The physical performance of a rubber compound is governed by its resistance to attack from the medium within which it functions. Rubbers may be attacked by a variety of media, such as oxygen, chemicals, solvents, fuels and oils.


Oil and Fuel Compatibility

The measurement of the volumetric swell of a rubber in a particular oil or fuel gives an indication of the potential effect of the media on the performance of the rubber component. For practical purposes, the oil-resistance or fuel-resistance of a rubber is a measure of its ability to retain its utility when in contact with the oil or fuel. This resistance of a vulcanized rubber compound to mineral-based or petroleum-based oils is purely physical phenomenon, and a volumetric swell of 20% is considered a practical limit for dynamic applications. A higher figure can be accepted for static applications.

In practice, the total exposure of a rubber product is rare, for under normal assembled conditions only one side or part of a surface is in contact with the media and the volumetric swell will then probably be less than a third of the swell of a totally exposed specimen. The degree of swell of a rubber compound varies not only wit the type of rubber, but also with the type of oil or fuel, and the most convenient method of determining this content is by ascertaining the aniline point of the fluid (Figures R-1 and R-2).