Patent GB-427634-A (GB)
Title: Improvements in or relating to electric welding machines
IPC: B23K11/24
Filed: 1933-10-20
Abstract: 427,634. Electric welding. NEW PROCESS WELDERS, Ltd., Scotts Road, Southall, and HOHS, F. C., 8, The Green, Heston, both in Middlesex. Oct. 20, 1933, No. 29101. [Class 83 (iv)] [See also Group XXXVII] In an electric welding-machine in which the movable electrode is operated by fluid pressure, the fluid pressure acts directly on a reducing valve for limiting the pressure to a pre-set value and also on an electric starting switch to start the welding current when the pre-set limit of pressure is attained. The movable electrode may be mounted on a pivoted arm the rear end of which may be jointed to the piston rod 4<a> of a pneumatic or hydraulic motor the cylinder 5 of which is jointed to the framing of the machine. The flow of fluid is controlled by inlet and exhaust valves 7, 8, which may be operated by a spring - returned pedal 10 and passes through a reducing valve 12 into the cylinder via a conduit 9. A hammering action during closing of the electrodes may be prevented by a regulating valve 29 or by connecting the space behind the piston with the atmosphere through a restricted aperture or regulating valve, a non-return valve being provided in this case for permitting rapid ingress of air when the piston is returned by the spring 6. The reducing valve is carried by a rod attached to a diaphragm 16 controlled respectively on opposite sides by an adjustable spring 17 and by fluid on the low pressure side of the valve. The low pressure side also communicates with a chamber containing a similarly controlled diaphragm 19 which carries a rod 22 for operating the lever 23 of the starting switch 14 when or just before the pre-set pressure is reached and the valve 12 closed. The adjusting screws 18, 21 of the springs 17, 20 are geared together. A pressure gauge 13a may be provided in the conduit 9. When the switch 14 is closed the coil 25<a> of a contactor switch is energized to close the contactor 25 to complete the primary a, b. The contactor 25 is opened at the end of the welding operation by a self holding relay 26, which may be energized to draw the contactor x away from the contact y and connect it with the contact z by a relay 27 responding to the surge of secondary current occurring on completion of the weld as described in Specification 427,328, [Group XXXVII]. Alternatively the relay 26 may be energized by operation of a hand switch 33 or either arrangement may be used, a change-over switch being provided. The hand switch 33 may also be positioned so that it may be operated by further movement of the pedal. The relay 26 remains energized until the switch 14 is re-opened. The pedal may be locked in operative position by a spring-returned detent 30 operated by an electromagnet 31 energized from the primary circuit. In making a succession of similar spot welds, the valves 7, 8 may be operated automatically through a core 38, Fig. 4, controlled by a pair of oppositely acting solenoids 39, 40. The solenoid 39 is arranged in series with a hand or foot switch 36 and with a switch 34 closed by a projection 35 on the piston rod when the movable electrode reaches its retracted position. Energization of the solenoid 39 moves the core 38 to reopen the valve 7 and close the valve 8. When the relay 26 is energized to open the welding circuit the solenoid 40 is energized to reverse the valves 7, 8. A series of welds may thus be effected as long as the switch 36 is held closed. According to the Provisional Specification the reversing solenoid may be dispensed with if a single spot weld only is required. The cylinder also may be hinged to the end of the electrode arm and the piston rod to the framing. Specification 157,922, [Class 83 (iv)], also is referred to.