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BearingsBearings

LubricationLubrication

& &

CoolingCooling

Roger BortignonRoger Bortignon

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FrictionFriction

FrictionFriction is: is:

the resistance opposing any effort to roll or slide one the resistance opposing any effort to roll or slide one object over anotherobject over another

 

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Causes of FrictionCauses of Friction

• minute minute imperfectionsimperfections on surface on surface interactinteract

• adhesionadhesion between surfaces causes between surfaces causes attraction attraction

• deformationdeformation or or indentationindentation of one of one object into anotherobject into another

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Kinds of FrictionKinds of Friction

1) 1) Fluid frictionFluid friction:: is less than solid friction but is less than solid friction but

it existsit exists

2) 2) Static frictionStatic friction: resistance to movement : resistance to movement

between 2 bodies in contact & at restbetween 2 bodies in contact & at rest

3)3) Kinetic FrictionKinetic Friction::

a)a) Sliding frictionSliding friction: resistance to continued : resistance to continued

movement once set in motionmovement once set in motion

b)b) Rolling FrictionRolling Friction: one body rolling over : one body rolling over

another – the least of the 3 frictionsanother – the least of the 3 frictions

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Overcoming FrictionOvercoming Friction

Static “Coefficient of Friction”Static “Coefficient of Friction” = = force to move the objectforce to move the object

weight of the objectweight of the object

Kinetic “Coefficient of Friction”Kinetic “Coefficient of Friction” = = force to keep the object movingforce to keep the object moving

weight of the objectweight of the object

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Coefficients of FrictionCoefficients of Friction• coefficient of friction: The coefficient of friction: The forceforce required to slide an object, required to slide an object,

divided bydivided by the the weightweight of the object of the object

MaterialsMaterials StaticStatic Kinetic - SlidingKinetic - Sliding

hard steel on hard hard steel on hard steelsteel

0.78 (dry)0.78 (dry) 0.42 (dry)0.42 (dry)

steel on graphitesteel on graphite 0.21 (dry)0.21 (dry)0.09 (lubricated)0.09 (lubricated)

aluminum on mild aluminum on mild steelsteel

0.61 (dry)0.61 (dry) 0.47 (dry)0.47 (dry)

glass on glassglass on glass 0.94 (dry)0.94 (dry)0.35 (lubricated)0.35 (lubricated)

0.40 (dry)0.40 (dry)0.09 (lubricated)0.09 (lubricated)

cast iron on cast ironcast iron on cast iron 1.1 (dry)1.1 (dry)0.2 (lubricated)0.2 (lubricated)

0.15 (dry)0.15 (dry)0.07 (lubricated) 0.07 (lubricated)

steel on babbitt steel on babbitt 0.42 (dry)0.42 (dry)0.17 (lubricated)0.17 (lubricated)

0.35 (dry)0.35 (dry)0.14 (lubricated)0.14 (lubricated)

Teflon on steelTeflon on steel 0.040.04 0.040.04

Tire on PavementTire on Pavement 1.7 (approximate)1.7 (approximate)

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Angle of ReposeAngle of Repose

• angle of reposeangle of repose: the angle at which an object begins to slide: the angle at which an object begins to slide

Coefficient of static frictionCoefficient of static friction = = YZYZ = Tangent of angle of repose = Tangent of angle of repose

XZXZ

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What have we learned so far…What have we learned so far…

Friction is determined by…Friction is determined by…

1) force (PSI) pressing materials together1) force (PSI) pressing materials together

2) coefficient of friction for those 2 materials2) coefficient of friction for those 2 materials

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BearingsBearings

• Purpose of a bearing:Purpose of a bearing:

1)1) reduce frictionreduce friction

2)2) support a load/rotating shaftsupport a load/rotating shaft

a)a) radial radial

a)a) axialaxial

• Bearing classifications:Bearing classifications:

1)1) friction bearings (aka: plain bearings)friction bearings (aka: plain bearings)

2)2) anti-friction bearingsanti-friction bearings

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Friction BearingsFriction Bearings

• 3 types of friction bearings…3 types of friction bearings…

1)1) JournalJournal bearing: crankshaft, piston pin, camshaft bearing: crankshaft, piston pin, camshaft

2)2) GuideGuide bearing: valve guide bearing: valve guide

3)3) ThrustThrust bearing: crankshaft end thrust bearing: crankshaft end thrust

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Bearing surface heavily embedded with foreign particles. Note Bearing surface heavily embedded with foreign particles. Note

bright rings from raised material surrounding largest particlesbright rings from raised material surrounding largest particles

Precision Insert Friction Bearing Essential CharacteristicsPrecision Insert Friction Bearing Essential Characteristics

• Embedability: Embedability: inserts are designed to totally absorb abrasive inserts are designed to totally absorb abrasive particles or pass them off completelyparticles or pass them off completely

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Precision Insert Friction Bearing Essential CharacteristicsPrecision Insert Friction Bearing Essential Characteristics

• ConformabilityConformability: inserts are designed to distribute the : inserts are designed to distribute the load uniformly even when the shaft or bearing bore is load uniformly even when the shaft or bearing bore is out of round.out of round.

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Oil StarvationOil Starvation

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

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Plain bearing advantages…Plain bearing advantages…

• small package sizesmall package size

• high speed capabilityhigh speed capability

• lower costlower cost

• easily replacedeasily replaced

• can tolerate greater levels of debris in the lubricant can tolerate greater levels of debris in the lubricant

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3 types of 3 types of anti-frictionanti-friction bearings… bearings…

1)1) Tapered rollerTapered roller bearings bearings• tapered rollerstapered rollers are used in heavy radial & are used in heavy radial &

thrust loads & typically run at lower thrust loads & typically run at lower speeds.speeds.

2)2) BallBall bearings bearings• ball bearingsball bearings are designed for light to are designed for light to

moderate radial loads, limited thrust loads moderate radial loads, limited thrust loads & are better suited for high speeds.& are better suited for high speeds.

3) 3) NeedleNeedle bearings bearings

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• ball thrust bearingsball thrust bearings

• needle thrust bearingsneedle thrust bearings