Cast urethane insulators

Polyurethane elastomeric compounds may be cast into many sizes and shapes of industrial parts, varying from a few ounces to many hundreds of pounds. They bring to electrical manufacturers tough, semi-resilient elastomeric compounds which can absorb high impact and mechanical abuse without fracturing. With correct selection of materials, one can offer products that will be satisfactory at very low to moderately high temperatures and, at the same time, will be exemplary under high humidity conditions. Good temperature performance and resistance to reversion under high humidities are two important criteria which must be fulfilled by cast urethane insulators in addition to the usual mechanical and electrical requirements. Many of the earlier developments in urethanes failed to recognize reversion, usually manifested by a softening and depolymerization into a sticky liquid under high humidities. This objection has been overcome by new grades of urethanes reviewed in this paper.