Method for welding thermoplastic materials

A method of butt welding two coaxial sections of thermoplastic pipe, comprising:

• positioning a thermoplastic welding rod between said sections so that respective adjacent ends of said sections are in contact with opposite sides of said welding rod, said welding rod having a solid core of said thermoplastic material and a resistance element comprising a wire spirally wound about said core and embedded in said rod below the surface of said rod a sufficient depth such that burning of said thermoplastic during welding is substantially prevented when a welding current is applied to the resistance element, but not so deep that burning of the thermoplastic material of the core occurs prior to softening of said adjacent ends, and said core extending in a circumferential direction of said pipe sections;
• then applying a current to said welding rod for a time and of sufficient intensity to cause said welding rod and said adjacent ends of said pipe sections to melt and fuse;
• applying pressure axially of said sections to urge said sections together;
• and
• maintaining said pressure after said electrical current has been discontinued until said fused ends and welding rod have solidified.

A method of welding two sections of thermoplastic pipe, comprising:

• bending and forming a flexible welding rod into a shape that conforms to the shape of surfaces of the sections to be welded, the welding rod comprising a solid core of thermoplastic material and a resistance element for melting the thermoplastic material, the resistance element comprising a plurality of wires wound about a thermoplastic core in a spiral configuration and embedded in said rod below the surface of said rod a sufficient depth such that burning of said thermoplastic during welding is substantially prevented when a welding current is applied to the resistance element, but not so deep that burning of the thermoplastic material of the core occurs prior to softening of said sections, each wire being spaced from each other wire along the length of said welding rod;
• positioning the shaped thermoplastic welding rod between the sections so that respective adjacent ends of the sections are in contact with opposite sides of the welding rod;
• applying a current to the welding rod for a time and of sufficient intensity to cause the welding rod and adjacent portions of the pipe sections to melt and fuse to form a weld;
• applying pressure to urge the sections together at the weld;
• and
• maintaining the pressure until the weld has solidified.