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

Bearing data – generalDimensionsThe dimensions of the metric sizes ofPTFE composite and POM compositedry sliding bushings in the bore diameterrange 4 to 160 mm, inclusive,are in accordance, with a few exceptions,with those specified in ISO3547-1976 and DIN 1494/1:1983.The dimensions of the inch-sizebushings, the flanged bushings andthe thrust washers have not beenstandardised.TolerancesBushings: The tolerances for the outsidediameter of the metric sizes ofSKF PTFE composite and POM compositedry sliding bushings correspondto DIN 1494/1:1983. To check thevalues, the procedure given in DIN1494/2:1983 should be used. For allsizes, the tolerances for the width Bare a uniform ± 0,25 mm.Flanged bushings: For all sizes,when mounted, the tolerances are auniform ±0,5 mm for the flange diameterD 1 and for the width B 1+0,05/–0,20 mm.Thrust washers: The tolerances forthe diameters are given in the producttable. The tolerances for the height are• 0/–0,05 mm for PTFE compositethrust washers• 0/–0,10 mm for POM compositethrust washers.Strip: The tolerances for the height are• 0/–0,05 mm for PTFE compositestrip• 0/–0,10 mm for POM compositestripOperating clearanceThe operating clearance of bushingsdepends on the recommended shaftand housing tolerances. Guidelinevalues for bushings in metric sizes are26given in Tables 1 and 3 and forinch-sized bushings in Tables 2 and4 .Excessive clearance may have anegative influence on the service life ofPTFE composite bushings if they arenot lubricated.Permissible operating temperaturerangePTFE composite dry sliding bearingscan be used at temperatures between–200 and +250 °C.The operating temperature range forPOM composite bearings is –40 to+110 °C, although brief periods ofoperation at +130 °C are permissible.The service life of SKF compositedry sliding bearings will be shortenedwhen operating at temperatures abovea given value. This is taken intoaccount when calculating the basicrating service life by the temperaturefactor c 3 (➔ Diagram 5 , page 12).Running-inDuring a short running-in phase therewill be some transfer of material fromthe covering layer of bearings madefrom PTFE composite to the counterface.After this transfer has taken place,the characteristic low friction and wearproperties of these bearings will beobtained.Electrical propertiesBearings made from POM composite,because of their acetal resin coveringlayer, may act as electrical insulatorswhen new. To avoid the build-up ofstatic electricity, components at riskshould be earthed.Product designationsSKF metric composite dry sliding bearingsare identified by designationsmade up of a prefix PCM which mayhave a fourth letter indicating the typeof bearing (e.g. PCMW for a thrustwasher) followed by 6 to 9 figures givingthe dimensions (d, D, B/H) in millimetresuncoded. The small bushingscarrying the additional suffix /VB055are an exception to this: the outsidediameter is 0,5 mm larger than indicatedin the designation. The actualmaterial used is identified by a suffix:B for PTFE composite and M for POMcomposite. For example, PCM 081008M is a POM composite bushing withd = 8 mm, D = 10 mm and B = 8 mm.The inch-size bearings have similardesignations, but in this case the prefixis PCZ and the size (d, B) is shownin 1/16ths of an inch, e.g. PCZ 1208 Bis a PTFE composite bushing with d =12/16˝ = 3/4˝ and B = 8/16˝ = 1/2˝.