WO1979000478A1

WO1979000478A1 - Spraybooth for use in electrostatic powder coating

Info

Publication number: WO1979000478A1
Application number: PCT/GB1978/000017
Authority: WO
Inventors: J Toff
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-01-05
Filing date: 1978-10-02
Publication date: 1979-07-26
Anticipated expiration: 1980-07-05
Also published as: EP0007370A1; GB1588503A

Abstract

A spraybooth or similar enclosure used in the application of powder materials by electrostatic means for surface coating. The spraybooth being fabricated in such a manner as to comprise an exterior non-porous surface (24) and interior porous surface (23) forming a plenum chamber through which gaseous materials, ionised otherwise, may be introduced to prevent or minimise the disposition of the oversprayed powder materials upon the interior surfaces (23) of the spraybooth or enclosure.

Description

SPRAYBOOTH FOR USE IN ELECTROSTATIC POWDER COATING

Technical Field

This invention relates to a spraybooth spraychamber or enclosure in which the application of dry powder materials for the coating of surfaces is carried out for example by electrostatic coating means. Background art

It is known that during the application of dry powder materials by electrostatic means, and particularly by electrostatic spray means, that there is to a greater or lesser extent a varying but significant quantity of oversprayed material which does not become attached to the article or articles being coated at the first application.

Such oversprayed powder material is encouraged by means of externally induced air movement to be removed from the interior of the spraybooth or spraychamber so that it may be re-used subsequently- One of the claimed advantages for the application of dry powder materials in coating processes is the ability to recover the over¬ sprayed materials for re-use. In order to realise such advantage fully it is necessary to recover such oversprayed materials each from the other without such materials having become cross contaminated. It is necessary therefore and desirable that each material be applied separately and that when it is desired to change from one material or one colour of material to another such change is carried out efficiently. To this end it is necessary to remove all trace of the material or colour of material to be changed from the interior surfaces of the spraybooth spraychamber or enclosure being employed in order to contain the powder materials which are oversprayed so that they may be removed and collected for re-use. It is therefore necessary to clean the interior surfaces of the spraybooth spraychamber or enclosure which process is time consuming.

In order that the powder material being employed in the coating process shall remain adhered to the surface of the articles being coated for a sufficient time and with sufficient adhesive force to permit the coated articles to be handled into the next stage of the coating process, for example the fusion by heat processing of the powder layer into an homogeneous cured film, such powder materials are normally of such electrically resistive nature as to prevent the rapid dissipation of the acquired electrostatic charge which would result in losses of desired electrical adhesive forces. Having become electrostatically charged a significantly high proport of the oversprayed materials which have not become adhered to the articles being coated are attracted to the interior surfaces of the spraybooth spraychamber or enclosure in which the coating process is being carried out. Since the rate of dissipation of the electro¬ static charge upon the particles of material forming the overspray to the surfaces of the interior of the spraybooth spraychamber or enclosure in which they are .being employed is slow and the resultant adhesive forces significant the easy and rapid removal of the powder from such interior surfaces when it is desired to make a colour or material change is difficult and time consuming. Several methods are known whereby it is intended that such difficult or time duration may be reduced or minimised and the cleaning of the interior surfaces of the spraybooth spraychamber or enclosure facilitated. For example the design of the interior sections of the spraybooth may be such as to provide for such sections upon which th oversprayed powder material may come to rest to be at such angle fro the horizontal plane as to cause all but the minimum of such over¬ sprayed materials to fall into the exhaust ventilation ducting and t be removed from the interior of the spraybooth. Alternatively the structure of the spraybooth spraychamber or enclosure may be execute in plastic or similar dielectric material so as to reduce the availa alternative electrical earth attraction which a metal or otherwise electrically conductive spraybooth structure may present to that of the primary electrical earth attraction presented to the charged particles of powder by the articles being coated. This" technique coupled to the reduction in the emission rate of powder materials fr the spraygun or applicator is intended to so limit the quantity of oversprayed material to a level at which such oversprayed material may be permitted to be wasted with a consequential lowering of the economic disadvantage of such wastage. A further alternative variation of the system described employing a spraybooth of plastic or similar construction is for the introductio of metal or otherwise similarly electrically conducting panels or grids into the interior area of the spraybooth which, being both supported upon electrically insulating supports and situated within the electrostatic field caused by the discharge electrodes of the applicators or sprayguns, become charge!with a like polarity to the charge induced upon the powder material being employed so that the

3 _ O latter become repelled from such panels by the electro-magenetic forces present. The powder material thus repelled is thereby induced to remain in proximity to the articles being coated for a longer

80 period of time with a consequential increase in the quantity of such powder material which is likely to become deposited upon the surfaces of the articles being coated at the first application. Similar electro-magnetic repulsion of the oversprayed material may also be achieved by the positioning of electrostatic discharge

85 electrodes within the interior area of the spraybooth spraychamber or enclosure which emit electrostatic discharge of the same polarity as the charge induced upon the powder materials. In none of the alternative methods described is the electrical attraction and subsequent adhesion of the particles of oversprayed

90 powder materials to the interior surfaces of the spraybooth spraychamber or enclosure prevented. Such attraction and adhesion takes place upon surfaces which are electrically conductive or of a dielectric character whenever there is an electrical potential difference between such surfaces and the charged powder materials.

95 Additionally with the employment of either insulated metal panels or discharge electrodes situated within the interior area of the spraybooth as described a possible spark discharge between such panel or electrode and electrically earthed workpiece can take place with the resultant possible ignition of the cloud of powder materials

100 being employed-

Disclosure of invention

The present invention has for its object to provide improved means for the reduction of attraction and -retention of oversprayed powder materials upon the interior surfaces of a spraybooth spraychamber or

105 enclosure in which coating of articles with powder materials by electrostatic means is carried out.

In the manufacture of the spraybooth spraychamber or enclosure in accordance with the present invention means for the prevention of attraction and deposition of oversprayed powder materials upon the

110 interior surfaces of the spraybooth spraychamber or enclosure are incorporated within the interior surfaces themselves.

Such means preferably comprise an interior surface which is fabricated in whole or in part from materials having a degree of porosity which will permit the movement of gaseous materials to be induced through

115. the interior surface towards the interior of the spraybooth spraychamber or enclosure by pneumatic, electrical or other means. Brief description of drawings

The invention will be better understood from the following detailed description in conjunction with the drawings wherein -

120 Figure 1 is a schematic side elevational view of an electrostatic powder coating installation operating according to a' conveyorised throughpass technique. Figure 2 is a schematic- cross sectional view through an electrostat powder coating installation operating according to a

125 conveyorised throughpass technique taken substantially alo the line B - B of Figure 1 . Figure 3 is a schematic side elevational sectional view through an electrostatic powder coating installation operating accord to a conveyorised throughpass technique taken substantiall

130 along the line A - A of Figure 2 •

Referring to the drawings illustrating an installation or apparatus 10 depicted in Figure 2 the installation will be understood to poss a spraybooth spraychamber or enclosure 11 in the form of a lengthwi extending tunnel, the roof section 11a of which possesses a lengthw

135 extending slot 12 through which extends the suspension means, for instance in the form of hooks 13, of a conveying device 14 which is guided above roof 11a and suspended by support 22. The articles 15 which are to be coated are suspended by the hooks 13 and enter and leave the spraybooth spraychamber or enclosure through the openings

140 in the end walls.

During the passage of the articles 15 through the spraybooth spraychamber or enclosure they pass the head of a spraygun or applicator 16 which receives through cable 19 the high voltage generated by power supply 20. The high voltage is applied to the

145 powder coating materials which are contained in reservoir 18 and fe through a supply hose 17 to the discharge end of the- spraygun or applicator 16 where they are induced towards the earthed substrate o the articles to be coated 15 substantially in the direction represe ed by lines 21.

150 The spraybooth spraychamber or enclosure 26 is supported upon base section 25 and consists substantially of a structure having an exte non-porous surface 24 separated from an interior porous surface 23 s as to form a space or plenum chamber into which gaseous material ma be introduced by means of suitably positioned inlet connections 27. The gaseous materials thus introduced pass through the interior porous surface 23 substantially in the direction indicated by lines 28 and prevent oversprayed powder materials which have not become attached to the articles being coated 15 from becoming deposited upon the interior surfaces of the spraybooth spraychamber or enclosure 23 and assist in transporting such oversprayed powder materials so that they become influenced in the direction indicated by lines 29 and 30 by the ventilating forces created by motorised fan 34 of the dust collecting device 35 and removed from the interior of the spraybooth spraychamber or enclosure 11 through ventilation duct 36. Where it is desired to introduce ionised gaseous materials into the spraybooth spraychamber or enclosure to aid and enhance the repulsion of oversprayed materials from the interior surfaces 23 a multiplicity of discharge electrodes 33 are positioned in the plenum chamber formed between the Interior surfaces 23 and the exterior surfaces 24 and supplied with high voltage through cable 32 from a power supply 31. Best mode of carrying out the invention

The invention may be carried into practice in various ways, but the following may be instanced as a convenient practical arrangement of the spraybooth spraychamber or enclosure according to the invention. In this arrangement the interior surface having a de ree of porosity is so positioned in relation to the exterior surface of the spraybooth spraychamber or enclosure as to provide a plenum. The introduction of a gaseous material into such a plenum formed by the interior and exterior surfaces of the structure, where such exterior surfaces are non-porous, resulting in the movement of such gaseous material through the pores of the interior surface of the structure thereby repelling the oversprayed powder material from becoming deposited upon such interior surface. Another convenient practical arrangement for the spraybooth spraychamber or.enclosure according to the present invention would be for a multiplicity of electrical discharge electrodes to be positioned within the plenum formed by the interior and exterior surfaces of the structure and connected to a source of high voltage so that the gaseous material passing into the interior of the spraybooth spraychamber or enclosure becomes ionised with a like polarity of charge to that of the powder materials being employed in the coating process providing further repulsion of the oversprayed powder material from the interior surfaces of the spraybooth spray- chamber or enclosure by means of an electro-magnetic nature. • 195 The multiple discharge electrodes being within the plenum thus reducing the possibility of spark discharge between such electrode and the earthed workpieces or articles being coated.

The oversprayed powder materials having become prevented from sett upon the interior surfaces of the spraybooth spraychamber or enclo

200 in. the manner described are removed from within the spraybooth spraychamber or enclosure by conventional means such as a dust collecting device inducing powder laden air carrying the overspray powder materials to be exhausted from the interior of the sprayboo spraychamber or enclosure and collected in such dust collecting de

205 in a manner amply described in prior art. Industrial applicability

The use of a spraybooth spraychamber or enclosure in the process o the coating of surfaces with powder materials by electrostatic mea where such spraybooth spraychamber or enclosure is fabricated in t

210 manner herein described is intended to prevent significant deposit of oversprayed powder materials upon the interior surfaces of such spraybooth spraychamber or enclosure causing the time required to spent in the cleaning of such interior surfaces when it is desired make a colour or material change to be minimal or non-existant.

Claims

215 ClaimsWhat I claim is -

1. An electrostatic powder coating installation comprising a spraybooth spraychamber or enclosure structure for use with a spraygun or applicator having an interior and exterior

220 surface substantially separated from each other so that the structure is in the form of a plenum chamber or series of plenum chambers.

2. An electrostatic powder coating installation as defined in claim 1 where the interior surface or surfaces of the structure

225 is fabricated from material or materials which are substantially porous and the exterior surface or surfaces is fabricated from material which is substantially non-porous so that gaseous materials introduced into the plenum formed by the interior and exterior surfaces of the structure pass through the interior

230 surface into the interior of the structure.

3. An electrostatic powder coating installation as defined as defined in claims 1 and 2 whose plenum chamber formed by the interior and exterior surfaces of the structure contains a multiplicity of electrical discharge electrodes.

235 4. An electrostatic powder coating installation substantially as hereinbefore described with reference to the accompanying drawings.