Lubrication
Nizwa College of Technology
Friction
Friction is the force resisting the relative
motion of surfaces or material elements in
contact.
The ratio of the force of friction between two bodies and the
force pressing them together is known as co-efficient of
friction (μ)
Ff/ N = constant (μ)
Ff = μ N
Reducing frictional resistance
Friction between moving parts in contact is
unavoidable -but it is desirable to keep this to as
low as possible
• Provide a fine or smooth surface finish.
• Replacing the one of the material having lower
coefficient of friction.
• Introducing a fluid film which separates the
parts slightly thus reducing the friction
(Lubrication)
• Installing balls, rollers or needles between the
sliding surfaces which replace the sliding
movement by rolling action (Bearings)
Lubrication
• Lubrication is the process, or technique
employed to reduce wear on surfaces in
close proximity, and moving relative to
each another
• Lubrication is effected by introducing a
substance called lubricant. The lubricant
film can be a solid, (graphite), a liquid, a
semi solid (grease) or exceptionally a gas
Objectives of Lubrication
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To reduce frictional resistance
To reduce wear on the bearing surfaces
To protect the bearing surfaces from
corrosion
To carry away heat from the bearing
To reduce noise from the moving
components of the machine
Different Lubricating conditions
• Dry Lubrication- No lubricant present
between the surfaces
No oil film
• Boundary lubrication (Thin film) -This
condition is found on machine slide ways
(Lathe cross slide, milling machine table).
Thin oil film
• Full film lubrication- The surfaces are
separated by thick film of lubricant and
there will not be any metal-to-metal
contact
Thick oil film
• Mixed lubrication- Boundary and full
lubricating conditions(Hydro dynamic)
Hydrodynamic lubrication
(Lubricant is dynamic)
At Rest
Starts to Rotate
At Running
(Mixed Lubrication)
(Full Film Lubrication)
Hydro static Lubrication
(Lubricant is static)
Properties of Lubricant
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Viscosity - Resistance of a liquid to flow
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Oiliness- Ability of the lubricant to stay in
place between the bearing surfaces
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Stability –Retention of properties as
long as possible (Oxidization, Biological
degradation, Dilution)
Types of Lubricant
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Animal oils - From animal fats
Vegetable oils - From plant seeds
Mineral oils - Hydrocarbons obtained
from minerals
Synthetic oils - From various chemicals
Grease - Semi-fluid lubricant
Dry - Molybdenum disulphide, Graphite
Additives
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The properties of a lubricant can be
improved by adding certain chemicals
Anti oxidants
Foam depressants
Corrosion inhibitors
Detergent Dispersers
Oiliness improvers
Selection of Lubricant
The selection of lubricant depend on:
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Type of mechanism being lubricated
Type of lubricating system
Rate of heat removal
Cost
Selection of Lubricant -typical examples
Feature
Lubricant
Lubricating
system
Heat removal
Plain
bearing
Oil
Hand
Low
High
Light duty
Circulating
High
Low
Continuous
Porous
Low
Low
Low speeds
Grease
Hand
Nil
High
Light duty
Oil
Oil mist
low
Low
High cost
Oil bath
low
Low
Churning
Splash
Moderate
Low
Used in gear
box
Packed
Nil
Low
Long life
Central
Nil
Low
Convenient
Bath
Moderate
Low
Simple gear
box
High
Low
Hi-duty gears
Hand
Nil
High
Hi-duty gears
Housing filled
Nil
Low
Low speeds
Rolling bearing
Grease
Gears
Oil
Circulating
Grease
Maintenance
cost
Comments
Lubricating Methods
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Oil can
Oil gun
Grease packing
Wick type
Bath type (Splash)
Circulation (pressure)
Oil cane &Grease gun
Housing
Oil cane
Grease Nipple
Grease Gun
Fill
Shaft
Oil cane
Grease Gun
Bath Type (Splash)
Housing
Gears
Oil
Grease packing & Wick Type
Wick
Oil
Housing
Grease
Shaft
Grease Cap
Bearing
Ball bearings
Grease Packing
Wick Type Lubrication
Circulation (pressure)
Oil filter
To various
Moving parts
Oil Filter
Relief valve
Oil Pump
Relief Valve
Sump
Coarse Filter
Oil Pump
Gaskets& Seals
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Sealing is the process of preventing
gases, liquids and solids escaping
from containers or mechanisms.
Seals can be broadly divided into two
categories:
Static seals - where there is no
movement at the contact points.
Dynamic or Mechanical seal
- where
there is movement between the contact
points.
Selection of seal
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The choice of seal to be used on a
particular application is determined by
the following factors:
Property of the material being contained
Amount and speed of any movement
Operating pressure
Life expectancy
Operating temperature
Seal Materials
Non-metallic materials:
• Felt, rubber, asbestos, cork, plastics,
P.V.C, paper, cloth etc.,
Metallic materials:
• Copper, lead, tin, plated steel, beryllium,
and often a combination of several
materials is used to make a particular seal
or gasket.
Gaskets
Gaskets are static seals used to prevent
fluids or gases passing across mating
surfaces, where there is no movement, on
a mechanical assembly
Gasket materials- cork, rubber, asbestos,
plastic and metallic materials.
Fitting gaskets
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Important rules to follow when fitting a gasket
Conformation
The sealing pressure should be sufficiently high to
make the gasket conform to the joint surfaces.
Too little pressure can result in voids in the joint where
leakage could occur.
Too much pressure can result in distortion of both
gasket and joint surfaces.
Condition of joint surface
The mating surfaces of the joint should be:Free from burrs and indentations. '
Reasonably flat and mate together.
Clean and free from oil, grease and other materials.
Reasons for leakage in the joint
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Wrong gasket material
Incorrect fitting gasket
Poor Joint surfaces
No conformation
Distortion of surfaces
Inaccurate tensioning
Dynamic or Mechanical Seals
Mechanical seals are used where there is
movement between the parts being sealed
Types
Radial lip seal
Exclusion seal
Clearance seal
Ring seal
Face seal
Diaphragm seal
Packing
Radial lip seals
Parts of Lip Seal
• Frame
- stainless steel, Monel metal, titanium, bronze ,hastalloy.
Lip - rubber, nitrile, chloroprene, ethylene, propylene.
• Spring
-stainless steel, monel, titanium hastallloy.
Features
• Take up Little space
• Easy to install
• Low cost
• Accommodate slight misalignment.
• One of the most widely used.
Fitting mechanical seals
Guide lines to fitting seals
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Make sure that the correct type of seal is used, particularly when
replacing a seal
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Ensure that the housing shaft and seal is in good condition and free
from dirt and other foreign matter
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Lubricate the surfaces of seal, shaft and housing if necessary
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Use a suitable assembly tool if needed
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Use a cone or sleeve over any sharp corners of the shaft
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Check seal for correct operation before applying power to drive
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After a short period of use inspect seal for leaks or other failures
Seals &Gaskets-Examples