FRICTION AND TRANSFER OF SOME POLYMERS IN UNLUBRICATED SLIDING.

Abstract

THE PAPER DEALS MAINLY WITH THE FRICTION OF PTFE AWD HIGH DENSITY POLYETHYLENE SLIDING OVER HARD CLEAN FLAT SURFACES.THE BEHAVIOUR OF THESE POLYMERS IS SOMEWHAT ANOMALOUS AND IS CONTRASTED WITH THE BEHAVIOUR OF SECONDS NORMALSECONDS POLYMERS; THAT IS VIRTUALLY ALL OTHER POLYMERS.THE FRICTION AND TRANSFER BEHAVIOUR FALLS INTO TWO GROUPS.(I) AT LOW SPEEDS THE FRICTION IS LOW (GM # 0.05) A THIN FILM OF POLYMER IS DRAWN OUT OF THE SLIDER AND ADHERES TO THE COUNTER SURFACE.ITS THICKNESS IS OF ORDER 50-200AA AND THE MOLECULAR CHAINS ARE HIGHLY ORIENTED IN THE SLIDING DIRECTION.THIS BEHAVIOUR DOES NOT APPEAR TO DEPEND ON THE CRYSTALLINITY OR BAWD STRUCTURE OF PTFE OR ON THE SPHERULITE SIZE OF PE.IF, HOWEVER, BULKY OR STRAGGLY SIDE-GROUPS ARE INCORPORATED INTO THE POLYMER BACKBONE, THE FRICTION AND TRANSFER INCREASE RESEMBLE THOSE OF SECONDS NORMALSECONDS POLYMERS.THE BEHAVIOUR APPEARS TO BE CONNECTED WITH A SMOOTH MOLECULAR PROFILE.(II) AT HIGH SPEEDS OR LOW TEMPERATURES THESE SECONDS LOW-FRICTIONSECONDS MATERIALS GIVE A HIGH FRICTION (GM # 0.3) AND THE TRANSFER IS MUCH HEAVIER CONSISTING OF LUMPS OR SMEARED FILMS OF POLYMER, SEVERAL 1000 AA THICK.THE BEHAVIOUR IN THIS REGIME MAY BE DETERMINED BY CRYSTALLITE SIZE, THE BAND STRUCTURE OF THE POLYMER OR THE MOLECULAR WEIGHT.EXPERIMENTS ON HIGH DENSITY PE CONTAINING A MIXTURE OF CUO AND PB/SUB 3/O/SUB 4/ SHOW THAT THE FILLER HAS NO INFLUENCE ON THE FRICTION OR WEAR BEHAVIOUR AT LOW SLIDING SPEEDS.BUT AT HIGH SLIDING SPEEDS THE WEAR AGAINST A SMOOTH STEEL COUNTERFACE IS MARKEDLY REDUCED.THE FILLER APPARENTLY FUNCTIONS BY PRODUCING A STRONGLY ADHERING POLYMER FILM ON THE STEEL SURFACE.(A.)