Patent Publication Number: US-3879277-A

Title: Method and apparatus for electropainting small articles

Description:
United States Patent [191.  
 Guzzetta et al.  
 [ METHOD AND APPARATUS FOR- ELECTROPAINTING SMALL ARTICLES [75] Inventors: Franklin H. Guzzetta; Roy A.  
 Brown, both of Monroe, Ohio [73] Assignee: Armco Steel (lorporation,  
 Middletown. Ohio 221 Filed: Apr. 27, 1973 [21] Appl.No.:355,03 2  
  521 [1.8. CI 204/181; 204/300 EC 511 rm. c1 801k 5/02 [58] Field at Search; 204/181, 300 EC [56] I References Cited UNlTED STATES PATENTS ll/l970 Ncss 204/l8l 8/l&#39;974 Haney et al 204/18] [4 1 Apr. 22, 1975 Primary E.\&#34;aminer- Howard S. Williams Attorney, Agent, or FirmMelville, Strasser. Foster &amp; Hoffman [57] ABSTRACT &#39;Electr&#39;opainting of small articles by the electrical deposition of an organic film from a suitable paint solution. A first electrode is provided to give a designated charge to the articles and a second electrode is provided to give an opposite charge to the solution, whereby the resin and pigment components of the paint solution will migrate towards the article. The new approach is that of sandwiching the articles to be coated between a moving, supporting electrode and a stationary electrode, both of these electrodes (the first&#34; electrode) usually being at the same potential, the other, oppositelyeharged electrode (the second I electrode) being elsewhere located within the paint solution. The&#39;sandwiching action is accomplished within the solution.  
 11 Claims, 2 Drawing Figures METHOD AND APPARATUS FOR ELECTROPAINTING SMALL ARTICLES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to electropainting. usually the electrical deposition of an organic film from an aqueous paint solution simultaneously on a plurality of conductive articles in a suitable container. This invention has particular application to the electropainting of small articles such as rivet sleeves. screws. nuts. bolts and other fasteners.  
 2. Description of the Prior Art No search of the United States patent art has been made directed to the specific invention which is the subject of this application. There are a number of issued patents relating to electropainting generally. Typical of these are U.S. Pat. No. 3.6l6.392 Haney. the patents cited therein. and Swedish Pat. Nos. 322.390 and 308.049. Such electropainting may involve immersing the articles in an aqueous paint solution while in a conductive container and passing current through the container and solution to irreversibly deposit an organic coating on the articles. Various refinements have been made on this process such as. for example. the application of a conversion coating as taught in the said Haney U.S. Pat. No. 3.6l6.392. The art teaches generally the use of electrodes. an anode and a cathode. immersed in an electrocoating solution through which the articles to be painted are passed.  
 SUMMARY OF THE INVENTION This invention involves the use of a moving screen or grid comprising an endless belt which is moved through a bath of an appropriate paint solution and on which the items to be painted are deposited. In a typical arrangement this screen will constitute a first electrode. and the second electrode will be located elsewhere in the container holding the bath; it may be that the container itself will constitute this second electrode. In the instant invention a third&#34; electrode is provided and this comprises a stationary but flexible screen or grid so arranged that the articles to be painted will be moved between it and the first mentioned screen on which they were deposited: this stationary screen and moving screen will usually be at the same potential and together will constitute the &#34;first&#34; electrode. The other (the *second) electrode may be located between the flights of the endless belt constituting the moving screen. or elsewhere in the bath: it may even be. as indicated above. the bath tank itself. if so desired.  
  The third. stationary electrode is so located within the bath that the articles to be painted are introduced between it and the moving screen&#39;or grid. This third electrode is preferably flexible and is weighted down so that the items are subjected to a shearing action as they are moved through the solution during the electropainting process. whereby good electrical contact is made during the process. Simply to place small articles such as very light rivet sleeves. screws and the like on a belt moving through the solution heretofore has not proved acceptable. By sandwiching them. however. between the two grids or screens in the manner taught herein. dramatically improved yields of acceptable painted items have been achieved.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic showing of one electropainting system in which the instant invention may be incorporated. and  
  FIG. 2 is an enlarged view. partly in section and partly diagrammatic. showing that part of the electropainting system which comprises the instant invention. both in terms of method and apparatus.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I, by way of background. a typical electropainting apparatus for the coating of small articles may include a hopper for the feeding of the articles to be painted to some sort of means 11 for metering the articles into the paint bath: such metering means could, for example. comprise a vibratory bowl to help insure that the articles will enter the paint bath other than in a mass of agglomerated material. The paint bath. which will incorporated the invention. is generally indicated at 12 and will be described in greater detail shortly. The painted articles may then proceed through a water spray booth 13 for rinsing excess paint from the freshly electropainted articles. Article separating means generally indicated at 14 and 15 are provided at the incoming and discharge ends respectively of the water spray booth; these separating means 14 and 15 may constitute a separate invention and application. After the articles are conveyed through the electropainting paint bath and through the water spray bath. and having been subjected to the means 14 and 15 for separating the painted articles one from the other. such articles are then conveyed through a suitable oven 16 in which the electropainted articles are baked at the proper temperature. As the baked. painted articles leave the oven 16. they may be cooled in the area 17 and either boxed at the area 18 or conveyed by suitable means 19 to another station 20 if such articles are to be further treated.  
  It will be understood that the foregoing general description of the method and apparatus illustrated in FIG. 1 is exemplary only; other general arrangements for electropainting are possible. It may be. for example. that the articles to be painted will be given one or more preliminary treatments before they enter the electropainting bath. One such treatment could be the application of a conversion coating. as taught in the said Haney U.S. Pat. No. 3.6l6.392 before the articles even reach the hopper 10. Other preliminary treatments may be accorded such articles prior to their entry into the electropainting bath and related apparatus. The freshly electropainted articles may be thereafter handled as indicated in FIG. 1 and the description thereof but it is to be understood that such disclosed bath treatments are not a limitation on the instant invention which will now be described in connection primarily with FIG. 2.  
  The improvement in the method and electropainting apparatus. especially useful for the coating of small articles. is shown in FIG. 2. Heretoforc. when attempting to coat small articles. the yield of acceptable painted articles has not been very good. often only in the range of to percent: to be successful. a yield in excess of percent is required and. of course. a yield closer to percent is desirable. Such improved results are achieved by this invention.  
  The novel approach of the instant invention is that of sandwiching the articles to be coated between a moving. supporting electrode and a stationary electrode. both electrodes usually being at the same potential and together constituting a first electrode. The moving electrode comprises a screen or grid 21 driven by one or more of the rollers 22 in a manner known in the art. the driving means not being shown. The stationary electrode is indicated at 23 and comprises a flexible screen or grid suitably supported above the top flight of the grid 21; such stationary electrode 23 may. for example. be attached to the slide 24 down which the articles 25 come as they enter the paint bath 26 contained within the paint basin 27. Suitable weights 28 are disposed about the top side of the stationary electrode screen or grid 23 so as to maintain such electrode 23 within the bath 26 in close proximity to the upper flight of the moving screen or grid 2]. The arrangement of the weights 28 and stationary. flexible grid 23 is such as to urge the grid 23 towards the grid 21 so that the articles 25 are sandwiched therebetwecn so as to obtain a shearing action on the articles to be coated. This provides good. improved electrical contact during the electropainting process.  
  The first electrodes 21 and 23 are usually at the same potential. The other electrode. the second electrode. is at a potential opposite that of 21 and 23. and is indicated as comprised of a grid 29. A suitable source of DC power is indicated at 30 and appropriate conduits 3] and 32 extend therefrom to the first electrodes 21. 23 and to the second electrode 29.  
  It will be understood that the electrode 29 will be suitably supported in the bath 26 within the basin 27 and may be suitably attached between and supported from the walls of such basin in such manner as will be obvious to one skilled in the art. but not shown. The electrode 29 may be insulated from the paint basin 27 or it may even be in electrical contact therewith in those instances where itis deemed desirable to pass an electric current through the container as well as through the solution.  
  In any event it will be understood that the power source 30. via the conduits 31 and 31a. in the preferred embodiment illustrated. will provide-the grids 21 and 23 with the same electric potential while this source 30, through the conduit 32, will supply the grid 29 with electric current at a different potential. As noted.&#39;the upper stationary grid or screen 23 is weighted down by the weights 28 such that a shearing action on the articles 25 to be coated allows good electrical contact to be made during the process; the grids 21 and 23 are so located as to provide good electrical contact by these two surfaces which engage the articles under some shearing action.  
  In some instances the conduit 31 may not be connected to the weighted grid 23. Such an arrangement would allow this grid to float up to its potential which will normally be the potential of the wire-mesh endless belt 21 due to the conductivity of the metal articles being coated. This weighted grid 23, however, could conceivably be at a different potential than the belt 21.  
  in an exemplary arrangement the endless belt 21 and weighted grid 23 could together constitute the first electrode. for example. the anode. In such arrangement the metallic grid 29 constituting the second electrode would be the cathode. This would be the set up when anodic paints are employed. Although there are advantages to the use of anodic paints in that they liberate oxygen thereby to reduce the possibility of hydrogen embrittlement. they are not the only type employed. Thus. in some instances the members 21. 23 may constitute the cathode while the member 29 would be the anode. And as noted above. regardless of which type paint is employed. at times there may be no direct connection between the power source 30 and the weighted grid 23; likewise the other connection from the power source might be directly to the bath tank 27 itself rather than to any grid 29. The arrangement shown in FIG. 2. however. is that which is preferred.  
  In summary. the method and apparatus of this invention are intended for incorporation in electropainting systems generally. The problem is to coat a great number of small articles simultaneously and the specific task is that of getting them charged while in contact with the coating media. The novel feature is the method and apparatus for making the necessary electrical contact, that is. the sandwiching of the articles to be coated between the moving. supporting electrode 21 and the stationary. flexible electrode 23, both of these electrodes normally being at the same potential. Weighting down the flexible grid 23 insures a shearing action on the articles to be coated and this in turn insures that good electrical contact will be made during the process.  
  It will be understood by those skilled in the art that improvements may be made in the method and apparatus of this invention without departing from the scope thereof and that while the invention has been described in terms of certain particular structures and manipulations. the invention is not to be so limited except to the extent that such structures and manipulations are specifically set forth in the subjoined claims.  
  The embodiments ofthe invention in which an exclusive property or privelege is claimed are defined as follows:  
  1. In that method of electropainting a large number of small articles which comprises the steps of providing a bath of electropainting solution containing suitable coating components. providing a first grid means for moving the articles through the bath. introducing the articles into the bath and onto the grid means. providing a source of suitable electric power. providing a first electrode for placing one charge on said articles and a second electrode for placing an opposite charge on said solution while said articles are in said bath. whereby the components of the solution will migrate to the articles. the improvement which comprises the steps of providing a second flexible grid means in said bath in position to be engaged by said articles. and sandwiching the articles between said first and second grid means while moving the articles through said bath.  
  2. The method of claim 1 in which said first grid means serves as said first electrode.  
  3. The method of claim 2 including the step of charging said second grid means at the same potential as said first grid means.  
  4. The method of claim 3 including the step of forcing said second grid means into contact with said articles while said articles are on said first grid means and within said bath whereby to obtain a shearing action on said articles and whereby to increase the charge imparted to said articles by said first and second grid means.  
  5. A method of electropaining a large number of small articles by depositing the articles onto a moving grid comprising a first electrode having a certain potential. moving said first electrode and the said articles thereon through an electropainting bath. charging said bath by an electrode which has a potential different from said certain potential. providing a third electrode in said bath in position to be engaged by said articles. and sandwiching said articles between said third electrode and said first electrode while said articles are in said charged bath.  
  6. The method of claim 5 including the step of insuring that said articles are simultaneously engaged by said first and said third electrodes while said articles are being moved through said charged bath. whereby to obtain a shearing action by which the charge placed on said articles is increased.  
  7. The method of claim 6 including the step of charging said third electrode at said certain potential.  
  8. Apparatus for use in electropainting a large numher of small articles which comprises: a container for holding an electropainting bath having suitable coating components. a movable grid adapted to move articles through said bath. means to introduce articles into said bath and onto said grid. means to charge said grid at a certain potential. means to charge said bath at a different potential. and added flexible. stationary grid means to engage said articles while on said movable grid within said bath.  
  9. The apparatus of claim 8 including means to charge said added grid means at said certain potential.  
  10. The apparatus of claim 9 including means to weight said added means so as to insure that said articles are sandwiched between said grid and said added means in simultaneous contact with both said grid and said added means whereby to obtain a shearing action on said articles to obtain good electrical contact while the articles are in the electropainting bath.  
 ll. Electropainting apparatus including a paint basin adapted to contain an electropainting bath. a moving screen adapted to be at least partially submerged within said bath. a stationary but flexible screen adapted to depend into said bath above said moving screen. means to discharge articles to be painted between said screens. means to charge said bath at one potential. means to charge said screens at a differential potential. and weight means on said flexible screen to force said flexible screen into contact with said articles while on said moving screen within said bath. whereby to insure a shearing action on the articles to he painted and thus obtaining good electrical contact on the articles while