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Agenda. Introduction Bearing Function Physical Behavior in a Rotating Bearing Bearing-Parts & Types Mounting-on Shaft & in Housing Design & Engineering Tolerances, Fits & Clearances Forces & Life Lubrication Illustrate Behavior, Design & Engineering Case Histories & Post Mortems.
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Agenda • Introduction • Bearing Function • Physical Behavior in a Rotating Bearing • Bearing-Parts & Types • Mounting-on Shaft & in Housing • Design & Engineering • Tolerances, Fits & Clearances • Forces & Life • Lubrication • Illustrate Behavior, Design & Engineering • Case Histories & Post Mortems
Function, Behavior, Parts, Types, & Mounting • Brgs. are joints between rolling & stationary • Most machines have multiple bearings • #rolling element brgs.>>#journal brgs. (oil film) • Fascinating Physical Behavior • clearances about 0.0001 inch for typical bearing • hydroplaning on thin oil film, millionths of inch • demonstrate bearing defect frequencies • PartsTextbook Figs. 10-17,18,19, seals & shields* • Types & Ratings Text Figs. 10-20&21 & reverse side* • MountingText Sec. 10.11 + pillow block * & mounting* *shown on the reverse side of this handout
Design & Engineering • Tolerances, Fits & Clearances • these 3 are mutually exclusive • Tolerances- of components, 5 ABEC grades • Fits-brg. to shaft & brg. to housing • radial internal Clearances • 50mm bore brg. clearance0.00055 inch • mounting (interference fit) & running removes ~80% clearance • clearance shifts to unloaded side (top) • changes in fit, load, thermal growth alters clearance
Design & Engineering Con’t • Forces • Recognized: static wt., drive forces, dynamic forces • Unrecognized: misalignment, restrain thermal growth • Life • Fatigue Life = Constants x (brg. rating/applied load)3 • If applied load= radial & axial loads, X & Y factors • Factors Limiting Life & % of brgs. in that factor • Reach Fatigue Life (8%) • Poor Fabrication (8%) • Under Designed (16%) • Poor Handling & Install (33-%) • Poor Lubrication (33+%)
Design & Engineering Con’t • Lubrication • Purpose • film between ball & raceway • lubricate sliding between cage & balls • protect surfaces from rusting/corrosion • carry away heat • Oil vs. Grease • oil is ideal, grease is oil in a carrier/thickener • Systems • grease, oil reservoir, recirculating oil • increasing cost, complexity & performance
Illustrate Behavior, Design & Engr.with Case Histories & Post Mortems • Bearing Wear Patterns-Good & Bad • Brg-A; frosted band in center of inner race • Defect Frequency sodetect faults before failure • Brg-B; spall on outer race • Brg-C; spalls 1800, marks 1800,oval ring, hsg. ecc. • Brg-D photo melted/bent shaft; taper lock not tight • Brg-E shaft spinning in brg.; hi temp environment; assumed thermal growth for shaft but none for brg.
Examine Bearings “Before” ClassSee More Than a Class Pass Around • Bearing A-frosted band in raceway is normal wear • Bearing B-spall in raceway, detect with vibration • Bearing C-spalls 1800, marks 1800, fretting ID • Bearing D-photo, melt/bent shaft, inner ring blue & dented by balls, balls blue, outer ring straw color • Bearing E-shaft spun in bearing • Bearings F1 & F2-pillow block, brg. spherical in hsg., eccentric lock to shaft, F1 “clicks” as rotates
Questions-Oil Film Thickness • How is oil film thickness created? • What happens if the oil film is too thin? • If brg. rpm increases, thickness inc/dec? • If oil viscosity increases, thick. inc/dec? • If bearing temp. rises, thickness inc/dec?
Summary-Potential Exam Questions Name the major parts of a bearing Type-most common, good axial, good hi radial lb. Best way to attach brg. to shaft, 1 other way Difference-Tolerances, Fits, & Clearances Forces-name 1 recognized, 1 unrecognized Life-relationship to load, what if axial & radial load, what are 2 major factors that limit life Lubrication-2 purposes, discuss oil vs. grease How did a case history illustrate brg. fundamental Discuss physical action between ball & raceway How solve problem with post mortem or brg. freq.
