Tribology of elastomeric seal materials
Elastomers are the most commonly used materials for various sealing applications owing to their low modulus of elasticity, large elongation-at-break, and high Poisson's ratio. Most seals operate in the presence of lubricants; therefore the sealing elastomeroil interaction plays an important role in determining the tribological performance of elastomers. Furthermore, at times, such as starting up periods, the seals may also operate under dry condition and the seal material can be affected by high friction coefficient and wear. In this work, the tribological behaviour of different sealing elastomers has been studied. The influence of ageing of a sealing elastomer in different lubricants on its tribological behaviour has been investigated. Further studies pertaining to the influence of lubrication on the abrasive wear of a sealing elastomer have also been carried out. The results show that the friction coefficient of an elastomer in lubricated sliding against a hard counterface, at low contact pressure, depends on the surface topography of the elastomer but at high contact pressure, it is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. (Even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction). Ageing of the nitrile rubber in ester base fluids leads to reduction of friction coefficient. In unidirectional dry sliding of an elastomer against a counterface, the friction coefficient decreases during the running-in period. The longest running-in periods have been observed when the elastomers slide against relatively smooth surfaces. Depending on the elastomer-lubricant compatibility, abrasive coarseness, geometry of sliding contact area and contact pressure, the two body abrasive wear of elastomers may increase or decrease in presence of lubricants. Aging of nitrile rubber in lubricating fluids increases the abrasive wear both in dry and lubricated conditions. The abrasive wear of nitrile rubber in ester base fluids and rapeseed oil are higher than that in the mineral oils.
School:Luleå tekniska universitet
Source Type:Doctoral Dissertation
Date of Publication:01/01/2009