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

LubricationFig1POM composite bushing with lubricationholePTFE composite bearingsPTFE composite bearings have gooddry sliding characteristics and do notrequire lubrication. The presence orcontinuous supply of oil or other fluidmay be advantageous, however. Evenfluids not normally associated with lubrication,such as water, kerosene orparaffin, may be used.Lubrication improves the removal ofheat from the bearing position and theformation of a hydrodynamic lubricatingfilm has a very favourable effect onthe wear behaviour of the bearing andconsiderably extends bearing life.If periodic relubrication with greaseis used to enhance sealing or to protectthe counterface against corrosion,bearing life will also be extended. Asingle initial application of grease whenmounting PTFE composite bearingsmay, however, have a negative influenceon bearing life, as the grease willform a paste-like mixture with the wearparticles produced during running in.This “paste” will increase bearingwear.Age-resistant lithium base greasesare preferred for operating temperaturesup to 80 °C, while at higher temperatures,silicone greases should beused. Greases containing solid lubricantssuch as molybdenum disulphideare totally unsuitable.POM composite bearingsPOM composite dry sliding bearingsrequire an initial application of greaseon mounting. Relubrication is notrequired but the presence or constantsupply of lubricating fluid or periodicgrease relubrication serve to extendbearing life considerably.For this reason POM compositebushings having a bore diameter of 10mm and above and a width of 12 mmor more are supplied as standard witha lubrication hole (➔ fig 1 ). The holedimensions and position are in accordancewith DIN 1434-3:1983. The samegreases as those recommended abovecan be used.24