US2550657A - Electrostatic coating method and apparatus - Google Patents

Description

April 24 1951 H. P. RANSBURG 225505657 ELEcTRosTATc COATING METHOD AND APPARATUS y Filed Dec. 28, 1945 i sheets-sheet;

April 24, 1951 H. P. RANSBURG 2,550,657

ELEcTRosTATc coATING METHOD AND APPARATUS Filed Dc. 2a, 1945 2 sheets-sheet 2 INVENTOR. HAROLD 10. R/I/VU/QG Patented Apr. 24, 1951 ELECTRSTAJTIC COTING METHGD AND APPARATUS Harold Pi Ransburg,

by direct and mesne as Electro-Coating Corp., corporation of Indiana Application December 28, 1945, Serial No. 637,692

. 7 Claims. 1

"This invention relates to the electrostatic coating of articles, and relates in particular to the application of a iinish coating to an article in an electrostatic field, l. Y y

Part of the disclosure set forth hereafter,

which has not been claimed herein, is the sub- -ject of a patent application of mine, Serial No.

(Cl. Hdl- 93) lll air stream against a stream of the liquid to break up or atomize the liquid stream. When employing such an atomizing apparatus in connection with coating in an electrostatic iield, complete depositing of all the atomized liquid carried by the stream is rendered dificult, in part due to the turbulence or swirling which occurs at the extremities of the stream, which tends to carry the particles out of the influence of the electrostatic iield, or interferes with the desired disposition of the particles in the neld. A reduction in air pressure employed in atomizing the liquid necessitates a reduction in liquid being atomized, so vthat adequate coverage cannot be obtained in the same time interval, and in some instances adequate coverage cannot be obtained on all parts Without excessive coating on other parts which results in a run or sag of the coat.

It is an object of the present invention to provide an electrostatic coating process which effects eicient utilization of the coating material.

Another `object is the electrostatic coating of a series 01E-articles which are maintained in a xed position relative to the path of travel thereof. i

A further object is the provision of an electrostatic coating process which results in depositing a coat of improved uniformity of masking quality. Y

A further object is the electrostatic coating of a series of articles in a manner to control the amount of coating material vdeposited on various surfaces of the article.

A further object is the sprayingr of coating material uponan article in a manner to control the 4amount of coating material electrostatically deposited on those surfaces of the article which are not in the direct path of the spray jet.

In accordance with one feature of the kpresent invention, an object to be coated is moved Indianapolis, Ind., assignor, signments, to Ransburg Indianapolis, Ind., a

through Aan electrostatic depositing zone and there is successively applied thereto a plurality of nonintermingled streams of nely divided coating material, preferably at such time intervals that there is formed a single blended layer of coating material thereon. By suitably ar.- ranging the direction of the streams or sprays of coating material at different electrostatic coating zones, one area of the article initially receives a light deposit or dust coat in the first treatment and a heavy deposit in the subsequent treatment, and areas which initially receive a heavy deposit in the rst treatment receive a light depositin the subsequent treatment with the result that all areas become covered by a coat of uniform hiding quality. ln the absence of an electrostatic field, other operating conditions remaining the same,V it would not be possible-to obtain a preliminary light ancillary deposit on an area followed by a heavier deposit on the same areas from a Acommon stream such as is obtained by the present invention.

According to another feature of the invention in the case of an article having areas to be coated which mutually bar each other to direct impingement of the particle stream, a plurality of articles are positioned in an ionizing electrostatic ieldto provide a relatively Weak electrostatic eld between adjacent articles while the articles are moving in a predetermined path through the electrostatic coating zone, and a stream of finely divided material is directed toward one barrier area, subtending area or intercepting surface which results in a relatively heavy deposit of material on the barrier area. In this `case the spray is directed so that during part of the time some of the particles will pass in a relatively straight path through the region or space between the articles where a relatively Weak iield exists andV will enter the strong ionizing and precipitating region on the opposite side and will bedeposited on the protected areas on that side of the respective articles. This results in the deposit of a relatively. heavy coat on the barrier 'area of the articles opposite the spray, and a relatively light coat on protected areas of the articles.

In those cases Where a uniform coating over the article is desired a second stream of .nely

vdivided material is directed toward the lightly 'coated area, at another station along the, path of travel of thev article removed from the nrst 3 posit of material while some particles pass in a relatively straight path through the region or space between the articles where a relatively weak field exists and will enter the strong ionizing andprecipitating region on the. oppositeside and will be deposited on that side. is that each barrier and protected area receives two or more deposits at such time interval that they are blended into a unitary heavy coat so that the article becomes coated overall by-'a coat of substantially uniform hiding quality.

In practice the invention may be carriedoutby providing two jets of finely dividedfliquid' material at points spaced along the path of movement of an article, each of the jets possessing a component of velocity toward saidpath anda component of velocity parallel to said path, the latter velocity components of the two streams having opposite directions relative to each other and maintaining an electrostaticV eld froma of'reduced strength therebetween, and streams of nelydivided liquid material are directed'from oppositesides ofthe path of 'movement to enter thespaces betweenV the articles .at-spaced stations sc that at each station, some of the; material passes through and isv deposited won those surfaces of the article which are not kin the direct pathiof the spray streams in addition to the deposits: on those-'areas directly in the path' of said streams.

The relation of the thickness of deposit in the areas: of Aheavy deposit to that in the lightly coated areas, may be cimtrolledl under given particle-,stream conditions, by the positioning of the article in the electrostatic field, by the posi-l tioning of the spray gun or other'device ern- 'ployed by the spacing between the spray guns, by Aadjusting cf fluid deliveryl of the spray guns and by other factors. Thus; for'example, where the article to be coated presentsva numberof pairs of mutualbarrier areas, it maybe possible by selection of one pair of mutual barrierareas to receive the direct'V stream of particles, to provide su ciently heavy deposits onall protected areas from the stream of particles that pass throughthe weak iieldfso that only twoy spray stationsare necessary to adequately coat the article; Where the two spray'stations employ streams direct-edl toward` each other, they are `p ositionedso as to avoid mutual interference .and the ,consequent billowing, and` by precipitating'the coating particles from the respective streams, the electrostaticv field obviates, interference-of v'the paint bearingrstreams. Fixed or movableispray guns may beemployed at the spray stations, as desired, thek use-of a; movablegun ineffect being to increase the intercepting area ofthe article being coated.

The invention may be practiced with .or without provision of an air exhaust for the carrier air, depending on the conditions. of'operation. Where an air exhaust isemployed, the-location ,of the exhaust port is preferably adjacent the eX- tremity of `one or more of the streams of coating material.Y

4 Theinventionrwill,bedescribedlin greater detail in connection with the accompanying draw- The result" ings wherein are illustrated preferred embodiments of the invention by way of example and wherein:

Figure l is a partly diagrammatic sectional top view cfa preferred einbodimentbf the invention,

Figure 2is a side view ofFigure l', parts being in section,

Figure 3 is a side view of an article on an enlarged scale,

Figure 4 is a partly diagrammatic view on a distorted scale explaining the invention and showing a top View of articles to be coated, and

Figurezf is a. diagrammatic sectional top view of 'a modification.

Referring to the drawing in Figures 1 and 2 there is diagrammatically shown a spray booth I constructed of suitable material and having entrance and exit sections 2 and 3 through which passes a conveyor which is diagrammatically illustrated at il.' Apairof electrodeframesaand S, are spaced on oppositesidesof the-conveyor.

path atY the entrance; end. Each .frameprefierably carries a plurality ofsuitable'-ionizingelece trodes, suchaslflne wiresfl givinga corona-discharge-when connected: tov aY suitable -source, of highl potentialA and which`V serve asrsourcesof ionization. A similar pair ofelectrodeframesf'tl and 9 carrying suitable ionizingelectrodesfi'.'are positioned at the exit endS on opposite sides' of the conveyor. The frames, 6, 8i and Slare` connected preferably by lead Wires- 'and 9( to;the same source of high potential.' If` desired the frames 5, 8 and 9 maybe unitedV into azpair of frames' extending along Ythe conveyor.

The objects to be coated, shown as automobile window frames or garnish mouldingsJ (Figs, 2 and.3) have vertical portions Il and |2and end portions I3 and I4 surrounding anaperture-IS which has a large area relative to the area of the surrounding frame portions. The mouldingsgare supported in a column from` the conveyor by suitable spring hooks YI 'l (Fig. 2,) engaging-.the inturned flanges or beadsl I8 (Fi'g; 4), eachvframe being maintained inclined with respect'to'itszpath 2 of travel through the apparatus and'overlapping the adjacent frames to form a' columnof parallel members. The preferred axisof inclination to the pathgof travel is about 45; The spacing of the frames` along the conveyor preferablyis such thatonly a weak` electrostatic fieldbetween the framesis provided, and in the embodimentillustrated this-space i9 Yis less than the'width of a frame:

A spray gun v2! of `any suitable type is located at the ventrance end of the conveyor,A and is positioned to direct axdiverging stream of finely dividedparticles preferably. air atomized and" suspendedin acarrier air streaml at the-window frames in the electrostatic field between the elec.;- trodeframes'i andl; Anynumber of spray guns 2| may be employed, four'ibeinggshown (Fi'g; 2), andthe axisiof the spray' gun 2|v (Fig; 4); may be substantially parallel to the inclination vofthe window frames. AsV the frame members are moved by the/conveyor they pass successively through the spray from guns 2l so that'the eX- terior subtending surface 22 of the end member i2 of each frame intercepts the spray todeposit particles directly on the intercepting surface. The frame also divides thestream so that part of the stream or spray passes between adjacent framemembers. yOf the-part which passes between adjacent frame members, part is deflected and .depositedby the electrostatic ifield upon. the side portions 24 of the forward frame member and the` interior face 26 of portion II thereof; part is deected by and towards the'adjacent rearward'frame member and is deposited upon the side portions and the interior portions 26 thereof; and some rof the spray is impelled through the weak electrostatic iield in the space between the frames and into the ionizing electro- 'static iield between electrode 5 and the column of frames, vand under the conning and repelling influence of this portion of the electrostatic field is directed backwardly and deposited on the exterior faces 21 of portions Il. The frames thus receive heavy deposits in the directly exposed or subtending area 22, and relatively lighter deposits inV protected areas. This action is made possible by the spacing of the frames along the conveyor which provides a field surrounding the stream passing'between the frames that is strong enough to deflect part of the stream to cause deposition of particles upon the side portions 24 and 25 of adjacent frames, and which is' weak enough to allow a substantial portion of the spray to pass completely through "to the opposite ends 21 of the frames where it is confined and redirected by the plurality ofionizing elements 1,'its direction being reversed by the eld sofas tov cause deposition of the particles on ends 27. In this connection it will be noted that the provision of a plurality of ionizing sources 'i on at least one side of the column of articles is of particular value` `in confining the spray stream to'prevent it passing out of the inuence of the electrostatic field. Adjacent the exit end of the booth is a second bank of spray guns 2s of Ia type like that previously described, the guns of the second bank be- I Aing positioned at exit leg 3 of the conveyor to direct a stream of nely divided particles suspended in a carrier air stream at the window frames in the electrostatic eld between electrode frames 8 and 9. rl'he frames approach the spray Aguns 28 with the outside surface 2'.' of portion I I facing the spray guns 2-8, which may be disposed with their axes substantially parallel to the iniii ticles from the guns under influence of the electrostatic eld, and part of the overspray which passes the outside of ends II is deiiected by the electrostatic eld and deposits on the inside 29 ofend I2 and the side faces of members II, I2, I3 and I4. The arrangement thus provides that certain areas previously receiving acoat from theA electrostatically deposited overspray are directly exposed to the particle stream and receive a di- :i

rect coating in the subsequentoperation before the rst coat has set or dried, so that the two dcposits are blended into a unitary layer. It will be understoodthat the spray guns 2i and 28 may be disposed with their axes inclined to the plane of the mouldings'as much as labout 15, that is, in the embodiment shown at an inclination of 3Q to to the line of travel of the mouldings.

At the middle of the booth .are located exhaust chambers 3| (Fig. l) connected at the top by a depositing zone. Furthermore, the exhaust air Ycurrent acts as a deflecting force to keep the particles in the electrostatic field between the electrodes and the column of larticles where it is subject to the electrostatic depositing force. The elimination of billowing in the region of deposit remote from the spray gun is conducive to depositing uniform or smooth layers or coatings, and in general, contributes to the eicient performance of thecoating operation.

In the modification illustrated in Figure 5, the conveyor 40 has a bend or elbow 4I of about 90 and in their course through the apparatus from the entrance to the exit end the frames are turned through by reason of the change of direction of the conveyor, while maintaining their position relative to their path of travel. The spray booth 42 is similarly formed about the conveyor and yat the exterior corner 44 of the booth is located the exhaust chamber y45 connected by a duct to a suitable fan or exhaust system. Exhaust ports 4l are located to withdraw thecarrier air from the extremities of the spray so that the exhaust air current travels longitudinally of the columns of articles in the direction from the spray guns toward the exhaust. Thus interference of the two carrier or spray air streams is reduced or eliminated, with consequent reduction or elimination of billowing or turbulence in the depositing zone. For coating some articles, it may be desirable to dispose the spray guns to introduce the spray substantially tangentially to and in the direction of movement of the articles at one position, and at another position substantially tangentially to and opposed to the direction of motion. v

If desired, there may be provided a series of ionizing electrodes across the bottoms of the pairs oi frames 5, 5 or 8, 9 to thus provide a substantially trough shaped or U-shaped ionizing electrode. Various other modifications maybe made in the invention without departing from the spirit or scope thereof.

claim:

l. Apparatus comprising booth means having entrance and exit portions, said portions being disposed at an angle to each other, means for conveying an article to be coated through said portions, means for providing an electrostatic eld over the surface of an article as it is moved through said entrance and exit portions, means for directing separate streams of finely divided coating material into said iields in said entrance and exit portions and generally 'toward 'the apex of said booth means for electrostatically depositing said material on the surfaces of said article whereby the'material blends into a single layer, and gas moving means located in the vicinity of said apex and intermediate said entrance and exit portions for preventing interference between said streams and for facilitating the electrostatic deposition of coating material on said article.

2. Apparatus for coating` articies, comprising a conveyor for conveying the articles in spaced relation successively through adjacent rst and second coating zones, a booth enclosing said zones and into, through, and out of which the conveyor moves the articles over a predetermined path, said booth having an air-outlet opening located near the adjacent ends of said two coating zones, means for providing high-voltage lelectrostatic -rields over and contiguous to the surfaces of arin the Adirection of article movement and .in the `second coating Zone a movement of .air counter to the direction of article movement, and -means for directing separate streams of iinely divided coating material into said iields from the upstream ends thereof generally toward saidl air outlet opening for electrostatic deposition on articles in the coating zones.

3. Apparatus for electrostatically coating a series of similar articles in each of which one of the three mutually perpendicular, over-all dimenl'sions is materially less than either of the other two, said apparatus comprising a conveyor for moving the articles over a predetermined path, said conveyor including article supports for supporting the articles with the planes defined by the two greatest dimensions of Yeach at substantially equal acute angles to the direction of motionof said conveying means, a booth enclosing adjacent .first and second coating zones through which the articles are successively moved by the ,conveying means, said booth having an air outlet opening located near the adjacent ends oi the coating zones, means for withdrawing air through said outlet opening to induce in the rst coating zone a movement of air in the direction of article motion and in the second coatingzone amovement of air counter to the direction of article motion, a first spray-discharge device located adjacent the upstream end of the iirst coating zone Vat one side of the article path and discharging a spray of liquid coating material into vthe first coating Zone generally parallel to the planes of the articles therein and in the general direction of air movement through such first coating zone, a second spray-discharge device located adjacent the upstream end of the second coating zone on the opposite side of the article .path and discharging a spray of liquid coating material into the second coating zone generally kpar-allel to the planes of the articles therein and in the general direction of air movement through such second coating zone, and means for providing over and contiguous to the surfaces of the articles in each coating Zone a high-voltage electrostatic field promoting the deposition of the coating material onto the articles.

4. Apparatus for coating articles, comprising a conveyor for conveying the articles in spaced relation successively through adjacent iirst and second coating zones, a booth enclosing said zones and into, through, and out of which the conveyor moves the articles over a predetermined path, said booth having an air-outlet opening located near the adjacent ends of said two coating zones, first and second coating-material discharge devices located to discharge streams of finely divided liquid coating material into the respective coating zones near the upstream ends thereof, said two devices being located on option to the article-path and on the opposite sidey thereof from the associated coating-material discharge device, vsaid electrode being. arranged transversely of the stream of coating .material discharged from such device and extendingboth llongitudinally and laterally of the article-path whereby coating-material particles which cross Vthe article-path-without becoming deposited on articles will be charged by said electrode, electrostatically redirected toward the article-path, and electrostatically deposited on the articles.

5. A method of electrostatically coating a plurality of articles, which comprises moving the articles in succession and in spaced relation over a predetermined path successively through first land secondA coating zones, creating inthe first coating zone a movement of air in the direction of article movement andr in the second coating zone a movement of air counterto the direction rof article movement, discharging separate IStreams of iinely divided liquid coating material into said coating zones from the upstream ends thereof, eachof said streams being directed generally in the direction of air movement in the coating zone into which it is discharged, and maintaining over and contiguous to the surfaces ofthe articles in each coating zone a high-voltage electrostatic eld to cause electrostatic deposition of the coating material onto the articles, said two coating Zones being adjacent whereby the coating material deposited on the articles in the two coating zones blends into a single layer.

6. A method of coating a plurality of similar articles in each of which one of the three mutually perpendicular, over-all dimensions is materially less than either of the other two, comprising moving the articles through a. first coating zone over a predetermined path while maintaining the articles in substantiallyparallel relation and at an acute angle to such path, then immediately moving the articles through a second coating zone while maintaining them in substantially parallel relation and atan acute angle to their path of movement, creating in the iirst coating zone a movement of air in the direction of articlernotion and in the second coating zone a movement of `air counter to the direction of article motion, discharging intoeach. coating zone adjacent the upstream end thereof a spray of liquid coating material directed toward the article path, generally parallel to the planes of the articles, and in the general direction of air movement in the coating Zone, and maintaining .over and contiguous to the surfaces of the articles in each coating zone a high-voltage electrostatic field promoting the deposition of the coating material onto the articles.

7. .The invention setforth in yclaim 2 with the addition that said conveyor moves over a curved path between said first and second coating zone and tangentially of .such curved path within said The following references are of record in the le of this patent:

UNITED STATES PATENTS .Number Name Date 1,855,869 VPugh Apr. 26, 1932 .2,247,963 Ransburg July l, 1941

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