Patent GB-458420-A (GB)
Title: Improvements in or relating to a method and apparatus for spraying powder or the like
IPC: B05B7/14
Filed: 1935-06-18
Abstract: 458,420. Applying powders &c. by spraying. MARR, P. G., Rydens End, Rydens Avenue, Walton-on-Thames. June 18, 1935, No. 17567. [Class 100 (ii)] Relates to the application to surfaces of powder, flock, or other finely-divided material and particularly to coating adhesive surfaces of structural steelwork with metallic powder, by spraying the material from a container by means of compressed air admitted into the powder below its free level, which always lies below the outlet of the container, to provide a cloud space at the top of the container, and consists in subdividing a main current of air within the body of powder at or near the bottom of the container into streams of air bubbles or air pockets, which flow in the powder towards the outlet of the container, aerate the powder substantially throughout its depth, and on leaving the free level of the powder carry particles with them and produce a cloud, this subdivision of the main air-current taking place without mechanical stirring of the powder. The powder is placed in a container 16 comprising vertical portions 22, 23 connected by a conical portion 24, and compressed air from a pipe 92 passes through a vertical bore 32, Fig. 2, into horizontal passages 31, and by impinging against the side walls of the part 24 is broken up into streams &c. which pass upwards through the powder and produce a cloud in an upper chamber 34 .. 36 which is of conical construction so as to direct non-ejected powder back into the container. The mixture of powder -and air is ejected through an outlet 37 to which is connected a spray gun comprising a flat nozzle angularly adjustable with respect to a handle. To avoid having too dense a jet, a conical or pyramidal baffle 39 is arranged inside the chamber 36, and to prevent powder from settling on the baffle, a stem 40 to which the baffle is secured is loosely connected to a stationary member 41 so as to be capable of vibration. The base chamber 23 is of such height that when no powder is in the portions 22, 24 there is still sufficient left to cause the current of air to break up into streams. The air streams, or the cloud in the case of a low powder-level, are guided by a central tube 44 provided with wings 46, the powder being placed in the outer space from which it passes into the tube by an opening 223 ; a conical cap is preferably placed on top of the tube 44 when filling with powder. The air is dried before it enters the container by allowing it to expand in a condenser 72 and so deposit its moisture. The container may be heated by electricity &c. to keep the powder dry, but, preferably, the compressed air heated by the compressing operation is passed through an outer jacket 76 on its way to the condenser 72. The air from the condenser passes through a reducing- valve 86 to the pipe 92, a branch pipe 94 being provided to supply air to the powder-laden air passing through the. outlet 37, or to the cloud-chamber 35. To prevent powder from being forced back into the pipe 92 when the air supply is cut off, a fine-mesh screen in the form of a calico bag 96, Fig. 2, is interposed between the air inlet and the powder ; the screen also assists in breaking up the air into fine streams. In modifications: (1) the air enters the container horizontally and leaves by a slanting cloud chamber ; (2) the air enters and leaves by horizontal passages, and baffles are provided near the inlet and outlet ; (3) a baffle in the form of a metal disc is arranged centrally below an outlet at the top of a conical cloud chamber provided on a cylindrical container, and a solid conical baffle rests on top of the powder and is movable with changes in level of the top surface ; (4) the movable baffle of (3) is in the form of an annulus surrounding a perforated guide tube ; (5) air is admitted by radial inlets to an annular base chamber provided with a conical guide member for guiding the powder into the chamber ; (6) the guide tube 44 of Fig. 1 has a funnel-shaped extension joined to the part 22.