GB485792A - Improvements in or relating to electric welding tongs - Google Patents

Abstract

485,792. Electric welding; switching systems. KELLER & KNAPPICH GES. March 2, 1937, No. 6258. Convention date, March 6, 1936. [Class 83 (iv)] [Also in Group XXXV] In electric spot-welding tongs in which the control contacts are closed by hand only when the electrodes have been pressed together with a definite adjustable pressure by hand with simultaneous compression of a spring, a maximum current relay, on the attaining of the predetermined maximum current strength, closes a control circuit containing the control contacts and also an auxiliary contact which interrupts the primary circuit and at the same time maintains the control circuit closed until the control contacts are again separated by hand. The copper electrodes 3, 4 are respectively carried by pivoted jaws 1, 2, of which the jaw 2 is integral with the handle 6, and the jaw 1 is carried bv a lever 7 movable over a rod 13 secured to the handle 8 and separated by a spring 12 from an adjustable nut 14 screwed on the rod 13. Between the ends of the spring and the lever 7 and nut 14 are mounted plates carrying contacts 17, 18 in the control circuit of the welding transformer 23. On pressing together the handles, which are spring-opened, the electrodes engage the work, whereupon further pressure on the handles compresses the spring 12 until the contacts 17, 18 are engaged so as to initiate welding. The control circuit containing the contacts may comprise the secondary circuit of a second transformer 33 so as to step down the mains voltage of 220 to about 12 volts. When the contacts are engaged, coil of relay 34 is energized so as to connect contacts 31 by arm 31<1> and so close the welding circuit. When welding is completed a maximum current relay 21 consisting of an open soft iron ring arranged on the secondary lead of transformer 23 attracts a weighted contact arm 24 so as to operate a contact spring 27<1> and thus close contacts 27, 28. Coil of relay 22 is thus energized and armature 32<1> attracted so as to break the circuit of relay 34 at 29, 30 and thus open the welding circuit. The armature 32<1> is thus brought into contact with the contact 32 and when the contacts 27, 28 open, current through coil of relay 22 is maintained through contact 32, until the circuit is broken by hand manipulation of the tongs. The flexible leads 25, 26 to the electrodes may be enclosed in rubber pipes through which a current of water is led for cooling purposes, and the handles may be coated with insulating material. The transformer and switch gear may be arranged in a container moved on rollers or suspended so as to move the apparatus from one position to another. The Specification as open to inspection under Sect. 91 shows a form, Fig. 5 (Cancelled), in which the contacts 17<1>, 18<1> are directly connected to the handles. This subject-matter does not appear in the Specification as accepted.