Electrically heated dental casting mould - has PTC element and transformer with tappings and control for LV at low temp. stepped up at full load

摘要

An electrically heated casting mould for dental purposes, consists of a melting crucible with a heating coil made from a material with a positive resistance temp. coefft. The heating current is supplied via control circuit. The heating element is protected in that the voltage is kept relatively low when heating over the lower temp. range. The voltage is increased for the high temp. ranges. This prevents any precipitation of alloys onto the heating element. It also eliminates transient currents and mechanical stresses. The supply is via a transformer with two voltage tappings. There is a relay with change-over contacts and an electronic output regulator which controls the switching programme of the current to the heating element.