US3797457A

US3797457A - Coating of surfaces with powder

Info

Publication number: US3797457A
Application number: US00121945A
Authority: US
Inventors: R Bushnell
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-03-06
Filing date: 1971-03-08
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19
Also published as: FR2084237A5; DE2110691A1

Abstract

This invention relates to the surface-coating of a metal or other article or articles with powder and comprising an inclined sheet made of material porous to air or other gas and down which the powder is caused to flow, air or other gas being blown through such sheet to cause turbulence above the sheet to assist the downward flow of the powder, the powder particles being electrostatically charged so that they will be attracted from the space above the inclined sheet by the article or articles to be coated when such articles are moved past the turbulent space above the inclined sheet, the length and position of the inclined sheet being such that every part of the surface or surfaces to be coated passes closely adjacent to the space over the inclined sheet. Any powder which is not attracted away from the space over the inclined sheet and escapes from the bottom of such sheet is caused to pass into a main powder reservoir from which the powder is conveyed to the top of the inclined sheet to flow down such sheet.

Description

United States Patent 1191 Bushnell COATING OF SURFACES WITH POWDER [76] Inventor: Roger Brian Bushnell, 49 Parkland Grove, Ashford, England 22 Filed: Mar. 8, 1971 21 Appl. No.: 121,945

[30] Foreign Application Priority Data Mar. 16, 1970 Great Britain i. 10950/70 [52] U.S. Cl 118/630, ll7/DlG. 6, 118/636, 118/DlG. 5 [51] Int. Cl B05b 5/00 [58] Field of Search ll8/DIG. 5, D16. 24, 620, 118/621. 630, 629, 636; 1l7/DlG. 6; 317/3;

[451 Mar. 19, 1974 Primary Examiner-Mervin Stein Assistant Examiner-Leo Millstein Attorney, Agent, or FirmBrisebois & Kruger [57] ABSTRACT This invention relates to the surface-coating of a metal or other article or articles with powder and comprising an inclined sheet made of material porous to air or other gas and down which the powder is caused to flow, air or other gas being blown through such sheet to cause turbulence above the sheet to assist the downward flow of the powder, the powder particles being electrostatically charged so that they will be attracted from the space above the inclined sheet by the article or articles to be coated when such articles are moved past the turbulent space above the inclined sheet, the length and position of the inclined sheet being such that every part of the surface or surfaces to be coated passes closely adjacent to the space over the inclined sheet. Any powder which is not attracted away from the space over the inclined sheet and escapes from the bottom of such sheet is caused to pass into a main powder reservoir from which the powder is conveyed to the top of the inclined sheet to flow down such sheet.

7 Claims, 6 Drawing Figures PATENTEUMAR 19 1974 SHEET 1 OF 2 Inventor Allomey PATENTEDHA 1 m4 379?.457

SHEET 2 BF 2 Inventor Attorney 1 COATING OF SURFACES WITI-I POWDER finishing materials of a powdered nature). Although applicable to the surface-coating of articles of other shapes, the invention is more especially intended for the surface-coating of flat plates.

Hitherto, the surface-coating of metal articles with powder has often been effected by means of a powderspraying device,- which projects the particles of the powder through an electrostatic field on to the surface to be coated, the electrostatic charge thus applied to the particles serving to ensure their firm adhesion to the surface. It is not essential that the article to be coated should be made of metal, and it is even practicable to carry out such electrostatic coating on articles made of materials commonly regarded as insulating materials provided that they have a sufficient degree of conductivity to be able to dissipate the electrostatic charge to earth. Thus, for instance, it is possible to coat articles of wood or plaster or hardboard provided that such articleshave for example a moisture content inexcess of about 10 per cent. It is likewise possible to coat a sheet'of paper or fabric, when a metal plate is placed behind such sheet and in close contact therewith. It is usual to submit the article to a curing process after such electrostatic deposition to ensure permanency of the coating. I

It is difficult, however, with such electrostatic coating as hitherto practised to obtain an even thickness of powder over the whole area of the surface to be coated.

The present invention hasfor its primary object to provide'an improved apparatus for the surface-coating of a metal-or other article or articles with powder whereby a high degree of uniformity in the thickness of the deposited coatingwill be obtained, and a further object is to provide an apparatus which readily lends itself to the surface-coating of a successive of articles within a predetermined limit of size.

The apparatusaccording to the present invention for the surface-coating of a metal or other, article or articles with powder, comprises in combination an inclined sheet made of material porous to-air or other gas but not to the powder particles, means whereby the powder is caused to flow down the inclined sheet, means for blowing air or other gas upwardly through the inclined sheet to produce turbulence in the space immediately above the sheet and thereby to cause the powder particles to hover over the sheet in their downwardflow along the sheet, means for electrostatically charging such powder particles, and means for moving the article or articles past the turbulent space immediately above the inclinedsheet whereby the charged particles will be attracted from such turbulent space onto the surface or surfaces to be coated, the length and position of the inclined sheet being such that every part of the surface or of each surface to be coated passes closely adjacent to the turbulent space above the sheet.

A sheet, through which air or other gas is blown upwardly (whether the sheet is mounted horizontally or in an inclined position) to produce turbulence in the space immediately above the sheet will, for convenience, be hereinafter referred to as a fluidizing sheet.

Preferably the particles of the powder are electrostatically charged by means of a metallic body, which extends close to the said inclinedfluidizing sheet in a position which will not interfere with the passage of powder particles towards the surface or surfaces .to be coated, and to which a highvoltage electrostatic charge is applied.

Conveniently, those particles of the powder, which escape past the lower end of such inclined sheet without being attracted away therefrom to the surface or surfaces to be coated, may be caused to pass down into a powder reservoir, from which the powder particles are lifted by a suitable conveying arrangement to the upper end of the inclined sheet for a further passage down such sheet. Thus, the particles escaping from the lower end of the inclined sheet may be caused to pass into an inclined channel containing a second inclined fluidizing sheet through which air or other gas is blown to produce the desired turbulence to assist the passage of the particles down into the powder reservoir.

The powder reservoir may contain a further fluidizing sheet through which air or other gas is blown to maintain the powder in a state of turbulence above such further sheet in the reservoir. Asuitable conveying arrangement, which may consist of a mechanical conveying device or a pneumaticv system, is then used for conveying powder up from the reservoir into a space, within a chamber above yet a further fluidizing sheet in such chamber through which air or other gas is blown, such chamber being provided with an outlet through which powder is fed to the upper end of the first inclined fluidizing sheet for a further passage down such inclined sheet in readiness to be attracted to the surface or surfaces to be coated. Means may be pro-. vided for controlling the rate of flow of the powder through such chamber outletto the upper end of the first inclined fluidizing sheet.

The invention may be carried into practice in various ways, but the following may be instanced as one convenient practical arrangement of surface-coating apparatus according thereto, in which FIG. 1 illustrates a typical example of a fluidizing sheet, of which use is made inthe apparatus,

. FIGS. 2 and 3 show the main portion of the surfacecoating apparatus in section respectively on the line IIII of FIG. 3 and on the line IIIIII of FIG. 2,

FIGS. 4 and 5 are partial sectional views taken respectively on the lines lVIV and V-V of FIG. 2, and

FIG. 6 is a diagrammatic front view illustrating the use of the apparatus in practice.

In the typical example of fluidizing sheet illustrated in FIG. 1, the sheet A is shown as mounted horizontally. The material of which the sheet is made has sufficient porosity to permit air or other gas to be forced upwardly through it, while preventing the powder particles from passing through the sheet. The sheet may be made of ceramic material or of plastics material or of other materials (for example a fabric which is reinforced or otherwise supported so as to be substantially rigid and to afford agenerally smooth surface along whichthe powder can flow) having the appropriate degree of porosity. The sheet A is a box-like structure A, so that there is a closed space A beneath the sheet intowhich air or other gas is forced through the pipe A so that it will penetrate through the sheet A and produce some degree of turbulence in the space A immediately above the sheet, so that powder flowing over the sheet will be prevented from settling on the uppersurface of the sheet. The walls of the box-like structure A, which may be made for example of polyvinyl chloride, may, wholly or in part, extend above the upper surface of the sheet with or without a top cover, to retain the powder over the sheet as it flows along such upper surface.

Four of such fluidizing sheets are used in the preferred arrangement. The first of these B, mounted horizontally in its box-like structure B, provides above the sheet a compartment B" for supplying powder to the upper-end of the second fluidizing sheet C which is mounted at an angleto the horizontalsufficient to ensure that the powder will flow down over the upper surface of such fluidizing sheet.

On the rear sideof the second fluidizing sheet C (that is the right-hand side as viewed in FIGS. 3 and 4) the space C immediately above the sheet is left open to permit some of the powder particles to be attracted rearwardly away from the space C above the upper surface of the sheet. A metal plate or rod C, for example a ferrite rod, or a flat wire mesh (hereinafter termed the discharge blade is mounted in a generally vertical plane along the rear side of such second fluidizing sheet, but does not project above the upper surface of the sheet. A high voltage charge is applied to such discharge blade, thereby electrostatically charging the powder particles flowing down the second fluidizing sheet C.

At its lower end, the second fluidizing sheet C extends into (or nearly into) the box-like structure D containing thethird fluidizing sheet D, also mounted at an angle to the horizontal sufficient to ensure powder flow down along its upper surface, such inclination however, being opposite to that of the second fluidizing sheet C so that the third fluidizing sheet D is (forthe most part) underneath the second fluidizing sheet C. At such lower end, the space above the third fluidizing sheet D communicates with the space E above the fourth fluidizing sheet E, which is mounted horizontally in a box-like structure E constituting a main powder reservoir.

-Air or other gas is fed through pipes F at high pressure to the closed spaces B C D and E beneath the four fluidizing sheets, so as to be forced through such sheets in the manner described above with reference to FIG. 1 to cause the powder above the sheets to be raised slightly above the upper surfaces of the sheets and thus maintained in a mobile condition in its passage through the apparatus.

Means, such for example as a pneumatic system or (as shown) a' continuously driven mechanical conveyer device G having paddles or buckets G, are provided for conveying powder from the space E above the fourth fluidizing sheet E upwardly into the supply compartment B above the first fluidizing sheet B, in readiness to be fed to the upper end of the second fluidizing sheet C. Means, such for example as a manually adjustable gate H, may be provided, if desired, for controlling the amount of powder delivered through the outlet H from the supply compartment 8'' to the top of the second fluidizing sheet C. While gravity may be relied upon to cause the flow of powder from the supply compartment B to the second fluidizing sheet C, means may be provided, if desired, in the supply compartment for driving the powder from such compartment to such second fluidizing sheet.

Thus, the powder is caused to flow in a continuous cycle, from the space E above the first fluidizing sheet B in the supply compartment down the inclined second and third fluidizing sheets C and D into the main reservoir E, from which it is conveyed back into the space B above the first fluidizing sheet B, fresh powder being introduced into such reservoir 1:. as rquired to make up for the powder attracted rearwardly from the space C above the second fluidizing sheet C and any other powder losses from the apparatus.

The fourth fluidizing sheet and the parts associated therewith are mounted within an outer casing J having an inclined opening J in its rear wall parallel and adjacent to the space C above the second fluidizing sheet C.

It will be appreciated that such fluidizing sheets cause the particles to be freely suspended in the spaces above the sheets, thereby facilitating the movement of the particles and reducing the forces necessary to effect such movements and generally increasing the speed and efficiency of operation of the device.

The metal or other articles K to be coated (usually in the form of flat plates or sheets mounted vertically) are conveyed in turn along a horizontal conveyer track, diagrammatically indicated at K in FIG. 6, extending across the rear of the above described parts outside the casing J. The vertical dimensions of the articles to be coated are such that, in their movement along the horizontal conveyer track K behind the inclined window J, the whole of the surfaces thereof to be coated will pass the space C immediately above the second fluidizing sheet C. Since the powder particles in such space C are electrostatically charged by the discharge blade C, they will be attracted rearwardly away from such space through the window J by the metal or other articles K, whereby all parts of the article surfaces facing the window J will be uniformly coated with the powder which, owing to the electrostatic charge, will firmly adhere to such surfaces, in readiness for curing by heat treatment in the well-known manner to provide a-permanent coating thereon.

It will be appreciated that the foregoing arrangement has been described by way of example only and that the invention may be carried into practice in other ways. Thus, for instance, although the arrangement has been described especially with reference to the coating of flat sheets, it is not limited thereto and can be applied to the coating of surfaces of other shapes. Thus for example a cylindrical surface can be coated, provided that the article bearing such surface is rotated about its own axis as it is moved past the second fluidizing sheet. In the case of articles of more complicated shape, for example having recessed areas, it may be desirable in some instances to supplement the electrostatic coating action by the addition of airjets suitably located behind the discharge blade to assist the powder to penetrate into such recessed areas. Such air jets would not normally be provided, and are only added for special cases. Further, the article or articles to be surface-coated need not be moved horizontally past one side of the inclined sheet, but may be moved along any convenient path or paths such that they will remain close to the turbulent space above the inclined sheet throughout the length of such space. Thus there could be two or more such paths, for example at either or both sides of the turbulent space or above such space.

What I claim as my invention and desire to secure by Letters Patent is:

1. Apparatus for the surface-coating of a metal or other article or articles with powder, comprising in combination an inclined sheet made of material porous to air or other gas but not to the powder particles, means for causing the powder to flow down the inclined sheet, means for blowing air or other gas upwardly through the inclined sheet to produce turbulence in the space immediately above the sheet and thereby to cause the powder particles to hover over the sheet in their downward flow along the sheet, means for electrostatically charging such powder particles, and means for moving the article or articles past the turbulent space immediately above the inclined sheet in a position such that the charged powder particles will be attracted on to the surface or surfaces to be coated, the length and position of the inclined sheet being such that every part of the surface or of each surface to be coated passes closely adjacent to the turbulent space above the sheet.

2. Powder caoting apparatus as claimed in claim 1, in which the said means for electrostatically charging the powder particles comprises a metallic body extending close to the inclined sheet in a position which will not interfere with the passage of the powder particles towards the surface or surfaces to be coated and to which a high voltage electrostatic charge is applied.

3. Apparatus for the surface-coating of a metal or other article or articles with powder, comprising in combination an inclined sheet made of material porous to air or other gas but not to the powder particles, means for causing the powder to flow down the inclined sheet, means for blowing air or other gas upwardly through the inclined sheet to produce turbulence in the space immediately above the sheet and thereby to cause the powder particles to hover over the sheet in their downward flow along the sheet, means for electrostatically charging such powder particles, means for moving the article or articles to be coated past and closely adjacent to the turbulent space immediately above the inclined sheet whereby the charged powder particles will be attracted on to every part of the surface or surfaces to be coated, a powder reservoir, means for causing those particles of the powder which escape past the lower end of the inclined sheet without being attracted away from the turbulent space above the sheet to the surface or surfaces to be coated to pass into the powder reservoir, and means for moving powder from the powder reservoir to the upper end of the inclined sheet for a further passage down the inclined sheet. 7

, 4. Powder coating apparatus as claimed in claim 3, in which the means for passing the powder particles from the inclined sheet to the powder reservoir comprises a second inclined sheet similar to the said inclined sheet, means for mounting the second inclined sheet to extend down from the lower end of the first inclined sheet to the powder reservoir, and means for blowing air or other gas through such second inclined sheet to cause turbulence in the space immediately above it to assist the flow of the powder particles escaping from the lower end of the first inclined sheet to the powder reservoir.

5. Powder coating apparatus as claimed in claim 4, including within the powder reservoir a further sheet similar to the two inclined sheets for receiving in the space immediately above such further sheet the powder from the lower end of the second inclined sheet, and means for blowing air or other gas upwardly through such further sheet to produce turbulence in such space immediately above the sheet.

. 6. Powder coating apparatus as claimed in claim 3, including a powder supply chamber adjacent to the top of the inclined sheet having an outlet through which powder can pass to the upper end of the inclined sheet for flow down such inclined sheet, a further sheet similar to the inclined sheet within such chamber, means for blowing air or other gas upwardly through such further sheet to produce turbulence in the space immediately above such sheet communicating with the said outlet, and conveying means for conveying powder from the powder reservoir into the space in the powder supply chamber above the said further sheet.

7. Powder coating apparatus as claimed in claim 6, including means for controlling the rate of flow of the powder through the outlet from the powder supply chamber to the top of the said inclined sheet.

Claims

3. Apparatus for the surface-coating of a metal or other article or articles with powder, comprising in combination an inclined sheet made of material porous to air or other gas but not to the powder particles, means for causing the powder to flow down the inclined sheet, means for blowing air or other gas upwardly through the inclined sheet to produce turbulence in the space immediately above the sheet and thereby to cause the powder particles to hover over the sheet in their downward flow along the sheet, means for electrostatically charging such powder particles, means for moving the article or articles to be coated past and closely adjacent to the turbulent space immediately above the inclined sheet whereby the charged powder particles will be attracted on to every part of the surface or surfaces to be coated, a powder reservoir, means for causing those particles of the powder which escape past the lower end of the inclined sheet without being attracted away from the turbulent space above the sheet to the surface or surfaces to be coated to pass into the powder reservoir, and means for moving powder from the powder reservoir to the upper end of the inclined sheet for a further passage down the inclined sheet.

4. Powder coating apparatus as claimed in claim 3, in which the means for passing the powder particles from the inclined sheet to the powder reservoir comprises a second inclined sheet similar to the said inclined sheet, means for mounting the second inclined sheet to extend down from the lower end of the first inclined sheet to the powder reservoir, and means for blowing air or other gas through such second inclined sheet to cause turbulence in the space immediately above it to assist the flow of the powder particles escaping from the lower end of the first inclined sheet to the powder reservoir.

6. Powder coating apparatus as claimed in claim 3, including a powder supply chamber adjacent to the top of the inclined sheet having an outlet through which powder can pass to the upper end of the inclined sheet for flow down such inclined sheet, a further sheet similar to the inclined sheet within such chamber, means for blowing air or other gas upwardly through such further sheet to produce turbulence in the space immediately above such sheet communicating with the said outlet, and conveyiNg means for conveying powder from the powder reservoir into the space in the powder supply chamber above the said further sheet.