2. 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
3. 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)
4. 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
5. Objectives of Lubrication
• 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
6. Different Lubricating conditions
• Dry Lubrication- No lubricant present
between the surfaces
• Boundary lubrication (Thin film) -This
condition is found on machine slide ways
(Lathe cross slide, milling machine table).
No oil film
Thin oil film
7. • Full film lubrication- The surfaces are
separated by thick film of lubricant and
there will not be any metal-to-metal
contact
• Mixed lubrication- Boundary and full
lubricating conditions(Hydro dynamic)
Thick oil film
10. Properties of Lubricant
• Viscosity - Resistance of a liquid to flow
• Oiliness- Ability of the lubricant to stay in
place between the bearing surfaces
• Stability –Retention of properties as
long as possible (Oxidization, Biological
degradation, Dilution)
11. Types of Lubricant
• 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
12. Additives
The properties of a lubricant can be
improved by adding certain chemicals
• Anti oxidants
• Foam depressants
• Corrosion inhibitors
• Detergent Dispersers
• Oiliness improvers
13. Selection of Lubricant
The selection of lubricant depend on:
• Type of mechanism being lubricated
• Type of lubricating system
• Rate of heat removal
• Cost
14. Selection of Lubricant -typical examples
Feature Lubricant
Lubricating
system
Heat removal
Maintenance
cost
Comments
Plain
bearing
Oil Hand Low High Light duty
Circulating High Low Continuous
Porous Low Low Low speeds
Grease Hand Nil High Light duty
Rolling bearing Oil Oil mist low Low High cost
Oil bath low Low Churning
Splash Moderate Low
Used in gear
box
Grease Packed Nil Low Long life
Central Nil Low Convenient
Gears Oil Bath Moderate Low
Simple gear
box
Circulating
High Low Hi-duty gears
Grease Hand Nil High Hi-duty gears
Housing filled Nil Low Low speeds
15. Lubricating Methods
• Oil can
• Oil gun
• Grease packing
• Wick type
• Bath type (Splash)
• Circulation (pressure)
20. Gaskets& Seals
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.
21. Selection of seal
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
22. 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.
23. 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.
24. Fitting gaskets
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.
25. Reasons for leakage in the joint
• Wrong gasket material
• Incorrect fitting gasket
• Poor Joint surfaces
• No conformation
• Distortion of surfaces
• Inaccurate tensioning
26. 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
27. 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.
28. Fitting mechanical seals
Guide lines to fitting seals
• Make sure that the correct type of seal is used, particularly when
replacing a seal
• Ensure that the housing shaft and seal is in good condition and free
from dirt and other foreign matter
• Lubricate the surfaces of seal, shaft and housing if necessary
• Use a suitable assembly tool if needed
• Use a cone or sleeve over any sharp corners of the shaft
• Check seal for correct operation before applying power to drive
• After a short period of use inspect seal for leaks or other failures
