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Lubrication

Lubrication. daveravindra40@gmail.com. Wear. Is a progressive loss of substance from the surface of the machine part during the mechanical action.

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Lubrication

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  1. Lubrication daveravindra40@gmail.com

  2. Wear Is a progressive loss of substance from the surface of the machine part during the mechanical action.. The small the asperities the closer the contact, that’s so call finer surface therefore clean highly polished surfaces come in close contact & when they are in relative motion friction & wear take place. In the presence of pressure alone, it is possible to weld two finely finished surface & cohesive forces come into play fully & this is the basis of cold welding.

  3. Lubrication. Lubrication may be defined as:-“The reduction of friction and wear between two relatively moving surface, by the interposition of some other substances between the surface & the substance introduced is known as lubricant”.

  4. There are two basic mechanism by which reduction of friction may be achieved.(I) Solid Lubrication:- in which the two surface are coated by substance like graphic (lower coefficient of function)(II) Fluid Lubrication:- in which the two surface come contact from the fluid film & resistance to motion is due to the stickiness or viscosity of the fluid.

  5. Mechanism of Lubrication 1.Complete fluid Lubrication ORThick-filmORHydrodynamic Lubrication:- Boundary film Bulk lubricant Load Velocity Thick layer of lubricant

  6. Bearing lining Thick film of Lubricant Rotating shaft in floating lubricant

  7. In this, the sliding/moving surface are separated from each other by a thick-film of fluid (at least 1,000 Athick), so that direct surface to surface contact & welding of junctions rarely occurs. In such system friction depends on (1)the viscosity (2) thickness of the lubricant (3) the relative velocity (4) area of moving surface. This type of lubrication are provided :- In light machines like watches, clock scientific instruments. Etc. Hydrocarbon oils are considered to be satisfactory lubricants for fluid-film lubrication.

  8. In such system friction depends on (1) the viscosity (2) thickness of the lubricant (3) the relative velocity (4) area of moving surface. This type of lubrication are provided :- In light machines like watches, clock scientific instruments. Etc. Hydrocarbon oils are considered to be satisfactory lubricants for fluid-film lubrication.

  9. CH3 COOH 2.Boundary Lubrication ORThin-film:- Boundary film Bulk lubricant Load Velocity Absorbed thin layer of lubricant Molecular Orientation

  10. This happen when(iii) the load is very high(iv) the viscosity of the oil is too low. In mineral oil we have a symmetrical molecule with a CH3 group at each end but in fatly acids a COOH group at one end and have been offered as an explanation of the improved oiliness of the fixedoils because of COOH group would greater affinity for the metal surface & CH3 group would be repelled. For boundary lubrication the molecule should have(I) Long hydrocarbon chains (II) Lateral attraction between the chains .

  11. 3.Extreme-pressure Lubrication:- To meet these extreme-pressure conditions, special additives are added to mineral oil. These are called “Extreme – Pressure Additives”. These additives form more durable surface on metal & capable with standing at very high load (pressure) & temperature. Additives are organic components having active radicals or groups such as (a) Chlorine (as in chlorinated esters) (b) Sulphur (as in sulphurized oils) (c) Phosphorus (as in tricresyl phosphate)

  12. Mechanism of EP lubricants :- Sulphur & Chlorine present in those additives react with metal & form sulphides & chlorides. FeS + RSχ-1 Fe RSχ + FeS + R’Cly FeCl2 +R’Cly-2 + S S + Fe FeS

  13. Animal & Vegetable oils;- Ex- Vegetable oil:- Olive oil, Palm oilAnimal oils:- Whale oil, Tallow oil Before petroleum industry, Oil of the vegetable & animal origins are generally used as lubricant. They possess good oiliness (properties of oil sticks to the surface). However used very rarely due to following demerits.

  14. Mineral or Petroleum oils ;- Oiliness of petroleum oil can be increased by the addition of high molecular compound like oleic acid[CH3 (CH2)7 CH =CH (CH2)7 COOH ], strearic acid [ CH3(CH2)16 COOH] . Oil obtained from crude petroleum distillation, as a residues. Residues are either, paraffinic OR asphaltic, are on distillation gave various oil fractions of different viscosity.

  15. Petroleum & Petrochemicals Petroleum & Composition of crude oil. Petroleum ;- Is a Dark viscous oily liquid known as Rock oil (In LatinPetrameaning Rock&oleum meaningoil) Formed by bacterial decongestions of the remains of animals.

  16. Composition of Crude oil Element Carbon Hydrogen Sulphur % 80.87 11.1 – 15.0 0.1 – 3.5 Oxygen Nitrogen 0.1 – 0.9 0.4 – 0.9

  17. Conditions for Oil Refining Petroleum is heated to 360C in the absence of air in a furnace to vaporize it before fractional distillation.

  18. Blended oil :- No single oil seves as the most satisfactory lubricant for many of the modern machineries Following type of additives are use :- like vegetable oil & fatly acids (2) Extreme – pressure additives :- (3) Thickness - like polystyrene, polyesters etc (which mol wt. between 300 –3000) are added to give the lubricating oil of higher viscosity.

  19. Semi – solid Lubricants OR Greases Greases are used in following situations : - (1) When a machine is worked at slow speeds & high pressures & temperature like bearing & gears.(2) Where oil cannot be maintained in position due to bed seal. Composition of Greases :- It is a composition of lubricating oil together with gelling agent which gives stiffness to the mixture.

  20. Examples of solid lubricants are:- Solid Lubricants • Graphite • Molybdenum disulfide (MoS2) • Talc

  21. Graphite :- 1. Graphite consists of a mesh work of hexagonal carbon rings. Separated from the upper layer of the unit crystal cell by a distance of about 3.4 A. 2. Widely used solid lubricants. 3. It is very soapy to touch, non inflammable, not oxidized in air below 3750C. 4. When graphite dispersed in oil called oildag. 5. When graphite dispersed in water called aqua dag.

  22. Str.Of Graphite:- Sp2 Hybridisation :- 1.42A 3.4A

  23. Uses :- As lubricants it is used in open gears, chains, cast iron bearing, railway track-joints,

  24. The End

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