GB1347599A - Method of making resin encapsulated electrical coil - Google Patents

Abstract

1347599 Resin-encapsulated electrical coils MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 20 June 1972 [22 June 1971 (3)] 28889/ 72 Heading B2E A method of making a resin-encapsulated electrical coil comprises: immersing the coil in a mixture of a liquid curable resin, a curing agent and a gelling agent, said mixture being in the form of a sol.; withdrawing the coil from the mixture; and curing the resin adhering to the coil said mixture being caused to gel after immersion of the coil but before said curing. The mixture is such that, as the temperature increases from t 0 , the gelling agent dissolves at t 1 to cause the viscosity to rise and the mixture to gel. When the temperature reaches t 3 the mixture once again becomes a sol. which reverts to a gel when the temperature is lowered below t 2 . The gelling agent remains dissolved even on cooling below t 1 . The coil may be immersed in a mixture above temperature t 3 then withdrawn and cooled, the resin being subsequently cured. Alternatively the coil is immersed in the original sol. which is heated above t 1 to gel the mixture, then the coil is withdrawn, and the resin is cured. Another method is to immerse the coil in the original sol., to withdraw the coil, then heat the coil to gel the mixture adhering thereto or to withdraw the coil into an atmosphere at a temperature sufficient to gel the original sol. The resin can be left to cure or heated to cure without exceeding t 3 . In the examples the resin is epoxy resin and the curing agent is boron tri-fluoride monoethylamine. Several coils may be immersed simultaneously.