Bearings Lubrication Roger Bortignon 1 Friction is the

Bearings & Lubrication Roger Bortignon 1

Friction is… ü the resistance opposing any effort to roll or slide one object over another 2

Causes of Friction • minute imperfections on surface interact • deformation or indentation of one object into another 3

Kinds of Friction 1) Fluid friction: is less than solid friction but it exists 2) Static friction: resistance to movement between 2 bodies in contact & at rest 3) Kinetic Friction: a) Sliding friction: resistance to continued movement once set in motion b) Rolling Friction: one body rolling over another – the least of the 3 frictions 4

Bearings • Purpose of a bearing: 1) reduce friction 2) support a load/rotating shaft a) radial a) axial • Bearing classifications: 1) friction bearings (aka: plain bearings) 2) anti-friction bearings 7

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 8

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 9

Friction bearing advantages… • physically compact • high speed (rpm) capability • low cost • easily replaced • can tolerate greater levels of debris in the lubricant 13

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 limited axial • offer lower friction levels than #1 a 2 b c 14

Bearing Surfaces • the rolling elements in a bearing 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 15

More anti-friction bearings… • ball thrust bearings • needle thrust bearings 16

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 17

Lubrication - Oil Lubricating oil is designed to… ü Lubricate moving parts (minimize wear/reduce friction) by separating the two moving parts Engine oil is also designed to… ü Cool engine parts by absorbing heat ü Clean engine via detergents that are added to the oil ü Seals the area between the rings and the cylinder wall to improve combustion ü Quiets the engine by separating moving parts 18

Engine Oil • Oil viscosity: its resistance to flow or rate of flow. • Low viscosity oil = thinner (think baby oil) • High viscosity oil = thicker (think honey) • • Viscosity Grade: determined by… Society of Automotive Engineers (SAE) lower numbers = thinner oil higher numbers = thicker oil • Oil Service Classification: determined by the American Petroleum Institute (API) Ø refer to handout 20

Synthetic (man-made) Engine Oils 1) Synthetic motor oils will withstand higher engine temperatures than petroleum based oils Ø 600°F compared to… Ø 450°F for petroleum oils 2) Synthetic oils will begin lubricating at lower temperatures than petroleum oils Ø -58°F degrees, compared to… Ø -35°F degrees for petroleum based oils 3) Synthetic oils are more “slippery” than petroleum oils Ø less wear and tear Ø cooler engine Ø better performance 21

Lubrication Systems 1) Splash Lubrication: • used with a “dipper” (horizontal shaft) • or “oil slinger” (vertical shaft) 22

Splash Lubrication Systems Continued 2) Barrel pump – common on many vertical shaft engines 23

Full Pressure Lubrication System • uses a positive displacement oil pump • pump feeds pressurized oil to bearing surfaces, camshaft, connecting rod and valve train • can be used in combination with splash system 24

Oil Filtration 3) Full Flow System 25

Lubrication - 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 26

• National Lubricating Grease Institute NLGI Grade Appearance Consistency food analog 000 fluid cooking oil 00 fluid applesauce 0 very soft mustard 1 soft tomato paste 2 moderately soft peanut butter 3 semi-fluid vegetable shortening 4 semi-hard frozen yogurt 5 hard smooth pate 6 very hard cheddar cheese spread Wheel Bearing Grease 27