Patent GB-539660-A (GB)
Title: Improvements relating to electric flash welding machines
IPC: B23K11/04
Filed: 1940-01-11
Abstract: 539,660. Hydraulic machines. GORDON, S. H., and YOUNG, W. F. Jan. 11, 1940, No. 640. Addition to 505,848, [Group XXII]. [Class 69 (ii)] [Also in Group XXII] In an hydraulic electric flash welding machine as described in the parent Specification, in which a reciprocating motion between the welding heads during pre-heating is maintained by fluctuations in the fluid pressure due to the meeting together of the cold unsoftened work parts, the moving head is driven in both directions by hydraulic means supplied with liquid by a mechanically driven reversible pump the reversing means of which is under control of a device sensitive to the pressure of the liquid which causes the forward movement of the head. The speed of feed is thus independent of the temperature of the liquid. The movable head 18 carries a forward feeding cam 16 and through tie-rods 24 and cross head 22 a return cam 20. The pump consists of a double cam comprising a fixed cylinder 26 moving cam 28 and fixed cam 30, the cylinder being connected by pipe 32 to forward feed cylinder 10 and the bore in the cam 28 being connected by bore 36 in cam 30 and pipe 34 to return cylinder 12. The cam 28 carries cross-head 38 provided with nuts 40, 42 threaded on screw spindles 44, 46 geared to a shaft 58 driven by a belt 62 from a reversible electric motor 64. The reversing switch 66, Fig. 1, is pressed by a spring 68 to rotate the motor in the forward direction and is reversed by an electromagnet 70 in a circuit containing a normally open switch 72, when this is closed by increase of liquid pressure due to meeting of the ends of the cold work parts. As soon as the work parts separate again the pressure in the cylinder 10 falls and the switch 72 opens and the motor resumes its original forward feed. After flashing temperature is reached the forward movement continues uninterruptedly and eventually the parts are butted together to complete the weld and cut off the welding cement. In Fig. 4, a normally closed pressure switch is used, reversal of the motor is delayed so that the work parts remain in contact for an appreciable time before being again separated and the resumption of the forward feed is controlled by the drop in welding current due to separation of the parts. A handle 76 is operated to close switches 78, 80 and open switch 82. Main contactor coil 84 is energized through circuit a. b, c, switch 78 to close switches 86, 25 and connect the primary of the welding transformer 88 to the mains A, B, C. Closing of switch 80 energizes forward feed contactor coil 90 through circuit containing contacts 106, forward limit switch 92 and interlock switch 94 on the reverse motor contactor 96. When the coil 90 is energized contacts 98 are closed so that the motor rotates to move the cam 16 in a forward direction until the work parts meet whereupon contacts 108 are closed by energization of relay 104, coil 90 remaining energized by circuit through switch 72 and contact 101. When the pressure in pipe 32 exceeds a give limit due to engagement of the cold work parts the switch 72 is opened and the coil 90 de-energized. The contact 100 is thus closed but closing of contact 102 is delayed by a variable dash pot 110. Closing of contact 100 causes coil 112 of the reverse motor contactor 96 to be temporarily energized through contacts 114F of a plug switch 114 which is held closed by the rotation of the motor. The motor reverses momentarily and then stops. The work parts are in contact at this time and are heated up until the dash pot 110 allows contacts 102 to close so that the coil 112 becomes energized through switch 80 and contacts 108, 102 in circuit l, m to close contacts 96 to reverse the motor. When the parts separate the current in the primary of the transformer drops and the contact 108 is opened and coil 112 de-energized. Contact 94 is thus closed and coil 90 again energized through contacts 106 to resume forward motion. This cycle of operations is repeated until the work parts obtain flashing temperature whereupon the switch 72 remains closed and the head 18 continues to move forward until an adjustable cam 115 on the cross-head pushes down a lever 116 to open a valve 118 so that high pressure oil from an independent source enters the cylinder 10 to move the head forward at increased speed to complete the weld. At the same time a valve 120 is opened to allow oil in the return cylinder 12 to escape into an oil reservoir 122. Switch 126 is also opened to de-energize coil 84 to cut off welding cement and close contacts 106 and switch 124 is also closed. By closing a switch 124 there is a circuit from a, b, c, through 80, 124, 101, 90, 92, 94, i.e. switch 124 is shunted down pressure switch 72 to keep motor running forwards in spite of opening of switch 72 by high pressure through valve 118. The pump cam 28 continues to move forwards, oil from the cylinder seeping through relief valve 128 into the reservoir. A projection 130 on the cross head 38 eventually opens the switch 92 to deenergize the coil 90 to open contacts 98. Momentary re-energization of coil 112 is effected through contact 100 and switch 114 and the motor then stops. After removing the work the handle 76 is raised, the lever 116, due to eccentrically mounted pivots, being raised at the same time. Switches 78, 80, 124 are thus opened and switches 82, 126 closed and valves 118 and 120 are closed. Closing of switch 82 energizes coil 112 through the back limit switch 144 so that the motor is reversed. The head 18 is eventually arrested by a stop 134 and further movement of the cam 28 results in oil being displaced past relief valve 136 into reservoir, the cylinder 26 at the same time receiving oil from reservoir through non-return valve 138. A record non-return valve 140 is similarly provided for the bore in the cam 28. When a projection 142 on the cross-head 38 opens the back limit switch 144 the coil 112 is de-energized. Consequent closing of contact 94 momentarily energizes the coil 90 to close contacts 98 through contacts 114B of switch 114 and the motor starts forward temporarily and then stops. Switch 114, Fig. 5, comprises a sleeve 150 frictionally mounted on motor spindle 152 and having an arm 154 moving a member 156 horizontally to close contacts 114B or 114F, the member being returned by springs 162 to neutral position when the motor stops.