Soil Burial Tests: Effect of Soil Burial Exposure on the Properties of Casting Resins

Casting resins are thermosetting materials (thermosets) which are hardened by crosslinking at ambient or elevated temperatures. Casting compounds consist of a resin and a hardener or curing agent in one or more parts. The cured plastic can have a wide range of properties by selectively compounding inert additives, such as particulate or fibrous fillers, flexibilizers, colorants, and fire retardants. In production, the two-part formulations are metered, mixed, and finally dispensed into molds or potting containers to encapsulate electronic devices. The encapsulated units may be heated to develop the optimum in physical and electrical properties. Casting resins most commonly used are stvrene-polyesters, epoxies, polyurethanes, and silicones. 1 Representative casting formulations used widely in the Bell System, styrenepolyester and epoxy, have been used over ten years and have a minimum service life requirement of twenty years. 43 44 T H E BELL SYSTEM TECHNICAL JOURNAL, JANUARY CHEMISTRY OF CASTING R E S I N S