Lubrication

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Lubrication
Nizwa College of Technology
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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
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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)

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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

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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

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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
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• 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
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Hydrodynamic lubrication(Lubricant is dynamic)
Starts to Rotate (Mixed Lubrication)
At Running (Full Film Lubrication)
At Rest
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Hydro static Lubrication(Lubricant is static)
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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)

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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

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Additives

• The properties of a lubricant can be
  improved by adding certain chemicals
• Anti oxidants
• Foam depressants
• Corrosion inhibitors
• Detergent Dispersers
• Oiliness improvers

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Selection of Lubricant

• The selection of lubricant depend on
• Type of mechanism being lubricated
• Type of lubricating system
• Rate of heat removal
• Cost

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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
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Lubricating Methods

• Oil can
• Oil gun
• Grease packing
• Wick type
• Bath type (Splash)
• Circulation (pressure)

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Oil cane Grease gun
Housing
Grease Nipple
Grease Gun
Oil cane
Fill
Shaft
Oil cane
Grease Gun
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Bath Type (Splash)
Housing
Gears
Oil
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Grease packing Wick Type
Housing
Grease
Grease Cap
Ball bearings
Grease Packing
Wick Type Lubrication
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Circulation (pressure)
Oil Filter
Relief Valve
Oil Pump
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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.

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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

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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.

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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.

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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.

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• Reasons for leakage in the joint
• Wrong gasket material
• Incorrect fitting gasket
• Poor Joint surfaces
• No conformation
• Distortion of surfaces
• Inaccurate tensioning

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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

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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.

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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

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Seals Gaskets-Examples
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