GB1588503A

GB1588503A - Installation and method for electrostatic powder coating of articles

Info

Publication number: GB1588503A
Application number: GB269/78A
Authority: GB
Original assignee: Toff J D
Current assignee: Toff J D
Priority date: 1978-01-05
Filing date: 1978-01-05
Publication date: 1981-04-23
Also published as: EP0007370A1; WO1979000478A1

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

(54) INSTALLATION AND METHOD FOR ELECTROSTATIC POWDER COATING OF ARTICLES (71) 1, JOSEPH DENNIS TOFF, a British subject of 15 Cavendish Drive, Edgware in the County of Middlesex, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an installation and method for electrostatic powder coating of articles in a spraybooth, spraychamber or other enclosure structure.

It is known that during the application of dry powder materials by electrostatic means, and particularly by electrostatic spray means, 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 oversprayed 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 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 power materials which are overpsrayed 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 process 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 been electrostatically charged a significantly high proportion of the oversprayed material which has not become adhered to the articles being coated is 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 electrostatic charge upon the particles of powder 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 difficulty 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 oversprayed powder materials might come to rest to be at such an angle from the horizontal plane as to cause all but the minimum of such oversprayed materials to fall into the exhaust ventilation ducting and to be removed from the interior of the spraybooth.

Alternatively the structure of the spraybooth, spraychamber or enclosure may be -executed in plastics or similar dielectric material so as to reduce the available alter native electric earth attraction which a metal or otherwise electrically conducting spray booth structure may present to the primary electrical earth attraction presented to the charged particles by the articles to be coated.

This technique coupled to the reduction in the emission rate of powder materials from the spraygun or applicator is intended to so limit the quantity of oversprayed powder 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 spray-booth of plastics or similar structure is the introduc ,tion of metal or similarly electrically con ducting panels into the interior area of the spraybooth which, being both supported upon electrically insulating supports and situated - within the electrostatic field of the disdliarge electrodes of the applicators or sprayguns, become charged with a like polarity to the powder materials being em- ,ployed which become electrically repelled from such panels. The powder materials thus repelled are induced to remain in proximity to the articles being coated for a longer period of time with a consequential increase in the quantity of - such powder materials which is deposited upon the articles being coated.

Electrical repulsion of the oversprayed powder materials may also be achieved by the positioning of electrical dischare elec trodes within the interior of the spraybooth, spraychamber or enclosure which emit electrostatic discharges of the same polarity as the charge upon the powder materials .'being.employed with similar affect.

In none of the alternative methods referred to is the electrical attraction and subsequent adhesion by the particles of over sprayed powder material to the interior sur faces 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. Addi .tionally, with the employment of either the insulated metal panels or the discharge elec trodes within the interior of the spraybooth as described, a possible spark discharge between panel or electrode and earthed workpiece could take place with consequent ignition of the cloud of powder material being 'employed.

The present invention has for its obiect to provide improved means for the reduction of attraction and retention of oversprayed powder materials upon the interior surfaces of the spraybooth, spraychamber or enclosure in which the coating process is carried out.

According to one aspect the invention provides an electrostatic powder coating installation comprising a spraybooth, spraycharmber or other enclosure structure for use with a spraygun or applicator, the structure having an interior surface and an exterior surface spaced apart to form at least one plenum chamber therebetween, the interior surface being substantially porous and the exterior surface being substantially non-porous, and electrical discharge electrode means within the plenum chamber, whereby in use of the installation gaseous material introduced into the plenum chamber is there ionised by the electrode means and ionised gaseous material passes from within the plenum chamber through the porous interior wall to the interior of the structure. Preferably the plenum chamber or chambers surround substantially the entirety of the interior of the structure. Desirably the electrical discharge electrode means comprises a multiplicity of electrodes.

According to another aspect the invention provides a method of electrostatic powder coating of articles in a coating installation that has a spraybooth, spraychamber or other enclosure structure and uses a spraygun or applicator for propelling electrically charged powder material towards the articles, the method including the step of introducing gaseous material into a plenum chamber that has a porous surface surrounding the interior of the structure, ionising the gaseous material in the plenum chamber to a like polarity of charge as that of the powder material, and causing the ionised gaseous material to flow to the interior of the structure through the porous surface.

The flow of gaseous material through the porous interior surfaces together with the electrostatic repulsion of powder material due to the ionisation of the gaseous material, combine particularly effectively to prevent the oversprayed powder material from settling upon the interior surfaces of the spraybooth, spraychamber or enclosure; and this whilst yet effectively eliminating the risk of spark discharge between the electrode(s) and the earthed workpiece.

The oversprayed powder material having been prevented from settling upon the interior surface in the manner described is removed from within the spraybooth, spraychamber or enclosure by conventional means such as dust collecting device inducing the powder laden gaseous material e.g. air, carrying the oversprayed powder materials to be exhausted from the interior of the structure and collected in such dust collect-ing device in a manner amply described in prior art.

The prevention of significant deposits of oversprayed powder materials within the spraybooth, spraychamber or-enclosure in accordance with the ;arrangements described causing the time required to be spent in cleaning the interior surfaces of the spraybooth, spraychamber or enclosure when it is desired to make a colour or material change to be minimal or non-existant.

The invention will be better understood from the following detailed description of a preferred embodiment shown in the accompanying drawings wherein: Figure 1 is a schematic side elevational view of an electrostatic powder coating installation operating according to a conveyorised through pass technique.

Figure 2 is a schematic cross sectional view through an electrostatic powder coating installation operating according to a conveyorised through pass technique taken substantially along the line B-B of Figure 1.

Figure 3 is a schematic side elevational sectional view through an electrostatic powder coating installation operating according to a conveyorised through pass technique taken substantially along the line A-A of Figure 2.

Referring to the drawings in the illustrated installation or apparatus 10 depicted in Figure 2 will be understood to possess a spraybooth, spraychamber or enclosure 11 in the form of a lengthwise extending tunnel, the roof section 1 la of which possesses a lengthwise 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 1 la 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 openings in the end walls.

During 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 current generated by power supply 20. The high voltage current is applied to the powder coating materials which are contained in reservoir 18 and fed through a supply hose 17 to the discharge end of the spraygun or applicator 16 where they are induced towards the earthed substrate of the articles to be coated 15 substantially in the direction represented by lines 21.

The spraybooth, spraychamber or enclosure 26 is supported upon base section 25 and consists substantially of a structure having an exterior non-porous surface 24 separated from an interior porous surface 23 so as to form a space or plenum into which a gaseous material may be introduced by means of suitably positioned inlet connections 27.

The gaseous material thus introduced passes through the interior porous surface 23 substantially in the direction indicated by lines 28 and prevent oversprayed powder materials which has not become attached to the articles being coated 15 from becoming deposited upon the interior surfaces of the spraybooth, spraychamber or enclosure 26 and assist in transporting such oversprayed material 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 collect-ing device 35 and removed from the interior of the spraybooth, spraychamber or enclosure 11 through ventilator duct 36.

To ionise the gaseous material prior to its introduction into the spraybooth, spraychamber or enclosure to aid and enhance the repulsion of oversprayed powder materials from the interior surfaces 23, a multiplicity of discharge electrodes 33 are positioned in the plenum between the interior surfaces 23 and exterior surfaces 24 and supplied with high voltage current through cable 32 from a power supply 31.

WHAT I CLAIM IS:- 1. An electrostatic powder coating installation comprising a spraybo oth, spraychamber or other enclosure structure for use with a spraygun or applicator, the structure having an interior surface and an exterior surface spaced apart to form at least one plenum chamber therebetween, the interior surface being substantially porous and the exterior surface being substantially non-porous, and electrical discharge electrode means within the plenum chamber, whereby in use of the installation gaseous material introduced into the plenum chamber is there ionised by the electrode means and ionised gaseous material passes from within the plenum chamber through the porous interior wall to the interior of the structure.

2. An electrostatic powder coating installation as defined in claim 1 wherein the plenum chamber or chambers surround substantially the entirety of the interior of the structure.

3. An electrostatic powder coating installation as defined in claim 1 or claim 2 wherein the electrical discharge electrode means comprises a multiplicity of electrodes.

4. The method of electrostatic powder coating of articles in a coating installation that has a spraybooth, spraychamber or other enclosure structure and uses a spraygun or applicator for propelling electrically charged powder material towards the articles, the method including the step of introducing gaseous material into a plenum

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The prevention of significant deposits of oversprayed powder materials within the spraybooth, spraychamber or-enclosure in accordance with the ;arrangements described causing the time required to be spent in cleaning the interior surfaces of the spraybooth, spraychamber or enclosure when it is desired to make a colour or material change to be minimal or non-existant. The invention will be better understood from the following detailed description of a preferred embodiment shown in the accompanying drawings wherein: Figure 1 is a schematic side elevational view of an electrostatic powder coating installation operating according to a conveyorised through pass technique. Figure 2 is a schematic cross sectional view through an electrostatic powder coating installation operating according to a conveyorised through pass technique taken substantially along the line B-B of Figure 1. Figure 3 is a schematic side elevational sectional view through an electrostatic powder coating installation operating according to a conveyorised through pass technique taken substantially along the line A-A of Figure 2. Referring to the drawings in the illustrated installation or apparatus 10 depicted in Figure 2 will be understood to possess a spraybooth, spraychamber or enclosure 11 in the form of a lengthwise extending tunnel, the roof section 1 la of which possesses a lengthwise 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 1 la 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 openings in the end walls. During 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 current generated by power supply 20. The high voltage current is applied to the powder coating materials which are contained in reservoir 18 and fed through a supply hose 17 to the discharge end of the spraygun or applicator 16 where they are induced towards the earthed substrate of the articles to be coated 15 substantially in the direction represented by lines 21. The spraybooth, spraychamber or enclosure 26 is supported upon base section 25 and consists substantially of a structure having an exterior non-porous surface 24 separated from an interior porous surface 23 so as to form a space or plenum into which a gaseous material may be introduced by means of suitably positioned inlet connections 27. The gaseous material thus introduced passes through the interior porous surface 23 substantially in the direction indicated by lines 28 and prevent oversprayed powder materials which has not become attached to the articles being coated 15 from becoming deposited upon the interior surfaces of the spraybooth, spraychamber or enclosure 26 and assist in transporting such oversprayed material 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 collect-ing device 35 and removed from the interior of the spraybooth, spraychamber or enclosure 11 through ventilator duct 36. To ionise the gaseous material prior to its introduction into the spraybooth, spraychamber or enclosure to aid and enhance the repulsion of oversprayed powder materials from the interior surfaces 23, a multiplicity of discharge electrodes 33 are positioned in the plenum between the interior surfaces 23 and exterior surfaces 24 and supplied with high voltage current through cable 32 from a power supply 31. WHAT I CLAIM IS:-

1. An electrostatic powder coating installation comprising a spraybo oth, spraychamber or other enclosure structure for use with a spraygun or applicator, the structure having an interior surface and an exterior surface spaced apart to form at least one plenum chamber therebetween, the interior surface being substantially porous and the exterior surface being substantially non-porous, and electrical discharge electrode means within the plenum chamber, whereby in use of the installation gaseous material introduced into the plenum chamber is there ionised by the electrode means and ionised gaseous material passes from within the plenum chamber through the porous interior wall to the interior of the structure.

chamber that has a porous surface surrounding the interior of the structure, ionising the gaseous material in the plenum chamber to a like polarity of charge as that of the powder material, and causing the ionised gaseous material to flow to the interior of the structure through the porous surface.

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

6. The method of electrostatic powder coating of articles substantially as hereinbefore described with reference to the accompanying drawings.

7. An article coated with powder by use of an installation or a method as claimed in any preceding claim.