Abstract: This invention relates to an adaptor for connecting a non-metallic pipe to a threaded metallic element, such as a sprinkler head, in leak-tight fluid communication. The adapter comprises a plastic coupling unit which is adhesively secured at one end to plastic pipe and adapted at the other end thereof to receive a threaded metal insert which may be threadably connected to a metal element, such as a sprinkler head. The adapter of the invention is particularly suitable for use in high pressure fire extinguishing systems.

Abstract: A joint configuration for joining two articles of thermoplastic material by thermal bonding using an electrical heating element, wherein a female fitting having a portion with an enlarged diameter receives the end of an inserted pipe on two raised portions constituting lands on the inner diameter of the fitting, and the central annular recess between the two lands receives and positions the electrical heating element which fuses the thermoplastic material. The two lands, each compressed against the outside of the inserted pipe by an external clamp, confine and retain the fused thermoplastic material within the central annular recess to effect an increased internal pressure which promotes the formation of an extensive, continuous, and sound bond between the fitting and the inserted pipe.

Abstract: A bifilar resistance element for use in preparing heating elements used in thermal bonding and the like, wherein two electrically conducting wires are embedded in a thermoplastic sheath which is fusible when sufficient current is passed through the bifilar resistance element. A heating element is prepared by joining the pair of wires in a length of the bifilar resistance element together at one end to form an electrically conductive path and then winding the length into a spiral shape. Two articles of thermoplastic material may be bonded together by placing the heating element in a recess simultaneously adjacent both articles with a pair of leads to the heating element extending externally from the two articles to be bonded, and applying an electrical current so that the thermoplastic sheath and a portion of the adjacent articles themselves are fused, to bond the articles together upon cooling.