Electric soldering iron having a PTC heating element

摘要

A soldering iron is heated by an electric resistance heating element comprising a PTC thermistor having a positive temperature coefficient. The soldering iron has an elongated bit of copper with a cone shaped bit tip and a cylindrical back portion coupled with said bit tip. The back portion has a pair of arms and a slit between the arms for accepting the heating element with spring contact whereby the arms operate not only to transfer the heat to the tip, but also to fix the heating element in the slit tightly. The PTC thermistor is made mainly of Barium-titanate and has the additive of a small amount of calcium for improving the withstand voltage of the thermistor so that a commercial power supply can supply the power directly to the soldering iron. The total contact area S.sub.1 between the PTC thermistor and the back body being from 1.0 cm.sup.2 to 25 cm.sup.2 and the transverse cross sectional area S.sub.2 of the back body which contacts the thermistor being from 0. 1 cm.sup.2 to 3.0 cm.sup. 2.