Patent GB-491757-A (GB)
Title: Improvements in or relating to electric spot or seam welding apparatus employing controllable discharge vessels
IPC: B23K11/24
Filed: 1937-10-06
Abstract: 491,757. Control systems for resistance welding. SIEMENS-SCHUCKERTWERKE AKT.-GES. Oct. 6, 1937, Nos. 27146, 27147, and 27148. Convention dates, Oct. 6, 1936, Nov. 3, 1936, and March 9,1937. [Class 38 (iv)] [Also in Groups XL and XXII] Thermionic and like control ; switching control.-In electric control apparatus for spot or seam welding by means of arc discharge vessels, an interrupter device is arranged successively to remove blocking means in the control circuit of the main discharge vessels the ignition periods of which are then varied in accordance with a predetermined fixed programme cycle, following which the discharge vessels are again blocked. Fig. 1 shows an arrangement in which a pair of grid-controlled gas or vapour discharge tubes 5, 6, connected to be alternately active by condenser 7 as in a D.C.-A.C. inverter, are operated in accordance with a fixed programme by means of a light source 2, and a phot-electric cell 3 between which is interposed a programme disc 1 continuously rotated by a synchronous motor. The light impinges on the cell only for periods at intervals determined by the slots in the disc 1, and comprises twc beams, so spaced with respect tc disc 1 that they produce successivE impulses separated by a time interval equal to half a cycle of the main A.C. supply network. The control voltage developed across one half of the resistance 8 is applied to block or release a pair of oppositely and parallel-connected discharge vessels (not shown) in the A.C. network comprising the welding transformer. Each slot in the disc 1 produces a control impulse which provides, in one A.C. cycle exactly the same control voltage for the two vessels in the welding circuit proper whereby both vessels are ignited at exactly the same instant. The impulses from cell 3 are amplified at 4 and applied over transformer 16 to the vessels 5, 6 ; the anode supply for all the tubes is derived from a potentiometer 9 across D.C. source. The disc 1 also carries a rotary switch 10 co-operating with two contacts 11, 12 the former energizing relay coil 152 to open contact 151, while contact 12 when closed by the conducting segment 13 energizes coil 153 to close contact 151 and thus short-circuits transformer 16 to render control of the vessels 5, 6 from the disc 1 inoperative. 18 is a pedal switch actuated by the welding operator, the contacts O and W corresponding to " open " and " welding " conditions in the welding circuit, while the switch is connected through condenser 17 to the negative pole of potentiometer 9. On contact O the rotary switch contact 11 is inoperative and the short-circuiting contact 151 remains closed ; on contact W conditions are unchanged until the rotary contact 13 reaches contact 11, when a charging impulse drawn by condenser 17 energizes relay coil 152 to open contact 151 and the programme of operations continues until contacts 13 and 12 coincide when coil 153 is energized to re-close contact 151 to complete the fixed cycle. Thus even if switch 18 is kept depressed, only one cycle is traversed as long as the switch 19 is on contact P for spot-welding. On contact N (seam-welding) the welding current is applied until switch 18 is 'released. The programme disc 1 is intended to be changed to suit different metals to be welded and the welding current-programme may be accompanied by appropriate variations in pressure between the metal and the welding electrodes to secure satisfactory welds. Fig. 3 shows a typical pressure-time curve covering the entire pressure variation cycle, the current cycle being displaceable as a whole or partly with respect to the pressure cycle. The current programme is usually commenced just as the pressure falls, e.g. at time t3, but this depends on the material to be welded. Fig. 4 shows one method of controlling the pressure programme, omitting the parts devoted to control of current programme only, such as are shown in Fig. 1. The phases of the operating cycle are initiated by a cam-disc 121 actuating contacts 122 ... 126 when rotated by a motor as for disc 1 of Fig. 1. The pressure between the welding electrodes 102, 103 is governed by a pneumatic system fed from a compressed air supply at 104 through a main valve 105. The pressure tending to raise the piston in the cylinder 101 is derived from a reservoir 106 fed through regulator 107. With the electricallyoperated valves 111, 109 in the positions shown,. pressure from 104 is cut-off from the upper part of cylinder 101 which is open to atmosphere through valve 109. On closure of the D.C. supply switch 117, the valve is operated and closes the exit to atmosphere of cylinder 101 while admitting compressed air thereto over valve 111 and the pressure regulator 113; electrodes 102, 103 are thus pressed together. As soon as the pressure above the piston of 101 reaches a given value the manometer 131 closes its contact and prepares a circuit for the cam contact 123 which is closed, after a definite delay, to energize relay 127 from the source 116. This first pressure phase corresponds to t0 to t1, Fig. 3. Relay 127 opens contact 128 to remove the blocking from the main discharge vessels in the welding circuit, and also closes contact 129 to prepare circuits for the cam contacts 124, 125 and 126. The control of the welding current programme is then initiated as in Fig. 1. Continued rotation of disc 121 closes contact 124 and applies positive bias to grid of vessel 119 from source 132; 119 ignites to energize and open valve 114 whereby the pressure in 101 falls at a rate determined by the escape regulator 115 (t3 to t5, Fig. 3). The cam disc 121 then closes contact 125 to ignite discharge vessel 118 which energizes valve 111, thus closing the compressed air supply through regulator 113 and opening the supply to 101 from 104 through regulator 112, which is set to a lower pressure than regulator 113; this change has no effect as valve 114 is still open. Further rotation of disc 121 closes contact 126 to ignite vessel 120 by means of the source 134 of positive grid bias. Vessel 119 at once extinguishes by virtue of the inverter connection of the two vessels and valve 114 re-closes. The pressure between the electrodes 102, 103 now rises to a valve determined by regulator 112 (phase t5- t6, Fig. 3); and falls again to zero by opening of valve 109 when the pedal switch 117 is opened by the welding operator. The main discharge vessels are then again blocked by closure of contact 128 of relay 127. The pedal switch may have an auxiliary relay which automatically re-opens the switch after it has been closed for a certain time. The above description applies to spot-welding; for spot-seam welding switch 117 is kept closed and cam switch 138, 139 is operated, switch 140 being now open. The spot-weld cycle is thus repeated at regular intervals determined by the cam disc 138, 139. The times at which the various operations of the cycle are initiated are variable by varying the relative positions of switches 122 ... 126 round the cam disc 121. The cam disc 121 and the current programme disc 1, Fig. 1, can be mounted on the same shaft or may be combined in one disc. In a modification, Fig. 5 (not shown), the vessel 118 is dispensed with and the electric control circuit is otherwise modified in detail.