Patent GB-452729-A (GB)
Title: Improvements in or relating to electric welding machines
IPC: B23K11/31
Filed: 1935-03-01
Abstract: 452,729. Electric welding; electric switches; electric supply apparatus. WATKIN, H. G., 480, Aigburth Road, Liverpool. March 1, 1935, No. 6448. [Class 83 (iv)] [See also Groups XXXV and XXXVII] In an electric welding-machine, particularly a transportable machine for welding small gauge material in orthodontic work, the flow of current is controlled by a time switch including a contactor strip and a brush device which is operated by a trip catch to pre-set it at one side of the strip against the action of a reaction means and then release it so that the reaction means traverses it over the strip to close the welding circuit for a predetermined time, means such as a mains switch maintaining the circuit open during the presetting period. The electrodes or work pieces 19 are mounted in inclined turrets, 18, 24, held in set position by notches and spring catches 25. The upper electrode is carried on a lever 15 pivoted at 14 and operated by a spring 29 adjusted by a screw 30 to determine the welding pressure. The electrode is held in retracted position by a pair of springs 31 acting through a yoke 32 carrying a pair of headed pins 33. These springs are compressed, in order to allow the spring 29 to become effective, by connecting the yoke to a Bowden wire mechanism operated by a treadle 41. To facilitate transport of the machine, the Bowden mechanism is in two parts connected near the machine by a detachable coupling 37. Pivoted at 55 is a quadrant insulating plate 54 having a contact plate 53 on part of its surface. The quadrant is adjustable on its pivot and held in position by a spring pawl 57 engaging notches 58. Over this plate is traversed a roller 51 carried by an arm 50, which is mounted on a pivot 48 together with an insulating block 46. On the yoke 32 is pivoted at 42 a spring-controlled trip-catch or pawl 43, which normally engages the block 46, and the extension 45 of which carries the movable contact 45<a> of the main switch. The tapped primary circuit of the transformer is connected to the fixed contact 45b while the contact 45<a> is connected by a wire 78 to the arm 50. The plate 53 is connected by a wire 79 to a pilot switch consisting of a carbon contact 66 carried by a bell-crank lever 61 and a fixed carbon contact 67 connected to the other terminal of the primary so as to obtain a rapid break of the circuit and so avoid damage to the switch 51, 53 by spark discharges. The primary circuit contains a hand switch and a pilot lamp is connected across the switch to indicate when the apparatus is switched on. When the treadle is depressed the yoke 32 is pushed forward to allow the spring 29 to bring the electrodes together. At the same time the pawl 43 moves the roller 51 on to the non- conducting portion 54 of the plate. On continuing the pressure the contacts 45<a>, 45b are engaged and then the pawl moves on its pivot 42 to release the arm 50, which is returned by a torsional spring so as to effect the weld. Before the roller 51 is disengaged from the part 53, a projection 70 thereon engages the arm 61 of the bell-crank lever to break the circuit at the contacts 66, 67. If it is desired to utilize the treadle to govern the duration of current, the switch 51, 53 may be short-circuited by adjusting the plate 54 so that an extension 59 thereon engages a fixed contact 60. According to the Provisional Specification, the current may be fed direct to the switch arm, an abutment being provided for tripping the catch.