Patent GB-240159-A (GB)
Title: Improvements in and relating to arc welding apparatus
IPC: B23K9/12
Filed: 1925-09-16
Abstract: 240,159. British Thomson-Houston Co., Ltd., (Assignees of Noble, P. 0.). Sept. 16. 1924, [Convention date]. Uniting by fusion.-In an automatic arc seam-welding apparatus the welding-head is traversed with respect to a work-supporting device, which carries a number of articles to be welded and is arranged to be moved to present the articles in turn laterally to the welding position when the traversing motion is stopped at the completion of each weld. The metallic electrode 3, which is automatically fed, e.g. as described in Specification 179,613, [Class 38 (iii), Electric motor control systems &c.], to keep the length of the arc constant, is carried by a head 6, which is traversed along the seam to be welded by a screw 7 and gearing 8 from a reversing electric motor 9. A series of tubes 1, 2, to be welded are secured in clamps 14-17 on a table 10, fed laterally when the motor 9 is stopped, by rack and pinion gearing 11, 12 from a motor 13. Alternate traverses of the head 6 are in opposite directions and in order to render the arc more stable the connection of the welding circuit to the work is made alternately at opposite ends so that 'the welding commences at the part of the work nearest this connection. For this purpose the clamps 15, 16 may be insulated and the clamps 14, 17 uninsulated, or switches may be used in which case all the clamps may be insulated. When the switch 29 is closed, the coil 21 is energized to close the welding switch. When the welding arc is established, a current passes from the lead 35 through the contacts 36 of a switch 25, coil 33 to lead 37 through a contactor which is automatically closed by energizing a relay 34 operated as described in Specification 179,613, [Class 38 (iii), Electric motor control systems &c.], by a second relay connected across the arc, or by other means so as to keep this circuit closed only when the arc voltage is below a predetermined value. Operation of the coil 33 of the reversing contactors 32, 33 causes rotation of the motor 9 and traverse of the head 6. When the head engages a limit switch 22, a current passes from the switch 22 through the contacts 24 of switch 25 to energize a relay 26 so as to break the circuit at 27 and make it at 28. The welding circuit is thus broken and the relay 34 de-energized, the motor 9 being dynamically braked and stopped. A coil 30 is at the same time energized to operate a contact 31 and set the motor 13 in operation to move the table 10. When the table reaches its required position, cam-shaped lugs 33 or 39, push down a spring- returned plunger 40 carrying a pivoted dog 42 so as to push over the switch 25, which breaks the circuit from switch 22 to relay 26, which is thus de-energized. The motor 13 is thus dynamically braked and stopped and the welding circuit again closed. The coil 32 is now energized by current passing through lead 35, contacts 36<1> of switch 25 and lead 37 so as to rotate the motor 9 in the other direction. When the welding-head engages the limit switch 22<1>, a current passes from this switch through the contacts 24<1> of the switch 25 to energize the relay 26 to break the welding circuit and again start the motor 13. The table 10 may be arranged to move in both directions. In a modification, Fig. 3, the articles 1, 2 may be mounted in a carrier 10<a> rotated by a Geneva mechanism from an alternating motor 13<a> and carrying with it a rotatable switch drum 43, which takes the. place of the switch 25 and has two contacts operating respectively between contacts such as 24, 24<1> and 36, 36<1> of Fig. 1. In another form, Fig. 4, the welding head 6 has a member 55, which towards the end of its traverse compresses one of the springs 59 engaging a stop 60 on a rod 62, which is pushed axially to close contacts 53<b> and 55<a> and to open contacts 55<b> and 53<a> or vice versa. The rod is held in its end positions by a spring-pressed plunger 63 engaging one of the grooves 64, 65. The alternating current work feeding motor 13<b> is operated when either of the coils 30<b>, 30<b1> are energized by current from the mains 52 respectively through the lead 66, contacts 55<a>, lead 67 and contacts 55 and through the lead 66, contacts 55b, and contacts 55. The coil 21 of the welding switch is energized when either of the contacts 53<a>, 53<b> are closed, the circuits in either case passing through the contacts 53. The motor 9 for traversing the welding-head has reversing contactors 32, 33 controlled by a relay 34 as in the other forms, through contacts 54. The contacts 53, 54, 55 are operated by the motor 13b. In order to reduce the speed of the motor 9 at the beginning or end of the traverse, e.g. for cases in which the ends of the articles are to be machined, a resistance 68 in the circuit of the field winding 9<1> may be short-circuited by a push-button switch 69. In order to effect this reduction of speed automatically, a resistance 75, Fig. 5, may be short-circuited when a projection 70 or 71 on the welding-head pushes forward a contact 72 or 73 so as to bridge the. contacts 72<a>, 72<b> or 73<a>, 73<b>, the circuit being completed either through the contacts 33<a> or 32<a> controlling the arc traversing motor 9. In the form shown, the contacts 32<a> and 33<a> are interlocked so that the speed is reduced only towards the ends of each traverse.