Weld indicating weld connecting sleeve for thermoplastic pipes - having thermally released spring element or colour changing element

摘要

Thermoplastic pipes (2) are connected together using a welding sleeve (1) having a heating element (4) embedded near its inside wall (3) and a pin-shaped weld indicator element (7,7') retained in a bore (5) in its wall (6), the element having additional means (15;18,19,20,21;27,27') for enhancing the visibility of the welding action at the outer side of the connecting piece which are activated by heat generated during welding.