Short-Time Fabrication of Degraded Surface on Silicone Rubber Used for Insulators

Silicone rubber (SiR) insulators are degraded due to multiple stresses. To develop a degradation diagnostic technique, a lot of aged insulators are required. However, collecting a lot of several decades of used SiR insulators is difficult. Therefore, it is desired to fabricate the degraded SiR surface whose characteristics are similar to those of degraded SiR insulators in outdoor. To grasp the characteristics of the degraded SiR surface, we first investigated the characteristics of aged SiR insulators. Foreign matters on aged SiR specimens made the contact angle larger, and Si–O, Si–CH3, C–H, and O–H bonds decreased. Next, to fabricate the artificially degraded SiR surface, we proposed a 24 h—fabrication—cycle, which consists of a red clay adhesion process, an ultraviolet (UV) irradiation process, a surface heating process, a heat radiation process, and a surface cleaning process. We evaluated the effects of UV irradiation and surface heating, and then, it was found that a combination of UV irradiation for breaking molecular structure and surface heating for promoting low molecular weight (LMW) dispersion played an important role in adhering red clay to SiR. The contact angle and the chemical structure on the artificially degraded SiR surface, which was fabricated by UV irradiation for 6 h and surface heating at 20 °C or 40 °C, were similar to those of a SiR specimen aged ten years with the hydrophobicity of hydrophobicity class (HC) 2.