GB477988A - Improvements in or relating to resistance welding apparatus - Google Patents

Abstract

477,988. Photo electric control of welding-apparatus; valve relay circuits. PARSONS' CHAIN CO., Ltd., and LAMB, D. A. June 2, 1936, No. 15439. [Classes 40 (iii) and 40 (v)] Relates to resistance welding - apparatus, particularly for welding chain links. According to the invention, a photo-electric or selenium cell, located adjacent to the welding machine, is responsive to the radiant heat or light given off by the joint during welding, and through an amplifier or relay breaks the electric circuit or otherwise discontinues the welding process when the radiation reaches a certain magnitude. Preferably two cells are used in conjunction, one being the more sensitive to visible radiations and the other to infra-red rays. Fig. 1 shows the general arrangement of the whole installation, in which 4 is the link being welded, 19 being the secondary winding of the transformer supplying current to the link, and 17 being the tapped primary which is connected to a contactor Q<1>, Q<2> whereby a higher or lower welding voltage may be obtained. The radiations emanating from the weld are directed through an optical system, Fig. 3 (not shown) on to photo-electric cells in a casing 1. These cells C<1>, C<2>, Fig. 2, are utilized in conjunction with a valve V<1> and with grid-controlled discharge-tubes T<1> .. T<4> to control various functions in the operation of the machine. A transformer TR applies unidirectional voltage to the cells and to the valve V<1> through rectifiers V<2>, V<3> respectively, and has windings 11 connected to the discharge-tubes T<1> .. T<4> through relays L<1> ... L<4> respectively. In parallel with the cells and resistances R<1>, R<2> are resistances R<3>, R<4> and a potentiometer PO, the tapping point of the latter being connected to the cathode of V<1>, and, through a resistance R9, to the grids of T<1> ... T<4>. The grid potential of V<1> depends on the relative values of the equivalent resistances of the cells C<1>, C<2> and becomes more positive as the temperature of the weld increases. In the anode circuit of the valve V<1> are a resistance R<7>, four potentiometers P<1> ... P' in parallel, and a resistance R8, the sliders of the potentiometers being connected to the cathodes of the dischargetubes T<1> ... T<4>. The potentiometer P<1> adjusts the point on the characteristic of the valve V<1> at which the discharge-tube T<1> operates, provision being made at M for using a milliammeter to facilitate this adjustment. P<2>, P<3> and P<4> control the working of T<2>, T<3>, T<4> individually, while PO enables the temperatures at which the discharge-tubes operate to be increased or decreased simultaneously. The operation starts with the completion of a circuit through the solenoid of the contactor Q<1>, Fig. 1, by closure of a switch 20 by a cam in the machine, the circuit being normally closed through a pair of contacts N2 in the relay L2. The contactor Q<1> switches in a section of the transformer primary 17 giving a comparatively high secondary voltage. When a suitable temperature at the weld is reached, the discharge-tube T<2> operates, causing the relay N<2> to actuate the contactor Q<2>, whereby a lower voltage is applied to the link 4 during the later part of the welding process. Subsequently, at the required temperatures, T' actuates the relay L<4>, which cuts off a blast of air by which the swaging dies had previously been cooled : T<3> actuates the relay L<3> which brings welding mechanism into operation: and T<1> causes the relay L<1> to operate mechanism whereby the switch 20 is opened by its cam, and further rise in temperature is prevented. Specification 439,586 is referred to.