GB139919A - Improvements in and relating to automatic welding devices - Google Patents

Abstract

139,919. British Thomson - Houston Co., (General Electric Co.). April 11, 1919. Heating by electricity.-An automatic arc welding-device comprises an electric motor continuously feeding an electrode and having its field current regulated in response to changes in the arc pressure, so that the arc is maintained at practically constant length. As shown, the electrode consists of a wire 1 of 1/32 to 5/32 in. diameter, continuously fed from a reel 2 by guide-wheels 8, 9 which are driven through gearing 10 by the motor 11. The work to be welded consists of two pieces 3 clamped on a table 5 which is traversed in the direction of the seam by a screw 6. The armature of the feeding-motor 11 is connected in shunt to the are through a resistance 82, which protects it from high pressure at starting and is then cut out by an electro-magnet 37 in series with the arc. Current from a constant-pressure source is supplied to the field coils 40 of the motor through two resistances 48, 44. One resistance 43 is regulated by hand, and the other resistance 44 is provided with a short-circuiting switch 45 operated by an electro-magnet 46 in shunt to the arc. Variations in the welding-current cause the switch 45 to be kept in continuous motion, but the periods of closure decrease as the arc pressure rises, thus weakening the motor field and accelerating the feed. To protect the shunt electro-magnet at starting, it is short-circuited by a switch 50 actuated by an electro-magnet 51 in parallel with it. Resistances 49, 52 are in series with these two electro-magnets. Current for welding is supplied from the constant-pressure direct-current mains 16, 17 through a motorgenerator of the kind described in Specification 133,439. The motor 18 has a field coil 20 in series with the armature, and an assisting field coil in shunt to the armature through a regulating-resistance 22. The generator 19 has a field coil 23 connected to the mains through a regulating-resistance, and an opposing field coil 25 in series with the are. The starting pressure across the electrodes may be 60 volts, and the working pressure about 12 volts. A small reactance 26 may be included in the are circuit. In order to start the are, the end of the wire is thinned or sharpened, by means of wire-cutting pliers or otherwise. On coming into contact with the work, the point is volatilized by the rush of current.