AgendaFunction, Behavior, Parts, Types, & MountingDesign & EngineeringDesign & Engineering Con’tSlide 5Illustrate Behavior, Design & Engr. with Case Histories & Post MortemsExamine Bearings “Before” Class See More Than a Class Pass AroundQuestions-Oil Film ThicknessSummary-Potential Exam QuestionsAgendaIntroduction »Bearing Function»Physical Behavior in a Rotating Bearing»Bearing-Parts & Types»Mounting-on Shaft & in HousingDesign & Engineering»Tolerances, Fits & Clearances»Forces & Life»Lubrication Illustrate Behavior, Design & Engineering »Case Histories & Post MortemsFunction, Behavior, Parts, Types, & MountingBrgs. are joints between rolling & stationaryMost 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 frequenciesParts Textbook Figs. 10-17,18,19, seals & shields* Types & Ratings Text Figs. 10-20&21 & reverse side*Mounting Text Sec. 10.11 + pillow block * & mounting* *shown on the reverse side of this handoutDesign & EngineeringTolerances, 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 clearanceDesign & Engineering Con’tForces»Recognized: static wt., drive forces, dynamic forces»Unrecognized: misalignment, restrain thermal growthLife »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’tLubrication»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 & performanceIllustrate Behavior, Design & Engr.with Case Histories & Post MortemsBearing Wear Patterns-Good & Bad»Brg-A; frosted band in center of inner raceDefect Frequency so detect 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 tightBrg-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 AroundBearing A-frosted band in raceway is normal wearBearing B-spall in raceway, detect with vibrationBearing C-spalls 1800, marks 1800, fretting IDBearing D-photo, melt/bent shaft, inner ring blue & dented by balls, balls blue, outer ring straw colorBearing E-shaft spun in bearingBearings F1 & F2-pillow block, brg. spherical in hsg., eccentric lock to shaft, F1 “clicks” as rotatesQuestions-Oil Film ThicknessHow 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 QuestionsName the major parts of a bearingType-most common, good axial, good hi radial lb.Best way to attach brg. to shaft, 1 other wayDifference-Tolerances, Fits, & Clearances Forces-name 1 recognized, 1 unrecognizedLife-relationship to load, what if axial & radial load, what are 2 major factors that limit lifeLubrication-2 purposes, discuss oil vs. greaseHow did a case history illustrate brg. fundamentalDiscuss physical action between ball & raceway How solve problem with post mortem or brg.
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