US2428991A - Apparatus for spray coating articles - Google Patents

Description

Oct. 14, 1947. H. P. RANSBURG 2,428,991

APPARATUS FOR SPRAY COATING ARTICLES Filed Jan. 22, 1944 new a 14 19 .1

* maa arus FOR smut COATING narrows I Haroldjl'. Ransburg, Indianapolis, Ind., assignor to Harper J. Ransbur Ind., a copartnersl ip g Company, Indianapolis,

Application January-22, 1944, Serial No. 519,332

-7 Claims. (01. 91-18) v This invention relates to the electrostatic depo sition of coating materials, and more particularly to such deposition of coating materials upon articles which have a non-planar surface to be coated and which cannot readily be rotated while the coating material is being applied to them.

In electrostatic coating methods, an electrostatic field is created over the surface of the article to' be coated and finely divided coating material introduced into the field is caused to move to and be deposited upon the article by action of the field. When the article to be coated possesses a non-planar surface to be coated, dimculty is sometimes encountered in securing a coating of satisfactory uniformity. In some cases an improvement in the distribution of coating material over a non-planar surface of the article may be obtained'by rotatingthe article relative to the field as the coating is being applied: but

many articles having non-planar surfaces'to be coated are so proportioned that they cannot readily be rotated. Non-uniform deposition of coating material is generally undesiredand un economical; for in order to obtain an adequate coating of some portions of the article more coating material than would otherwisebe required must be deposited upon other portions.-

It is an object of'this invention to improve the I distribution of coating material over non-planar surfaces which are to be coated electrostatically and, in so doing, to conserve coating material. Another object of my invention is to improve'the distribution of coating material upon. articles which are moved progressively through an electrostatic field as the coating material is being applied. A further object of my invention is to obtain a satisfactory distribution of electrostatically deposited coating material without the necessity for rotating the articles as they are In carrying out my invention, I create the desired electrostatic field with the aid of an ionizing, or discharge, electrode which is especially shaped with regard to the non-planar surface to be coated; and during the coating operation, the 45 article (is supported with-such non-planar face presented toward the electrode. Where the coating operation is a continuous one in which a v plurality of articles to be coated are carried successively through the coating 'zone over a predetermined path, the articles are arranged so that ,their non-planar surfaces will be presented laterally of such path and the electrode is so disposed that such surfaces will pass opposite to it. Where the article to be coated is of material not election of deposited coating material.

I the discharge electrode which is specially shaped,

longitudinally extending wires I1. 0 through said supports or otherwise are connected to one terminal of electrical source of high voltage trical conducting in character and where, there-- fore, the surface will be disposed between two oppositely charged electrodes, either electrode may .be especially-shaped to control the distribu- Where it is I prefer. to construct it wlth a plurality of ionizing elements, conveniently fine wires; extending generally parallel to the path of article travel at the edges of a polyhedron.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims:

Fig. 1 is a perspective view showing the inven- Ltion as applied to one'form ,of article to be coated.

Fig. 2 is a perspective view showing the invention as applied to articles of different contour.

Fig. 3 is a perspective view illustrating the invention as applied to :articles having square corners.

Fig. 4 is a sectional view through a collecting electrode comprising a contoured surfaced article of non-conducting material and. a support therefor. V

5 There is shown in Fig. .1 an apparatus for coating cylindrical articles or articles of such general contopr as indicated at In. Said articles are conveyed through a spraying zone into which a coat- ,ing is sprayed from the spray guns indicated at my. They are carried through said zone by the hangers l2 drawnby the chain, l3 along'a conveyor track'l4. I

v Partially surrounding the line of travel of the articles, which in this illustration comprise mufflers for internal combustion engines, there is a discharge electrode comprising circular end frame supports l5 mounted upon insulating legs l6. Between the supports l5 there is a plurality of Said wires as indicated at I8. The other terminal of said source is grounded as is the conveyor track and articles as indicated at I9.

The end supports l5 of the discharge electrode 7 havetheir upper portions open. to leave a gap or opening through which the carriers may pass for conveying the articles axially thereof. Since the articles are grounded and the discharge electrode wires I! are maintained by the high voltage source at 1a high potential difference relative thereto, an electrostatic field'is induced therebetween. The'spacing of the discharge electrode with respect to the surface of-the articles is such as to maintain the most efiective electrostatic The coating material is directed in the form of a low velocity spray into the field induced between the electrode and article so that the spray particles become ionized and are electrically attracted to the article for deposition thereon.

In' a modification illustrated in Fig. 2 there is provided a belt type of conveyor H3 upon which curved plates H are carried through the electrostatic field in the direction indicated by the arrow. Wherein it is desired, for example, to coat the concave surface of the plates, the spray nozzles III are set up to project the coated material into the field toward such surface. maintaining the electrostatic force for the equal distribution of the spray coating within the curved side walls of the article, a discharge electrode I I1 is carried between curved supporting brackets H suspended from a suitable support by the insulating rods 6. The electrostatic field as above described is induced by reason of the conveyor-and' article as well as one terminal of a source of electric high'voltage beinggrounded as indicated at l9, while the electrode 1 I1 is connected to the other terminal of said source.

In the modified form of the invention illustrated in Fig. 3 an article 2! is of rectangular form with its surfaces to be coated extending at right angles. It may be carried through the spraying zone by the supporting fixtures 2l2 extending upwardly from the conveyor belt 2I3. With this form of article the discharge electrode 2 I I is mounted to extend longitudinally and about the article throughout the length of the spraying zone but spaced equally from the central portions of the several side walls. For this purpose the electrode is supported at each end upon-a frame 2|5 carried by insulating supports 2I6. However, in such a formed article having sharp angular bends or relatively sharp edges, there may be a. tendency for the coating material to be deposited in excess quantityon and near such bends or edges. To correct this, the electrode is so arranged as to be spaced from thesharp angular bends of the article at a greater distance than from the wall surfaces. This is illustrated in Fig. 3 wherein end frames 2l5 of the electrode are curved outwardly away from the bends of the article so as to carry the electrode at a greater distance therefrom than from the side wall surfaces.

- A further modification of the invention is disclosed in Fig. 4 wherein there is illustrated an article M0 having a contoured inner and outer surface, the outer contoured surface to be coated.

Said article in itself may be of poor conducting material and therefore mainly depends upon its For . 4 which overlie sections of relatively greater wallthickness, can be increased by providing the support 2 with generally corresponding protruding portions to decrease the distance between the protruding portion of the article surface and that portion of the conducting support 2 which lies opposite such protruding surface portion.

Whereas the invention has been illustrated and described 'herein by its application to certain specific forms of articles, it is understood, of course, that several nfodiflcations thereof are merely representative of many possible forms in which similar arrangements of an electrode may 1 be applicable, but wherein the electrode is so rial.

conducting support M2 for the establishment of the electrostatic field. .Said support may be mounted on a conveyor and grounded as above described. Therefore, the collecting electrode in this arrangement would comprise the article M0 in association with the support M2. 'In such an arrangement, the deposition of coating material on the outer surface of the article will depend tions of the article-surface, or upon surfaces conformed to the particular shape or form of the surface to be coated as to cause the coating material to be deposited with a satisfactory degree of uniformity.

It should be understood, however, that the conformation of the supporting conductor or of the charging electrode to the surface to be coated is not of a physical, but rather is of an electrical conformity. Thus said conductor may be distorted relative to the surface to be coated where more or less exact conformity would result in an undesirably uneven distribution of coating mate- Whatever arrangement is employed, the ionizing means, which charges the coating-material particles and which in'the preferred form of the invention embodies relatively fine wires, are angularly displaced about the path of article travel so that the lines of force of the electrostatic field, in any plane normal to the path of article travel, will converge toward the corners of a polyhedron. Y

The invention claimed is: r

. 1. Apparatus for coating an article having a contoured surface, including a support for such article, said article and support. therefor constituting a collecting electrode, a discharge electrode shaped to conform to the contour of the surface to be coated, means for supporting said electrode in substantially uniform spaced relation thereto, a source of high voltage electrically connected to said respective electrodes for providing an electrostatic field therebetween, and means for introducing finely divided coating material into said field, said discharge electrode being adapted by its conformity to said contoured surface to induce a substantially constant field strength for imposing uniform electrical depositing forces on said material,

2. Apparatus for coating a non-conducting article having a contoured surface, including an electrical conducting support for such article, said article and support constituting a collecting electrode, said support having a contoured surface similar to the surface to be coated and spaced electrically substantially equidistant therefrom, a discharge electrode mounted in spaced relation and arranged to conform to said contoured surface but located on the opposite side of said surface from the contoured portion of said support, a source of high voltage electrically connected to said electrodes for providing an electrostatic field therebetween and means for introducing finely divided coating material into said field, said conforming electrodes being adapted to induce a substantially constant field strengthfor imposing uniform electrical depositing forces ;on said material over the contoured surface of said article.

3. Apparatus for coating an article having a contoured surface, said article constituting a collecting electrode, a discharge electrode shaped to 'tion to substantially conform to the contour of the surface to be coated and substantially co-extensive therewith, means for supporting said discharge electrode in substantially uniform spaced relasaid contoured surface, a source of high voltage electrically connected to said respective. electrodes for providing an electrostatic field t erebetween, and means for introducing finely divided coating material into said field, said discharge electrode being adapted by its conformity to said contoured surface to induce asubstantially constant field strength for imposing uniform electrical depositing forces on said mate.- rial.

. 4. An electrostatic coating apparatus having in combination, a conveyor for moving discrete articles in a predetermined path, an electrode em ying a plurality of ionizing means disposed in general conformation to surface portions of the article presented laterally of the path of article travel, said ionizing means also being dis- 'tributed in at least three of the lateral faces of a polyhedron extending parallel to the path of travel of said articles, and means for introducing a dispersion of material between said articles and ionizing means.

5. The invention set forth in claim 4 with the addition that each of said ionizing means extends generally parallel to said path of article-travel.

6. 'An apparatus comprising means for moving a cylindrical object along a path parallel to its axis, an annular series of ionizing means angularly spaced about said axis and extending longitudinally thereof, and means for introducing a dispersion of material between said object and ionizing means.

7. An apparatus comprising means for supporting a trough shaped object and moving said object longitudinally, a trough shaped electrode embodying a plurality of ionizing means arranged in a polyhedron about said frameand extending longitudinally of said object, and means for introducing a dispersion of material between said object and ionizing means.

HAROLD P. RANSBURG.

aaranences 0mm The following references are of record in the file of this patent:

UNITED STATES PATENTS

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