Patent GB-735284-A (GB)
Title: Improvements in or relating to an electric resistance welding device
IPC: B23K11/00
Filed: 1951-05-23
Abstract: 735,284. Welding by pressure. HART, K. V. May 23, 1951 [June 6, 1950], No. 12048/51. Class 83 (4). In an electric resistance welding device comprising a clamping die and a movable die adapted to position the work-pieces, a variable pressure device gives a high follow-up pressure at a predetermined instant and a timer controls the impulse of welding current. Tubes 14, 16 to be welded together are positioned between a fixed die 11 and a movable die 15, the fixed die comprising two or more clamping members 12, 13 surrounding the part 14 and separately coupled to a corresponding number of transformers 17, 20. The movable die is yieldingly mounted on a reciprocating head 3 moving in guides 8, 9, and is coupled through flexible conductors 102 and a conductor ring 23 to the transformers. The conductor ring 23 and flexible conductors 102 are mounted through insulators on a fixed part of the machine frame 1 and permit relative movement between the die 15 and the frame. The head 3 is reciprocated by a crank-shaft 2 which carries an adjustable camoperated timing switch 28 determining the moment of application and the duration of the welding current impulse to the transformers 19, 22. The die 15 is mounted a preset distance X below the head 3 and yields against a spring, not shown, as the head 3 descends so that the welding parts are engaged at a controlled pressure for the weld impulse. As the head 3 reaches the bottom of its stroke it engages the die 15 and a higher forging pressure is applied to the weld. The transformers 17, 22 have their primaries connected together in series to a welding energy source 25 comprising a storage capacitor 26 charged by a transformer rectifier system and discharged through a gaseous discharge device 27 controlled from the timer switch 28. Gaseous discharge shunt devices 30, 33 coupled across the primaries of the transformers and also operated from the timer switch 28 are used to control the energy of the welding impulse according to the materials welded and type of weld. Each transformer is separately controlled from the timer 28 so that different welding impulses may be applied over different portions of the length of the weld. The timer 28 comprises a series of cam discs which are rotatably adjustable about the shaft 2, each disc operating one of a series of micro-switches. The end of one of the parts to be welded is machined in such a manner that line contact only is made during the initial formation of the weld, and the area of contact is gradually increased as the weld progresses. One end 112, Fig. 10 may be bevelled to give a steadily increasing area of contact as the work fuses or an end 110, Fig. 11, may be rounded to give an initially high rate of increase in area. Parts may also be welded where the line of weld is discontinuous and one of the butt-pieces (not shown) has a number of projections, the transformer combination permitting control of the welding current through each projection. In a modification a variable pressure is applied to the work during welding by a modified welding-head 123, Fig. 13, incorporating a magnetic device for varying the spring-loading on the upper welding die 134 during welding. The head 123 is slidably mounted by rods 124, 127 on the machine frame 121 and reciprocated by an eccentric 131. The welding die 134 is bolted to a plate 135 of magnetic material which is yieldingly depressed by an adjustable spring 141 in the body of the head and retained in position by a cover-plate 129. The head 123 has a core 145 which is magnetized by a solenoid 148 to attract the plate 135 against the pressure of the spring to the extent of about one-third to onefifth of the pressure of the spring. The solenoid is controlled by additional cams 153, 155 on the timer 28 so that as the head descends the solenoid is energized to reduce the pressure on the work. As the welding process proceeds the solenoid is de-energized and the full pressure of the spring applied to the work. Specification 735,335 is referred to.