An electric welding muff for joining thermoplastic line elements comprising a welding sleeve and an electrical resistance heating wire. The sleeve is formed of thermoplastic material. The heating wire is wound in a plurality of turns and embedded in the sleeve adjacent one of its lateral surfaces and...http://www.google.de/patents/US4349219?utm_source=gb-gplus-sharePatent US4349219 - Welding muff of thermoplastic material
