Bearings Lubrication & Cooling Roger Bortignon

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

minute imperfections on surface interact Causes of Friction minute imperfections on surface interact adhesion between surfaces causes attraction 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

Overcoming Friction Static “Coefficient of Friction” = force to move the object weight of the object Kinetic “Coefficient of Friction” = force to keep the object moving

Coefficients of Friction coefficient of friction: The force required to slide an object, divided by the weight of the object Materials Static Kinetic - Sliding hard steel on hard steel 0.78 (dry) 0.42 (dry) steel on graphite 0.21 (dry) 0.09 (lubricated) aluminum on mild steel 0.61 (dry) 0.47 (dry) glass on glass 0.94 (dry) 0.35 (lubricated) 0.40 (dry) cast iron on cast iron 1.1 (dry) 0.2 (lubricated) 0.15 (dry) 0.07 (lubricated) steel on babbitt 0.17 (lubricated) 0.35 (dry) 0.14 (lubricated) Teflon on steel 0.04 Tire on Pavement 1.7 (approximate)

Angle of Repose angle of repose: the angle at which an object begins to slide Coefficient of static friction = YZ = Tangent of angle of repose XZ

What have we learned so far… Friction is determined by… 1) force (PSI) pressing materials together 2) coefficient of friction for those 2 materials

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

3 types of friction bearings… Journal bearing: crankshaft, piston pin, camshaft Guide bearing: valve guide Thrust bearing: crankshaft end thrust

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

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

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.

Plain bearing advantages… small package size high speed capability lower cost easily replaced can tolerate greater levels of debris in the lubricant

3 types of anti-friction bearings… 1) Tapered roller bearings tapered rollers are used in heavy radial & thrust loads & typically run at lower speeds. 2) Ball bearings ball bearings are designed for light to moderate radial loads, limited thrust loads & are better suited for high speeds. 3) Needle bearings 1 2 3 1

ball thrust bearings needle thrust bearings