DGEBF epoxy blends for use in the resin impregnation of extremely large composite parts

Abstract

Large superconducting electromagnets used in fusion reactors utilize a large amount of glass/epoxy composite for electrical insulation and mechanical and thermal strengths. The manufacture of these magnets involves wrapping each superconducting cable bundle with dry glass cloth followed by the vacuum-assisted resin transfer molding of the entire magnet. Due to their enormous size (more than 100 tons), it requires more than 40 h for resin impregnation and the subsequent pressure cycles to ensure complete impregnation and removal of any trapped air pockets. Diglycidyl ether of bisphenol F epoxy resin cross-linked with methyltetrahydrophthalic anhydride with an accelerator has been shown to be a good candidate for use in composite parts requiring long impregnation cycles. Viscosity, gel time, and glass transition temperature of four resin-blends of diglycidyl ether of bisphenol F resin system were monitored as a function of time and temperature with an objective to find the blend that provides a working window longer than 40 h at low viscosity without lowering its glass transition temperature. Based on the results, a resin-blend in the weight ratios of resin:hardener:accelerator = 100:82:0.125 is shown to provide more than 60 h at low resin viscosity while maintaining the same glass transition temperature as obtained with previously used resin-blends.