MICROSCOPIC STUDIES ON THE MECHANISMS OF WEAR OF NR, SBR AND HNBR VULCANIZATES UNDER DIFFERENT CONDITIONS

Microscopic investigations, undertaken to understand the mechanism of wear of natural rubber (NR), styrene-butadiene rubber (SBR) and hydrog enated nitrile rubber (HNBR) vulcanizates abraded against hard rock, a knurled aluminium disc and a silicone carbide abrader under different conditions, are reported. The wear of NR and SBR vulcanizates against hard rock at low normal load (6 kPa) takes place by a fatigue wear me chanism and it switches over to frictional wear at high normal load (a bove 18 kPa). In HNBR vulcanizates the wear takes place by an abrasive wear mechanism. Ridges are observed on worn surface of swollen NR and SBR vulcanizates at low normal load, but at higher normal load the we ar takes place by catastrophic fracture and extensive plough marks alo ng the direction of abrasion are observed. The wear of NR and SBR vulc anizates proceeds by frictional wear, even at elevated temperatures. I n HNBR vulcanizates, the mechanism changes from abrasive wear at 25-de grees-C to frictional wear above 50-degrees-C. Above 50-degrees-C, rid ges are observed and the spacing between adjacent ridges increases wit h rise of temperature.