GB2110121A - Electrostatic spray coating - Google Patents

Abstract

Electrostatic spray coating apparatus has a tunnel (10) with coil electrodes (16) extending across an opening (14) in a side wall. A spray gun (18) has a cone- shaped distributor (24) fitted over the nozzle thereof and extending between the gun (18) and the electrodes (16). A high voltage supply is impressed on the electrodes (16) and the coating material is sprayed between the electrodes (16), such that the coating particles are charged and are attracted to an article passing through the tunnel (10), the article being at or near ground potential. <IMAGE>

Description

SPECIFICATION Improvements in electostatic spray coating apparatus This invention relates to electrostatic spray coating apparatus.

There are many known types of apparatus for spraying a coating material on a metal object to be coated, wherein the particles of the coating material are first electrically charged and the object is held at or near ground potential. The coating particles are sprayed towards the object and they are attracted thereto because of their charge to become deposited on the object. The coating material is susequently cured to produce a protective coating for the object. In many known types of apparatus, for example spray guns wherein an electrode extends centrally of and co-axially with the barrel, a high percentage of the coating particles do not become charged and in some cases the percentage of charged particles can be as low as 40%. Also, considerable electrical insulation of the gun may be required.

According to the present invention there is provided electostatic spray coating apparatus comprising means for receiving a supply of coating material, means for producing a spray of the coating material, and means for directing the spray past an electrical conductor, the conductor being located in the path of the spray and occupying an area greater than the cross-sectional area of the spray producing means whereby, when the conductor is connected to a source of high voltage electrical power, an electrical charge is imparted to the particles of the spray coating material.

Preferably the conductor comprises a plurality of substantially parallel coil electrodes.

Preferably also the conductor extends across an opening in a side wall of a passage through which an article to be coated is passed.

The means for receiving the coating material and the means for producing the spray may be incorporated in a spray gun with a distributor extending between the gun and the conductor.

The high voltage power may be a variable supply of 10-100 kv, and preferably 50-60 kv.

An embodiment of the present invention will now be described by way of example only with reference to the single figure of the accompanying drawing which is a diagrammatic perspective view of an apparatus according to the invention with part removed for clarity.

Referring to the drawing, an electrostatic spray coating appartus comprises a chamber or tunnel 10 through which can travel an article or object to be coated, for example, with a powder, such that the article can be stoved or enamelled. The article is retained at or near ground potential.

One side wall 1 2 of the tunnel 10 has an opening 14 across which is located an electrical conductor in a form of a plurality of parallel and horizontally extending coil electrodes 16. The electrodes 16 are connectible to a source of high voltage electrical power to receive a voltage normally in the range of 10-100 kv and preferably 50-60 kv.

An atomising device or gun 1 8 is provided externally of the tunnel 10 and is of any suitable conventional form having a nozzle facing towards the coil electrodes 16. The gun 1 8 is connected in an airline 20 and to a supply 22 of coating material, and is adapted to spray the coating material through the nozzle. A substantially conical distributor or spreader 24 is fitted over the nozzle of the gun 1 8 and extends between the latter and the electrodes 1 6 whereby to direct the sprayed coating material towards the electrodes 16.

The feed gun may be arranged such that the air and power mix is introduced tangentially thereto and is moved through the barrel helically about a central core member having an end diverter. Such an arrangement provides adequate mixing and improves distribution of the mix to the conductor.

In use, the high voltage supply is impressed on the coil electrodes 1 6 and the coating material is sprayed between the coils into the interior of the tunnel 1 0. The passage through the electrodes 1 6 results in a high voltage electrical charge being applied to the particles of the coating material, and the coating particles are attracted to the article which is at or near ground potential. As the coil electrodes 1 6 extend over an area considerably greater than the cross-sectional area of the nozzle of the gun 18, most of the coating particles are capable of passing close to an electrode whereby the particles can be charged, and this results in an increased percentage of the particles being charged and thus the apparatus being more efficient.As electrodes are not incorporated within the spray gun, the latter is not subject to the same insulation requirements as other conventional guns and this results in a reduction in the cost of the equipment and simplifies cleaning.

It is to be apreciated that other types of conductor may be utilised, for example a mesh which also presents a large surface area over which the coating particles can be sprayed. Also it will be appreciated that the electrode arrangement need not form part of a tunnel and can, for example, be located in a support connected to a spray gun through a distributor whereby the apparatus can be used at any desired location. Also, of course, coil electrodes may be used in other than the horizontal arrangement described. Further, a plurality of power feed arrangements can be utilised with the one conductor and the or each feed arrangement can be movable.

The apparatus described is relatively simple and inexpensive to manufacture and various other modifications may be made without departing from the invention.

Claims (9)

1. Electrostatic spray coating apparatus comprising means for receiving a supply of coating material, means for producing a spray of the coating material, and means for directing the spray past an electrical conductor, the conductor being located in the path of the spray and occupying an area greater than the cross-sectional area of the spray producing means whereby, when the conductor is connected to a source of high voltage electrical power, an electrical charge is imparted to the particles of the spray coating material.

2. Apparatus according to claim 1, wherein the conductor comprises a plurality of coil electrodes.

3. Apparatus according to claim 2, wherein the coil electrodes are in a parallel relation.

4. Apparatus according to claim 3, wherein the coil electrodes are arranged to extend substantially horizontally.

5. Apparatus according to claim 1, wherein the conductor comprises a mesh.

6. Apparatus according to any of the preceding claims, wherein the conductor extends across an opening in a side wall of a passage through which an article to be coated is passed.

7. Apparatus according to any of claims 1 to 5, wherein the conductor is located in a support connected to the spray producing means.

8. Apparatus according to any of the preceding claims, wherein the means for receiving the coating material and the means for producing the spray may be incorporated in a spray gun with a distributor extending between the gun and the conductor.

9. Apparatus according to any of the preceding claims, wherein the high voltage power is a variable supply of 10-100 kv.

1 0. Electrostatic spray coating apparatus substantially as hereinbefore described with reference to the accompanying drawings.