THIS INVENTION relates to a powder fluidising system for applying electrostatically charged powdered material to a surface to be coated. The charged particles are attracted to and adhere to the surface which is earthed or subjected to an electrostatic charge of opposite polarity. The coated surface is then subjected to heat to fuse the particles and bond the resultant film to the surface. Such applicators (hereinafter referred to as "applicators of the type described") generally comprise means located adjacent the inlet end of the applicator for entraining the powder in a stream of air or other gas, a charging duct formed of electrically non-conducting material through which the entrained material passes so that frictional contact generates an electrostatic charge on the particles of the powder, and a discharge nozzle for directing the charged particles towards the surface to be coated. Any uncharged particles and any charged particles which do not reach the surface and fall to the floor and may be recovered for subsequent use.

PRIOR ART

In order to ensure that the particles of powder are effectively charged it is desirable that the powder be uniformly distributed prior to it passing through the charging duct. One form of applicator widely used in Australia and elsewhere is described in Australian Patent Specification Nos. 543359 and 543360. The fluidising system is described in Specification No. 543360 and comprises a cone shaped spreader or diffuser which is positioned with its apex facing against the direction of flow of the powder. The conical diffuser spreads the powder and it passes through a series of opening aligned with the curved tubes forming the charging section of the

applicator, the diameter of the openings being less than the diameter of the charging tubes.

THE INVENTION

It has been found that if the powder is passed through the openings into a mixing chamber and air is fed into the mixing chamber through a number of other openings the turbulence generated in the mixing chamber ensures that the powder is effectively fluidised before entering the charging section of the applicator.

Thus in one form the invention resides in an applicator of the type described characterised in that the means for fluidising the powder comprises a conical spreader having its apex directed into the inflowing powder, a mixing chamber, a first series of openings through which the spread powder passes into the mixing chamber and a second series of openings through which air under pressure is directed into the mixing chamber.

DESCRIPTION OF THE EMBODIMENT

The invention will be better understood by reference to the following description of one specific embodiment shown in the accompanying drawings wherein:-

Figure 1 is an elevation showing the general outline of the applicator;

Figure 2a is a sectional view of the inlet end of the applicator;

Figure 2b which is a continuation of Figure 2a is a sectional view of the discharge end of the applicator;

Figure 3 is an elevation of a diffuser fitted in the inlet end of the applicator;

Figure 4 is an end view of the diffuser in the direction indicated by lines 4-4; and

Figure 5 is an end view of the diffuser in the direction indicated by lines 5-5 in Figure 3.

In the embodiment shown in the drawings the applicator is generally cylindrical in configuration and as seen in Figures 2a and 2b comprises an inlet section 11, a diffuser section 12, a charging section 13 and a discharge section 14. Means 15 are provided at the inlet end for coupling the applicator to a hose (not shown) through which the powdered material is fed. A coupling 16 to be connected to a supply of compressed air is provided together with an earthing terminal 17. The diffuser comprises a disc like member 18 which is provided with external grooves 19 to accommodate O-rings 20 which seal on the inside surface of the casing when the diffuser is in position. The rear face of the disc 18 is provided with a conical separator 21 the apex of which faces the incoming powdered material. A series of passages 22 leading from the rear to the front of the disc are formed in the disc 18. An annular groove 23 is formed in the outer face of the disc so that when the diffuser is in position it is aligned with the air connection 16. A second series of passages 24 lead from the annular groove 23 to the front face of the disc 18 which is provided with a flange to receive one end of a shroud or skirt 25, the outer face of which is fitted with O-rings 26 which seal against the inside of the casing. A shaft 27 projects forwardly from the disc 18. The skirt 25 forms the mixing chamber into which the powder is discharged from passages 22 and air from the passages 24. The turbulence which is assisted by the forwardly projecting shaft ensures that the powder is effectively fluidised before it enters the charging section of the applicator.

The charging section of the applicator may be of any suitable configuration but is preferably is that shown in the drawings and which is the subject of a concurrent

application related to our Australian Provisional Patent Application PK4169/91.

The powder charging system shown in the drawings comprises a passage 62 which is substantially annular, the diameter of the annulus increasing and decreasing progressively along the length of the passage. The passage 62 is formed between a plurality of bead-like members 64 and a plurality of modules 66.

The bead-like members 64 have a central bore. The bead¬ like members 64 are arranged sequentially and have a rod 68 (shown in broken lines in Figures 2a and 2b) passing through their bores. The bead-like members 64 are positioned loosely on the rod 68 such that they are able to move longitudinally and transversely with respect to the rod 68.

End caps 70 and 72 retain the rod 68 in position and the bead-like members 64 on the rod 68. The end caps 70 and 72 are connected to respective ends of the rod 68 by screws passing through holes in the end caps 70 and 72 and into screw-threaded bores in the rod 68. An end member 76 is positioned between respective two end bead-like members 64 and the respective end caps 70 and 72.

The modules 66 surround the bead-like members 64. The modules 66 are retained in place by an outer tube 78 and by the end caps 70 and 72. The outer tube 78 extends between the end caps 70 and 72.

Preferably, the outer tube 78 is made of metal. An end module member 80 is positioned between the respective end two modules 66 and the respective end caps 70 and 72.

Each of the bead-like members 64 is essentially in the form of a pair of frusto-conical portions with abutting bases and with an axial bore.

Each of the modules 66 is of substantially cylindrical form with an axial bore therethrough. The wall of this axial bore tapers inwardly from each opening of the bore to the middle of the bore such that the bore has a larger diameter at each opening than at the middle of the bore.

The bead-like members 64 and modules 66 are offset from one another such that each bead-like member 64 is positioned half inside each of two adjacent modules 66. In this way, the passage 62 is substantially annular with the diameter increasing and decreasing progressively a number of times along the length of the passage.

The bead-like members 64, modules 66, end bead-like members 64 and end module members 80 are made of electrically non- conductive material.

The intermediate connector part 16 is connected with the main body part 18 by a screw-threaded connection 84. Similarly, the outlet part 20 is connected with the main body part 18 by a screw-threaded connection 86.

The manner of use and operation of the present invention will now be described.

The powder inlet tube 15 is connected to a hose (not shown) through which paint powder is transferred from a colour bin. The powder enters and is deflected by the conical deflector 21. The powder is deflected toward the first face of the disc-like member 30 and into the powder inlets 22.

Simultaneously, air enters the annular groove 23 and passes through the gas inlets 24 into the mixing chamber.

The powder and gas mix in the chamber and the powder fluidized.

The (fluidized) powder then passes through the holes in the end cap 70 and into the passage 62, the space between the bead-like members 64 and modules 66 that forms the passage 62 being sufficient to create turbulence when the powder passes through the passage 62 at a selected speed(s) determined by the gas pressure.

This turbulence is caused by the configuration of the passage 62.

This turbulence causes the powder to become electrostatically charged through frictional contact with the walls of the passage.

The powder applicator is easily disassembled for cleaning and then reassembled for operation. The outlet section 14 may be removed from the main body of the applicator and an end cap 70 or 72 removed. The individual bead-like members 64, modules 66, end members 76 and end module members 80 then easily slide out of the outer tube 78. This enables cleaning to be effected. Reinsertion of the bead-like members 64, modules 66, end members 76 and end module members 80 into the tube 78 is readily done. The end cap 70 or 72 is replaced as is or outlet section 14. The powder applicator is thus reassembled.