Patent GB-1301806-A (GB)
IPC: B23K9/025
Filed: 1971-04-19
Abstract: 1301806 Welding by fusion A O SMITH CORP OF TEXAS 19 April 1971 [26 Jan 1970] 20409/71 Heading B3R Consumable-electrode, submerged-arc welding of a seam, e.g., as shown, a longitudinal seam of a pipe 1, is effected by two arcs started simultaneously at the opposite ends of the seam and moved inwardly, the two welds thus effected being merged by overlapping operation by -one of the arcs, said merging being accomplished while fused flux along the overlapping portion remains electrically conductive. First embodiment (Figs. 2-4) Apparatus.-Two laterally adjustable welding units 3, 4 each comprise a carriage 13 movable along a beam 12. Each carriage supports a carriage drive motor 17 driving a pinion 16 engaging a beam rack 15, an electrode wire feed motor 23 driving feed rolls 22, a flux hopper and nozzle 32, 34 provided with a controlling solenoid valve 35, and a control box 36 having an associated transformer 30 and cooperating with a floor-mounted control panel. The controls may comprise solid state, cam, or, as shown, relay switches. Welding current is supplied to each electrode through a line starter 28, transformer 37 and cable 26. A self-latching cam switch 38 on the unit 3 is closed by an adjustable cam arm 39 on the unit 4. A pipe holding device comprises relatively movable upper and lower gripping jaws 9, 11. Operation.-Closure of a self-latching switch 37, Fig. 4, energizes, for each unit, the line starter 28 for welding current, and a unit control circuit to effect, through normally closed switches 41, 42, 43 respectively wire feed, flux supply, and forward movement of the carriage. The switch 37 is kept manually closed until the units have moved sufficiently to permit a parallel cam-operated switch to close, said cam-operated switch remaining closed until return of the units to the pipe ends. Welding proceeds from both ends of the pipe until, when the units meet, the cam switch 38 is operated to act sequentially on the units 3, 4. In unit 3, closure of the switch 38 opens the switches 41, 42, 43 to stop, respectively, wire feed, flux supply and forward carriage drive. The stopping of the carriage drive motor is accompanied by dynamic braking thereof, e.g. by reversing armature polarity. Closure of the switch 38 also effects (i) closure of a switch 40 whereby a reverse timer 44, after a delay, closes a switch 45 to effect reverse travel of the unit 3 carriage, (ii) closure of a switch 46 whereby a burn-off timer 47 effects delayed cutting of welding current so as to burn off the electrode end clear of the weld, and (iii) closure of a switch 50 to energize a timer 49 for control of the unit 4. As the unit 3 proceeds reversely, the forward travel of the unit 4 is maintained until it welds into the hot weld left by the unit 3, the electrically conducting fused flux of the hot weld permitting arcing of the unit 4. After an overlap, predetermined by the timer 49, cam switch and arm 38, 39 length, and speed of travel of the unit 4, the latter stops welding and reverses its travel under control of a circuit similar to that for the unit 3. In a modification, Fig. 10, each unit 3, 4 carries three electrodes 51, disposed along the weld line, the three electrodes of the unit 4 being sequentially de-energized during weld overlap. The three electrodes of each unit are carried on a support 54 pivotally hung from the carriage 13 on a horizontal pivot shaft 55 so that the electrodes may follow the seam under guidance of a follower roller 53 connected to the support and engageable between the pipe edges. To prevent tracking the follower roller 34 through a weld, the roller is retractable from the seam under control of a double-acting pneumatic cylinder 59 in turn controlled by a solenoid valve actuated by the switch 38. When the roller is retracted, the electrodes are laterally locked in position, for the short remaining distance of the weld, by an air brake 62 energized, via a solenoid valve, on closure of the cam switch 38.