CONTROL METHOD FOR ELECTRICITY CONDUCTION OF ELECTRIC FUSION-WELD TYPE PIPE JOINT

PURPOSE:To prevent an insufficient fusion welding from occurring by discriminating certainly an aperture of a pipe joint by a method where a lower limit for electricity conduction-stop time, an upper limit for electricity conduction-atop time, and a temperature rise rate by electricity conduction-stop according to an aperture size are obtained, and electricity conduction to a heating wire is controlled from those values. CONSTITUTION:A power is supplied to a heating wire 2 provided on an inner surface of a thermoplastic resin made joint, and the joint body is fusion welded to a thermoplastic resin made pipe 50 fitted onto the inner surface by heating electricity conduction. A temperature sensor 6 is fitted to a pipe joint 1 to detect initial temperature To of the pipe joint 1. Electricity conduction stop temperature Te is obtained from the initial temperature To, and temperature rise rate Tp, Tp=(T-To)/(Te-To) is obtained from temperature T of the pipe joint 1 when certain set time St has elapsed in conduction of electricity, and the aperture size is discriminated. Besides, upper and lower limits for electricity conduction stop temperature rise rate are obtained. Electricity conduction to the heating wire 2 is controlled from the electricity conduction-stop time and the electricity conduction-stop temperature rise rate. Thereby, excess fusion weld by excessively heating the fusion welded part between the pipe 50 and the pipe joint 1 and inferiority in fusion weld by excess electricity conduction fusion weld time are not caused.