613,907. Electric welding. MARTIN, B. Sept. 14, 1944, Nos. 17622/44, 2365/45 and 8205/45. [Class 83 (iv)] [Also in Group XXXV] In an apparatus for arc welding metal or alloy studs, tubes, &c., to metal or alloy plates &c., the chuck for holding the stud &c. is offset from the pole or poles of an electromagnet, which has a spring-returned armature transversely disposed to the core and adapted for limited movement towards or away therefrom, the energization of the magnet and welding circuit being electrically controlled. The electromagnet which is formed with parallel.poles 5, 6 and has the coil 24 mounted on the pole 5, is secured by screws 9 in a housing 1 which carries a removable handle 16 and also three triangularly arranged peripherally grooved or screwthreaded adjustable support pins 3. For machine use the handle is removed and an aperture 17 in the casing and bar 4 of the magnet applied to the stem of a drilling machine &c. The aperture is normally filled by a plug 18. In the rear wall of the casing is pivoted at 27 an armature 7 which is connected by a screw 29 and slot to a slide 30 provided with flanges for sliding in or on guides in the rear wall of a forward casing 2 secured by screws to the main casing. A pivoted armature is stated to cause less impact than a free armature and avoids scattering of molten metal or return of the stud to the plate. The armature engages a spring-pressed plunger 57 contained in the cylinder forming the pole 6 which is adjustable by a screwed plug 60 in the casing. The end of the plunger which passes through the plug may be normally flush with the top of the casing, so that the amount it projects through the casing when the arc is struck indicates the length of the arc. Slide 30 carries a stop screw 44 which may engage a stop-screw 45 to limit the downward motion of the slide. The slide is separated by an insulating block 36 from the clamp 39 carrying the chucks. The stud is thus out of alignment with its actuating magnet. The chuck is slotted and provided with a series of slotted collets 48 which hold the stud and are connected to the chuck by a bayonet slot, the chuck being closed by a screw mounted in a ring 49. A plug 53 may be screwed in the upper end of the chuck to contain a screw 55 for engaging the end of the stud. If desired the plug and screw may be omitted. The cables are secured to the tool by clamps 13 and one terminal of the welding circuit is secured by a twin-cable 41 to sockets on a plate 38. The control circuit whereby the magnet and welding contactor are energized contains a safety switch by which the circuit is kept broken unless the chuck is provided with a stud &c. and the apparatus pressed on to the plate into operative position. For this purpose a switch body 61 on the lateral face of the pole 6 contains a plunger contact 63 pressed by a spring 65 into contact with a contact pin 68, adjustable in the armature, the upper end of the plunger engaging the bore of a contact plate 66 connected to the lead so as to connect in in the circuit when the stud is in operative position. The pin 68 is also adjustable so that the safety switch may be rendered inoperative when necessary, e.g. if the welding circuit is to be maintained until the weld is complete, as in the case of welding aluminium alloy studs. In operation, with the apparatus in operative position and the switch 68 thus closed, the push button switch 70, Fig. 5, is closed so as to energize the coil 71 to close the welding contactor 72. At the same time the contactor 74 is closed so that the magnet coil 24 is energized by the circuit passing over contacts 81 so as to strike the arc. The duration of the arc is determined by an arc timing device. One form of arc timing device described operates on the charging or discharging of an electric condenser. In this case by the closure of contacts 74, current passes through a regulating resistance 75 and time-adjusting variable resistance 76 to the coil 78 of the timer and for charging the condenser 79. When the condenser is charged the coil 78 is energized to lift the plunger 80 to open the contacts 81, 82, to de-energize the coil 24 and discharge the condenser with the arc still maintained. The stud is pressed by the spring towards the plate and as the travel is greater on this return motion due to the melting of the end of the stud, the contact pin 68 travels sufficiently for the safety switch to open and thus de-energize the coil 71 and so open the welding circuit at 72 and the electromagnet circuit at 74. As the stud is returned at practically the exact moment or just before the main welding circuit is broken, the rise of current in that circuit on short-circuiting the arc is thus minimized. The armature may be carried by a parallel motion mechanism so that it moves parallel to itself along a straight line path, so that the chuck may be mounted directly on the armature. The upward motion of the armature may be limited by a stop sleeve on the plug 60, the spring 58 being coiled about the extension of the sleeve, or by a stop-screw on the plate 32 engaging the upper face of the slide 30. When welding small studs, the switch 70 and time-adjusting resistance 76 are fitted in a small case 89, Fig. 7, carried by the operator and connected to the main control of the welding tool by a cable. The stud may also be operated pneumatically and direct or alternating current used. In the latter case the material forming the magnetic circuit of the electromagnet is laminated or slotted. For alternating current also the stud may have a fusible projection 85, Fig. 6, and a pellet or wad 86 of compressed fibrous material such as steel wool is interposed between the stud and the plate so as to strike the arc. The wad may be provided with a hole or recess to receive the end of the projection. In this case, the electromagnet is used merely to maintain the arc until the stud is pressed on the plate. In another method of striking the arc a stud with a fusible projection may be first contacted with the plate, whereupon after closing the welding circuit, and before the projection is completely fused, the stud is moved away from the plate over a limited travel, the distance of withdrawal being thus less than the required arc length. The are formed on the lift of the fusing projection almost instantly completes the fusion of the projection without explosive violence. The stud and the projection may be metallised with aluminium or other metal of high electrical conductivity. When welding either with direct of alternating current on a vertical or inclined surface the end of the stud may be surrounded by a screen or sleeve of non-conducting refractory material to minimize the dropping of molten metal by gravity, the sleeve having in addition to slots in the edge, a sector 88 over an angle of 90 degrees or more removed on the upper side so as to provide a free vent upwards of the expanding air or gases generated on striking the arc and so to minimize the blow-out action on the arc. Specifications 156,836, 196,322 [both in Class 83 (iv)], 580,732, 580,757 and 613,981 are referred to.