Patent GB-580732-A (GB)
Title: Improvements in and relating to the welding of metal studs and the like to metal plates and the like
IPC: B23K9/20
Filed: 1942-11-10
Abstract: 580,732. Welding. MARTIN, H. Nov. 10, 1942, Nos. 15888/42 and 15984/.43. [Class 83 (iv)] [Also in Group XXXV] In welding studs, tubes, &c., to plates &c., particularly steel and steel alloy studs to steel and steel alloy, surfaces, an instantaneous arc is formed between the stud and plate, and after a predetermined delay the stud is pressed into contact with the plate, while minimizing impact, and the heat of the arc crater in the plate is controlled to ensure that on contact of the stud with the plate the latter at the crater is only in a plastic condition, the current being maintained until the weld is completed. Scattering of molten metal by impact of the stud with the crater in the plate is thus avoided. The arc may be started with or without first bringing the end of the stud into direct contact with the work. It may be formed instantaneously by first coating the end of the stud or stud and plate with a metallic or chemical paint, paste or powder or by coating or applying thereon by a metallizing spray or high-conductivity metal such as aluminium. The instantaneous formation of the arc may also be effected when direct current from a generator is utilized by using a series transformer between the generator and the supply line which reacts on the shunt excitation of the generator to secure an instantaneous response of the generator to sudden increased or decreased demands. In case of alternating current supply the arc may be struck by withdrawal of the stud from the work when a highfrequency. current, e.g. of 600 cycles is used. The supply in this case must be provided with a frequency changing apparatus to effect the rest of the operation. As an alternative the gap between the stud and plate may be ionised by a discharge through a rectifier, or from a magneto or ignition coil, or filled by use of an insert of thin-metal tubing which may have a serrated edge or by a small fusible ball or wad of fibrous metallic material such as stud wire wool. In this case the parts may be shrouded with an unbonded, finely-divided material such as calcium-magnesium silicate with alumina and/or an alkaline earth halide. Impact may be minimized in the case in which the stud is pressed against the plate by a spring, particularly in portable apparatus, by a damping means such as a copper cylinder shrouding the arc striking solenoid core or by a pneumatic or other fluid pressure dash pot or by fitting the solenoid core as a piston within the coil former or by connecting it by a rigid brass &c. wire to a rack moving with the stud and in mesh with a train of gears. In another form the stud may be pressed forward by a solenoid or by compressed-air. When using a spring to complete the weld in the event of using alternating current and with the arc formed by melting the fusible ball, the solenoid core is held against a stop and prevents the forward movement of the stud after formation of the arc until the required moment. In order to secure satisfactory heating conditions at the time of contact with the plate the current density is reduced at this stage. This may be effected by using a shouldered stud with a reduced end so that on application of the stud to the plate to complete the weld the arc expands over the full area of the stud. When using alternating current the effect may be produced by using a transformer which has a drooping characteristic or by an impedance which may be inserted in the primary or secondary circuit of the transformer. With direct current an adjustable low resistance diverter circuit may be inserted in parallel with the series winding of the generator to reduce the magnetic field, or where the tool is one of a series operated off the same generator a resistance may be inserted by a contactor in the individual welding circuits. With alternating current the contactors may be replaced by a valve control employing a triode valve. The arc is centralised by neutralising coils or magnets and supplying the current by mercury bath contacts or by a double conductor connected to one pole of the supply or by clamping the plate between jaws lined with copper, brass, &c., the liners being separately connected to one pole of the supply. The connection from the pole leading to the plate may also consist of a spring-pressed copper or beryllium-copper rod applied to the plate beneath the axis of the stud. In a portable direct current apparatus in which the stud 24 with a pointed and part smooth end is secured by a chuck 20 to a spring- pressed insulator 19 connected to the core 18 of an arc-striking solenoid 15, the core is surrounded by a copper or like retarding sleeve 30 which may be grooved for the reception of oil or grease to assist the damping action. A contact screw 26 on the upper end of the core engages a spring-controlled plunger 27 for indicating the desired length of arc. The solenoid casing 1 has mounted thereon handle brackets 3 for a hand grip 4, containing a press switch 5 and is provided with an adjustable collar 7 containing guides 9 for adjustable legs 10. Internal arcing or welding of the stud to the chuck is avoided by facing the chuck with beryllium-copper. The direct current generator has an armature 35, Fig. 7, with series and shunt field coils 36, 37, and the primary 38, of a transformer included in the main welding circuit with the secondary 39, in series with the shunt field coil 37 for reacting thereon to effect instantaneous striking of the arc. A camshaft 41, driven by a synchronous alternating current motor 42, and provided with a slotted cam 44 for closing a holding circuit, has three cams 46, 47, 48 which respectively co-operate with contacts 49, three contacts 55, 56, 57 and contact 58. The contact 49 which is pivoted and manually adjustable is electrically connected to the coil 53 of the welding contactor 54 so as to close the welding circuit, the circuit to the solenoid 15 being a.t the same time closed. The contacts 55, 56, which normally shortcircuit a limiting resistance 56<1> for reducing the current demand on the control circuit when the solenoid 15 is short-circuited, are separated by the cam 47 to throw the contact . 56 into engagement with contact 57 to short-circuit the solenoid 15. The contact 58 is included in the circuit of the coil 59 of contactor 60 for closing the diverter circuit 40 to reduce the magnetic field and thus reduce the current density at the moment of contact of the stud with the plate. The switch 62 may be opened by another cam on the shaft 41 to insert the resistance 61 for a similar purpose. When welding small studs with a large capacity generator a current limiting and regulating resistance is also used. A portable alternating current apparatus in which the gap between the stud and plate is at first filled by a ball of steel wire wool has a casing 63, Fig. 2, provided with adjustable legs 10 and handle brackets 65 as in the previous form. The stud is .pressed against the plate by a solenoid 68, having a fixed core 66, engaging ribs 70 in the casing and a movable core 72 which is normally held by counterbalancing springs 75 in contact with a screw 88. The cores have brass shading rings in oppositely or diagonally disposed positions. The chuck 20 is secured' to a head carried by but insulated from, a pair of rods secured to the bridge 73 to which the core 72 is secured. The main welding circuit contains the secondary 90, Fig. 8, of a transformer and is closed by a contactor 54, operated by a coil 53, connected to a control circuit through the contact 49 and cam 46. The cam 47 cooperates with contact 92 to close the circuit of the solenoid 15, to press the stud against the plate. Limitation of the welding current at this time may be produced by introducing an impedance in the primary or secondary circuit under control of another cam on the shaft 41. In an alternating current apparatus to be mounted by an adapter 93, Fig. 5, in the spindle of a drilling machine or in a tool-post, the chuck 20 is carried by, but insulated from, a piston rod 98, secured to a compressed-air piston 101. Instead of using an arc striking solenoid the stud is retained in raised position by friction in the gland 97. The cylinder 94 is provided with a vent 104 and has a terminal plate 105 for securing the current leads 108 to a block 109, having a pointer 112 co-operating with a scale 111 connected to the cylinder to indicate the position of the piston in the cylinder. The supply of air is controlled by a solenoid operated valve 121, controlled by the cam and contact 47, 92 of the last modification. The movable core 120 of the solenoid has a shading ring 124. The valve is normally held closed by a spring 122 and its casing has vents 132, 133. Air is supplied through'a union 125, with an exchangeable orifice plate 131 for varying the speed of the piston 101. For underwater welding a loose slidable sleeve 134, Fig. 10, of stoneware, porcelain, lava, or other insulating and preferably refractory material encloses the end of the stud so as to limit generation of steam, prevent excessive swirling or eddying in the region of the weld and retain molten metal round the weld. The shield is converted by a spring 136 to the stud chuck 20 so as to apply it to the plate and has one or more pairs of slots 141, or three spaced slots to vent excess steam. The cavity containing the solenoid core of Fig. 1 may be provided with a relief valve for use under water. Specifications 156,836, 183,787, 196,322, [all in Class 83 (iv)], and 580,757 are referred to.