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Properties of Rubber 2016-12-29T09:16:45+00:00

PROPERTIES OF RUBBER
 

Effect of Contact Media

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).

 

thermo Engine lubricating oil (D.Eng.RD.2472 B/O) and ASTM oil No.1
Engine lubricating oil (D.Eng.RD.2472 A/O)
D.Eng.RD.2479
EssoTerresso 43
Shell Tellus 68
Aviation turbine oil (D.Eng.RD.2490)
Shell Tellus 37
ASTM No. 2 oil
Hydraulic oil (DEF 2001A)
ASTM No. 3 oil
Hydraulic oil (DTD 585)
Aviation turbine fuel (D.Eng.RD.2482)

White spirit

As a general guide, high nitrile rubber may be used in a fluid whose aniline point is in excess of 30°C. A polychloroprene rubber may be used in fluids whose aniline point does not fall below 100°C.

Figure R-1 (Some typical aniline points)

 

 

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Figure R-2 (Limits of volumetric swell in high and low aromatic oils)

 

Simply expressed, a higher aniline point causes a lower volumetric swell in the rubber. For example, a high nitrile rubber may be used in a fluid whose aniline point is greater than 30°C, but a polychloroprene rubber should only be used in fluids whose aniline point is greater than 100°C. From Figure R-2, it should be noted that ethylene propylene, natural rubber and butyl are unsuitable for use in the high aromatic oil or fuel their performance will be very suspect for any exposure in excess of splash contact.