Silicone rubber shaft seals

Auto uses are said to account for about one-third of the 30000 tonnes of silicone rubber consumed annually around the world (in turn about 10% of total silicone consumption). Specific uses include shaft sealing rings, spark plug caps, O-rings (the major market for the fluorosilicones), gaskets, coolant and heater hoses for buses and trucks, and ignition cables. 

Silicone rubber as a shaft seal and backing material has a number of special applications. It can be used over a temperature range of —60°C to 260°C (—76°F to 500°F) in air or suitable fluids. Its abrasion resistance is good with hard shafts having a 0.000254 mm RMS surface finish. Commercial grades of silicone rubber are compatible with most industrial chemicals up to 260°C (500°F). In lubricating oils, the limiting temperature is 120°C (250°F), but special types have been developed for use up to 200°C (392°F). 

Oil drops of 2-5 /iL were introduced into 0.4 cm i.d. capillary tubes containing the aqueous phase. The more viscous heavy oils were heated for a short period to facilitate this addition. The tubes were then sealed with a tightly fitting silicon-rubber septum. A teflon screw was used to apply pressure on the septum after the capillary tube was inserted into the shaft of the tensiometer. In this manner, temperatures up to 200°C were achieved without loss of liquid. 

The useful screw-thread connector is becoming widely available. The simplest is the screw-capped adapter (Fig. 2.32) where the screw-capped joint is associated with a ground glass cone. The figure shows the silicone rubber ring and PTFE washer, and the adapter is useful for the insertion of gas tubes, thermometers or stirrer shafts. The screw-thread connection principle has been applied to the connection of water hoses to condensers and vacuum lines to Buchner flasks, to securing simple sealing septa to flasks, etc. 

At high shaft speeds and negligible Ap values labyrinth seals can be utilized, whose narrow openings build up a high dynamic pressure [109]. Lip seals are practicable at Ap values < 1 bar, particularly for laboratory devices. They are made of rubber or silicone plastics and often have to be cooled. Generally slip properties have to be maintained with a liquid (usually silicone oil). 

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