A puncture test has been used to investigate the lubrication and wear of metal by rubber. Cylindrical metal indenters are used to puncture a rubber surface under controlled conditions. Several mechanisms are investigated which affect both the lubrication and wear of the metal. A self-lubrication effect is reported whereby there is a drop in puncture load over successive punctures, which correlates with a strong increase in the contact angle of water against the metal surface and is associated with a reduction in metal wear rate. It is suggested that this is due to the formation of a rubbery layer on the metal surface. The wear rates of several different metals are studied and at least one metal showed an enhanced wear rate for its hardness, suggesting some mechanism of polymer radical attack. In most cases, however, metal and rubber hardnesses were the dominant factors in determining wear rates.
1, IntroductionWear of one material by another is usually considered in terms of the wear of a softer material by a harder one. However, hard materials can be worn by softer materials, as illustrated by the wear of a diamond stylus by repeated use on a gramophone record or the wear of stone steps by pedestrian traffic.Some recent work has suggested that polymer radicals formed by the rupture or degradation of the polymer surface can react chemically with metal oxide layers and act either to decrease or increase rates of wear in different circumstances. Thus Vinogradov etal. [1] found in the course of investigating the sliding of polymer discs against metal surfaces that modification of the contacting surfaces could occur both due to polymer degradation (associated with local frictional heating) and to metallization of the polymer surface. They concluded that in at least one case increasing readiness of polymer oxidation reduced the wear rate against steel. Gorokhovskii etaL [2-4] also reported modifications to the structure of steel chips ground together with polymethyl methacrylate (PMMA) associated with progressive mechanical degradation of the polymer. Gorokhovskii etal. also found that the addition of a small amount of polymer (~5%) to abrasive particles could increase the rate of wear of metals 0022-2461/84 $03.00 + .12 by a factor of two to three. The phenomenon was however reversed when larger amounts (> 10%) of polymer were present, when some reductions in wear rate were observed. Gent and Pulford [5,6] have also reported chemical effects. The wear rate of steel razor blades held against rotating solid rubber wheels was, for example, reported to be almost 70 times greater for polyisobutylene-coisoprene than for ethylene propylene rubber of similar hardness. The authors attributed this effect to the direct attack upon metals of free radical species generated by the mechanical rupture of elastomer molecules.In the present study surface effects associated with the wear and lubrication of cylindrical metal indentors were studied by using the indentors to puncture the surfaces of solid rubber blocks. In such a case, si...
