Lifetime prediction of silicone rubber cold shrinkable joint based on accelerated thermal aging

Abstract

With the development of cold shrinking technology over the last decade in China market, cold shrinkable joints have been gradually replacing pre-molded slip-on and heat shrinkable joints. Nowadays, silicone rubber material has been widely applied as cold shrinkable joints due to its excellent dielectric and mechanical performance. Still, there are some potential risks on the functioning of related cold shrinkable joint products. One of the key concerns is the ability to function in a wide range of cable sizes after long periods of strain during storage. A simple way to erase the concerns is to test the lifetime at ambient condition directly. However, it is quite time consuming, which usually takes for at least 2 years. Since the evolution of the shrinkable behavior is mainly determined by the viscoelastic properties of silicone rubber material, another quick test method has been widely used to predict the lifetime of silicone rubber materials combining accelerated aging and extrapolation method. In this paper, the aging behavior under various temperatures in air was investigated. The 3-layer ring samples that cut from the cable joint were pre-expanded onto mandril then aged in the temperature ranging from 75oC to 120oC. The deformation rate was recorded as a function of time while the threshold value is chosen as 15% in consideration of design margin. The lifetime is then extrapolated by Arrhenius equation according to ISO 11346. Result shows that the current pre-expanded silicone rubber cold shrinkable joint can be safely stored at room temperature for at least up to 2 years. This method can not only be used for instructing storage period in the factory but also for the lifetime prediction of cable joints in run.