Patent GB-863190-A (GB)
Title: Heat-fusible material spray gun and method for coating a surface with a heat-fusiblematerial
IPC: B05B7/22
Filed: 1959-02-23
Abstract: 863,190. Spraying fusible materials. METCO Inc. Feb. 23, 1959 [june 30, 1958], No. 6237/59. Class 69 (3). A spray gun housing 2 has a chamber 3, Fig. 1, with an outlet nozzle 4, electrodes 1, 5, between which an electric arc is struck, an inlet 6 for a fluid capable of conversion to plasma by the arc, which plasma flows from the nozzle and heats and projects fusible material fed into its path. The material 16, which is in powder form, is delivered from a hopper 7 into a stream of carrier gas supplied at 10 which supplies the material to the nozzle via a passage 12. The plasma fluid flows through the arc between the electrodes and constricts it; at least some of the fluid is converted to plasma i.e. is brought to an energy state of particle activity above the gaseous state, at least a portion of the atoms of the material being stripped of one or more electrons which are also present in the free state. The plasma thus brings the material to a sprayable, at least heat softened form and propels it from the gun. Electrode 1 is non-consumable and electrode 5 is an annular liner, and a high amperage relatively low voltage are is maintained between them. The arc may be initially struck by imposing a high-voltage high-frequency current between them. A vibrator may be attached to the housing which may be water cooled. An alternative construction of gun is described with a water-cooling system, and wherein the powder is fed from a hopper into the plasma stream after the latter leaves the gun orifice ; the plasma fluid causes the electric arc to extend through the gun nozzle, although the plasma stream is free from the arc when it contacts the powder. The gun of Fig. 3 has electrodes 303, 317, a water-cooled body 301 and a water-cooled sleeve 310. Plasma gas is fed to the body at 330 and flows to a chamber 332 and through the arc to a plasma chamber 323. The latter has a nozzle bore 324 through which is fed a wire 326 of heat fusible material, and the plasma fuses and projects the material. A cap 333 supplied with compressed air at 335 and provided with air outlets 336 assists in the atomization and projection. In Fig. 4 the gun has electrodes comprising a wire 403 of heat fusible material to be sprayed and a sleeve 413 within the outlet of a nozzle 408. Plasma gas is delivered at 419 and passes through passages 421, 422 to a gas space 423, and then flows through the arc set up between the wire and a rib 414 of the sleeve to the front of the nozzle where it acts on the end of the wire to spray it. Compressed air to assist in the spraying operation is fed at 416 and flows through passages 417, 418. In order to prevent arcing between the hot wire and other parts of the nozzle a sheath of air, bled from the main air supply, passing through the gun, may be passed between the nozzle wall and the plasma stream past the arc in the direction of the nozzle outlet. In a further construction an electric arc is set up in a gun between a rod electrode and the gun nozzle, and also between the rod and a wire of heat-fusible material which passes through the nozzle at right angles to the rod. A plasma gas is fed through the arc and acts on the wire to heat and spray it. A number of plasma producing generators may be arranged around the axis of the spray stream as is shown in Fig. 6. A body 601 has gas spaces 606, 606a with rod electrodes 611, 611a and plasma gas feed inlets 605, 605a. Electric arcs are set up between the electrodes and the inlets of outlets 607, 607a, and the plasma gas flows through the arcs and the outlets and acts as plasma upon the heat-fusible wire 608. Further embodiments are described in which the electrodes are shielded from contact with the plasma forming gas, and an inert gas is fed as an envelope adjacent those parts to be shielded. Plasma forming gases include argon, helium, hydrogen, nitrogen, air, oxygen, carbon dioxide, and certain mixtures thereof. Specification 863,189 is referred to.