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Bearings & Lubrication Roger Bortignon. Friction. Friction is… the resistance opposing any effort to roll or slide one object over another. Causes of Friction. minute imperfections on surface interact deformation or indentation of one object into another. Kinds of Friction.
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Bearings & Lubrication Roger Bortignon
Friction Friction is… • the resistance opposing any effort to roll or slide one object over another
Causes of Friction • minute imperfections on surface interact • deformation or indentation of one object into another
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: • Sliding friction: resistance to continued movement once set in motion • Rolling Friction: one body rolling over another – the least of the 3 frictions
Bearings • Purpose of a bearing: • reduce friction • support a load/rotating shaft • radial • axial • Bearing classifications: • friction bearings (aka: plain bearings) • anti-friction bearings
Friction Bearings • 3 types of friction bearings… • Journal bearing: crankshaft, piston pin, camshaft • Guide bearing: valve guide • Thrust bearing: • controls crankshaft end thrust 1
Friction Bearings • small 4 cycle engines use the engine parts as the wear surfaces • crankshaft connects directly to the connecting rod • camshaft spins directly in the engine block • larger engines use replaceable wear surfaces called… • precision insert bearings
Friction bearing advantages… • physically compact • high speed (rpm) capability • low cost • easily replaced • can tolerate greater levels of debris in the lubricant
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
Bearing Surfaces • the rolling elements in a bearing roll on bearing races… • rolling elements are made from high-carbon chromium steel which also contains small amounts of manganese and silicon inner race outer race
More anti-friction bearings… • ball thrust bearings • needle thrust bearings
How do bearings reduce friction? • chief cause of rolling friction: deformation • steel wheel on steel rail: .002 Coefficient of Friction • riding a bike with a flat tire: very high Coefficient of Friction • this is why bearings surfaces are hard • bearings & their races are very hard • smaller “footprint” & a lower Coefficient of Friction • this is a compromise between size & strength
Lubrication - Oil Lubricating oil is designed to… • Lubricate moving parts (minimize wear/reduce friction) by separating the two moving parts Engine oil is also designed to… • Cool engine parts by absorbing heat • Clean engine via detergents that are added to the oil • Seals the area between the rings and the cylinder wall to improve combustion • Quiets the engine by separating moving parts
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) • refer to handout
Synthetic (man-made) Engine Oils 1) Synthetic motor oils willwithstand higher engine temperaturesthan petroleum based oils • 600°F compared to… • 450°F for petroleum oils 2) Synthetic oils will beginlubricating at lower temperaturesthan petroleum oils • -58°F degrees, compared to… • -35°F degrees for petroleum based oils 3) Synthetic oils are more “slippery” than petroleum oils • less wear and tear • cooler engine • better performance
Lubrication Systems • Splash Lubrication: • used with a “dipper” (horizontal shaft) • or “oil slinger” (vertical shaft)
Splash Lubrication Systems Continued 2) Barrel pump – common on many vertical shaft engines
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
Oil Filtration 3) Full Flow System
Lubrication - Grease • grease is oil that has a thickener added to increase its viscosity • 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 • without being squeezed out between moving parts • or forced out from gravity or centrifugal force
National Lubricating Grease Institute NLGI Wheel Bearing Grease