GB285513A - Method of and means for electrical resistance welding - Google Patents

Abstract

285,513. Allgemeine Elektricitats- Ges. Feb. 18, 1927, [Convention date]. Systems depending on static transformers.-In resistance welding the preliminary heating is carried out at a high voltage which is reduced to a lower value when the actual welding is to take place. The primary of the welding transformer has tappings connected to a graduated control switch fitted with two contact fingers b, c mechanically connected but electrically insulated from one another and adjustably related so that one always switches on any desired higher stage than the other. When the pedal switch f is closed, the finger b is operative and the work n is subjected to high voltage. On releasing the switch f a circuit through the coil h is momentarily established in virtue of the contact m and the switch g is closed and locks itself in this position, the finger c then becoming operative with consequent reduction of the welding voltage. When welding is complete the transformer current increases sufficiently to close the overload relay l with consequent energization of the coil i to open the switch g. The relay l is constructed with a time lag. The regulating arm of the current transformer k supplying the relay is mechanically coupled to the finger c so that the current supplied to the relay bears a constant relation to the welding current irrespective of the position of the finger b and the welding voltage.