1 Bearings & Lubrication Roger Bortignon

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

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

4 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

5 Overcoming Friction Static “Coefficient of Friction” = force to move the object weight of the object weight of the object static friction is also referred to as starting frictionstatic friction is also referred to as starting friction Kinetic “Coefficient of Friction” = force to keep the object moving weight of the object weight of the object kinetic friction is also referred to as sliding or rolling frictionkinetic friction is also referred to as sliding or rolling friction

6 Coefficients of Friction coefficient of friction: The force required to slide an object, divided by the weight of the objectcoefficient of friction: The force required to slide an object, divided by the weight of the object MaterialsStatic Kinetic - Sliding hard steel on hard steel 0.78 dry 0.42 dry aluminum on mild steel 0.61 dry 0.47 dry glass on glass 0.94 dry 0.35 lubricated 0.40 dry 0.09 lubricated cast iron on cast iron 1.1 dry 0.2 lubricated 0.15 dry 0.07 lubricated steel on babbitt 0.42 dry 0.17 lubricated 0.35 dry 0.14 lubricated Teflon on steel Tire on Pavement 1.7 approximate

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

8 Friction Bearings 3 types of 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 thrustcontrols crankshaft end thrust 1

9 Friction Bearings small 4 cycle engines use the engine parts as the wear surfacessmall 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…larger engines use replaceable wear surfaces called…  precision insert bearings

10 Bearing surface heavily embedded with foreign particles. Note bright rings from raised material surrounding largest particles Precision Insert Friction Bearing - Essential Characteristics 1) Embedability: inserts are designed to totally absorb abrasive particles or pass them off completely

11 Precision Insert Friction Bearing - Essential Characteristics 2) Conformability: inserts are designed to distribute the load uniformly even when the shaft or bearing bore is out of round.

12 Oil Starvation Bearing surface streaked and smeared from shaft contact due to breakdown or lack of adequate oil film. Heat discoloration and most severe damage near center.

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

14 2 categories of anti-friction bearings… 1) cylindrical roller bearings (a) 1) cylindrical roller bearings (a) used in radial & axial load applicationsused in radial & axial load applications needle type (a) & tapered rollers (b) are variations of cylindrical rollersneedle type (a) & tapered rollers (b) are variations of cylindrical rollers 2) ball bearings are designed for radial loads & sometimes limited axialare designed for radial loads & sometimes limited axial offer lower friction levels than #1offer lower friction levels than #1 2 b c a

Bearing Surfaces the rolling elements in a bearing roll on bearing races…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 siliconrolling elements are made from high-carbon chromium steel which also contains small amounts of manganese and silicon 15 inner race outer race

16 More anti-friction bearings… ball thrust bearingsball thrust bearings needle thrust bearingsneedle thrust bearings

17 How do bearings reduce friction? chief cause of rolling friction: deformationchief 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 hardbearings & their races are very hard   smaller “footprint” & a lower Coefficient of Friction this is a compromise between size & strengththis is a compromise between size & strength

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

19 Bearings Ride On A Film Of Oil

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

21 Synthetic (man-made) Engine Oils 1) Synthetic motor oils will withstand higher engine temperatures than petroleum based oils   600°F compared to…   450°F for petroleum oils 2) Synthetic oils will begin lubricating at lower temperatures than 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

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

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

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

25 Oil Filtration 3) Full Flow System

26 Lubrication - Grease grease is oil that has a thickener added to increase its viscositygrease is oil that has a thickener added to increase its viscosity  lithium is often the thickener rust and corrosion additives are addedrust and corrosion additives are added “tackifiers” may it cling better to parts“tackifiers” may it cling better to parts antifriction additives such as Molybdenum may be incorporatedantifriction additives such as Molybdenum may be incorporated easier to seal in (and prevent leaks) than oil iseasier to seal in (and prevent leaks) than oil is better than oils under heavy loadsbetter than oils under heavy loads it is designed to remain in contact with parts and lubricate as wellit 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

27 National Lubricating Grease Institute NLGINational Lubricating Grease Institute NLGI NLGI GradeAppearanceConsistency food analog 000fluidcooking oil 00fluidapplesauce 0very softmustard 1softtomato paste 2moderately softpeanut butter 3semi-fluidvegetable shortening 4semi-hardfrozen yogurt 5hardsmooth pate 6very hardcheddar cheese spread Wheel Bearing Grease