| 摘要 |
PURPOSE: To uniformize the heating of a member to be heated and to stop the heating thereof at the time of the appearance of the optimum welding condition by cutting off the supply of electricity to the resistor arranged in plastic constituting the member to be heated at when the short-circuit of a resistance wire by the welding of an insulating coating layer is detected. CONSTITUTION: A weldable joint 1 is formed by fitting the end parts of cylindrical pipes 6, 8 of a heat-meltable resin in the central opening 4 of a connection sleeve 2 of a heat-meltable resin. An electric heating type resistor 10 is provided in a sleeve 2 and is provided with crossing points shown by 11a, 11b, 11c by one conductor and coated with an electrical insulating layer 13. The melting temp. of this layer is set between the lowest temp. higher than the melting temp. of plastic and the highest temp. lower than temp. receiving thermal destruction of a member. Therefore, when this layer is melted, at least a part of the crossing points of the resistor generates a short-circuit. Since the conductor is connected to a current measuring means 21, the first short-circuit can be immediately detected. Therefore, the moment a short- circuit is generated these changes are detected and a command for cutting off a current is issued by opening a circuit 23. |
