Bearings Lubrication 1 Friction Causes minute imperfections on

Bearings & Lubrication 1

Friction: Causes • minute imperfections on surface interact • deformation or indentation of one object into another 2

Friction Reduction via Bearings • Purpose of a bearing: 1) reduce friction 2) support a load/rotating shaft a) radial b) axial • Bearing classifications: 1) friction bearings (aka: plain bearings) 2) anti-friction bearings 3

Friction Bearings • 3 types of friction bearings… 1) Journal bearing: crankshaft, piston pin, camshaft 2) Guide bearing: valve guide 3) Thrust bearing: • controls crankshaft end thrust 1 4

Friction Bearings • small 4 cycle engines use the engine parts as the wear surfaces Ø crankshaft connects directly to the connecting rod Ø camshaft spins directly in the engine block • larger engines use replaceable wear surfaces called… Ø precision insert bearings 5

Friction bearing advantages… • physically compact • high speed (rpm) capability • low cost • easily replaced • can tolerate greater levels of debris in the lubricant 6

2 categories of anti-friction bearings… 1) cylindrical roller bearings (a) • used in radial & axial load applications • needle type (a) & tapered rollers (b) are variations of cylindrical rollers 2) ball bearings • are designed for radial loads & sometimes axial • offer lower friction levels than #1 a 2 b c 7

Bearing Surfaces • the rolling elements in a bearing (the balls or cylinders) roll on bearing races… inner race outer race • rolling elements are made from high-carbon chromium steel which also contains small amounts of manganese and silicon 8

More anti-friction bearings… • ball thrust bearings • needle thrust bearings 9

Ceramic Bearings • are harder yielding greater wear resistance • are corrosion resistant • have a superior surface finish quality • have superior ball geometry • are lighter weight & have better high speed capability • are ideal for low lube of self-lubricating applications • are non-magnetic and non-conductive • can operate in extreme temperatures 10

How do bearings reduce friction? • chief cause of rolling friction: deformation Ø steel wheel on steel rail: . 002 Coefficient of Friction Ø riding a bike with a flat tire: very high Coefficient of Friction Ø this is why bearings surfaces are hard • bearings & their races are very hard Ø smaller “footprint” & a lower Coefficient of Friction • this is a compromise between size & strength 11

Lubrication – Oil & Grease Lubricants are designed to… ü Lubricate moving parts (minimize wear/reduce friction) by separating the two moving parts remember Plastigage? 12

Lubrication with grease… • grease is oil that has a thickener added to increase its viscosity Ø lithium is often the thickener • rust and corrosion additives are added • “tackifiers” may it cling better to parts • antifriction additives such as Molybdenum may be incorporated • easier to seal in (and prevent leaks) than oil is • better than oils under heavy loads • it is designed to remain in contact with parts and lubricate as well Ø without being squeezed out between moving parts Ø or forced out from gravity or centrifugal force 13