GB636343A - Improvements in and relating to the welding of metal studs and the like to metal plates and the like - Google Patents

Abstract

636,343. Electric welding. MARTIN, H. May 1, 1947, No. 11761. [Class 83 (iv)] [Also in Group XXXV] In arc stud welding, in which the arc struck between stud and work is maintained for a predetermined time, the weld circuit is broken, just as or before the stud contacts the plate, by means depending on the greater length of travel of stud to plate than the lift for striking the arc. The means comprises a control rod moving in or parallel to the axis of the stud operating means, and is set in an insulating bush and contacted directly or indirectly by the operating means so that movement of the stud as the apparatus contacts the work moves the rod to close a control circuit, and opposite movement as the stud moves towards the work after heating, allows the rod to follow the operating means only to the extent to break the control circuit. The arc length and duration are controlled by the circuit which initiates arcing on raising the stud; reduces the current before moving the stud to the work; cuts off the weld current just as or before the stud contacts the work; and may control a preheat period. In a fluid-pressure or solenoid apparatus the control device comprises a metal, spring-urged plunger 11 in an insulated bush 6 above the core 2 with a lower contact C engaged by a contact 13 on the core 2. The bush is adjustable along the axis for varying the arc length and the rod may be in a further spring plunger. For A.C. or D.C. operation the main welding circuit 26, 28, 30, 31 is closed by a contactor 27 energized through the contacts C, 13, when the start-button 34 is pressed. The solenoid 1 is simultaneously energized to lift the stud 3 and start the arc.. The contactor 27 also energizes by contacts 37 a contactor 29 shunting the current limiting resistance 28 and a potentiometer PQ which charges an arc-timing condenser 50 through a variable resistance 48, until a relay 41 operates to open a contactor 29 putting the current limiting resistance 28 in circuit and charging a further condenser 59 through a variable resistance 60 to control the period of reduced current. Time delay relay contacts 63 finally open to de-energize the solenoid 1 and a spring 23 forces the stud 3 towards the plate 5. The control contacts C, 13 then separate because of the longer stud path and the system is de-energized. In a modification the plunger 11 operates control contacts indirectly and the reduced current is achieved by diverting some of the D.C. generator series field, Fig. 4, not shown. In another form the timing elements are ganged for common operation. In a modification for A.C. use, Fig. 5, not shown, preheating, and synchronism of the control reactor are achieved through a further main contactor, and the arc time condenser circuit is replaced by a geared solenoid and spring contacts. In a further modification for single-phase A.C. transformer supply, preheating is provided with two condenser/relay circuits and a link is arranged for eliminating the pre-heat timer and permitting the use of the circuit on D.C. Specification 580,732 is referred to.