Patent GB-505848-A (GB)
Title: Improvements relating to electric flash welding machines
IPC: B23K11/04
Filed: 1937-11-17
Abstract: 505,848. Electric welding. GORDON, S. H., and YOUNG, W. F. Nov. 17, 1937, Nos. 31658/37 and 445/38. [Class 83 (iv)] A fluid-operated automatic electric flash welding machine is provided with a device responsive to the alteration of fluid pressure consequent on the meeting together of the hard ends of the work pieces during the flashing period for reversing the direction of the feed, so that a reciprocating movement of one of the work pieces is maintained until the work pieces attain a flashing temperature at which no resistance is opposed to their approach so that no alteration of pressure occurs and a continuous movement of approach is resumed in order to comptete the weld. The slide 20 carrying the movable work piece 26 may be connected to a lever 36 operated by compressed-air through a piston 42 having a plunger extension 46 moving in a dashpot cylinder 48 filled with oil. The work pieces are connected to the secondary of a transformer, the primary 76 of which is closed by an electromagnetic relay 82 when a hand switch 86 is closed. At the same time a solenoid 90 is energized through a circuit 92 containing a switch 120, 118 and switch 86 so as to raise a valve 56 to admit pressure to the cylinder 44 for the forward stroke. Motion of the plunger 46 raises the pressure in the cylinder 48 which is connected to a tank 72 through a pipe 64 and an adjustable needle valve 66. The cylinder 48 communicates by a pipe 106 with a chamber 104 closed by a flexible diaphragm to, which is secured the rod of a switch 94. When pressure in cylinder 48 increases the switch 94 is closed against the action of a spring and completes a circuit through the solenoid 90 independently of the switch 120, 118. When the feed is stopped by engagement of the unsoftened ends of the work, pressure falls in the cylinder 48 and switch 94 opens to de-energize the solenoid 90 and so brings the pipe 62 into communication with the supply 50 to reverse the stroke of the piston 42. Air also passes through pipe 110 to return liquid from the tank 72 into the cylinder 48 by way of the pipe 70 and spring-pressed non- return valve 114. When the disc 120, which is frictionally mounted on a rod 122 on a bracket 124 carried by the piston rod, engages the contacts 118, the solenoid 90 is re-energized and the forward stroke resumed. Such cycle of operations continues until the ends of the work are heated to flashing temperature whereupon since no fall in pressure occurs in the dashpot a continuous forward feed is effected. When a lug 138 on the slide engages a stop 136 on a rod 134 connected by a bellcrank 132 with a spring-closed valve 130 carrying a switch 88 in the circuit of the relay 82, the valve 130 is operated to open the switch 88 and cut out the welding current, the dashpot exhausting direct through pipe 68. The solenoid 90 remains energized by a spring-pressed disc 126 on the rod 122. The friction fit of the disc 120 on the rod 122 is provided since each successive reciprocation of the slide carries the slide a little further to the left. The disc 120 after disconnecting the contacts 118 encounters an adjustable stop 125. The flexible diaphragm may be replaced by a spring-pressed piston or Bourdon tube. In a hydraulic machine, the fluid passes from the supply 146, Fig. 3, through the solenoid operated valve 144 by way of the needle valve 148 to the cylinder 142 to effect the forward stroke. A normally closed switch 150 is connected to the diaphragm or piston and when the work pieces come together the rise in pressure in the cylinder opens this switch and de-energizes the solenoid 90 so that the reverse stroke is effected, the oil from the right-hand of the cylinder exhausting through the check valve 152. A switch 151 is provided in the circuit of the solenoid through switch 150 to prevent reenergizing of the solenoid during the reverse stroke and to maintain the solenoid circuit after energizing thereof. The ram 140 is directly connected to the slide 20. In either form of apparatus in order to effect resumption of the forward stroke, the switch 120, 118 may be replaced by a switch which is actuated electromagnetically as a consequence of the diminution of current in the welding transformer which occurs when the work pieces separate. Such switch may comprise a pivoted armature 158, Fig. 4, closed by an adjustable spring 160 for completing the circuit 156 to energize the solenoid 90. When the work pieces come into contact the current in the welding transformer energizes a coil 162 in series with the transformer primary so as to open the switch 158 and so de-energize the solenoid. When the work pieces separate the current through the coil 162 falls and the switch 154 recloses. The diaphragm may operate a valve to bring into action hydraulic or pneumatic control mechanism instead of operating a switch.