US2741218A - Electrostatic coating apparatus - Google Patents

Description

April 10, 1956 E. P. MILLER 2,741,218

ELECTROSTATIC COATING APPARATUS Filed Nov. 10 1950 2 Sheets-Sheet l 28 6 25 /-28 I2 lO I I i I Y I II I 1 g i; 1

i :1 H: 1 I n 1 1' 13 l .I|; I all l l I I Fig. 3

IN VEN TOR.

EMF/P) E M/LLER April 10, 1956 E. P. MILLER -ELECTROSTATIC COATING APPARATUS 2 Sheets-Sheet 2 Filed NOV. 10, 1950 IN VEN TOR.

EME/i) P. MILLER Fig. 6

ATTORNEY ELECTROSTATIC CGA'IING APPARATUS Emery P. Miller, Indianapolis, Ind, assignor to Ranshurg Electra-Coating Corp, Indianapolis, Ind, a corporation of Indiana Application November 18, 1959, Serial No. 194,915

3 Claims. (Cl. 118-51) This invention relates to improvements in methods and apparatus for electrostatically coating articles of manufacture.

One feature of the invention is directed to a coating method in which a series of articles is conveyed along a predetermined path in spaced relation to and between two electrodes which are held at a high electrical potential relative to the articles to ionize and precipitate upon the articles particled coating material from a source directed approximately normal to said path at the position of closest approach of the path to said source and past and along side of one of said electrodes toward said articles. The articles are thus presented directly to the spray to collect by mechanical impingement a portion of the coating material and are so positioned with respect to the electrodes as to collect by electrical precipitation rebounding particles escaping from the mechanical impingement process and other particles which cross the path of travel of the articles. two coating forces, high coating eficiencies are obtainable.

Another feature of the invention resides in spacing the articles along the path in such a manner that coating material particles at the edge or fringe of the spray pattern will pass between the articles to that side of the article path which is opposite the spray source. There they will be reversed by the electrostatic action of an electrode on that side of the path to be precipitated upon these surfaces of the articles which are not in the direct impingement path' of the spray.

A further feature resides in having the electrode adjacent the spray source composed of two parts, one on either side of said spray, so that the spray in moving toward the article passes between and comes under the charging influence of one or the other of these parts.

A similar two-part electrode can be placed on the side of the article path remote from the spray source to influence particles moving through the spaces between articles.

The invention further contemplates that the spray source can be reciprocated or oscillated about a mean position so that the issued coating material will impinge directly upon the article as it moves along its predetermined path. in addition it contemplates that the.electrode might also be similarly oscillated or reciprocated in coordination with the spray source.

In addition, another feature of the invention resides in having the conveyor, which carries the articles, make two traversals between the charged electrodes 'soj-that coating material directed past one of the electrodes will? have the opportunity either of impinging upon articles moving along the first path or passing between these It also contemplates plac'mg a third electrode intermediate the two paths of conveyor movement.

By thus combining the which they are supported from the conveyor. The

atent i) 2,741,213 Patented Apr. 10, 1956 ice In all the above features it is contemplated that the coating material will be directed toward the article path in a direction which is approximately normal to the path. It is further contemplated that this direction will be gen erally normal at the position of closest approach of the path to the source of the spray of coating material. In this way the material will be initially applied to the article both by mechanical and electrical forces as soon as possible after leaving the atomizer and the tendency will be to have a full wet coat of material built up on the article promptly. Such a full wet coatwill absorb into its surface, without harmful results as to appearance, that material which is electrically precipitated onto the article at the opposite side of the article path and which is drier because it has been in the air as atomized particles for a longer time.

This quick formation of a wet coat is advantageous over normal electrostatic methods since it permits the coating material to be formulated with faster solvents and thus overall drying requirements are reduced.

wherein the invention contemplates that the spray source directs coating material toward the articles over a path which is along side of but still in particle-charging relation to the electrode, the electrode will not be' exposed to the direct blast of the wet spray particles from the source and hence will not accumulate by direct impingement coating material which later under the influence of the field will string off and be carried to the parts asobjectionable slugs. This is highly important in any operation that is intended for continual use in a production manner.

These and other features of the invention will be made apparent from the following specifications and claims.

in the accompanying drawings:

Fig. Us a plan view of one embodiment of the invention as used for finishing index tabs and is taken along line "1-1 of Fig. 2,

Fig. 2 is a side elevation of the apparatus of Fig. 1,

Fig. 3 is an'isometric view of the rack used to hold the tabs during the painting operation,

Fig. 4 is a plan view of another embodiment of the invention in which the conveyor makes two passes through the field,

Fig. 5 is a partial elevation taken along line 5-5 of Fig. 4,

Fig. 6 is a front view of apparatus embodying another modification of the invention as incorporated with an overhead conveyor, and I Fig- 7 is'a plan view of a modification .of the invenn'cmtn which the spray gun is moved simultaneously with one of the electrodes.

holding the articles 16 to be coated. These framesas shown in detail "in Fig. 3 have a series of wires 17 stretched across them and have two attachment members 18 by articles 16, here shown as metal index card tabs, are supported saddle-wise on these wires, one next to another, on-

all wires. The frame can be filled or not as desired. These frames are supported on the conveyor and carried by it't hrough the spray booth in the direction of the arrows 19 in Fig. 1. conveyor and spaced from 'it, is located an electrode .20

comprised of conducting frame 21 which serves to support In the booth, on one side of the.

. back side.

3 trodes, by conductors 24 and 25, are electrically connected to each other and to the one terminal of a high voltage source 26 whose other terminal is grounded as at 27.

' Since the conveyor, the carrying frames, and the articles source of high voltage is energized. The gradient of this field is high adjacent the electrodes 20 and 23 because of the nature of the ionizing elements and thus any particles in their vicinity will become charged and be repelled by the field'toward the articles which are connected to the other terminal.

Coating material in finely atomized form is introduced into this field from outside by an atomizing device 29 positioned to direct the spray past and adjacent electrode 20 into the field and generally normal to the path of travel of the conveyor at the position of closest approach of the articles to the gun. As the articles 16 are carried through the spray booth their front side 30 is thus subject to and receives coating material from the direct mechanical impingement action of the spray as well as from the precipitating action of the field. They also receive on theirfront sides material which has become charged by passing the front electrode but which has escaped being attached to the article because of air bounce or turbulence. Such particles, after bouncing off the article, are reversed again and urged toward the articles by the action ofthe field. Still other particles from the atomizer 29 will pass between the articles on the frame and enter the field between the back side of the articles and the second electrode 23. Under the action of this field most of these particles will have their direction reversed and will be returned to the articles to supply the coating on their This phenomenon of material being redirected to coat surfaces not in the direct impingement pattern of the atomizer is referred to as wrap around and accounts in a large measure for the added eificiencies'obtained by the method of this invention. Lateral surfaces, such as the sheared edges of the tabs shown herein, are also coated V by this action. Any coating material particles escaping these multiple forces of precipitation are carried with the evaporating solvent fumes into the plenum 12 by the exhaust.

This method is particularly suited for finishing this article since it is desirable that the inside surface of the back leg of the tab immediately behind the tab window 31 be coated to present a good appearance when a legend card is not in the tab. The direct action of the atomizer acting on the front of the tab carries coating material to this area through the window opening while the overspray coats the remaining portions of the article. One atomizing unit thus suifices to do the complete operation. By mechanical spraying alone, three atomizers are needed for this same coating operation.

I If it is desired to increase the area of the support frame and thus increase the number of articles which can be sprayed per foot of conveyor, the atomizer can be moved up and down in a plane parallel to the plane of the article support frame and thus distribute its material over a larger area than is permitted by simple divergence of the spray pattern. The spray can also be initiated and stopped in relation to the position of the article support frame on'the conveyor and thus material will be saved which would be, sprayed into the space between frames if the atomizer was left on continuously.

Another modification of the invention is shown in plan view in Fig. 4 and further detailed 'in Fig. which is a partial elevation along lines 5-5 of Fig. 4. In this modification a spray booth 100 is arranged with an open face 101 opposite an exhaust plenum 102. A floor supported conveyor 103 enters one side of this booth at 104, travels across its width on path 105, doubles back and returns essentially parallel to the first path on path 106 to leave the same side of the spray booth at 107. The articles 108 are supported on this conveyor on spindles 109 which rotate with respect to the conveyor chain 110 by virtue of the sprocket 111 coming into contact with rack 112. The parts are thus rotated as they pass over paths 105 and 106 within the booth.

Electrodes 113 in the form of extended fine wires are located at one side of path 105 and supported by insulator 114. In this modification additional electrodes .115. and 116 are located between the paths 105 and 106 and on the opposite side of 106 respectively. These electrodes are connected together by means not shown and are connected to the high voltage supply 117 through a suitable conductor 118. In this manner an electrostatic field is established between the electrodes and the immediately adjacent articles on the conveyor. This field has its highest gradient adjacent the electrodes 113, and 116 and in these regions a concentration of charged atmospheric particles exists.

An atomizing device 119 is positioned on a mounting 120 and directed to introduce its spray in a direction generally normal to the path of article travel. The spray also is introduced generally between two electrode elements 113 from a position which is on the opposite side of these elements from the articles. To add to the coating received by these larger discrete articles, the gun in this modification is arranged to oscillate on the support 120. A tube 121, bearinged for rotation on rod 120, has the gun support 122 attached to its one end and a rod 123 attached to its other. This assembly is biased by the action of spring 124 toward normally occupying a position in which rod 123 is against stop 125. Since rod 123 extends forward across the conveyor when it is in this normal position, motion of the conveyor brings one of the spindles 1&9 into contact with this arm when the spray gun is directed for direct'spray impingement upon the article'on the contacting spindle. As the conveyor moves further the rod 123 is carried along with the contacting spindle. At a predetermined advanced position along the conveyor, depending upon the length of the rod, the rod will slip out of contact with the spindle and return quickly to a position where it is resting against stop 125. Since the spray gun follows the motion of rod 123, it will likewise follow each article as it moves past the electrodes. A pair of switches 126 and 127 are arranged to be. activated by the spindles passing on the conveyor and are connected with the gun operating mechanism (not shown) in such a way that the spray will be turned on while the gun is moved forward with the article and is off when the gun is returning to its normal position. With this arrangement full advantage is taken of the mechanical action of the spray in coating the object while maximum electrical precipitation forces are exerted upon coating material particles which escape direct impingemerit upon articles passing along path 106. Such particles will either be applied to articles on path 106 by the field between the articles and electrode 115 or will impinge' directly upon or be electrically precipitated upon articles on path 105. If they escape both these actions they may be captured by the field between electrode 116 andarticles on path 105. In case some material escapes deposition it will be carried away with the evaporating solvent fumes by the exhaust created in plenum 102. a

Fig. 6 illustrates another modification of the inven- 7 tion. In this drawing, which is a front view of the apparatus, a conveyor 200 carries articles 201 into and through a spray booth 202. The front of the booth is open and at its rear there is an exhaust plenum (not shown). The

conveyor enters the side of the booth, turns and travels away from exhaust plenum toward the front of the booth. Articles 201, indicated here as external jackets for water heaters, are supported from the conveyor by hanger 203 v and are carried by it through the booth.

In thebooth, on both sides of the conveyor, there is an oscillating mechanism 204 which carries a spray gun 205 and an electrode element 206 in spaced relation to the article surface. The electrode is supported by insulator 207 which serves to isolate it from the oscillating mechanism so it can be connected to one terminal of a high voltage source 208 by spring connection 209 and conductor 210. By means of this source the electrode is maintained at a high electrical potential with respect to the article which is grounded as at 211 and a field therefore exists between them which has a gradient capable of charging particles adjacent the electrode.

A spray of coating material is introduced past the electrodes by the spray gun 205 and travels essentially normal to the article. Being charged by proximity to the electrode, it is then put onto the article surface by the combined mechanical action of the spray and the electrodepositing action of the electrostatic field.

To obtain distribution over the article surface, the oscillator 204 is caused to move the electrode and spray gun up and down in a vertical plane parallel to the article surface between the extreme positions of the gun and electrode shown in dotted lines and as indicated by the arrows 212.

With this arrangement a single gun and electrode assembly on each side of an article can be used to simultaneously and efiiciently coat opposite sides of single articles. If the object is cylindrical it can be rotated while passing the gun stations to have its entire surface coated or, if it is rectangular, it can be indexed and carried past another similar station to have its other twosides finished. The exhaust air moving parallel to the path of conveyor travel serves to carry away evaporating solvent fumes and any material which might escape deposition.

Fig. 7 illustrates in plan view another modification in which articles 300 move along a conveyor, illustrated by line 301, past and between fixed electrodes 302 and movable electrode 303. A spray gun 304, movable with and mounted on the same support mechanism 305 as are electrodes 303, is arranged to be turned ofi and on by the action of switches 306 and 307. It is aimed to direct a spray of coating material between the two electrodes 303 toward and normal to the path of travel of articles 300.

The electrodes 303 are isolated from the support mechanism 305 by insulators 308 and thus can be connected to a high voltage source 309 as by conductor 310. Electrodes 302 are connected to the same terminal of the voltage source by conductor 311. The other terminal of the source is grounded as at 312. The conveyor and thus the articles 300 are grounded as at 313. An electrostatic field capable of charging and precipitating particles of material introduced into it is thus established between the electrodes 303 and 302 and the articles 300.

In operation switch 307 is tripped by an object supporting spindle on the conveyor as the conveyor moves in the direction of arrow 314 and turns on the spray from gun 304 when the gun is aimed directly at a preceding article on the conveyor. By an arrangement not shown, support mechanism 305 is arranged to move parallel to and in step, with conveyor 301 when switch 307 is tripped. I-t continues this motion and the gun continues to spray until switch 306 is activated, at which time the gun is turned off and the support 305 returns rapidly to its original position. The cycle is repeated when switch 307 is again tripped by the following spindle. By this arrangement the spray gun and the precipitating electrode 303 are moved with the conveyor from the position shown in full lines to the position shown in dotted lines While the spray is activated and directed for normal impingement upon an article and they return to their original position past the spaces between the articles with the spray turned ofi.

Whereas the electrodes are all shown as ionizing in character, it is understood that the electrodes which are located on that side of the conveyor path opposite to the spray gun may be non-ionizing in character such as an extended plate.

From the above described modifications it will be evident that the invention allows added efiiciencies of coating application to be obtained by combining in a parallel manner the mechanical action of a spray jet and the precipitating action of an electrostatic field. It is also apparent that surfaces facing the atomizer, as well as those not facing it, can be coated simultaneously using this method.

What is claimed is:

1. Apparatus for coating a plurality of articles, comprising means for moving the articles successively and in spaced relation over a predetermined path making two passes through a coating zone, a discharge electrode at the coating zone spaced transversely from one of said passes and on the opposite side thereof from the other pass, a spray means disposed on the opposite side of said electrode from said passes and arranged to discharge a spray of coating-material particles past and in proximity to said electrode and thence successively across said two path-passes, and a high voltage source connected to said electrode and said articles to establish therebetween an electrostatic field for electrically charging the sprayed particles of coating material and electrostatically depositing them on the articles respectively traversing said two passes.

2. Apparatus as set forth in claim 1 with the addition of a second electrode positioned at said coating zone on the opposite side of both said passes from the first mentioned electrode and electrically connected to it to reverse and project toward said passes the coating-material particles initially projected across such passes between articles respectively traversing them.

3. Apparatus as set forth in claim 2 with the addition of a third electrode positioned in the coating zone between said two path-passes and electrically connected to the other two electrodes.

References (Iited in the file of this patent UNITED STATES PATENTS 1,124,858 Caruso Ian. 12, 1915 2,097,233 Meston Oct. 26, 1937 2,221,338 Wintermute Nov. 12, 1940 2,334,648 Ransburg et a1 Nov. 16, 1943 2,373,604 Schweitzer Apr. 10, 1945 2,442,986 Ransburg June 8, 1948 2,463,422 Ransburg et al. Mar. 1, 1949 2,509,448 Ransburg May 30, 1950 FOREIGN PATENTS 591,474 Great Britain of 1947

Claims (1)

1. APPARATUS FOR COATING A PLURALITY OF ARTICLES, COMPRISING MEANS FOR MOVING THE ARTICLES SUCCESSIVELY AND IN SPACED RELATION OVER A PREDETERMINED PATH MAKING TWO PASSES THROUGH A COATING ZONE, A DISCHARGE ELECTRODE AT THE COATING ZONE SPACED TRANSVERSELY FROM ONE OF SAID PASSES AND ON THE OPPOSITE SIDE THEREOF FROM THE OTHER PASS, A SPRAY MEANS DISPOSED ON THE OPPOSITE SIDE OF SAID ELECTRODE FROM SAID PASSES AND ARRANGED TO DISCHARGE A SPRAY OF COATING-MATERIAL PARTICLES PAST AND IN PROXIMITY TO SAID ELECTRODE AND THENCE SUCCESSIVELY ACROSS SAID TWO PATH-PASSES, A HIGH VOLTAGE SOURCE CONNECTED TO SAID ELECTRODE AND SAID ARTICLES TO ESTABLISH THEREBETWEEN AN ELECTROSTATIC FIELD FOR ELECTRICALLY CHARGING THE SPRAYED PARTICLES OF COATING MATERIAL AND ELECTROSTATICALLT DEPOSITING THEM ON THE ARTICLES RESPECTIVELY TRAVERSING SAID TWO PASSES.

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