US2446953A

US2446953A - Apparatus for electrostatically coating articles

Info

Publication number: US2446953A
Application number: US575955A
Authority: US
Inventors: Harold P Ransburg
Original assignee: Ransburg Corp
Current assignee: Ransburg Corp
Priority date: 1945-02-03
Filing date: 1945-02-03
Publication date: 1948-08-10
Anticipated expiration: 1965-08-10

Description

H. P. RANSURG APPARATUS FOR ELECTROSTATICALLY @DATING ARTICLES Filed Feb. 5, 1945 3 Sheets-Sheet 1 m@ ma H. P. RANSBURG 2,44%,953

APPARATUS FOR ELECTROSTATICALLY C OATING ARTICLES Filed Feb. 3. 1945 s'sneets-sheet s Patented Aug. 10, 19.48

APPARATUS FOR ELEOTRD'STATIOALLY COATING ARTICLES Harold P. Ransburg, Indianapolis, Ind., assignor,

by mesne assignments, to Ransburg Electro- Coating Corp., Indianapolis, Ind., a corporation of Indiana Application February 3, 1945, Serial No. k575,955

(Cl. lil-48)v 'l Claims. I l x This invention relates to the coating of articles lwith a protective and decorative coating material, and particularly wherein the coating material is t be applied by electrostatic precipitation, as generally disclosed in Letters Patent'of Pugh No. 1,855,869, granted April 26, 1932, and Letters Patent of Ransburg and Green, No. 2,334,648,

granted November 16, 1943.

The apparatus herein disclosed is most desirable and advantageous when the coating material is a liquid, which when suitably atomized,

tends to adhere securely to any object with which it comes in contact. The invention is directed to correcting one of the maior deficiencies and obiections to the electrostatic coating process as normally employed, in that it provides an effective apparatus for freeing the atmosphere which surrounds the spray area, of that small but highly objectionable percentage of charged particles of coating material which escape effective precipitation onto the article to be coated.

In the ideal electrostatic coating operation a finely divided coating material is carried into an electrostatic iield established between an electrode system and the article to be coated at a rather slow velocity and in such a direction that the material will remain in the field long enough for complete precipitation to take place. But such ideal condition is never completely realized in actual practice. There are certain factors which preclude realization of this ideal because such factors individually or collectively cause some portion of the coating material to escape the intended action of the field. Since these factors are inherent in the method, one always finds a small percentage of the coating material leaving the spray booth at one point or another. yThis stray material coats and defaces objects, merchandise and adjacent equipment not intended to be coated. Furthermore, since the particles of stray material have passed through the field and have become charged, they will be attracted to objects to which uncharged particles would not normally be attracted.

My invention, therefore, provides means for substantially eliminating this objection. This means includes apparatus for establishing a second electrostatic iield for the express purpose of electrically depositing those charged particles, which escape the intended coating operation, onto a collector surface such as removable plates which cannot be damaged. A suitable arrangement lfor accomplishing the invention is illustrated in the attached drawings.

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

Fig. l is a perspective view of an electrostatic spray installation with a portion of the spray booth broken away.

Fig. 2 is a vertical section taken through the right-hand side of the spray booth.

Fig. 3 is a schematic drawing showing a plan view of the spray booth and electrode system.

Fig. 4 is a sectional .view of a non-conducting article to be coated.

In the drawings there is shown by way of illustration of the invention, an electrostatic spray booth I'Ii which is provided with an entrance opening indicated at Il in the side wall thereof through which the articles I2 to be coated are conveyed into the booth. As shown, the spray booth is elongated and so arranged that the articles are conveyed longitudinally and centrally thereof, after entering through the entrance opening in the side wall, and toward the open exit end in which one or more spray guns I3 are mounted. Thus, after entering the booth through the entrance opening in the side wall they are conveyed in a curved path through a portion of their travel in the direction of the arrows as shown in Fig. 3,

For. providing one terminal of the electrostatic eld, there is mounted within the booth oppositely disposed discharge electrodes. Said discharge electrodes are shown herein as comprising one or more supporting frames Il suspended from the top of the booth by the insulating hangers I5. Each frame carries a plurality of spaced ne electrode wires I6 arranged in vertical parallel relation and suillciently far apart to avoid electrostatic interference with one another. The electrode frames and wires are electrically connected through a conductor I1 with one terminal of a source of high voltage indicated at I8. Th'e other terminal of said source is grounded. The electrode frames I4 are supported in spaced relation to the path of travel of the articles I2 and are arranged to conform to the curved portion of the path of travel and extend toward the entrance opening I'I in the booth. This is best illustrated in the schematic drawing of Fig. l3.

The articles I2 to be coated are herein illustrated as comprising buckets suspended by hangers I9 from a mono-rail support 2li mounted in the top of the booth. They are conveyed through the booth and between the discharge electrodes by the conveyor chain 2| connected to the roller Supporting brackets 22 carried by the monoraiL 3 In coating certain articles, such as buckets. it is dirable to cause them to rotate as they pass through the spray booth, and this is accomplished by providing a swivel `connection between the hangers il and brackets 22, which in..

cludes a roller 2l on said hanger arranged for frictional engagement with a track Il. Thusjas they are conveyed through the coating sone, they are slowly rotated.

For creating the electrostatic field of the coating sone, the conveyor and, therefore, the articles or their supports are grounded to provide acollecting electrode oppositely disposed relative to the discharge electrode. Thus, through the mev` dium of the source of high voltage Il there is created a high potential diiference betweenthe discharge electrode wires It and the articl which comprise the collecting electrode. Thus. an electrostatic field is created when the articles are conshown (Fig. 3) a pair of spaced spray guns II directing the coating material into the eld along both sides of the .path of travel of the articles, it is to be understood that in some installations, depending upon the character of the article, the discharge electrodes and spray g-uns may be arranged onlycn one side of the path of travel of the article.

As the atomized coating particles are introduced into the field, they are ionized by the neat, s series or adjustable as ma. :s uumably mounted upon the brackets Il depending fromthetopofthebooth. Asshownhereintbe tie rods 2l are provided with depressed portions at each end thereof, the bars 21 from which the 'platesllarehungbeingcarriedbytheouterdepression and the insulating hangers4 il by whim the discharge electrodes are supported being car- 'ried by the inner depression. In this manner.

the spacing of thel plates It relative to the discharge electrode remains constant so as to maintainat all times the prescribed intensity of this field. However, the discharge electrode, together' with the plates 26, may be adjusted in proper spacedrelationtothenearsurface ofthea'rticles Iltobecoateddependinguponthesiseordiameterof'the articles. 'Ihusyasthesiseordiameter of the articles may be altered, the tie rods 2| may be moved back and forth on supporti! without changing the spaced relation of the collecting plates 2l with respectto the discharge lectrode.

By providing the collector il in the form of a series of spaced plates 2l, it may be more conveniently removed for cleaning or scraping than would otherwise bethe case if it were of continuous construction. Also, by reason of the spacing 'of the plates, air may freely pass between and corona discharge of the electrode I4. Il, and if their direction of movement, inertia and velocity are properly controlled and adjusted, they'wlll be attracted to the grounded collecting electrode in the form of the articles I2 to be coated. However, it still remains that stray particles of coating material will escape the field of the coating sone and be lost so far as the coating of the articles is concerned. These particles will have passed through or near the discharge electrode and will. therefore, -have become ionized so as to be attracted to and adhere upon surrounding.

structures and objects in the-general neighbor-V hood.

For the purpose of overcoming this objection and controlling the deposition of the stray particles, a second electrostatic ileld is provided. This second field is arranged adjacent to and outside of the ilrst ileld of the coating zone. and is preferably of lesser intensity. For .this purpose, a secondary collecting electrode surface is provided which is grounded and so spaced from the discharge electrode, on the opposite side thereof from the articles, to provide a second electrostatic field of less intensity. As the stray particles which have become ionizedin passing through the coating ileld and discharge electrode escape to the outer or second eld, they will become attracted to and deposited upon the secondary grounded collecting electrode.

In the form of the invention herein disclosed the walls ,of the spray booth I0 are of insula g material. Spaced from the walls there is provi ed alsecondary collecting electrode surface in the form of a plurality of grounded collecting plates Il.' Said plates may be arranged in alignment and hung from the supporting bars. 21 by hooks to enable them to be conveniently removed for scraping or cleaning. The bars 21 may be calabout them, carrying the stray vparticles of coating material so as to avoid any repelling air currents or turbulence such as would prevent such deposition of stray particles on their collecting surface. lIt is also desirable that the edges of the collecting plates be curved to prevent exposure of a sharp edge to the electrostatic forces which may Vconcentrate the lines of force. such as to cause the stray particles of material to be reionized and repelled.

An'exhaust fan 25 is provided at one end of the booth Il and preferably directly opposite the guns il as shown in Fig. 3. 'Ihe purpose of this exhaust fan is to cause air movement in the direction of the issuing streams from the guns I vI, to facilitate the movement of air past the electrodes Il, Il and 2l without creating repelling air currents or air turbulence.

By reason of the above arrangement, wherein two 'electrostatic fields are provided, one' preferably of greater intensity for the coating sone and one preferably of lesser intensity to, provide a stray particle collecting sone, there has been devised apparatus for controlling the material, such as to substantially eliminate the destructive and objectionable character thereof. Similarly, the reclaiming ofthe coating material electrostatically deposited upon the collecting plates. has been made more practical by lrranging them for convenient removal, scraping or washing; or by other known means of reclamation, such asproviding a water curtain to continuously cleanse and remove the deposited particles. Thus, the material may be reclaimed, and damage to surfaces in and about the premises, eliminated.-

Whereas the article to be coated is shown and described herein as a bucket for illustrative purposes. it may be of any character comprising either conducting or non-conducting material. Thus. if it is of non-conducting material, an

electrode element Ila having a connecting lead Isa is associated therewith as illustrated in Fig. 4.

In either case the article, with or without the eleas comprising ticles including a discharge electrode spaced from said articles, a collecting electrode having a surface spaced from said discharge electrode on the other side thereof from said articles, means for establishing aprimary electrostatic iieldfbetween said discharge electrode and articles and a" secondary electrostatic field between said dis- -charge electrode and collecting surface, and

means for atomizing coating material into said primary field for electrostatic deposition on said articles, said secondary field acting to precipitate on to said collecting surface material escaping from said primary field into said secondary field.

2. Apparatus for electrostatically coating articles including a discharge electrode spaced from said articles, a collecting electrode comprising a plurality of spaced electrically connected lplates arranged in series and in spaced relation to said discharge electrode on the opposite side thereof from said articles, means for establishing a primary electrostatic fleld between said discharge electrode and articles and a secondary electrostatic ileld between said discharge electrode and plates, and means for atomizing coating material into said primary field for electrostatic deposition on said articles. said secondary field acting to precipitate on to said plates material escaping from said primary field into said secondary field.

3. Apparatus for electrostatically coating articles including a discharge electrode, means for positioning the articles to be coated in spaced relation to said electrode, a collecting electrode having a surface spaced from said discharge electrode on the opposite side thereof from said articles, a source of high voltage having one terminal electrically connected with said discharge electrode and the other terminal electrically connected with the support for said articles and collecting electrode, said source establishing a primary electrostatic fleld between said discharge electrode and articles and a secondary electrostatic eld .between said discharge electrode and collecting electrode surface, and an atomizing means mounted to direct a spray of atomized coating material into said primary field for electrostatic deposition on said articles, whereby stray material escaping from said primary field into said secondary eld will be electrostatically deposited on said collecting electrode surface.

4. Apparatus for electrostatically coating articles including a pair of discharge electrodes, means for conveying articles between said electrodes in spaced relation thereto, a series of collecting electrode plates removably supported in spaced relation to each of said discharge electrodes on the opposite sides thereof from said articles, a source of high voltage having one terminal electrically connected with said discharge electrode, and the other terminal electrically connected with said conveying means and electrode plates, said source establishing a primary electrostatic eld between said articles and discharge electrodes and a secondary electrostatic eld between said electrodes and their respective series of collecting electrode plates, and an atomizing means mounted to direct a spray of coating material into said primary fieldI for electrostatic deposition on said articles, whereby stray material escaping from said primary eld into said secondary field will be electrostatically deposited on said collecting plates.

5. Apparatus for electrostatically coating articles comprising a spray booth having top and side walls, a conveyor operatively mounted in said booth for conveying the articles to be coated therethrough, a plurality of tie rods adiustably supported by said booth for movement toward and away from the path of travel of the articles carried by said conveyor, a series of dis-4 charge electrode elements carried by said tie rods at one end thereof adjacent to the path of travel of said articles, collecting electrode plates car.- ried by the opposite end of said tie rods respectively in fixed spaced relation to said discharge electrode elements and away from the path of travel of said articles, a source of high voltage having one terminal electrically connected with said discharge electrode elements and the other terminal electrically connected with said conveyor and collecting electrode plates to establish primary and secondary electrostaticflelds therebetween respectively, and an atomizing agent mounted to direct a spray of atomized coating material into said primary ileld for electrostatic deposition on said articles, said secondary field causing electrostatic deposition of material escaping from the primary field into the secondary field upon said collecting plates.

6. Apparatus for electrostatically coating articles including a discharge electrode spaced from said articles, a collecting electrode comprising a plurality of spaced electrically connected plates arranged in series and in spaced relation to said discharge electrode on the opposite side thereof from said articles, means for establishing a primary Aelectrostatic field between said discharge electrode and articles and a secondary electrostatic eld between said discharge electrode and plates, each of said plates having a rearwardly and inwardly curved edge formed thereon in spaced parallel relation to the next adjacent plate, tie rods for removably supporting said plates at one end thereof and the discharge electrode at the other end thereof whereby said plates and discharge electrode will be maintained in xed spaced relation, brackets for adjustably supporting said tie rods to permit adjustment of said discharge electrode and collecting plates toward and away from the path of travel of said articles to maintain their spaced relation from the surface of said articles to be coated, and means for atomizing a coating material into said primary field for electrostatic deposition upon the surfaces of said articles,V said secondary field acting to electrostatically precipitate onto said plates stray material escaping from said primary field.

7. Apparatus for electrostatically coating articles including a discharge electrode, means for conveying saidarticles past said electrode in spaced relation thereto, a plurality of spaced collecting plates supported in spaced relation to said discharge electrode, a source of high voltage having one terminal electrically connected with said discharge electrode, and the other terminal electrically connected with said conveying means and plates, said source establishing a primary electrostatic field between said articles and discharge electrode and a, secondary electrostatic field between said electrode and said collecting plates, an atomizing means mounted to direct a spray of coating material into said primary field for electrostatic deposition on said articles, whereby stray material escaping from said primary field into said secondary fie.d will be electrostatically deposited on said collecting plates, and means for drawing air through said plates from adjacent said electrode.

HAROLD P. RANSBURG.

7 gmmcns crrm The following reterencs dre of record in the me of this patent: v v

' Number UNITED STATES PATENTS Name Date Chubb Aug. 10, 1920 Hopkinson Mar. 2, 1926 Numbr