Patent GB-990533-A (GB)
Title: Electrical spraying apparatus and methods
IPC: H05H1/42
Filed: 1962-06-13
Abstract: 990,533. Spraying fusible materials. PLASMADYNE CORPORATION. June 13, 1962 [June 13, 1961], No. 22718/62. Heading B2F. An electrical spraying apparatus has a gas inlet and a gas outlet in the form of a passage extending through a first electrode spaced from a second electrode to permit the creation between the electrodes of a gas heating arc, the apparatus also having at least two inlets 54, 55, for introducing the same or different spraying materials into the passage downstream of the arc, the spraying material inlets being connected to separate sources 50, 51, of spraying materials and lying between the ends of the passage and downstream of the second electrode. The front electrode 18, preferably of copper, is shaped to include a nozzle passage 25 and has a stem 19 which, in conjunction with a metal (e.g. brass) front housing element 15 and an insulating body 13, defines a front coolant chamber 39. The rear electrode is a screw threaded rod 28, e.g. of copper, to which a rear electrode rod 30 is soldered, e.g. of thoriated tungsten. The rod 28 screws into a stem 29 in the centre of a metal (e.g. brass) rear housing element 16, the insulating body 13 being held between the housing elements 15, 16. 13 and 16 also define a rear coolant chamber 38 which is in communication with the chamber 39 through a duct 41. Ducts 37 lead to an annulus 36, whereby the stem 29 is cooled. The front end of the annulus 36 is closed by an insulating disc 24 which, with the inner wall 21 of a hollow in the body 13 and the rear of the electrode 18, defines a vortex chamber 23. Direct current at low voltage and high amperage is supplied from a source 43 through a cable 44 to the front electrode 18, normally positive. The cable 44 also conducts water to the coolant chamber 39. The return current from the rear electrode is conducted through a cable 45, which also conducts water from the coolant chamber 38. Inert gas from a pressure source 46, passing through a conduit 47, is introduced tangentially into the chamber 23 so that it whirls round the electrode rod 30 and through the passage 25. A spark is struck from an adjustable spark plug 57 to the front electrode 18 and ionizes the gas, so initiating an arc 26 between the rear electrode 30 and a point in the passage 25. There are at least two sources 50, 51 of powder which is conveyed by a propellant gas through conduits 52, 53 to separate passages 54, 55 in the electrode 18 and near its front surface, radial and separated by only a small angle, Fig. 3, this arrangement resulting in a higher rate of powder deposition from the spray than if introduced into the plasma jet by one path. By using different powdered metals alloying or sintering may be achieved in the jet itself, as well as mixtures of metals and ceramics. Instead of, or in addition to, powder, wire-feed devices may introduce consumable wires of spray material into the plasma jet through the passages 54, 55. The rear electrode is adjusted in position to cause the arc 26 to strike the passage 25 at a suitable point according to the nature of the material being sprayed and other factors as discussed in the Specification. The electrode is screwed-backwards or forwards by a knob 31 connected to the rod 28 and an internally threaded insulating knob 33 may be operated in the manner of a lock nut. A locking effect may also be achieved by giving the screw threading on the rod 28 and in the stem 29 slightly different characteristics. The conduits pass through an insulating handle 10 and a shield 11 protects the operator's hand from the heat of the jet.