Composite dry sliding bearings â maintenance-free and space-saving

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Selection of bearing sizeDiagram3Determination of specific bearingloadThe specific bearing load can bedetermined fromPOM compositePTFE compositeFp = K –– CLoad factor c 1Diagram4wherep = specific bearing load, N/mm 2F = dynamic bearing load, NC = basic dynamic load rating, NK = specific load factor, N/mm 2= 80 for PTFE composite material= 120 for POM composite materialPOM compositePTFE compositeFor flanged bushings it is necessary tocalculate the specific load of the bushingand flange separately. When calculatingthe specific bearing load for theflange the axial basic dynamic loadrating C a should be used instead of Cin the above equation. Values of C a willbe found in the product tables.Speed factor c 2Diagram5Determination of sliding velocityThe sliding velocity for SKF compositebushings and thrust washers can beobtained fromv = 5,82 × 10 –7 d β fTemperature factor c 3POMcompositePTFE compositePTFE compositePOM compositeDiagram6wherev = sliding velocity, m/sd = bore diameter of bushings andflanged bushings, mm= mean diameter of flange of flangedbushings = 0,5 (d + D 1 ), mm= mean diameter of thrust washers= 0,5 (d + D), mm (= dimension Jin product table)f = frequency of oscillation, min –1 ,or rotational speed, r/minβ = half the angle of oscillation,degrees (➔ fig 1 )A complete oscillation (from point0 to point 4) = 4 β. For rotation,use β = 90°.Surface roughness factor c 412
Calculation of servicelifeMany factors influence the life of a drysliding bearing, e.g. load, sliding velocity,operating temperature, surfaceroughness of the surface on which thedry sliding layer runs etc. Any calculationis therefore only approximate.The values obtained using the equationsgiven below for the basic ratingservice life are attained by the majorityof bearings and are often exceeded.This has been confirmed by rig testsand field experience.The basic rating service life for SKFPTFE composite and POM compositedry sliding bearings can be calculatedfromK MG h = c 1 c 2 c 3 c 4 c 5 ––––(pv) nwhereG h = basic rating service life, operatinghoursc 1 = load factor (➔ Diagram 3 )c 2 = speed factor (➔ Diagram 4 )c 3 = temperature factor(➔ Diagram 5 )c 4 = surface roughness factor(➔ Diagram 6 )c 5= factor for the type of load= 1 for point load (i.e. the loadedzone is always at the same positionon the bearing circumference)= 1,5 for rotating load (i.e. theloaded zone moves round thecircumference of the bearing)K M = factor depending on materialand bearing type= 480 for PTFE composite bushings= 300 for PTFE compositethrust washers= 1 900 for POM compositebushings and thrust washersp = specific bearing load, N/mm 2vn= sliding velocity, m/s= an exponent= 1 for PTFE composite bushingsand thrust washers= 1 for pv ≤ 1 for POM compositebushings and thrust washers= 3 for pv > 1 for POM compositebushings and thrust washersIf loads are very light and/or slidingvelocities very low and the value of theproduct pv• for PTFE composite bearings is lessthan the limiting value of 0,025 thenthe limiting value pv = 0,025 shouldbe used for the life calculations.• for POM composite bearings is lessthan the limiting value of 0,1 thenthe limiting value pv = 0,1 should beused for the life calculations.Calculation exampleThe suspension of a rail vehicle is tobe equipped with composite dry slidingbearings at the linkage position ofthe springs; in this case bushingsarranged in pairs are to be used.Design data:Pin diameter: d = 30 mmSurface roughness of pin: R a = 0,4 µmOperating data:Radial load at the linkage point:F r = 18 750 NHalf angle of oscillation: β = 1°(➔ fig 1 )Frequency of oscillation: f = 180 min –1Operating temperature: t = 30 °CBased on the design characteristics,PTFE composite bushing PCM 303420B having a basic dynamic load ratingC = 46 500 N is chosen. It is necessaryto check that the bushing can beused under the given operating conditionsand then to calculate the basicrating service life.As a first check that the bearing sizeis suitable (➔ Diagram 1 ) the specificbearing load p is calculated usingF 18 750p = K –– = 80 × ––––––––– ≈ 16 N/mm 2C 2× 46 500(with the specific load factor K = 80 forPTFE composite).The sliding velocity is calculated usingv = 5,82 × 10 –7 d β f= 5,82 × 10 –7 × 30 × 1 × 180= 0,0031 m/sAngle of oscillationϕ = angle of oscillation = 2 βA complete oscillation = 4 β(from point 0 to point 4)Fig1These values are within the permissiblerange I of the pv diagram for PTFEcomposite bearings. Furthermorethe load factor c 1 = 1 (➔ Diagram 3 ),the speed factor c 2 = 1(➔ Diagram 4 ),the temperature factor c 3 = 1(➔ Diagram 5 ),the surface roughness factor c 4 = 0,6(➔ Diagram 6 ), andthe factor for the type of load c 5 = 1,5as the load is rotating.The value of K M for PTFE compositebushings = 480. Thus using thebasic rating service life equation forSKF composite dry sliding bearingsK MG h = c 1 c 2 c 3 c 4 c 5 ––––(pv) n 480G h = 1 × 1 × 1 × 0,6 ×1,5 × ––––––––––16 × 0,0031G h = 8 700 operating hours13
Page 1 and 2: Composite dry sliding bearings- mai
Page 3 and 4: Maintenance-free andspace-savingDry
Page 5 and 6: Table1Series Characteristics PagePC
Page 7 and 8: Summary of characteristics of SKFPT
Page 9 and 10: Chemical propertiesThe chemical res
Page 11: Service lifeThe service life of a d
Page 15 and 16: PTFE composite bushings (metric siz
Page 17 and 18: PTFE composite bushings (inch sizes
Page 19 and 20: POM composite bushings (metric size
Page 21 and 22: POM composite bushings (inch sizes)
Page 23 and 24: Fig4Fig5Fig6The mating surface shou
Page 25 and 26: MountingSkill and care in mounting
Page 27 and 28: Composite bushings with metric dime
Page 29 and 30: Dimensions Basic load ratings Mass
Page 39 and 40: Composite thrust washersd 12 - 52 m
Page 41 and 42: Other related productsMaintenance-f
Page 43 and 44: SKF rod endsRod ends have been desi
Page 45 and 46: Linear guide for a car suspension s
Page 47 and 48: Bearing arrangementfor a heavyloade
Page 49 and 50: Coupling rod bearing arrangements f
Page 51 and 52: Bearing arrangement for the platfor
Page 54 and 55: The SKF group- a worldwide corporat
Page 56: © Copyright SKF 1999The contents o

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Composite dry sliding bearings â maintenance-free and space-saving