New toughened epoxy casting systems with improved crack resistance

Many high voltage components are subjected to relatively high thermal cycles. In castings, there is often a combination of metal inserts combined with insulating materials. The resulting difference of thermal expansion coefficients will lead to variable mechanical and electrical intrinsic stresses in the cast components. This calls for insulating materials which are able to resist crack propagation under all kinds of fast changing operational temperatures. Newly developed toughened epoxy casting systems for indoor and outdoor applications, and their advantages over the state of the art mineral filled systems, are presented in this paper. It is shown that these new innovative materials can successfully withstand temperature cycles between 150/spl deg/C down to -50/spl deg/C without being damaged, whereas traditional epoxy systems may already show cracking failures at 0/spl deg/C. These new materials are easily processable on conventional casting equipment. They exhibit slightly higher viscosity, but this can easily be controlled by using the rapid APG technique. Therefore it can be stated that these toughened materials may be used in all existing application fields whenever high crack resistance must be achieved under harsh operational conditions.