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LECTURE 5: Lubricants

LECTURE 5: Lubricants. Introduction. A substance introduced between two moving or sliding surfaces in order to reduce the frictional resistance is called as lubricant & the process as lubrication. 1. DTEL. 1. LECTURE 5: Functions of lubricants. 2. DTEL. 2. LECTURE 1 :- Mechanism.

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LECTURE 5: Lubricants

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  1. LECTURE 5: Lubricants Introduction A substance introduced between two moving or sliding surfaces in order to reduce the frictional resistance is called as lubricant & the process as lubrication. 1 DTEL 1

  2. LECTURE 5: Functions of lubricants 2 DTEL 2

  3. LECTURE 1:- Mechanism LECTURE 5:-Mechanism of lubrication Types MECHANISM 3 DTEL 3

  4. LECTURE 5:-Mechanism • Fluid film /Thick film / Hydrodynamic lubrication Moving surface → Rotating shaft Lubricant Thick Lubricant layer Bearing ←Moving surface The lubricant forms a thick film which physically separates two moving surfaces and fills the irregularities on the surface. Thus avoids direct contact between moving surfaces and reduces the friction. Light machines working at fair speed are lubricated by this mechanism. eg. Sewing machines, Scientific instruments, Clocks etc. • Coefficient of friction reduces to 0.001-.03 • The lubricating film is not less than 1000 A0 thickness • Viscosity plays important role, • Hydrocarbon oils with antioxidants are used 4 DTEL 4

  5. LECTURE 5:- MECHANISM • Boundary lubrication Moving surface → Stearic acid molecule Adsorbed lubricant molecules ←Moving surface Polar stearic acid molecule • A thin film (uni or bimolecular thickness) of the lubricant gets adsorbed physically or chemically on the metal surface and stick to it firmly which carries the load and also reduces the friction . • Boundary lubrication exist when • It is not possible to establish a full fluid film , • Load is very high • Speed is very low. • Viscosity of lubricant is too low • The oil film thickness may reduce to such a extent that metal to metal • contact occurs & oiliness becomes predominant . • Eg: • A shaft starts moving from rest,Journal bearings in diesel engine. • Heavymachines working at slow speed. 5 DTEL 5

  6. LECTURE 1:- LECTURE 5:- Mechanism • Boundary lubrication • Coefficient of friction reduces to 0.05- o.15 • The lubricating film less than 1000 A0 thickness • Oiliness plays important role • Oils containing fatty matter eg. Vegetable and animal oil are more suitable. 6 DTEL 6

  7. LECTURE 1:- LECTURE 5:-Mechanism • Extreme pressure lubrication • When the moving or sliding surfaces are under very high pressure and speed, a high local temperature is attended. Under such conditions ,liquid lubricant fails to stick to the moving parts and may decompose or even vaporize. • To meet this extreme pressure condition, special additives are added to the mineral oils. These are called as extreme pressure additives These additives react with metal surface form more durable films capable of withstanding high load and high temp. • Additives are organic compounds containing active groups like • Chlorine(chlorinated esters), • Sulpher (sulphurised oils), and • Phosphorous( tricrysyl phosphate). 7 DTEL 7

  8. LECTURE 5:- CLASSIFICATION of lubricants • lubricants • SOLID • Eg. Graphite • SEMISOLID • Eg.Greases • Vaseline, • Waxes • LIQUID • Eg. Oil • GASEOUS • Eg. Air,N2 8 DTEL 8

  9. LECTURE 5:-SOLID LUBRICANTS • Properties: • Used when heavy machineries at very high load & slow speed • Thermally stable • Do not catch fire under operating conditions • Smooth & reduce the friction • Generally used as dry powder or mixed with oil or water & formerly adhere to the metal surface 9 DTEL 9

  10. LECTURE 5:-SOLID LUBRICANTS Graphite • Graphite is a structural lubricant • Layered lattice structure, soapy to touch, non inflammable, • Plane contains large number of hexagonally arranged sp2 hybridized carbon atoms. • Two layers are 3.4 A0 apart & weak vander waals forces of attraction are present between them. • The interlaminer bonds can easily break and layers can slide over one another. • Used as oildag (IC engine) or aquadag (food industries), Graphite grease • Used in machine shop work, lathes, air compressors etc. Air compressor Lathe machine 3.4 A0 1.42 A0 10 DTEL 10

  11. LECTURE 6:-Semisolid lubricant Grease • Greases are semisolid lubricants obtained by mixing soap in oil • Vegetable oil + Alkali Soap + Glycerin • Soap + Hot oil Grease • Soap: Functions as a • Thickner • Enables grease to stick to metal • Decides its consistency • Decides its working temperature • Used when • heavy load and slow speed • Protection against dust, dirt, moisture is required by sealing • When spurting of oil is not allowed (Food, paper, textile & dyeing industry) • High oiliness, very high viscosity, low water& oxidation resistance, tixotropy. • Due to greater coefficient of friction oil is always preferred to grease • It is capable of supporting greater load at lower speed due to their shear resistance.. • Consistency changes with temperature. On storage tend to separate in oil & soap. • Cannot dissipate heat efficiently ,don’t require much attention 11 DTEL 11

  12. LECTURE 6:-PROPERTIES OF GREASES Consistency The consistency or yield value is defined as the distance in tenth of a millimeter that a standard cone penetrates vertically in to the sample under the standard conditions of load, temperature and time. • The standard conditions for the test are • Load…. 150gm, • Temperature….250C , • Time …5 secs • Significance: • The consistency of grease is a very important property from practical point of view and it depends upon the structure and properties of a gelling agent and the oil used in the preparation of grease. It helps in proper selection of grease for various machines DTEL 12

  13. LECTURE 1:- LECTURE 6:-PROPERTIES OF GREASES Drop point It is the temperature at which the grease passes from semisolid state to a liquid state. Significance: This determines the upper limit of temperature up to which the grease can function satisfactory. DTEL 13

  14. LECTURE 1:- LECTURE 6:-GASEOUS LUBRICANTS • These are simple low viscose lubricants. E.g.. Air, N2,O2,CF2, Br2, SF6 etc. • Properties: • Low viscosity hence show better bearing performance, genrates less heat than oils • Wide working temperature range • Over a wide range of temperature, state and properties do not change. Hence no freezing or melting. • As the viscosity of a gas increases with temperature, load carrying capacity increases with increasing temperature. • Resistant to contamination, radiations hence useful for food & pharmaceutical industries. • Applications: • Bearings in aerodynamics • Precision optical instruments • Precision grinding spindles • Dental drilling DTEL 14

  15. LECTURE 6:- LIQUID LUBRICANTS Animal & Vegetable oil Blended oil LIQUID LUBRICANTS Synthetic oil Mineral oil DTEL 15

  16. LECTURE 6:- Synthetic lubricants • For specific applications lubricating oils are artificially synthesized • They have specific required properties such as • High viscosity index, • Very high thermal stability • Very high flash & fire point • Very low cloud & pour point • Low to high viscosity & oiliness • Very good oxidation and chemical resistance • Useful in aircrafts, turbines, jet engines, timers, electronic devices 16 DTEL 16

  17. LECTURE 1:- LECTURE 6:- Synthetic lubricants • DIABASIC ACID ESTER • Widespread used as bases for low volatility greases & lubricants for gas turbines • Excellent viscosity , low volatility& High thermal stability • Noncorrosive to metals, nontoxic & stable to hydrolysis. Deteriorates rubber • Di-2 ethyl hexyl sebacate, (-500C to 2300C • SILICATE ESTERS • High viscosity index(150-200) • Low volatility • Poor oxidation resistance at elevated temperatures • Non corrosive to metals & nonreactive to plastic & rubber DTEL 17

  18. LECTURE 1:- LECTURE6:- Synthetic lubricants Silicones • These are organic compounds containing Si-O-Si linkage • Properties: • High viscosity index, • High Oxidation resistance • Good Chemical stability • Do not attack Rubber ,Plastic , paints • Not suitable for Iron surfaces (at least one surface should be nonferrous) • Silicone give good result only when one of the rubbing surface is nonferrous • Applications: • Silicone-200 –used for rubber plastic surfaces, as a moisture repellantin clocks, timers & electronics devices • Silicone-510 – low temperature lubrication. • Silicone-710 – thermal resistant lubricant for oven hinges, oven timer, automatic toasters, roller exposed to high temperature & high humidity. • Very useful for low temperature lubrication of small parts. 18 DTEL 18

  19. LECTURE 7:-PROPERTIES OF LIQUID LUBRICANTS • Flash and Fire point • Viscosity & Viscosity Index • Aniline point • Cloud and pour Point • Acid value • Saponification no. • Steam emulsification no.(SEN) 19 DTEL 19

  20. LECTURE 1:- LECTURE 7:-PROPERTIES OF LIQUID LUBRICANTS Flash and fire point Flash Point It is defined as the minimum temperature at which the oil gives off sufficient vapours to ignite momentarily when a flame of standard dimensions is brought near the surface of the oil. Fire Point The fire point is the lowest temperature at which the vapours of the oil burn continuously for at least for 5 seconds when the standard flame is brought near the surface of the oil. Closed cup Instruments Open cup instrument Pensky marten’s apparatus For oils having flash point 50- 3700c Abel’s apparatus For oils having flash point below 1200F Clevelands apparatus For oils having flash point below 1200F DTEL 20

  21. LECTURE 1:- LECTURE 7:-PROPERTIES OF LIQUID LUBRICANTS Flash and fire point Significance: • This ensures safety against risk of fire. A good lubricating oil should have flash point reasonably above the working temperature. • IT helps in proper storage, transportation & handling. • Used for identification of oil • Get an idea about contamination in oil • If flash point is high then oil is thermally stable & will not degrade & evaporate at high temperature DTEL 21

  22. LECTURE 1:- LECTURE 7:-PROPERTIES OF LIQUID LUBRICANTS Viscosity • It is the measure of internal resistance to the motion of a fluid & is mainly due to the forces of cohesion between the fluid molecules. It Decreases with increasing temperature . • Absolute dynamic viscosity (η) • It is the tangential force per unit area required to maintain a unit velocity gradient between two parallel planes in the in the fluid unit distance apart. • Unit in C.G.S. is poise and centipoises • Absolute Kinematic Viscosity (V) • The ratio of absolute viscosity to density for any fluid is known as absolute kinematic viscosity. • V = η /ρ • V = absolute kinematic viscosity η = absolute dynamic viscosity ρ = density of fluid • Unit in C.G.S. is stokes and centistokes • V = ct (For fluids having kinematic viscosity more than 10 centistokes) • V = ct- β/t (For fluids having kinematic viscosity less than or equal to 10 centistokes) • t = time of flow in seconds c = viscometer constant β = Coefficient of kinetic energy DTEL 22

  23. LECTURE 1:- LECTURE 7:-PROPERTIES OF LIQUID LUBRICANTS Viscosity • Significance: • Low load condition- low viscosity oil . • High load condition- High viscosity oil. • Viscosity is important property to make correct choice of lubricant under the given condition of load & speed. • A good lubricant should have proper viscosity to maintain a film under working conditions and should not cause undue friction. DTEL 23

  24. LECTURE 1:- LECTURE7:-PROPERTIES OF LIQUID LUBRICANTS Viscosity Index • The variation in viscosity of the oil under investigation with temperature is termed as viscosity index. Or • It is the numerical value of average slope of viscosity temperature curve in the temperature range of 100 - 2100F • This property is significantly important when the machines are working over a wide range of temperature. Eg. Aircraft engine, IC engines etc. V.I. = VL-VX x100 VL-VH Where, VL=Viscosity of Gulf oil standard at 1000F which has same viscosity at 2100F as that of the oil under test. VX = Viscosity of oil under test at 1000F VH =Viscosity of Pennsylvanian oil standard at 1000F which has same viscosity at 2100F as that of the oil under test. DTEL 24

  25. LECTURE 1:- LECTURE 7:-PROPERTIES OF LIQUID LUBRICANTS Viscosity Index • Significance • If VI is higher then the rate of change of viscosity with respect to temperature is lower. • Thus, the higher the viscosity index, the lower the rate at which its viscosity decreases with increase of temperature. • Hence, oils of high viscosity index i.e. those having flat viscosity temperature demanded for air-cooled internal combustion engines and aircrafts engines. • Oils of low viscosity are used in plain bearings for high speed equipment such as turbines, spindles, centrifuges whereas high viscosity oils are used with plain bearings of low speed equipment. DTEL 25

  26. LECTURE 1:- LECTURE 8:-PROPERTIES OF LIQUID LUBRICANTS Aniline point Aniline point is defined as “ the minimum equilibrium solution temperature for equal volumes aniline and oil sample” Significance: • Aniline point of an oil gives an indication of the possible tendency of deterioration of an oil when it comes into contact with packing ,rubber sealing etc. • Aromatic hydrocarbons have a tendency to dissolve natural and certain types of synthetic rubbers. • Contents of aromatic hydrocarbons are usually determined on the basis of aniline point of oil • Higher aniline point is therefore means lower percentage of aromatic hydrocarbons. A higher aniline point is desirable. DTEL 26

  27. LECTURE 1:- LECTURE 8:-PROPERTIES OF LIQUID LUBRICANTS Cloud & pour point Cloud Point- When an oil is cooled slowly in a standard apparatus at standard rate the temperature at which it becomes cloudy or hazy appearance is called as cloud point. Pour Point- It is the temperature at which oil just ceases to flow from the test tube when cooled at a standard rate in a standard apparatus when hold horizontally for 5 sec. • Significance : • A good lubricating oil should have low cloud and pour points. • Significant in cold countries & the systems working at low temperature for eg. Refrigeration systems, Aircraft engines .They should have very low cloud and pour points. • If a high pour point oil is used at the low temperature, it will jam the rotating spare parts under low load situation. • The Lubricant functioning by fluid film mechanism cannot function well if its pour point is high. [ DTEL 27

  28. LECTURE 1:- LECTURE 8:-PROPERTIES OF LIQUID LUBRICANTS Acid value • It is the number of milligrams of KOH required to neutralize free acid present in one gram of the oil. • Even the carefully refined oil possess slight acidity due to Small amount of non neutralized organic constituents or traces of residues during refining. • Acid value of a good lubricating oil should be less than 0.1 • Significance: • It indicates • Corrosive nature of lubricant (Low acid value desirable) • Oxidation tendency of oil. • Extent of deterioration due to oxidation & formation of gum& smudges • Greater values indicates that oil has been oxidized. DTEL 28

  29. LECTURE 1:- LECTURE 8:-PROPERTIES OF LIQUID LUBRICANTS Saponification no. It is the number of milligrams of KOH required to saponify 1g of oil. Mineral oils do not saponify at all ,but vegetable and animal oils do. • Every fixed oil has a definite Saponification value. Significance: • Identify whether the oil under consideration is mineral oil or fixed oil. • Identify the oil. • Any deviation from its standard value indicates ,the probability ofadulteration DTEL 29

  30. LECTURE 1:- LECTURE 8:-PROPERTIES OF LIQUID LUBRICANTS Steam Emulsion Number • The time in seconds in which the oil and water separate in distinct layer is called steam emulsion no. (S.E.N.) • When oils come in contact with water, have a tendency to form emulsion. • Emulsions easily collect dirt , grit, dust partials, which • cause abrasion and thus increase friction, wear & tear, deformation & • reduce the life and efficiency of the machine. • Hence it is essential that the lubricating oil should form such an emulsion with water which breaks off rapidly. • Significance: It helps in selecting proper oil for different jobs eg. • Steam turbine oils are often contaminated with stem or condensate and it is essential that the oil should separate out rapidly. Therefore oil should have low SEN. • In some cases like cutting emulsions the persistent emulsion formation is desired. Therefore oil should have high SEN. DTEL 30

  31. LECTURE 1:- LECTURE 4:-PROPERTIES OF LIQUID LUBRICANTS Steam Emulsion Number DTEL 31

  32. LECTURE 5:-CRITERION FOR SELECTION I.C.Engines • The IC engines work at high and over a wide range of temperature • Required properties : • High flash and fire point • High viscosity index • Good thermal and chemical stability and good heat transfer • Should provide a seal between piston rings and cylinder walls • High corrosion resistance to prevent corrosion of internal parts • Low acid value to prevent formation of sludge deposits • Low carbon residue DTEL 32

  33. LECTURE 1:- LECTURE 8:-CRITERION FOR SELECTION Gears • Gears are generally subjected to heavy or extreme pressure • Required Properties: • Good oiliness • High load carrying capacity • Proper viscosity & High Viscosity Index. • Good oxidation resistance • Extreme pressure properties • e.g. Thick mineral lubricating oil containing additives like • Cl, S, and P compounds is suitable for gears. DTEL 33

  34. LECTURE 1:- • Delicate Instruments LECTURE 5:-CRITERION FOR SELECTION The delicate instruments such as watches clocks, scientific equipment and sewing machines work at low load & low temperature. • Required Properties: • Low viscosity • Corrosion resistance • Fixed oils(animal or vegetable oils) such as olive oil, palm oil , Neat foot oil can be used satisfactorily. DTEL 34

  35. LECTURE 1:- LECTURE 8:-CRITERION FOR SELECTION Transformer In transformer lubricants are used • To insulate the windings. • To carry away the heat generated. Required Properties: • Low viscosity. • Good dielectric properties • Oils should be highly refined, dry, free from dust, dirt, metal particles • Good chemical stability and oxidation stability. • Transformers are subjected to high temperature, electrical stress, and there are copper (oxidation catalyst) windings • All these conditions are favorable to oxidation of used lubricating oil forming acids and sludge • Acids attack different parts while sludge coat the windings and interfere with cooling leading to high temperature which further accelerate the chemical reaction forming more sludge and acids. DTEL 35

  36. LECTURE 1:- LECTURE 8:-CRITERION FOR SELECTION Refrigeration system In refrigeration system or cooling systems oils have to work at very low temperature and are circulated through tubing. • Required Properties: • Low cloud and pour point • Low viscosity (For easy circulation) • Naphthalene based oils are mostly employed DTEL 36

  37. THANK YOU DTEL 37

  38. References: • BOOKS: • A Text book of Engineering Chemistry by S S. Dara; S.Chand & Co New Delhi. Eleventh Edition. • Engineering Chemistry by Jain & Jain; DhanpatRai & sons New Delhi. Sixteenth Edition. • WEB: • http://www.brighthubengineering.com/manufacturing- technology/73568-hydrostatic-lubrication/ • refractoriess.blogspot.com/.../properties-of- lubricants.html   38 DTEL 38

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