Patent GB-1287596-A (GB)
Title: Tube welding
IPC: B23K9/028
Filed: 1969-12-08
Abstract: 1287596 Welding by fusion ATOMIC ENERGY OF CANADA Ltd 8 Dec 1969 [9 Dec 1968] 59758/69 Heading B3R [Also in Division G3] In rotary electrode T.I.G. butt-welding of tubes end-to-end, particularly in respect of instrument tubing (e.g. stainless steel) in process industries and nuclear reactor monitoring, the tubes to be welded are held in coaxial abutting relation as a column by clamping means restraining axial elongation of said column under heating, said axial restraint being maintained during cooling. The gas used for shielding, e.g. argon or helium, also provides post-arc cooling. Apparatus. The welding set comprises a portable unit 12, a separate switch and indicator box 13, and a remote supply and control unit 14. The portable unit 12 comprises a head 20 and a separable handle 21. The head comprises a non- magnetic metal (e.g. aluminium alloy) body 26 having pivoted thereon a welding-chamberenclosing and gas-sealing cover 27. Tube end clamping V-seats 145 are formed either directly in the housing walls, or in interchangeable different-sized inserts (Fig. 10, not shown) mounted in said walls. Clamp arms 28 pivoted on the housing and arranged to snap into "open" position are tightened on to the tube ends by nuts 33 threaded on links 30 pivoted to the arms. The head has secured therein a one-piece insulation block 38 journalling an insulating spool 46, the block and spool being gapped at 40, 47 for tube accommodation. The spool is rotated via an input shaft 78, worm gearing 81, 80, a gear 76, and spaced gears (68), (68<SP>1</SP>) both meshing a gapped gear 66 fast with the spool, the spacing of the gears (68), (68<SP>1</SP>) being such as to ensure continuity of drive despite the gap. The spool has pivoted thereto an electrode support 56, e.g. of brass, comprising a screwtightened electrode clamp end 65 spring urged towards the workpiece. A ceramic plug 62, screw-adjustable in the support 56, has a rounded end 63 engageable with the tube periphery to maintain electrode/workpiece distance. The electrode, 64, is of tungsten with 2% thorium. Negative current connection to the electrode is via a spring-biased metal plug 88, a pair of flexible conductors 86, a stationary, spring-loaded, gapped, slip-ring 44 in the housing, a rotary, gapped, slip-ring 54 carried by the spool, and a flexible conductor (56<SP>1</SP>) connected to the support 56. Shielding gas is supplied to the welding chamber via an aperture (98) in the housing and a diffuser body 104 which may have, as shown, a semi-cylindrical inner surface perforated at 107 by uniformly distributed pores, or a finely perforated diffusing screen (Fig. 14, not shown) of sintered polycrystalline refractory such as carborundum or flexible woven or braided band such as glass cloth or braid. The diffuser body may be of transparent plastics for arc observation. The handle 2 includes a speed-controlled electric motor 112 having reducing gear trains 113, 115 at its opposite ends, said trains having respective output shafts 114, 116. The shaft 116 carries a bar magnet 135 arranged to complete an on-off switch cycle in a reed-type switch 134 for each increment, e.g. 15 degrees, of electrode rotation. The motor also supplies an output signal from a speed-responsive generator G1 (not shown in Fig. 7, see Fig. 22). The handle also supports, in a guide 119, a sliding rod 122 which is manually moved between a forward position in which its end 125 extends through the diffuser body 104 into the welding chamber and a rearward, retracted, position. In the forward position of the rod, a face 124 of the end 125, disposed in the weld plane, serves as a locating stop against which one of the tube ends is abutted prior to its clamping. The forward and rearward rod positions are maintained by a spring-loaded ball 126, in the rod, engaging depressions 126B, 126A in the guide 119. To disable the motor 112 when the rod is in other than its fully retracted position, a motor circuit switch 130 is closed only when an inward projection of a rod actuator pin 125 acts on a switch actuator pin 131 through a resilient metal strip 132. When the handle 21 is fitted to the head 20 and secured by screws 118, a tongue 117 of the motor output shaft 114 drivingly engages a slotted end 79 of the electrode drive input shaft 78; a button 91 connected to a negative input lead 23 contacts the spring-loaded plug 88; a positive earthing lead 22 engages and is screwretained in a housing aperture (84); a gas tube 97 engages in the housing aperture (98); and the guide tube 119 for the tube locating rod 112 engages in an aperture 106 in the diffuser body 104.  Control. The function sequence is detailed in Figs. 15- 21 and comprises an initial gas purge followed by H.F. arc striking and pre-heating, high amperage, arc current (to create a weld puddle) before electrode rotation. The arc current is reduced in stages during electrode rotation which continues after arc cessation. Gas flow is continued after electrode rotation cessation. Control is by programme switching which is responsive to electrode rotation and is self-homed to complete the operation cycle. In the event of arc extinguishing, e.g. at point 170C<SP>1</SP>, H.F. striking voltage is at once applied at 169A with high open circuit voltage 170A<SP>1</SP> to maintain even heating. The tube is initially filled with gas, such filling being maintained at a steady low pressure throughout the sequence. The control apparatus (Figs. 22, 23) comprises a two-station (see Fig. 1) stop-start switch and relay block 159; a gas and motor drive switch and relay block 160 including a gas valve solenoid ZG1; an H.F. voltage supply 161; a high open circuit voltage supply 162; an SCR- controlled main arc circuit supply 163; a manual- or auto-controlled weld programme register block 164 including arc currentdetermining adjustable potentiometers; a speed control sub-system 165 including a reversing switch SP and a motor speed pre-selecting rheostat 197; a graphic data-recording system 166; and a weld sequence control sub-system 167 including an electrode rotation responsive stepping switch ZS1 which is responsive to the reed switch 134 (1-SR in Fig. 22) and steps spring-loaded, simultaneously-acting, wipers 189, 183 along programme point banks 188, 187, respectively associated with the programme register block 164 and with self-homing means whereby the switch ZS4 is fully "homed" to act on switches 1-HS and 2-HS to end the cycle. The circuit comprises a known regulating means for the arc current comprising a magnetic amplifier firing control unit 178 in association with a D.C. amplifier 191, the error across R8, R9 in the arc circuit being compared with the selected potentiometer tap in the register 164. Emergency stop and inching control buttons PB2, PB4 are provided.