cost of dis-assembly, machining, and re-assembly, it is generally not
economically practical to re-groove sheaves.
Figure 6.11.4.2 Wear Gauges
6.11.4.3.
In addition, the sheave wheel gauge should contact the root area of the sheave wheel
for an arc of approximately 150 degrees.
6.11.4.4.
The surface finish of the rope groove should also be inspected. A rough finish in the
groove will result in excess abrasive wear of the wire rope and will decrease the life of the rope.
Severely worn sheaves will develop a corrugation pattern where the rope pattern is imprinted in
the sheave groove. This condition results in rapid wear of the wire rope. Flat spots on the root
diameter of the sheave can cause rope whipping problems when in service. This whipping will
cause accelerated fatigue of the rope strands eventually resulting in strand breakage.
Figure 6.11.4.4.1 A sheave corrugated by the rope's 'print'. This sheave will damage the rope
Figure 6.11.4.4.2 Worn versus Unworn Sheave Wheel Grooves
6.11.4.5.
The position of the groove in the sheave should also be examined. A groove that
appears to be off-center is likely the result of alignment problems in the wire rope reeving
system. When this occurs, the wire rope only contacts one side of the sheave wall when
entering and leaving the rope groove. This may result in one of the sheave flanges being worn
considerably thinner than the other one. In severe cases, one of the flanges may break due to
excessive loading and these sheaves need to be replaced immediately. This wearing can also
accelerate the wear on the wire rope. Any rope reeving system alignment problems should be
addressed, but are beyond the scope of this document.
6.11.4.6.
Sheaves can be supplied with rope grooves with a wide range of hardness values, from
a very soft untreated or annealed condition (around 180 BHN), to a very high hardness (up to 60
HRc). In general, higher hardness rope grooves will provide superior abrasive wear resistance.
Examples of hardening procedures include flame hardening, spin quench and tempering (ASTM
A-504), and carburizing. When checking the hardness of a sheave wheel rope groove, care
must be taken to check the hardness at the bottom of the groove. Special adapters for
hardness measuring instruments are often required due to the narrow radius of the surface to
be measured. Some heat treating procedures only harden the throat area of the groove,
therefore, any hardness readings taken on the inside flanges of the wheel can provide
erroneous hardness readings.
6.11.5.
Bore Inspection
6.11.5.1.
The wire rope sheave and hook block assemblies generally seen in steel mill service are
mounted on non-rotating sheave pins with bearings in the bores of the wheels. The majority of
these mill-duty cranes have anti-friction roller bearings assembled into the bores of the sheave
wheels. Older cranes may still have sheave wheels with bronze bearings.
6.11.5.2.
With sheave wheel assemblies, the bearings are fit into the bores of the wheels with a
tight fit, and fit over the sheave pins with a loose fit. In service, the wheels and bearings will
need to turn freely over these pins. At disassembly and assembly, the pin should be easily
displaced inside the bores of the bearings. Caution should be exhibited when handling these
assemblies since the sheave pin may be loose and can fall from the assembly during handling.
6.11.5.3.
A tight fitting sheave pin during disassembly should be noted because this may indicate
a problem with the bearing. Surveys conducted by the AIST have shown that the primary
reason for sheave replacement is due to bearing failure, so bearing inspection is critical.
6.11.5.4.
Sheave wheel bores need to be inspected for size, surface finish, and general overall
condition. Any deviations will need to be repaired by an approved procedure, or by replacement
of the sheaves. Bore fits should be in accordance with the bearing manufacturers’
recommended fit guidelines.
6.11.6.
Hub Face Inspection
6.11.6.1.
Wear on the hub face of a sheave wheel is generally not a reason for the replacement of
a sheave wheel. The buildup of abrasive dirt and grit between the sheave wheels on a sheave
pin can cause wear on the sheave wheel hub faces, as well as hindering the free-rolling action
of the sheave wheel itself. This buildup will cause abrasive wear on the hub faces of the sheave
wheels. This will be seen by circular wear marks on the hub faces. If the wear is severe, the
hub faces will require repair.
6.11.6.2.
In rare cases, sheave wheels have been found to rub against each other. This is not a
pre-designed or desired condition. If this occurs, larger problems may be present within the
sheave block that will require attention prior to the rebuilding of the assembly
6.11.7.
Related Hardware - The following sections briefly discuss other components that will require
attention during the rebuild of a sheave assembly.
6.11.7.1.
Bearings
6.11.7.1.1. As previously stated, according to AIST Crane Symposium surveys, bearing failures
are generally the major reason for the removal of the sheave block from service.
6.11.7.1.2. Bearings used in sheave wheels can be either anti-friction roller bearings or bronze
bearings. The vast majority of the steel mill sheave applications seen today, and virtually all
of the newer cranes being built, use anti-friction roller bearings. Therefore, only this style
bearing will be discussed.
6.11.7.1.3. Cranes with bronze bearings are beyond the scope of this paper.
6.11.7.1.4. Two general roller bearing styles dominate the cranes in service today: tapered
roller bearings and cylindrical needle roller bearings. Other bearing types, such as spherical
bearings, ball bearings, and other types of tapered roller bearings can be found in sheave
wheels, but these can be considered exceptions to the rule.
6.11.7.1.5. For specific bearing dimensions, load carrying capacities, and fit recommendations,
the appropriate bearing manufacturer catalogs should be referenced.
6.11.7.2.
Grease Seals - Special grease seals are available for use with the many sizes and
varieties of anti-friction bearings designated for sheave wheel use. These seal varieties include:
6.11.7.2.1. Metal seals and non-metallic seals made from conventional oil seal materials that
can be added to the basic bearing. Care should be taken when specifying the style of
grease seal required. The non-metallic seals have been known to melt in some of the very
hot applications that are present on certain steel mill crane applications.
6.11.7.2.2. Seals that are built into the bearing itself. These can generally found as an added
option for use on cylindrical roller bearings designed for sheave wheel service.
6.11.7.3.
Sheave Pins
6.11.7.3.1. The non-rotating sheave pins require a smooth finish for the loose fit mounting of
the inner race of the bearing.
6.11.7.3.2. Sheave pins are generally replaced due to wear. This wear is generally seen by the
imprint of the bearing inner race onto the pin surface. This imprint will be seen after the
sheave pin has been removed from service and inspected after bearing disassembly.
Sometimes the sheave pin disassembly will be difficult due to these imprints on the pin.
6.11.7.3.3. Sheave pins may, or may not, be hardened. The hardness can range from 180-220
BHN for untreated or annealed pins to 56-60 HRc for flame hardened or carburized pins. If
wear is seen on the pins, an increase in hardness is an acceptable remedy. Sheave pins
with hardness ranges near 300 BHN will show an appreciable increase in wear resistance
over a comparable 200 BHN sheave pin.
6.11.7.3.4. Sheave pins also contain grease lubrication paths for lubrication of the bearings.
These holes need to be cleaned prior to the reassembly of the sheave block. Good
maintenance practices should include the cleaning of all lubrication paths prior to assembly
to insure that no metal shavings or other foreign material that may have been used to
protect the holes during shipping are blocking the lubricating holes.
6.11.8.
Reference Sources
Specification for Electric Overhead Traveling Cranes for Steel Mill Service. AIST/AISE Technical
Report No. 6; June 2005
Wire Rope Users Manual; 4th edition; Wire Rope Technical Board; 2005
Whiting Crane Handbook; 4th edition; 1979
AIST/AISE Crane Symposium Surveys, various years
6.12. Rope Drum Inspection and Repair Guidelines
6.12.1.
Introduction and Purpose
6.12.1.1.
The purpose of this chapter is to provide guidelines for the inspection, repair, and
servicing of rope drums in overhead cranes.
6.12.2.
Scope
6.12.2.1.
This chapter applies to rope drums found on electric overhead traveling cranes for steel
mill service.
6.12.2.2.
Associated components that are assembled onto rope drums, such as gears, bearings,
and ropes, are beyond the scope of this guideline.
6.12.3.
Inspection
6.12.3.1.
The most important areas requiring inspection on a rope drum are the groove areas, and
the areas that seat or support accessory items such as the drum gear, the bearings, and any
seals.
6.12.4.
Groove Inspection
6.12.4.1.
The first items requiring inspection on a rope drum are the grooves. The actual groove
diameter of the drum, while important, is not as important as the size of the groove itself.
According to AIST/AISE Technical Report No. 6 (TR6), the radius of the grooves on a rope
drum should be 1/32 inch larger than the radius of the rope. This guideline does differ from the
sheave wheel groove guidelines listed in TR6. For inspection purposes of the rope drum
grooves to determine wear, the use of the sheave wheel guidelines is acceptable, as this allows
for the use of the sheave wheel radius gages, as described in the following paragraph. This
technique does agree with the chart supplied in the Wire Rope Users Manual, 4th edition (see
reference sources below).
6.12.4.2.
To check the size, contour, and amount of wear in the groove, a sheave wheel radius
gage is used. This gage is different than a standard radius gage in that the size indicated on
the gage is the rope size plus a nominal amount. Two types of sheave wheel gages are
available. The most common set of gages, and the type to be used for the inspections of rope
drum groove sizes, is the set of gages for minimum groove size.
6.12.4.3.
Inspection of the rope drum groove radius is performed by placing the gage in the throat
of the rope drum groove. Any rope drum with a groove radius smaller than the radius on the
worn gage set needs to be replaced or re-grooved.
6.12.4.4.
If the groove is worn, this can generally be seen by a decrease in the throat groove
radius. Daylight under the gage is not acceptable.
6.12.4.5.
The condition of the lands between the grooves also needs to be examined. The lands
should be intact, without deformation or loss of material. To visually evaluate wear, compare
the worn grooves and lands to the unworn grooves and lands holding the dead wraps of rope.
The dead wrap areas will show no wear. Consideration should be given to removing the drum
for repair if the lands have worn approximately half of the original thickness as found on the
dead wrap land.
6.12.4.6.
Groove wear location should be examined. Many times the groove will not show an off-
center wear to the naked eye, but the lands will show a slight deformation, generally towards the
apex of the drum grooves. Examination of this deformation can be detected from the radius
gages. Also, the OD of the lands will in many cases show a decrease in thickness in the worn
areas, proceeding to sharp corners. Sharp lands can cut into the rope, damaging the strands,
prompting replacement of the wire rope.
6.12.4.7.
The drum OD may also show a decrease in diameter in the worn areas of the grooves.
Laying a straight edge across the OD of the drum grooves, parallel with the centerline of the
drum, can show the decrease in the shell OD in the worn areas. The longer the straight edge,
the more distinct the change in OD will be seen.
6.12.4.8.
Groove finish is important. A rough finish will decrease the life of the rope. Corrugation
of the grooves is not allowed. Flat spots on the throat diameter of the drum can cause rope
whipping problems when in service. This can help accelerate the fatigue seen in the rope
strands.
6.12.4.9.
For inspection of the groove hardness, the hardness needs to be checked at the bottom
of the grooves. Do not inspect the hardness in the following areas: the non-grooved flat areas
between the grooves and at the outboard ends of the grooves; and in the areas near the tips of
the groove lands. One of the most common forms of groove hardening, flame hardening, may
only harden the bottom radius area of the drum groove, for an arc length of approximately 150
degrees. Inspection of the non-grooved areas, and / or the areas near the tips of the grooves,
can yield erroneous hardness readings. For obtaining the hardness in the root area, special
needle-nose hardness adapters (i.e. Equotip or Scleroscope) may be required.
6.12.4.10. One method of fixing worn grooves is to re-chase all of the grooves of the drum, thereby
giving the drum a new set of grooves. This means that the existing grooves will be chased in
their current positions. Care must be taken that the drum is not weakened to such an extent
that operational failure would occur, such as crushing. Engineering analysis of the drum
strength will need to be performed.
6.12.4.11. If the existing grooves need to be totally machined off, with new grooves chased onto
the drum body, too much of the drum diameter may be removed, so that an additional groove or
two may need to be added to allow for the proper amount of rope to be available for normal
service operation of the crane. Engineering will need to be consulted for this calculation, as well
as for the new drum strength calculation.
6.12.5.
Gear Seat Inspection
6.12.5.1.
The gear that assembles onto the rope drum is usually of two varieties. These are the
ring gear that mounts on a shoulder of the drum, and a conventional style gear designed to
mount on an adjacent shaft diameter of the drum. Whichever style of gear is used, the size and
finish of the gear seat, and the size and condition of the key seat are important areas requiring
inspection.
6.12.5.2.
The gear seat needs to be inspected for size, and compared to the bore size of the new
gear to assure that sufficient fit is present. In addition, the surface finish of the journal also
needs to be taken into consideration in order to assure that there is sufficient surface area for
the gear bore and gear seat to mount against each for proper power transmission.
6.12.5.3.
The condition and size of the keyway are also important. All keyways need to be
inspected.
6.12.5.4.
6.12.6.
Although beyond the scope of this section, it is advised that new keys be supplied.
Bearing Seat Inspection
6.12.6.1.
The bearing seat diameters require inspection for size and condition. Knowing the type
and size of bearing used, the bearing manufacture’s guidelines for size and fit can be consulted
for size and finish requirements.
6.12.6.2.
The scope of repair required will need to be determined after the inspection results are
known. The exact methods of repair can vary widely and can be determined by the resources
available to the repair facility.
6.12.7.
Oil / Grease Seal Journal Inspection
6.12.7.1.
The journals that support seals, whether for oil or grease, need to adhere to the size and
surface recommendations as published in the appropriate seal manufacturer’s catalog.
6.12.7.2.
The scope of repair required will need to be determined after the inspection results are
known. The exact methods of repair can vary widely and can be determined by the resources
available to the repair facility. The use of wear sleeves, if the proper sizes are available, is one
method of repair that can be employed.
6.12.7.3.
Many drum applications still use labyrinth seal systems that rely on the grease to provide
the proper sealing. Theoretically, since the retainer does not contact the shaft, no wear should
occur to the drum shaft. If wear does occur, the shaft will need to be repaired, subject to the
conditions listed above.
6.12.8.
Rope Clamps
6.12.8.1.
Rope clamp bolts or studs shall be inspected for torque in the field.
6.12.8.2.
Rope clamps are generally made with the actual rope drum diameter in mind. If the
drum diameter is decreased from remachining, it is recommended that new rope clamps, with a
new radius of curvature, be provided.
6.12.9.
Related Hardware
6.12.9.1.
Related hardware received with a rope drum assembly may include: bearings, bearing
retainers, rope clamps, seal retainers, and oil seals. All items need to be inspected, and
replaced as required.
6.12.9.2.
It is advised that all bearings, oil seals, and mounting hardware (such as bolts), be
replaced.
6.12.9.3.
Bearing retainers and seal retainers need to be inspected and brought back to OEM
print specifications.
6.12.10.
Reference Sources
Specification for Electric Overhead Traveling Cranes for Steel Mill Service. AIST/AISE Technical
Report No. 6; June 2005
Wire Rope Users Manual; 4th edition; Wire Rope Technical Board; 2005
Whiting Crane Handbook; 4th edition; 1979
6.13. Fabricated Spreader Beams
6.13.1.
Purpose
6.13.1.1.
This guideline is intended as an aid for plant maintenance personnel, crane and lifting
equipment service technicians who are responsible for periodic inspections. It will also assist the
end user in the understanding and inspection of large fabricated spreader beams that are
reeved directly to the overhead crane.
6.13.2.
Scope
6.13.2.1.
This guide is intended for large, non-powered, fabricated, welded construction, spreader
beams that are reeved directly to the crane. These beams include ladle beams, tundish beams
and the like.
6.13.2.2.
This guide is intended to supplement the training and experience of personnel who are
already qualified to perform inspections of cranes and lifting equipment.
6.13.3.
Nomenclature for Spreader Beam
Figure 6.13.3 Nomenclature for Spreader Beam
6.13.4.
The Inspection of the Spreader Beam
Inspection of Spreader Beam
Item
1
2
3
4
5
6
7
Points of Interest for Inspection
Description
Inspect the welds of
the spreader beam
Inspect the beam for
general overall
condition

Inspect all welds for any cracking, damage or defects. Cracked welds or
defective welds in critical areas must be repaired.

Inspect the plates for any cracking, wear, dents, etc.

Inspect the boss plates and the bores for support pins for excessive wear.

Visually inspect the pins for any exterior signs of wear and tear.

In most case these pins cannot be completely inspected because they are
generally covered or partially hidden by the sheaves or ladle hook or other
support structures. Ultra-sonic testing of these pins on an annual basis to
determine any internal defects is highly recommended.

Ensure keeper plates, retaining nuts, etc. are in place and secure.

Rope sheaves should be inspected for overall condition and wear in the rope
grooves. Sheaves should be held firmly in place between the beam support
side plates.

Sheaves should be rotated to ensure they are freely turning and that the
bearings are sound.

Ensure the bearings are well lubricated.

Other support structures such as clevis blocks, support linkages, crossheads,
limit striker plates, equalizer brackets, etc. should be treated like the
spreader beam, as outlined in Items 1 and 2.

Heat shields and/or other protective structures that do not affect the strength
of the spreader beam should be inspected for overall integrity and condition.

Fasteners, chains, lugs, etc. which holds the shield or protective structure to
the spreader beam should be also be inspected for overall integrity and
condition. Falling debris or pieces of structure are a safety hazard.

Check for wear on bushings and if bushings are to be greased check that
there is adequate lubrication.

Lifting chains, if applicable, should be inspected for wear and defects.
Sheave pin and
support pins
Sheaves and
bearings
Other support
structures
Heat shields or other
protective structures
Other Items
Table 6.13.4 Spreader Beam Inspection
6.13.5.
Inspection frequency:
6.13.5.1.
Using the Table 6.13.4, an inspection schedule can be developed for the spreader beam
base on the inspection frequency below:
6.13.5.1.1. Visual inspection of the spreader beam should be performed daily.
6.13.5.1.2. A detailed visual inspection of the spreader is recommended weekly to biweekly.
The frequency of inspection will depend on the service and operating conditions of the
crane. A written record that includes the date of inspection, the person who performed the
inspection, the spreader beam identification and the findings of the inspection should be
kept.
6.13.5.1.3. On a yearly basis, in addition to visual inspection, an NDT (non-destructive testing)
inspection by a qualified person should be performed on the spreader beam structure. All
support pins and sheave pins which cannot be accessed for NDT, should be ultra-sonic
tested to determine its integrity and condition. A written record that includes the date of
inspection, the person(s) who performed the inspection, the spreader beam identification
and the findings of the inspection should be kept.
6.13.5.1.4. Every four to five years (or more frequently depending on the service and operating
conditions of the crane) a complete strip, teardown and cleaning of the spreader beam and
its components should be performed. A detailed visual and NDT inspection of the spreader
beam and each of the individual components should be performed. Bearings should be
replaced, support pins and bushings checked for wear and defects, etc. A written record that
includes the date of inspection, the person(s) who performed the inspection, the spreader
beam identification and the findings of the inspection should be kept.
6.14. Lubrication Section
6.14.1.
Purpose
6.14.1.1.
The Purpose of this section is to provide simplified general lubrication guidelines based
on past experience of maintaining EOT cranes and their components. It is always advisable to
obtain, read, understand, and follow the crane manufacturer’s instructions. While many of the
crane manufacturers no longer exist as a source of information, there are petroleum/lubrication
companies that service the plants and are a valuable source for any general or special
lubrication needs. Most plants today have contracts with such companies to supply the oil or
other products for lubrication for all the mechanical equipment in the plant, cranes included. Just
remember the age-old directions for taking care of any machinery, “keep it clean, keep it tight,
and keep it lubricated”.
6.14.1.2.
The following sections are itemized by crane components. The lubrication types are
mentioned and should be referred to when requesting products from any supplier.
6.14.2.
Grease
6.14.2.1.
Motor Bearings.
6.14.2.1.1. Motors using roller bearings (not oil-bearing motors) should have grease applied as
required by the motor manufacturer.
6.14.2.1.2. Do not over-grease the bearings as the grease can push through the seals on DC
motors and contaminate the commutator.
6.14.2.1.3. It is recommended that the relief plug, located below the bearing, be removed while
adding grease to eliminate the possibility of over-filling the bearing.
6.14.2.1.4. If a small hand pump is used, only a few pumps should be necessary if a regular
preventive maintenance program is used.
6.14.2.1.5. The relief plug must be re-installed when finished.
6.14.2.1.6. Use EP-2 or AFB-2 type grease.
6.14.2.2.
Gearbox Bearings.
6.14.2.2.1. For gearboxes on cranes with specific bearings designed for grease applications,
high temperature greases should be used or a grease such as EPA1, which is waterproof.
6.14.2.3.
Couplings.
6.14.2.3.1. Couplings should be lubricated with grease having an anti-sling quality. This may
require at least two different delivery systems on cranes, one for bearings and one for
coupling lubrication to comply with the crane’s Preventive Maintenance (PM) program.
6.14.2.3.2. A high-temperature lubricant should be applied to the hoist drive mechanism
couplings, as the hoist motors can become overheated during extended use (a motor is
considered “hot” if the surface temperature is above 125o F).
6.14.2.4.
Sheave Bearings.
6.14.2.4.1. Sheave Bearings are typically tapered roller bearings.
6.14.2.4.2. Use EPA1 that is waterproof and high temperature rated or #1 EP. Lithium-based
high temperature grease can also be used.
6.14.2.5.
Plain Bearings for Pin Connections.
6.14.2.5.1. Where Bronze bushings, Sintered metal bushings, or Hardened Steel bushings are
used in bearing applications, the connection has limited rotational movement.
6.14.2.5.2. Examples include:
6.14.2.5.2.1. Connecting pins in bridge wheel trucks to equalizer trucks
6.14.2.5.2.2. Yokes in lower block side-plates for the crosshead connection that supports
the forged hook
6.14.2.5.2.3. Pins where blocks are connected to spreader bars or similar pin connections
where no full 360-degree rotation exists.
6.14.2.5.3. Without lubrication, wear rates occur at an increased rate causing bore distortion
and pin wear.
6.14.2.5.4. Often these bushings will have a curved groove on the inside bore to help
lubrication enter the bearing and cover the whole journal. Plain bearings can also have solid
graphite or other lubricant inserted in the walls of the bushing. Sometimes bushings are
installed as a modification or repair to correct oval-shaped pin bores by machining and reinstalling the bushings.
6.14.2.5.5. Use a standard grease for these bearings.
6.14.2.6.
Wheel Assembly Bearings
6.14.2.6.1. If spherical or tapered bearings are used in the wheel assembly, standard bearing
grease can be utilized.
6.14.2.6.2. If the bearings have the W-64 polyoil feature or an equivalent, a manufacturerspecified grease should be added to fill the void that exists between the bearing and the
retainer or capsule.
6.14.2.6.2.1.Failure to fill the voids can allow the polyoil lubricant to flow out into the voids
during use and not be re-absorbed back into the synthetic pack or sponge.
6.14.2.6.2.2.The grease used must be compatible with the polyoil lubricant.
6.14.2.6.2.3.If bearings with polyoil feature are used, then the W64E feature should be
specified. W64E has a higher temperature rating and an anti-corrosion additive. This
procedure applies to all polyoil bearings applications.
6.14.3.
Oils
6.14.3.1.
Spur and Helical Gearing on Hoist and Travel Drives
6.14.3.1.1. A light oil, classified as International ISO viscosity grade 100, is to be used.
6.14.3.1.2. Splash lubrication is designed into the gearbox; even on triple-reduction gearboxes.
6.14.3.1.3. On multiple reductions that are vertically mounted, a recirculating pump system
should be installed to circulate the oil from the bottom of the box to the top gear.
6.14.3.1.4. A check valve should be included in the piping circuit to hold oil at the pump during
inactivity. Long piping systems can deflect with normal crane movement causing the piping
to bend and crack resulting in leakage.
6.14.3.1.5. A “dip stick” should be incorporated into the design of the gearbox to monitor oil
levels.
6.14.3.2.
Worm Gearing
6.14.3.2.1. Worm drives have unique features and are found on cranes both as hoist drives and
travel drives.
6.14.3.2.2. The ideal worm gear lubricant is straight mineral oil containing 5 to 10% acid-free
tallow and having a viscosity of 150 seconds at 210o F. Adequate ‘film strength’ is critical for
proper lubrication of the worm drive system.
6.14.3.2.3. Oil pumps are also used in worm gear systems to apply oil to the steel worm during
operation.
6.14.3.2.4. Gearing failures on the worm or rim are sometimes caused by improper lubrication,
except upon initial start-up if the worm gear and rim gear are improperly aligned. Proper
alignment means correct shimming between the two in preparation for increased load.
6.14.3.2.5. A hoist drive will experience a shift in the load contact zone between the worm gear
and the rim gear when the load increases. If alignment has not been set up correctly, the
tooth contact will be in the wrong area resulting in “wiping” the worm gear to destruction.
The resulting high-contact stresses between the worm and the rim can damage the gears in
a short period of time.
6.14.3.3.
Plain Bearings for Rotating Shafts
6.14.3.3.1. Plain bearings including bushings of bronze, sintered metal and babbit can be found
in several components on older cranes. This includes high-RPM rotating equipment such as
wheel assemblies, gearboxes, line shafts and sheaves.
6.14.3.3.2. In wheel applications where oil is the lubricant, a light oil as outlined in item “B”
above is the most common lubricant used.
6.14.3.4.
Ensure that the bearing arrangement is properly sealed to avoid leakage. As an
example, trolley wheel bearings can dry resulting in the motor being unable to power the trolley
until the wheel sleeve bearing assemblies are re-lubricated.
6.14.4.
Gearing in High Temperature Environments
6.14.4.1.
There are some crane designs for operational applications such as an “In and Out”
Furnace crane where the normal operating condition involves the use of a mechanical grab to
position a steel slab inside a furnace for heating, and removal (high radiant heat from furnace
internals and hot slab) or ingot-stripper cranes using steel screws and bronze nuts to grip and
push the hot ingots from the molds.
6.14.4.2.
In these types of operations a very high temperature lubricant has been used
successfully to achieve lubrication even in these extremely high temperatures.
6.14.5.
Open Gearing
6.14.5.1.
Many currently operating hot metal cranes were designed with a large drum gear and
the small pinion that are not in a modern gear case but in a configuration of being relatively
exposed and protected with only what could be called a dust cover.
6.14.5.2.
In these applications, since the gears need lubrication, a pliable lubricant that is usually
delivered in softball-sized clear plastic bags is set in the gear mesh.
6.14.5.3.
Due to the consistency of the lubricant it both adheres and lubricates the pinion and
gear. This lubricant is periodically replenished with a new bag applied to the mesh.
6.14.5.4.
There are also some A-2 bridge and trolley drives with the same “open gearing”
situation, which also need frequently replenished lubrication. These are very messy and not
highly prized working arrangements. As the steel industry modernizes they will be scrapped
out. In the meantime they must be maintained. This lubricant is a pasty blend of heavy oil and
binder.
6.14.6.
Crane Wheel Flanges
6.14.6.1.
Crane wheels assemblies are one of the most often replaced components on the EOT
crane and at least 60-70 percent of the time the replacement is due to worn flanges. Using a
product to eliminate or nearly eliminate flange wear is a reliability improvement that can be a
substantial benefit.
6.14.6.1.1. Solid lubricant systems.
6.14.6.1.1.1.Stick graphite lubricants fit into spring loaded, square, applicator tubes that are
mounted close to the wheel flange at an angle on brackets that hold the tubes rigidly in
place. As the wheel rotates, the lubricant is applied to the wheel flanges and as the
wheel flanges contact the side of the railhead, the rail becomes lubricated as well. Both
the wheel flange and the side of the rail become polished and smooth.
6.14.6.1.1.2.Other systems use a molded product that is an arc shape with mounting
bracket and springs, allowing the arc to ride on both flanges. Springs push the
lubrication material onto the flanges. Lubrication is applied to the wheel flange due to the
contact pressure and temperature at the point of contact.
6.14.7.
Wire Rope
6.14.7.1.
Wire ropes require a preventive maintenance lubricant in the form of a light oil.
6.14.7.2.
In the case of impregnated wire rope, a solid lubricant is pre-applied to the rope. It may
require additional lubrication based on the manufacturer’s recommendation.
6.14.7.3.
When using any lubricant on wire rope, use care when applying so as to not over
lubricate. Excessive lubricant can create a fire hazard.