GB663222A - A method for coating surfaces - Google Patents

Abstract

<PICT:0663222/III/1> <PICT:0663222/III/2> <PICT:0663222/III/3> Surfaces are coated by means of a spraying pistol in which a powder of the coating material is conveyed by a stream of non - oxidizing gas, through an inner passage in the pistol; a combustible gas mixture is passed through an intermediate passage surrounding such inner passage; and a stream of high velocity air is passed through an outer passage surrounding the intermediate passage and having a converging outlet; the temperature of the flame produced by burning the combustible gas mixture and the velocity of the particles of powder being such as to cause such particles to become molten or plastic; and the stream of air moving at a sufficiently high velocity to project the molten or plastic particles on to the surface to be coated. The combustible gas mixture may be a mixture of oxygen, air or other oxygen containing gas and a fuel gas such as coal gas, acetylene, propane or butane or a mixture of or containing these gases; the non-oxidising gas may be a combustible gas such as coal gas or an inert gas such as nitrogen, helium or argon or may be partially burnt coal gas or producer gas; and the substance sprayed may be copper, zinc, aluminium, magnesium or alloys thereof, sulphur or natural or synthetic resins such as shellac or polythene. In the pistol shown, Fig. 1, a non-oxidizing gas carrying the powder to be sprayed is fed at 21 and passes at low pressure to the central bore 22 of the spray nozzle. A combustible gas supplied at 26 and oxygen supplied at 24 are mixed in the chamber 27, shown in detail in Fig. 2, and pass to the chamber 31 and flutes 9 at the outlet of which the mixture burns as an annular flame. Compressed air is supplied at 32, passing to the chamber 35 and emerging at high velocity through flutes 12, the air supply being controlled by a button 48 operating a springloaded valve. The powder is fed to the stream of non-oxidizing gas by a device similar to that described in Specification 644,280, [Group XXIX], the flow of conveying gas and entrained powder being controlled by the mechanism shown in Fig. 5 wherein non-oxidizing gas is fed to a chamber 67 at 66 and leaves through an aperture 69 controlled by a valve 68 connected to an adjustably spring-pressed diaphragm 71 actuated by the pressure of air from a conduit 72 connected to the air supply conduit 32 of the pistol. Specification 432,831, [Group II], also is referred to.