The formation of insulating silicon compounds on switching contacts

The type and amount of silicones that are released by silicone rubbers from several different manufacturers were determined. It was found that because the silicones reach the switching contact mainly as vapor, creep is not important. The amount of silicones released by some rubbers is large enough to cause contact failures for contacts that switch a load. The relation between the number of switching cycles until failure and the resistive load switched by the contacts of relays operating in an atmosphere containing silicone vapor was investigated. The voltage over the contacts was between 0 and 48 V, and the current was from 0 to 500 mA. Insulating silicon compounds are formed for all nonzero loads. It is found that these insulating compounds are formed due to degradation of the silicones in the arc or evaporating metal bridge, which occur when the contacts switch a load. Criteria and test procedures that can be used to evaluate silicone rubbers used near switching contacts are discussed