Patent GB-743574-A (GB)
Title: Improvements in or relating to apparatus for electric flash butt welding
IPC: B23K11/04
Filed: 1951-10-25
Abstract: 743,574. Automatic control systems for welding. RESISTANCE WELDERS, Ltd., and CUMMING, W. R. Oct. 20, 1952 [Oct. 25, 1951],- No. 25018/51. Class 38 (4). [Also in Group XXII] In apparatus for flash butt welding two workpieces including a pair of carriages movable relatively one to another to carry the workpieces, direct acting magnetic controlling means are provided which are sensitive to flashing current to control the relative movement of the carriages to avoid wide fluctuation of the flashing current; In an embodiment a workpiece 22, Fig. 1, is clamped on a fixed carriage 19 insulated from a base 10 and a workpiece 41 is clamped on a movable carriage 25. Rigid conductors 23, 42 which may have iron cores and connected to the carriages are joined to the secondary of a transformer 13 by conductors 44, 43 and tension springs 49 are connected between the carriages to urge them together. Alternatively, a magnet on a cable over a pulley may be used. The ram 52 of a piston 54 is arranged behind the carriage 25 to supply butting pressure and a valve 88 operated by a solenoid 89 controls air supply to the cylinder 55 of the piston. A ram 67 is provided to engage a limb 65 on the carriage to return the carriage 25 after welding and supply of air to its cylinder 66 is controlled by a valve 82 operated by a lever 81. When the lever 81 is in the full line position shown an operating switch 85 is open and air is supplied to cylinder 66 to urge the ram 67 to return the carriage, the switch 85 being closed when the lever 81 is in the broken line position. A return stop switch 69 breaks contact when the limb 65 is urged against a fixed stop 68 and a cut-out switch 78 on a stop 61 breaks contact when a rod moving with the ram 52 moves a predetermined distance forward. A block 63 mounted on the carriage 25 and held raised by a solenoid 64 when the latter is energized engages a butt valve switch 76 when it falls and a drop block switch 72 breaks contact when the carriage moves a predetermined distance forward relative to the ram 52. In operation the workpieces are clamped on the carriages with the lever 81 in the full line position. The lever 81 is moved to the broken line position to supply air to cylinder 66 to move the ram 67 and so allow the carriage 25 forward movement under the action of the springs 49. The making of switch 85 energizes a solenoid 90, Fig. 4, of a relay which closes its contacts 91, 92 and opens its contacts 93 ; closing of contacts 91 energizing solenoid 95 of a relay which closes its contacts 97 to supply the transformer 13. Flashing occurs between the workpieces and the current flowing in conductors 23, 42 causes repulsion therebetween and increases the gap between the workpieces. The current falls, the repulsion force falls and the springs urge the pieces together again. The flashing continues with substantially constant current. The closing of contacts 92 energizes the solenoid 64 and the block 63 is held raised and the switch 69 closes on forward movement of the carriage 25. Due to burning away the carriage moves relatively to the ram 52 and the switch 72 is broken to de-energize solenoid 64 so that the block 63 drops firstly on to the ram 52 and then between the carriage and the ram and closes switch 76. This energizes valve solenoid 89 and pressure is applied by ram 52 through the block 63 to butt the workpieces. Forward movement of the ram 52 breaks switch 78 and solenoid 95 is de-energized. Contacts 96, 97 open and current to the transformer ceases. After welding the lever 81 is placed in full line position to allow ram 67 to return the carriage and open switch 85, contacts 91, 92 being thus opened and contact 93 closed. Solenoid 89 is de-energized and valve 88 allows pressure to return ram 52. On complete return of carriage 25, the switch 69 is opened and solenoid 64 is de-energized, the block 63 resting on ram 52. In a modification, a ram operated by a solenoid supplied with current through a circuit including a magnetic amplifier having a saturable choke controlled by a transformer in the primary of the supply transformer is employed to provide an additional repulsive force. The force urging the carriages together may alternatively be provided in Fig. 1 by a solenoid acting on the carriage 25 and energized through a magnetic amplifier controlled by two windings. The first is energized from a constant D.C. source to saturate the choke whilst the second is fed from the secondary of a transformer in the primary circuit of the welding transformer, its effect being in opposition to that of the first winding. A constant repelling force may be employed.