ABRASION OF RUBBER BY A BLADE ABRADER - EFFECT OF BLADE SHARPNESS ANDTEST TEMPERATURE FOR SELECTED COMPOUNDS

Apparatus has been constructed to abrade the flat surface of a rubber disk by rotating it against a stationary knife-blade scraper at consta nt frictional torque. The ratio of worn surface area to sample volume is relatively large, giving high sensitivity of measurement. Rates of abrasion were measured for several rubber compounds over a range of fr ictional torque from 0.05 to 1.2 Nm, corresponding to frictional work input from 150 to 3,600 J/m(2) per rotation. For some materials, notab ly SBR compounds, the rate of abrasion decreased markedly as the exper iment continued, due to rapid wear and blunting of the blade. Polybuta diene compounds caused much slower wear. Different blades were worn aw ay at different rates, a zirconia blade showing the least wear. Also, different elastomers showed different sensitivities to blade sharpness , the rate of abrasion of a high-styrene (48%) SBR compound being redu ced the most with a blunted blade whereas the abrasion rate of polybut adiene (BR) was much less affected. Measurements were carried out with blades of known sharpness for several representative rubber compounds at various frictional torques and at two temperatures, 25 degrees C a nd 100 degrees C. The high-styrene SBR compound showed the lowest rate of abrasion. Unusually rapid abrasion was observed for SBR and BR com pounds when the frictional work input exceeded a critical value, close to the tear( fracture) energy at the same temperature. Also, periodic fluctuations in rate of abrasion were observed for rapidly-aging comp ounds at high temperatures. This is attributed to repeated formation a nd removal of a weakened surface layer.