Bearing Design Guide
Trelleborg Sealing Solutions
Updated March 200
Bearing Design Guide
About this Manual
The information in this manual allows the user to correctly design Orkot Hydro Bearings and gives
guidance on machining and fitting. This manual is intended for use by persons with technical training at
their own discretion.
Service and Support
A team of experienced and skilled engineers is available at Trelleborg Sealing Solutions. They offer a
full and complete service tailored to your specific requirements.
Websites
Visit the following websites for general and technical information on Orkot Hydro Bearings products
and applications. You may view and download literature and other useful documents.
www.orkothydro.com
www.tss.trelleborg.com
Contact Details
Please refer to our websites for the contact details of your nearest Trelleborg Sealing Solutions Office.
Alternatively, you can contact our Hydro Specialists at the following:
For Europe and Asia Pacific:
Trelleborg Sealing Solutions Rotherham, South Yorkshire, UK
Phone:
Fax:
Email:
+44 1709 789832
+44 1709 374819
peter.bakker@trelleborg.com
For Americas;
Market Segment Manager Hydro
Mr. Tom Carew
Phone :
Fax:
Email :
+1 905 372 4884, Mobile: +1 416 428 0610
+1 905 372 7364
tom.carew@trelleborg.com
Page 1 / 28
Bearing Design Guide
Contents
Page
Introduction
3
Material description
3
Material datasheets
4-5
Material features
6
Guidelines for design
- Bearing load on journal bearings
- Capability to accommodate shaft misalignment and
shaft deflection
- Bearing load as part of design recommendations,
within the design envelope
- Elasticity
- Effect of temperature
- P x V for polymer bearings, dry running / water-lubricated
- Friction, wear and lubrication
- Influence of moisture, atmospheric conditions, and ageing
- Recommendations for bearing dimensions
-Turbine components, oscillating motions
- Oscillating + permanent high load (spillway gates)
- Turbine Main shaft guide bearings
Press fit bearings and machining dimensions
Fitting methods
Machining instructions
Quality management systems and quality assurance
7
7
8
8
9
10
11
11
12
13
14
15-19
20
21- 23
24 - 26
27
Page 2 / 28
Bearing Design Guide
Introduction
Orkot is the brand name of a range of
composite bearing materials consisting of a
matrix of fabric-reinforced polymers from
Trelleborg Sealing Solutions. Two locations
manufacture Orkot exclusively, one in the
United Kingdom and one in the United States.
Originally called Orkot Factories, these
locations are now known as Trelleborg Sealing
Solutions Rotherham UK and Trelleborg
Sealing Solutions Eugene USA.
For over 50 years Orkot® Bearings have
established a long-standing reputation in
industrial, offshore oil & gas and shipbuilding
applications. Orkot TLMM and TXMM
bearing materials carry approval by
classification societies worldwide. Many
applications, such as steering and propulsion of
merchant and navy ships, involve safety critical
parts.
The early 1990s brought the introduction of
Orkot TXMM and TLMM to the hydropower
industry. These two Orkot standard materials
have established world-class reputations in
turbine applications such as: wicket gate/guide
vane bushings, turbine runner blade bushings,
water-lubricated main shaft bearings and other
equipment in dams such as spillway gates and
valves.
Orkot thermosetting materials, at the
molecular level, incorporate long chains of
chemically cross-linked polymer molecules in a
dense, 3-D network. This cross-linked
network insures the integrity of the solid
material. Once the polymer has become solid
(cured) it possesses a high mechanical and
chemical stability. Unlike in thermoplastic
polymers, the solidifying process in Orkot®
materials is irreversible. The polymer does not
exhibit a melting point at high temperature, nor
does it have a glass transition point at low
temperature. There is no risk of brittleness or
chatter when used in extremely cold, even
cryogenic conditions.
The polymer matrix is backed up by additional
reinforcement in the form of a woven fabric
made of synthetic fibers. Organic fibers, such
as cotton, are not used due to their tendency to
swell in water.
Manufacturing
The fabric and reinforced polymer matrix are
processed into either tube or flat sheets. After
subsequent curing, the result is a product
having a laminated structure, designed to
withstand extremely high pressure
perpendicular to the laminate.
Material description
Page 3 / 28
Bearing Design Guide
Material Datasheet, metric units
Parallel to laminate
Page 4 / 28
Bearing Design Guide
Material Datasheet, inch units
Parallel to laminate
Page 5 / 28
Bearing Design Guide
Lubricant additives
Orkot’s base polymer has the ability to
incorporate additional substances such as
friction modifiers. These are solid particles,
evenly dispersed throughout the product.
Combinations of friction modifiers are
specified to provide the best match with the
metallic mating surface and to meet the
demands set by the operating conditions.
Solid lubricants in Orkot TLMM and TXMM
grades are molybdenum disulphide and PTFE.
These solid lubricants, readily available in the
surface-to-surface contact area, provide low
friction when breaking free after long periods
of standstill, even under high permanent load.
Scuffing and galling problems, like those found
in metal-to metal contact, are effectively
avoided.
•
Orkot TLMM and TXMM are both
suitable for oil or grease lubrication
•
Orkot materials are chemically stable, and
do not age under UV radiation or ozone
•
Orkot does not contain asbestos or any
other environmentally hazardous/toxic
substances
•
Orkot maintains excellent dimensional
stability with low thermal expansion and
shrinkage
•
Orkot has reduced thermal softening and
high resistance to creep
•
Orkot materials work well as electrical and
thermal insulators
•
Orkot TXMM and TLMM do not
encourage galvanic corrosion (i.e. these
materials do not contain graphite)
•
The swell rate when submerged in water is
such a low value that it will have no effect
on the application or machining of the part
Material features
•
Unique combination of compressive
strength and elasticity
•
Low friction in static as well as in
dynamic conditions
•
Orkot provides excellent damping of
shocks and vibration and impact loads
•
Orkot TXMM can be operated
permanently in dry conditions
•
•
Orkot TLMM can be operated dry for
short intervals but is actually designed
for water-lubricated applications, high
load and oscillating movements
Orkot accommodates shaft misalignment
by deflection, avoiding excessive edge
loading
•
Orkot’s ability to be freeze fit using liquid
nitrogen, without danger of material
damage, offers considerable savings in cost
and time at assembly
•
Orkot TXMM is best suited for waterlubricated main shaft guide bearings
providing extended wear resistance at
start and stop
Page 6 / 28
Bearing Design Guide
Bearing load on journal bearings
It is common practice among designers to
express bearing load and bearing load capacity
as the pressure over the projected area of the
shaft:
Load force ________
P
=
bearing
Shaft diameter x Bearing length
This formula is a simplification, it does not tell
what the actual contact area is, nor does it tell
how the load is actually distributed or
concentrated in the contact area. When the
shaft and the bearing are both metals, with
similar elastic properties, Hertzian contact
pressures will occur. Hertzian pressures,
caused by load concentration, may reach 4 to
10 times the average bearing pressure. Running
clearance has a major influence on the peak
Hertzian pressure; therefore, the change in
clearance affects bearing wear and is often a
criterion for early bearing replacement.
However, polymer bearings are more elastic
than metal bearings by a factor 10 or more.
The elasticity of Orkot is in the order of 50 to
60 times that of most metals. This increase in
elasticity results is a wide contact angle for
Orkot bearings, with an even distribution of
the load. The Hertzian pressures found in metal
bearings will not occur, even when the shaft
clearance becomes extremely large.
Typically Orkot bearings can operate at much
larger clearances than metal bearings. The
criteria for acceptance or replacement are often
set by the function of the machinery or the
application, but not because of the bearing
itself.
Capability to accommodate shaft
deflection and misalignment
A feature directly related to a bearing
material’s elasticity is the capability to
accommodate shaft misalignment and/or shaft
and structure deflection. Shaft misalignment
against a stiff bearing material will result in
high contact stresses at the bearing edge, which
shortens service life. In high load applications
a stiff bearing will create increased mechanical
loads in the surrounding structure.
In this respect Orkot is not only distinctively
elastic by comparison to metal bearings but
also compares favorably with other polymer
bearings, which use stiff fibers such as glass
fibers or carbon.
The Orkot bushing’s capacity to handle major
misalignment has been applied in many heavyduty applications, with diameters ranging up to
1,000 mm (39.4 in) and dynamic loads up to
5,000 tons.
Bearing pressure, wear rate and service life
Depending on the operating conditions, (e.g.
boundary lubrication conditions) the bearing
pressure “P” is a useful parameter as one
element in Archard’s equation for estimating
bearing wear and service life. In its simplified
and theoretical form, “P” is directly
proportional to the wear life provided that all
other parameters stay the same. In practice,
bearing pressure does not always directly relate
to wear. Therefore, wear rate remains an
estimate. Nonetheless, the average pressure
“P” is a useful indicator for the operating
mode.
Page 7 / 28
Bearing Design Guide
Bearing load as part of design
recommendations & the design
envelope
Elasticity
The graph above shows a typical deflection
•
Fabric-reinforced composites exhibit what is
called an-isotropic behavior.
Orkot’s elasticity does not follow Hook’s
Law, as do metals, whereby deformation is
350
300
Compressive
strength
200
Visco-elastic behaviour
&
Memory Effects
200
M odulus
ca. 100 0
N /m m 2
120
100
Bearing
Pressure
N/mm2
10
20
30
40
50
60
H ysteresis,
resilien t
behav iour
B earing
P ressure
N /m m 2
% Deflection of wall thickness
5
Design envelope
• Max. Design Load
• Elasticity
• Resilient behaviour
curve of an Orkot journal bearing. The design
envelope has been indicated with a maximum
of 120 N/mm2 (17,400 psi). This is to be
understood as the limit of mechanical stress,
hence the bearing’s capability to withstand a
radial load and the shear forces generated when
moving or when breaking free from static. The
design envelope includes a distinct buffer,
designed to stay clear of elastic limits and
creep effects.
It should be noted that load capacity is not the
only design limit of which to be aware. For
example, the effects of local friction heat and
the presence or absence of cooling water
should also be taken into consideration.
10
15
20
% d eflectio n of w all thickn ess
D e s ig n e n v e lo p e
(s ta tic ) lo a d lim it
1 2 0 N /m m sq
directly proportional to pressure.
It may be seen from the graph that elasticity is
non-linear, there is an initial soft response to
load and then compression resistance gradually
increases.
•
Orkot’s elastic modulus changes with
geometry, the stiffness changing with
different thickness and diameter.
Page 8 / 28
Bearing Design Guide
Bearing Elasticity continued
Bearings manufactured from flat material, such
as washers and wear pads, have a different
stiffness than cylindrical bearings.
Contrary to a journal bearing under load, a flat
pad will be evenly compressed over the contact
area. Still there is an initial soft response, like
in a journal bearing, but less so and the
compressive modulus will be in the order of
2200 to 3000 N/mm2 (3.19 to 4.35x105 psi). A
wear pad’s compressive strength and resistance
to shear is further influenced by its shape and
the way it is being fitted. A number of
countersunk bolts are usually adequate to hold
a pad and to transmit shear forces. In high load
applications it is recommended to fit the slide
pad into a recess with a depth of approximately
half of the wear pad’s thickness.
Effects of Temperature
- Mechanical properties
•
The absence of a glass transition
temperature allows the application of the
Orkot materials at extremely low
temperatures.
• Orkot materials’ absence of a glass
transition temperature allows bushings to be
freeze fitted using liquid nitrogen.
• Orkot bushings of any size, even up to
2000 mm.(6 ½ ft.) diameter, are being
reduced by freezing. Only hand force is
required to fit the bearing, bringing
considerable cost and time savings.
• When operating temperatures are
intermittently above 65 oC (150°F) and up to
130 oC (266°F), a press fit is not suitable.
The bushing may become loose in its housing
when the machine is decommissioned and
cools to ambient. A practical solution will be
to bond the bushing in place.
- Temperature caused Dimensional changes
For outdoor applications a temperature range
of -30o to + 65 o C (-22° to 150°F) is generally
specified.
This is of particular importance when choosing
the interference; bushings should stay tight in
their housings even at the lowest operating
temperature. Unless specifically indicated, the
same temperature range applies for indoor
applications.
Material strength and elasticity are stable
within this temperature range. Beyond this
temperature range the following should be
remembered:
•
When designing journal bearings one needs to
consider the effects of thermal expansion or
thermal reduction.
•
A press fitted bushing requires a minimum
level of elastic compression to maintain a
positive pressure against the housing at the
lowest operating temperature.
• The running clearance must include an
added margin to accommodate the
reduction in clearance, realized when the
bearing thickness expands with the increase
in temperature.
Elasticity barely changes when the
temperature is lower than -30°C (-22°F)
even down to cryogenic.
Page 9 / 28
Bearing Design Guide
P.V. (Pressure x Velocity)
for polymer bearings
In practice Orkot has proven to be particularly
valuable in applications where:
•
The movement is irregular and/or
reciprocating
•
The load is permanent
•
There are extended intervals of standstill
•
The shaft speed is high and the bearing is
hydrodynamically operated, as in main
shaft guide bearings either horizontally or
vertically fitted
Greaseless, dry running
Polymer bearings are poor thermal conductors;
hence the conductive dissipation of friction heat
into the bearing housing is virtually zero. Also,
the bearing’s heat storage capacity is minimal.
This is a distinct difference compared to metal
bearings. In some applications one may
welcome this feature but in applications where
movement is very frequent, precautions must
be taken. If a movement takes place only over
a certain angle (oscillatory motions) friction
heat will accumulate locally in the shaft.
Orkot bearings perform outstandingly well in
conditions where grease or fluid lubrication
could become problematic, e.g. in slow and
oscillating motions. Increased operating
temperatures, often associated with highfriction coefficients, may result in high-energy
inputs. Ideally, friction should be kept as low
as possible, thus keeping the bearing
temperature and the temperature of the
surrounding parts similar. Orkot TXMM
offers the lowest coefficient of friction for dry,
greaseless operation.
Hydrodynamic operation of water lubricated
bearings
When the shaft spins continuously above a
certain minimum speed and the gap between
bearing and shaft is filled with water, a water
film is generated, separating the bearing from
physical contact with the shaft. This is termed
a hydrodynamic running condition. For Orkot
the fluid needs to be a proper coolant, e.g. a
water-based fluid. Oil-based fluids are not
effective. The design of such a bearing is the
job of a specialist. Pages 15-19 of this manual
deal with turbine main shaft guide bearings
operated hydrodynamically. Because of water’s
low fluid viscosity, the hydrodynamic running
mode allows a relatively low load of 0.5
N/mm2 (72 psi) and a unidirectional speed of 1
m/s (3.28 ft/s) or more.
Friction coefficient from start-up to full
hydrodynamic operation, shaft diameter 200
mm (7.9”). Bearing pressure 4.5 bar (65 psi)
tested over 2,000 hours.
Page 10 / 28
Bearing Design Guide
Friction, wear and lubrication
Orkot technical datasheets state friction
coefficients for a combination of bearing and
stainless steel shaft mating materials at specified
operating conditions. It is recognized that the
prediction of friction and wear is not set by
simple rules.
When two imperfect surfaces slide against each
other under pressure a number of issues affect
the resulting frictional force. Through our own
testing we have found that when polymers are
applied against metal surfaces the results of
standard test methods differ from real life
applications. Also, accelerated tests, done to get
faster results by increasing loads or speeds, do
not compare directly to actual application friction
and resulting wear.
Trelleborg Sealing Solutions endeavors to
provide practical, applicable data as much as
possible, thus avoiding trial and error at
installation.
Friction and Wear Test facilities at Trelleborg
Sealing Solutions Rotherham. Testing is done on
true scale, shaft diameter 100 mm (3.94 in).
Trelleborg Sealing Solutions Rotherham is
equipped with modern test facilities where
friction and wear can be examined on a
realistic scale. The shaft material including
surface finish and hardness can be specified by
the customer. Then test conditions are
determined in terms of load, speed and type of
motion. Water lubrication volume and clarity
can be set to simulate actual application
conditions.
Through years of testing a wealth of knowledge
on bearing behavior has been collected.
Consult your local Trelleborg Sealing Solutions
sales office about your specific project. Time
and money may be saved, especially when
there are various technical options to consider.
Influence of moisture, atmospheric
conditions and aging
Orkot® has been developed to exhibit minimal
reaction to its working environment. The use of
organic fibers has therefore been abandoned.
Fluids such as water and oil ride the surface of
Orkot®, but absorption is minimal. Long-term
full submersion tests in water show a wall
thickness increase of less than 0.1 % after one
year.
In practice, water absorption in a bearing 100 mm
ID x 120 mm OD (3.94 in ID x 4.72 in OD) for
one year, will cause a reduction in running
clearance of 0.02 mm (.0008 in). Such a low
value needs no further attention as it is
overshadowed by other design parameters such as
machining tolerances, thermal effects and running
clearance.
Orkot resin systems have proven resistance to
aging. Polar cold, tropical heat, sunlight or ozone
exposure, rain or drying wind have no degrading
effect on the strength or functionality of Orkot®.
Page 11 / 28
Bearing Design Guide
General recommendation for bearing
dimensions
The manufacturing process allows bearings to
be produced in any size, starting from a wall
thickness of 2 mm (.080in), and diameters
ranging from 5/16 in up to 79 in (8 mm up to
2000 mm). Above 79 in (2000 mm), bearings
are generally built and installed in segments.
If design parameters can be freely chosen the
following rule of the thumb is recommended:
Recommendations for Orkot Hydro
Bearings in specific operating
applications and conditions
Design recommendations for hydro bearings
relate specifically to function, operating
conditions and specific requirements of
assembly and fitting.
Subdivisions made:
Oscillating bearings on turbine components
Wall thickness = (0.03 x shaft diameter) +
1,5 mm ( .06 in) (the result to be rounded up)
and
Bearing length = 1 x shaft diameter
(This is not a fixed rule. Shorter as well as
longer bearings, up to 2 x shaft diameter are
being applied, depending upon the application.)
- Wicket gate / guide vane bushes
- Control linkage
- Servomotors
- Segments and pads for control ring guidance
- Runner blade bearings
Oscillating bearings under permanent high
load and long periods of standstill
and
- Spill gate hinges
- Safety valves
Running clearance = 0.001 x shaft diameter
for fluid lubricated bearings, operated
unidirectionally
Full rotation, continuously operating, waterlubricated bearings
For dry running and/or oscillating movements:
Running Clearance = 0.002 x shaft diameter
- Main shaft guide bearings
- fitted horizontally
- fitted vertically
Page 12 / 28
Bearing Design Guide
Recommendations for Orkot Hydro
Bearings designed for oscillating
motions on turbine components
- Wicket gate / Guide Vane Bushings
- Control linkage
- Servomotor
- Runner Blade Bearings
On Runner Blade bushings it’s even narrower:
Clearance = 0.4 x 10-3 x Diameter shaft
Please consult your local Trelleborg Sealing
Solutions sales office if you are considering a
tighter than recommended clearance.
Typically these applications:
To resolve these typical application
requirements we recommend bonding for thin
wall bushings. This means that thin wall
bushings may be supplied undersized on the
OD, leaving room for the bonding agent (see
fitting recommendations for bonding). The ID
can then be set to suit the shaft diameter and
alignment.
- To obtain perfect alignment of two bushings
fitted in a housing insert (pot) such as often seen
in wicket gate applications, we recommend line
boring or honing after assembly.
Guide Vane Bearings, Running Clearances
General (0.002 x Ds)
0.9
M in im u m C lea ran c e (m m )
- require minimal running clearances for
accuracy of control and turbine efficiency
- require minimal friction from static as well as
dynamic operation for the same reasons listed
above
- have alignment issues because three
independently mounted bearings run on the
same shaft
- require compromise to less than the standard
recommendation for wall thickness, especially
in a refurbishment
0.8
Tight (0.0008 x Ds)
0.7
Field experience
0.6
0.5
0.4
0.3
0.2
0.1
0
50
150
250
350
Shaft Diameter (mm)
Evaluating service experience, from wicket gate
/ guide vane applications, we found that good
results have been obtained by applying:
Clearance = 0.8 x 10-3 x Diameter shaft
Page 13 / 28
Bearing Design Guide
Recommendations for Highly Loaded,
Oscillating Orkot Hydro Bearings
experiencing long periods of standstill
- Spill Gate Hinges
- Safety valves
Requirements
- Apply adequate wall thickness
W min = (0.03 x Diameter shaft ) + 1.5 mm (.0in)
- Choose ample bearing clearance
Clearance min = 0.002 x Diameter shaft
- Apply press fit to secure the bearing
Press fitting, or an interference fit, may be
accomplished by using a conventional press or
tie rods to pull the bearing into the bore.
Note that freeze fitting, using liquid nitrogen,
makes the fitting job easy and fast. Freeze
fitting also works well to fit irregular shapes
such as trunnion bearings.
Page 14 / 28
Bearing Design Guide
Recommendations for full rotation,
continuous operation, water
lubricated Orkot Hydro Bearings
Main Turbine Shaft Guide Bearings
- horizontally fitted
- vertically fitted
Design
Because Orkot main shaft bearings operate
hydrodynamically, the following parameters
must be known:
•
•
•
•
pass through without causing damage to the
shaft or bearing. This design is suitable for most
turbines where shaft velocities are not high and
a clean source of cooling/lubricating water is
available.
Multi-groove designs can be manufactured as
staves, full or split bearings.
Radial load (N/mm² or psi)
Shaft diameter
Shaft speed (m/min or ft/min or rpm)
Water supply volume and quality
A variety of bearing designs can be
manufactured from Orkot TXMM for main
turbine shaft guide bearings. The types in order
of popularity are:
Multi-Groove or Stave Bearing
Staves are often used in existing housing
configurations. The staves are supplied to suit
the width and shape of the existing grooves.
Line boring is recommended to finish the ID
after installation.
Full bearings are normally fitted with an
interference fit. This can be achieved by press
fitting or freeze fitting.
This conventional bearing design has equally
spaced axial grooves to allow water to lubricate
and cool the bearing. It also enables debris to
Split bearings should be assembled with a slight
interference fit and mechanically fastened to the
housing. If a split bearing is to be finish
machined after installation it is recommended to
pre-machine the bearing halves with an
allowance ID. Then assemble and finish to size.
Page 15 / 28
Bearing Design Guide
Design recommendations for multigroove bearings, in metric units
For vertically positioned bearings the grooves
are equally spaced over the circumference.
For horizontally positioned bearings
the bottom (6 o'clock) groove should be omitted.
Bearings typically have 3 mm x 30O chamfer on
OD and ID.
Vertically fitted multi-groove bearing in metric sizes
Shaft Size
(mm)
Min Wall
Min
Min Shaft
Number of
Groove
Groove
Groove
Thickness
Interference
Clearance
Grooves
Angle
Width
Depth
A
B
B
W
D
(mm)
(mm)
(mm)
(Degrees)
(mm)
(mm)
30
-
60
8
0.15
0.10
5
72.0
8
4
60
-
100
9
0.22
0.10
6
60.0
8
4
100
-
150
10
0.34
0.15
7
51.4
10
6
150
-
200
12
0.43
0.20
8
45.0
10
6
200
-
250
14
0.56
0.25
9
40.0
12
7
250
-
300
14
0.70
0.30
10
36.0
12
7
300
-
350
16
0.84
0.35
11
32.7
14
8
350
-
400
16
0.97
0.40
12
30.0
14
8
400
-
450
20
1.11
0.45
13
27.7
16
10
450
-
500
20
1.25
0.50
14
25.7
16
10
500
-
550
22
1.40
0.55
15
24.0
18
11
550
-
600
22
1.50
0.60
16
22.5
18
11
Page 16 / 28
Bearing Design Guide
Design recommendations for
multi-groove bearings, in inch units
For vertically positioned bearings the grooves
are equally spaced over the circumference.
For horizontally positioned bearings
the bottom (6 o'clock) groove should be omitted.
Bearings typically have 1/8 in x 30O chamfer on
OD and ID.
Vertically fitted multi-groove bearing in inch sizes
Shaft Size
(inch)
Min Wall
Min
Min Shaft
Number of
Groove
Groove
Groove
Thickness
Interference
Clearance
Grooves
Angle
Width
Depth
A
B
B
W
D
(inch)
(inch)
(inch)
(Degrees)
(inch)
(inch)
1.18
-
2.36
0.315
0.006
0.004
5
72
0.315
0.157
2.36
-
3.94
0.354
0.009
0.004
6
60
0.315
0.157
3.94
-
5.91
0.394
0.013
0.006
7
51.4
0.394
0.236
5.91
-
7.87
0.472
0.017
0.008
8
45
0.394
0.236
7.87
-
9.84
0.551
0.022
0.010
9
40
0.472
0.276
9.84
-
11.8
0.551
0.028
0.012
10
36
0.472
0.276
11.8
-
13.8
0.630
0.033
0.014
11
32.7
0.551
0.315
13.8
-
15.7
0.630
0.038
0.016
12
30
0.551
0.315
15.7
-
17.7
0.787
0.044
0.018
13
27.7
0.630
0.394
17.7
-
19.7
0.787
0.049
0.020
14
25.7
0.630
0.394
19.7
-
21.7
0.866
0.055
0.022
15
24
0.709
0.433
21.7
-
23.6
0.866
0.059
0.024
16
22.5
0.709
0.433
Page 17 / 28
Bearing Design Guide
Twin Groove Bearing
Stave Bearing
This bearing has two large axial grooves at 90
degrees to the static shaft loading position and
allows superior hydrodynamic performance over
a wide range of shaft velocities. It was
developed from testing Orkot TLMM bearings
on a purpose designed shaft testing rig. The
design allows for a hydrodynamic film to
develop at low shaft velocities, reducing friction
and wear. Good hydrodynamic performance is
obtained with shaft velocities as low as 25
m/min. (82 ft/min). This design should be
limited to a maximum 300 mm (11.8 in)
diameter and may be used for vertical shaft
water pumps.
Stave Bearing
An alternative bearing design uses staves
machined from Orkot® TLM marine sheet. It
should be noted that a multi-groove Orkot®
Hydro Bearing can easily and more
economically replace the lignum vitae staves
used in some turbines. After removing the worn
staves and keeper strips, Orkot® bushes can be
machined to suit the carrier. This can be done in
the workshop or alternatively bored in place.
Page 18 / 28
Bearing Design Guide
Water Supply Requirements
To ensure optimum bearing life and prevent
overheating, the bearings must always be
completely filled with water. To accomplish this
it may be necessary to restrict water flow by
putting a restrictor ring at the outlet. The
bearing should never run in the dry condition,
and the water should not reach a temperature
higher than 90oF / 30oC nor a temperature
difference between in- and outlet of more than
5oF / 3oC.
Depending on the installation it may be
necessary to install a monitor and alarm system
that checks for adequate water circulation and
water level in the bearing.
The water supply required to maintain correct
lubrication and hydrodynamic running is
calculated using the formula:
0.18 litres / min / mm shaft diameter or
1.21 US gallons /min / inch shaft diameter
Water filtration
The cleaner the water, the better the bearing
performance and the longer the bearing will last.
However, clean water is a relative term.
Trelleborg Sealing Solutions design engineers
have learned that there are limits to how small
of a particulate may be filtered effectively.
In practice a two-stage filtration system; the first
stage using a 20-mesh strainer with slots at 0.8
mm / 0.034 in and a second stage using a 100mesh screen with openings at 0.1 mm / 0.005 in,
produced the best results.
continually growing on the surface of the filter
causing enough restriction to set off the alarms.
The continuing costs involved with a water
filtration system and maintenance costs must be
weighed against the replacement cost of the
bearing. As a bearing supplier we recommend
the best cooling water filtration system that is
economically feasible.
The useful life of an Orkot® main guide bearing
will depend upon several factors: water quality,
shaft alignment and speed, load and vibration,
and how often the unit is cycled (start up and
shut down).
Shaft Requirements
Orkot® bearings can be used with most
recognized shaft materials and is found to be
compatible with gunmetal, phosphor bronze,
Monel, Inconel® 625 and stainless steel
typically AISI 316L.
A shaft surface finish of 0.8 micrometers or 32
micro inches Ra is required to reduce beddingin wear. Orkot® TXMM tends to improve the
surface finish during running.
As with all bearings subject to the ingress of
abrasive particles, bearing life may be reduced.
If the bearing is subject to abrasive ingress,
consideration should be given to the use of
harder shaft liners or carbide coatings.
Attempts to screen the particulate to a smaller
size, using a 200-mesh screen, met with failure.
The 200-mesh second stage filter clogged often,
sounding the pressure differential alarms he had
installed. It was determined that bacteria were
Page 19 / 28
Bearing Design Guide
Press fitted bearings, machine-to
dimensions and as-fit dimensions
The housing diameter tolerance and housing
roundness play an important role when
calculating the interference fit for a bushing.
Upon assembly, either by press fitting or by
freeze fitting, the bushing will adapt itself to
the size and roundness of the housing. Upon
fitting, the bearing will be compressed but the
wall thickness changes very little. Therefore,
the inside diameter of the bearing must to be
machined to a larger diameter than required in
the as-fit condition.
Calculating the machining tolerances
to achieve the interference fit
Polymer bearings require a much larger
interference than metallic bearings. The
calculation of interference fit requires the input
of accurate data, including shaft and housing
sizes, tolerances and recommended minimum
running clearance in relation to the application.
The operating temperature range and estimated
workshop temperature are also required when
the bushing is to be machined.
The calculation of interference fit can be done
manually but it is more practical to use a
dedicated computer program that accounts for
Orkot® material properties. Such a program is
available from the bearing manufacturer.
Page 20 / 28
Bearing Design Guide
Fitting Methods
Orkot® Hydro Bearings can be fitted using any
one of the following methods:
Method 1:
Method 2:
Method 3:
Method 4:
Freeze fitting using liquid
nitrogen (immersion method)
Press fitting
Bonding
Mechanical fastening (screws)
For bushings retained by interference our
preferred method is to freeze fit using liquid
nitrogen. Descriptions of all methods can be
found in this section.
Freeze Fitting
This is a fast and efficient method of assembly
resulting in an Orkot® Hydro Bearing with a
secure interference fit. When frozen the thermal
properties of the Orkot® material allow ample
space between the bearing and housing. Orkot®
material does not become brittle at cryogenic
temperatures.
Method 1: Using liquid nitrogen (immersion
method)
Check the bushing dimensions before
commencing by measuring the OD in at least
three positions around the top, middle and
bottom of the bushing (a total of nine
measurements) making a note of the largest
figure recorded.
Check the ID of the housing in at least three
positions around the top, middle and bottom (a
total of nine measurements) making a note of
the smallest figure recorded.
Provide an insulated container capable of
withstanding a temperature of -197oC (-320oF).
The container must be large enough to
accommodate the bearing being fitted with
enough clearance on the OD to facilitate easy
insertion and removal of the bearing.
Place the bearing inside the container and make
efforts to reduce its internal volume. This can be
done by sealing off unused areas of the
container and filling voids by insulating. This
will reduce the amount of liquid nitrogen that
will be required.
Cover the bearing with the liquid nitrogen and
maintain this level for the duration of the
procedure. The liquid nitrogen level will
constantly drop as the liquid boils or turns to gas
and escapes into the atmosphere. Use an
insulated lid to cover the container whenever
possible. Once the liquid stops rapid boiling and
settles down to a simmer, the bearing can be
lifted slightly from the liquid and the upper
bearing OD measured to check for sufficient
size reduction. If the OD is not small enough for
a simple slip-fit into the housing the bearing
must be returned to the liquid for an additional
10 to 20 minutes and checked again.
Once sufficient clearance between the bearing
OD and the housing has been achieved the
bearing can be removed from the liquid nitrogen
and quickly transported to the housing for
fitting. Do not allow your skin to come into
contact with the liquid, the fixture or the frozen
bearing.
The apparatus used to transport the bearing after
freezing (e.g. polyester slings) must be resistant
to cryogenic temperatures and suitable to
support the weights involved.
Page 21 / 28
Bearing Design Guide
Ensure that the reduced bearing can be fitted
quickly and easily. Once the frozen bearing
comes into contact with any conductive surface
it will return to its original size and temperature
very rapidly.
Wearing isolative gloves, slide the bearing into
position, ensuring that it is held in place while
its temperature normalizes. It is advisable to
have a stiff flat board available, larger than the
OD of the bearing, to apply equal pressure to the
top of the bearing as it slides into place. Once
the bearing surfaces have cleared of the ice that
forms during normalization, supports can be
removed.
*Note:
Extreme care to avoid severe burns should be
taken when using liquid nitrogen. Adequate
ventilation should be provided as oxygen is
depleted when off gassing occurs in a confined
space. Suppliers of liquid nitrogen will provide
a data sheet advising on its use.
Method 2: Fitting with hydraulic press or
center-pull jacks
If a bearing is to be press fitted, installers should
ensure that they have the proper equipment
available to deliver the force adequate to press
the bearing fully into the housing. The ease of
fitting will vary depending upon the finish of the
housing, the ambient temperature and the
amount of interference. These factors should be
considered when calculating the force required.
When press fitting a bearing it is important that
it is in line and square with the bore before the
operation begins. An adequate chamfer on the
housing will prevent shaving of the bushing OD.
The force will vary depending upon the
condition of the housing, leading chamfers and
the length/diameter ratio.
Method 3: Bonding
This method of fixture will depend upon the
design employed. Orkot® material can be
bonded to itself and to metallic substrates.
Numerous adhesives are compatible with
Orkot and have been tested within our
laboratory facilities. Generally, the most
suitable adhesives are:
− Two-part Epoxies
− Toughened Acrylics
For specific details of bonding agents and
conditions please contact Trelleborg Sealing
Solutions.
Bushing dimensions when bonding
The bushing’s outside diameter should be
undersized in comparison to the housing bore,
leaving a small gap (stated by the adhesive
supplier as the filling gap). In addition, a
shallow spiral groove may be machined into the
bush OD (pitch is 0.7 x bearing length) as a
reservoir to help carry adhesive into the gap
when inserting the bearing. During insertion the
bearing is to be moved applying a rotational and
axial movement at the same time, like a screw,
to evenly spread the adhesive into the gap.
In case an adhesive is not premixed the activator
is applied to the bore and the adhesive is spread
over the bearing OD.
Page 22 / 28
Bearing Design Guide
Bonding continued
Common Terms:
•
•
•
•
The bonding agent is referred to as the
adhesive.
The material/surface to which the Orkot® is
to be bonded is the substrate.
The distance between the Orkot® and the
substrate is the gap.
The ability of the adhesive to bridge and fill
the gap is the gap fill.
•
Roughen the surface. Ideally where metals
are involved use shot blasting. Ensure any
remaining particulates are removed from the
surface. Generally, the slightly fibrous
surface of Orkot® does not require
roughening, though the use of abrasive
paper is acceptable so long as any dust is
removed.
•
The assembled components may need
support while the adhesive sets. The cure
time will vary with the conditions under
which the adhesive is used. A typical a rule
of thumb is that the cure time will half for
every 10°C / 20°F increase in temperature.
•
In terms of assembly, avoid butt joints in
favor of lap joints, so that load applied to the
adhesive joint will act across the assembly
in shear.
Preparation:
•
Suitable substrates are Orkot® materials
themselves and various metals (including
stainless steel).
•
Plastics such as polyethylene,
polypropylene, polycarbonate, PVC and
PTFE are unsuitable substrates for bonding
to Orkot®.
•
The key to effective adhesion is in the
preparation of the substrate and the Orkot®
material to be bonded.
•
Ensure no boundary layers such as oxides or
grease are present. If necessary degrease
with a suitable solvent ensuring local health
and safety guidelines are followed. Orkot®
can be degreased by using a quick wipe with
a solvent such as acetone, but exposure to
the solvent must be kept brief so as not to
attack the Orkot® material. Oxides can be
removed by use of fine abrasive paper or
wire wool.
Page 23 / 28
Bearing Design Guide
Machining Instructions
Orkot® materials are readily machined by
conventional machine shop techniques. As a
general guide, methods used for brass,
aluminium or lignum vitae will apply to Orkot®
materials. It is preferable to use tungsten carbide
turning tools with cutting speeds of 5.5 metres
(19 feet) per second. Orkot® materials must be
machined dry, without the use of coolant.
Cutting Angle for Tools (new drwg required)
Turning
Tungsten carbide tooling of the butt-welded
type using K20 grade carbide is suitable for
most applications. If carbide inserts are used,
aluminium grades with high positive rates give
best results, e.g. Plansee grade H10T, Sandorid,
Mitsubishi.
Figure 12
req’d).
Turning and boring (new drwg
Figure 13
Parting off
For heavy wall thickness, the internal and
external diameters should be machined
simultaneously to reduce vibration.
No asbestos is used in the manufacturing of
Orkot®, and the material is completely nontoxic. It is, however, advisable to use adequate
dust extraction when machining. If unavailable,
operators should wear dust particle masks.
For small volume work and machining of
chamfers, radii and other forms, high speed steel
gives good results, but tool life is shorter than
with tungsten carbide.
Page 24 / 28
Bearing Design Guide
Turning, cutting speeds
Diameter (mm)
Rpm
0 - 50
50 - 100
100 - 150
150 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700
700 - 800
800 - 900
900 - 1000
2100
1000
700
550
350
250
200
175
150
130
120
100
Table 12
Speeds in mm
Diameter (inch)
Rpm
0-2
2-4
4-6
6-8
8 - 12
12 - 16
16 - 20
20 - 24
24 - 28
28 - 32
32 - 36
36 - 40
2100
1000
700
550
350
250
200
175
150
130
120
100
Feed rates
Type of
machining
Turning
Boring
Parting
Roughing
Finishing
Unit
0.7
0.5
0.4
0.25
0.20
0.20
mm/rev
mm/rev
mm/rev
Table 14
Type of
machining
Turning
Boring
Parting
Feed Rates in mm
Roughing
Finishing
Unit
0.028
0.020
0.016
0.010
0.008
0.008
inch/rev
inch/rev
inch/rev
Table 15
Feed Rates in inches
Depth of Cut
Roughing:
Finishing:
10 mm or 0.4 in
3 mm or 0.12 in
Smaller cuts may lead to tools rubbing, causing
wear which produces excessive heat buildup in
the finished part.
Table 13 Speeds in inches
Page 25 / 28
Bearing Design Guide
Grooving
Drilling
Orkot® can be readily grooved on a lathe,
shaping, milling or boring machine with a 90
degree machining head. For most one-off
applications a lathe is adequate. A sharp high
speed steel tool ground to the correct form
should be clamped in a long boring bar with a
three degree clearance ground on the side of the
tool. No top clearance is required.
Orkot® is easily drilled using either conventional
high speed steel or carbide-tipped drills.
The chuck may be marked for the correctly
spaced number of grooves and each groove
shaped in turn. A 0.2 mm (0.008 in) depth of
cut should be used, for long bearings a steadyrest may be required. The machine fast traverse
(with the spindle locked) can often be used.
Linear speeds up to 10 m/min or 30 feet/min can
be achieved.
The following speed and feeds are suggested:
Drill Diameter
(mm)
5
10
15
20
25
30
Speed
Rpm
1600
800
600
400
350
300
Feed
mm/min
300
400
400
400
400
400
Table 16 Speeds and Feeds by Drilling (mm)
Drill Diameter
(inch)
0.2
0.4
0.6
0.8
1.0
1.2
Speed
Rpm
1600
800
600
400
350
300
Feed
inch/min
12
16
16
16
16
16
Table 17 Speeds and Feeds by Drilling (inch)
Page 26 / 28
Bearing Design Guide
Quality assurance
Quality check per production day and
production batch.
Full monitoring and traceability of products,
from base materials through production steps,
inspections and shipment.
Routine testing is performed to simulate the
extreme operational environments where Orkot®
materials are used.
BS EN ISO 9001: 2000
Certificates issued by third parties
In some applications certificates or approvals
are applicable. Orkot® materials hold certifying
/ qualifying documents for a variety of
applications such as:
- Food & potable water contact
- Railways
- Shipbuilding
- Hydro Electric applications
Management Systems and
Classification
Trelleborg Sealing Solutions operates a fully
integrated management system which
incorporates:
ISO 9001:2000 Quality Management System,
ISO 14001:2004 Environmental Management
System
OHSAS 18001:1999 Health and Safety
Management System
Strict quality control and testing ensure material
conformance and batch traceability.
Page 27 / 28
Bearing Design Guide
The information in this manual is based on
many years of experience in the manufacturing
and application of Orkot® products. However,
unknown parameters and conditions may restrict
general statements during usage. It is vital that
customers satisfy themselves as to the suitability
of individual products through adequate testing.
For this reason, and due to the wide range of
applications of our products, Trelleborg Sealing
Solutions can accept no liability as to the
suitability or correctness of our general
recommendations in individual cases. For
specific operating conditions please consult
your Orkot® Hydro Bearings technical
representative.
Non-Trelleborg Group trademarks are referred
to for technical advice only and do not express
any preference to the use of these products. The
genuine rights and liability of the owners of
these trade marks are applicable.
Inconel® is a trademark of INCO Alloys
International, Inc.
Stellite® is a trademark of Deloro Stellite
Orkot® is a trademark of Trelleborg Sealing
Solutions Ltd
The application limits for pressure, temperature
and speed given in this catalogue are maximum
values determined in the laboratory. During
practical applications it should be remembered
that due to the interaction of the operating
parameters, the maximum values must be set
correspondingly lower. For exceptional
operating conditions, please contact your
Orkot® Hydro Bearings technical representative.
This edition supersedes all previous brochures.
.
© Trelleborg Sealing Solutions. All rights reserved
This brochure, or any part thereof, may not be reproduced without our permission.
Page 28 / 28