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Lubrication

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)

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Lubrication

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  1. Lubrication Nizwa College of Technology

  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 heatfrom the bearing • To reduce noisefrom 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

  8. Hydrodynamic lubrication(Lubricant is dynamic) At Running (Full Film Lubrication) Starts to Rotate (Mixed Lubrication) At Rest

  9. Hydro static Lubrication(Lubricant is static)

  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 certainchemicals • 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

  15. Lubricating Methods • Oil can • Oil gun • Grease packing • Wick type • Bath type (Splash) • Circulation (pressure)

  16. Oil cane &Grease gun Housing Grease Nipple Grease Gun Oil cane Fill Shaft Oil cane Grease Gun

  17. Bath Type (Splash) Housing Gears Oil

  18. Wick Oil Shaft Bearing Grease packing & Wick Type Housing Grease Grease Cap Ball bearings Grease Packing Wick Type Lubrication

  19. Oil filter To various Moving parts Relief valve Oil Pump Sump Coarse Filter Circulation (pressure) Oil Filter Relief Valve Oil Pump

  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 burrsand 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

  29. Seals &Gaskets-Examples

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