Patent GB-1460613-A (GB)
Title: Method of and apparatus for plasma arc working of conductive  materials
IPC: B23K10/02
Filed: 1974-04-09
Abstract: 1460613 Welding by fusion; removing metal by fusion VSES NI PROEKT-KONSTRUKT I TEKHNOLOGICHE INST ELEKTRO OBORUDO 9 April 1974 15718/74 Headings B3R and B3V [Also in Divisions C7 and H5] In plasma arc welding, build-up deposition, and remelting and cathodic etch cleaning of surfaces, wherein a plasma arc 20 between a non-consumable electrode 1 and an electrically conductive workpiece 4 is constricted by a nozzle 6, the electrode and workpiece are connected to a D.C. source 3 for reverse polarity operation, the electrode has a facing 2 of refractory material such as W, W base alloy, Mo, Ta, Ha, the nozzle is connected to the negative terminal of the D.C. source by way of a toggle or automatic switch 9, a resistor 10 and a high voltage discharger 11 to provide an initial electrode/nozzle pilot arc (extinguished on striking of the main arc 20), and the ratio of main arc current to nozzle bore diameter is in the range of 50-100 A/mm. (preferably 60-100 for welding and 50-70 for build-up deposition or surface remelting or cleaning) so that at least a portion of the arc 20 is in electrical contact with the electrode facing. The reverse polarity operation provides for cathodic etch cleaning of a workpiece surface, removal of oxide films to produce high quality welds, and reduction in workpiece melting during build-up deposition. Plasma forming gas is supplied through a channel 12 and cooling agent is directed through inlet and outlet channels 13, 14 and 15, 16. If required, a further, shielding, gas is supplied through a channel 17 to issue from a nozzle 18 surrounding the nozzle 6. Examples of single pass, one-side, butt joint (without veeing) welding: Example 1 Workpiece and filler wire, in wt. per cent: Al 92, Mg 6À5, Mn 0À5, Si 0À4, Cu 0À1. Nozzle bore: 7À5 mm. diameter. Electrode facing: W and 5 mm. diameter. Plasma forming gas: A. Shielding gas: inert. Example 2 Workpiece and filler wire as in Example 1. Nozzle bore: 3 mm. diameter. Electrode facing: 97% W, 3% Y and 2 mm. diameter. Plasma forming and shielding gas: A. Example 3 Workpiece and filler wire, in wt. per cent: Al 99À3, Fe 0À3, Si 0À35, Cu 0À05. Nozzle bore: 10 mm. diameter. Electrode facing: 98% W, 2% La and 6 mm. diameter. Plasma forming gas: A. Shielding gas: A + O 2 . Example 4 Workpiece, in wt. per cent: C 0À1, Si 0À5, Mn 1À5, Cr 18, Ni 10, Ti 0À1, Fe 68À9. Filler wire, in wt. per cent: C 0À08, Si 1À0, Mn 1À0, Cr 20, Ni 10, Ti 1À0, Fe 66. Nozzle bore: 3 mm. diameter. Electrode facing: 97À5% W, 2À5% and 10 mm. diameter. Plasma forming gas: A. Shielding gas: CO 2 . Example 11 Workpiece and filler wire, in wt. per cent: Al 99À3, Si 0À35, Fe 0À3, Cu 0À05. Nozzle bore: 13 mm. diameter. Electrode facing: 98% W, 2% La, and 20 mm. diameter. Plasma forming gas: A. Shielding gas: He. Examples of build-up deposition: Example 5 Workpiece, in wt. per cent: C 0À22, Si 0À3, Mn 0À4, Fe 99À0. Filler wire, in wt. per cent: Cu 96, Mn 1À0, Si 3À0. Nozzle bore: 7 mm. diameter. Electrode facing: W and 4 mm. diameter. Plasma forming and shielding gas: A. Example 6 Workpiece, in wt. per cent: Si 2À5, Mn 0À5, Cu 97. Filler wire, in wt. per cent: Cu 93, Sn 6À6, P 0À4. Nozzle bore: 6 mm. diameter. Electrode facing: 97% W, 3% Y, and 3 mm. diameter. Plasma forming and shielding gas: A. Example 7 Workpiece, in wt. per cent: C 0À22, Si 0À3, Mn 0À4, Cu 99. Filler wire as in Example 4. Nozzle bore: 5 mm. diameter. Electrode facing: 97À5% W, 2À5% Y, and 10 mm. diameter. Plasma forming gas: A. Shielding gas: CO 2 . Example 8 Workpiece, in wt. per cent: C 0À2, Si 0À3, Mn 0À4, Fe 99. Filler wire as in Example 4. Nozzle bore: 6 mm. diameter. Electrode facing: 97% W, 3% La and 10 mm. diameter. Plasma forming gas: A. Shielding gas: A + CO 2 . Examples of surface remelting: Example 9 Workpiece, in wt. per cent: Ti 90, Al 7, Mo 2, Cr 1À0. Nozzle bore: 10 mm. diameter. Electrode facing: 97% W, 3% La, and 18 mm. diameter. Plasma forming and shielding gas: A. Example 10 As Example 9, but plasma forming and shielding gas: A + He.