ANALYSIS OF TWO-STAGE CURING REACTION OF EPOXY RESIN USED FOR ELECTRICAL INSULATORS

Abstract

It is known that there are serious issues of the delamination on the metalepoxy resin interface and the crack failure in epoxy resin due to cure shrinkage when epoxy resin is used as an encapsulating medium of insulators in electrical and electronic equipments. Though several papers have been reported on the attempts to predict the stress-strain behavior during curing reaction except for our reports, their simulation models are proposed with no consideration of cure shrinkage, heat generation in reaction, reaction progress, delamination and crack failure. In particular, the authors could not find reports on a practical multistage curing reaction process in consideration of all cure shrinkage, heat generation in reaction, reaction progress, delamination and crack failure. In this work, the authors attempted simulation with a finite element method for the following: a two-stage curing reaction process suitable for practical use from the start of potting to the completion of curing. Epoxy resin was potted between the inner and outer iron cylinders. The potted epoxy resin was cured under a given temperature before gelling and afterwards under a higher temperature during gelling (two-stage cure reaction process). In order to express the two-stage curing reaction process, the equation of cure reaction was corrected and the temperature dependence of viscoelastic properties was obtained from dynamic viscoelastic analysis. The change in circumferential strain on the surface of outer iron cylinder predicted by the simulation are in good agreement with the experimental one.