Presentation on theme: "Examine Bearings “Before” Class See More Than a Class Pass Around l Bearing A -frosted band in raceway is normal wear l Bearing B -spall in raceway, detect."— Presentation transcript:
Examine Bearings “Before” Class See More Than a Class Pass Around l Bearing A -frosted band in raceway is normal wear l Bearing B -spall in raceway, detect with vibration l Bearing C -spalls 180 0, marks 180 0, fretting ID l Bearing D -photo, melt/bent shaft, inner ring blue & dented by balls, balls blue, outer ring straw color l Bearing E -shaft spun in bearing l Bearings F1 & F2 -pillow block, brg. spherical in hsg., eccentric lock to shaft, F1 “clicks” as rotates
Agenda l Introduction »Bearing Function »Physical Behavior in a Rotating Bearing »Bearing-Parts & Types »Mounting-on Shaft & in Housing l Design & Engineering »Tolerances, Fits & Clearances »Forces & Life »Lubrication l Illustrate Behavior, Design & Engineering »Case Histories & Post Mortems
Function, Behavior, Parts, Types, & Mounting l Brgs. are joints between rolling & stationary l Most machines have multiple bearings l #rolling element brgs.>>#journal brgs. (oil film) l Fascinating Physical Behavior »clearances about 0.0001 inch for typical bearing »hydroplaning on thin oil film, millionths of inch »demonstrate bearing defect frequencies l Parts Textbook Figs. 10-17,18,19, seals & shields * l Types & Ratings Text Figs. 10-20&21 & reverse side * l Mounting Text Sec. 10.11 + pillow block * & mounting * * shown on the reverse side of this handout
Design & Engineering l 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. clearance 0.00055 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 l Forces »Recognized: static wt., drive forces, dynamic forces »Unrecognized: misalignment, restrain thermal growth l 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 l 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 l Bearing Wear Patterns-Good & Bad »Brg-A; frosted band in center of inner race l Defect Frequency so detect faults before failure »Brg-B; spall on outer race »Brg-C; spalls 180 0, marks 180 0,oval ring, hsg. ecc. l Brg-D photo melted/bent shaft; taper lock not tight l Brg-E shaft spinning in brg.; hi temp environment; assumed thermal growth for shaft but none for brg.
Questions-Oil Film Thickness l How is oil film thickness created? l What happens if the oil film is too thin? l If brg. rpm increases, thickness inc/dec? l If oil viscosity increases, thick. inc/dec? l If bearing temp. rises, thickness inc/dec?
Summary-Potential Exam Questions l Name the major parts of a bearing l Type-most common, good axial, good hi radial lb. l Best way to attach brg. to shaft, 1 other way l Difference-Tolerances, Fits, & Clearances l Forces-name 1 recognized, 1 unrecognized l Life-relationship to load, what if axial & radial load, what are 2 major factors that limit life l Lubrication-2 purposes, discuss oil vs. grease l How did a case history illustrate brg. fundamental l Discuss physical action between ball & raceway l How solve problem with post mortem or brg. freq.