Importance

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Abstract

An improved method and apparatus for electrically heat welding a thermoplastic fitting having an electric resistance heating element disposed therein. A controlled quantity of electric power is supplied to the heating element during the welding process to insure the making of a high quality weld. After the size of heating element and fitting are determined, a substantially constant voltage level electric power is supplied to the heating element of the fitting. When it is determined that the welding process is proceeding abnormally, the supply of electric power is terminated unless the abnormality is that the current level is too high. In that case, instead of terminating the welding process, the voltage of the electric power is reduced to that which results in current levels substantially equal to predetermined current levels for the size of heating element and fitting being welded which often results in a good weld being obtained even where the heating element is partially shorted out. Also, fires and other problems which have heretofore resulted due to such short circuits are prevented.

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First Claim