Patent Publication Number: US-2006011479-A1

Title: Method and apparatus for the bulk coating of components

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application is a continuation-in-part of prior U.S. patent application Ser. No. 09/952,132, filed Sep. 14, 2001. 
    
    
     1. Technical field  
      The present invention relates generally to the coating of components. More particularly, the present invention relates to a method and apparatus for the bulk electrocoating of relatively small components. The method generally includes: the preparation of the components to be coated, the placement of the components on transfer media in the form of a movable conveyor, the movement of the transfer media and its accompanying components through a coating-filled process tank, the subject of the uncoated parts to an electrically charged coating solution wherein the parts are coated, and the conveyed removal of the coated parts to a curing/post treatment/polymerization means.  
     2. SUMMARY OF RELATED ART  
      Electrocoating or electrodeposition is a process undertaken by the use of opposite polarity electrodes disposed in a spaced-apart array in a tank having a coating bath. The coating process is actually the application of coating by electrolysis and the charged particles, in this case the paint or coating solids, are attracted to the substrate forming an even and uniform deposit of coating thereupon.  
      Because conductivity is a requirement for electrocoating, the coated article must be conductive or at least must bear an electrically conductive surface. Accordingly, articles to be coated include those manufactured from steel, iron, zinc die-cast, aluminum, copper, brass, or composite materials. This type of coating is particularly valuable where the parts are of complex shapes having recesses and other difficult-to-coat surfaces. This method of coating is also valuable where many like parts must be coated with an identical coating on a volume basis. Accordingly, electrocoating has particular utility in the coating of appliances, metal furniture and in the automotive industry.  
      Many examples of the electrocoating processes are known in the industry. Some of these include rack and drum coating, the latter being represented by U.S. Pat. No. 5,433,834, issued to Belz et al. on Jul. 18, 1995. Another popular arrangement for electrocoating is characterized in the suspension or dipping system, whereby a plurality of parts are hung from an overhead conveyor and are pulled through an electrocoating bath. Examples of this approach include U.S. Pat. No. 4,263,122, issued to Urquhart on Apr. 21, 1981, U.S. Pat. No. 4,668,358, issued to Ball on May 26, 1987, U.S. Pat. No. 4,844,783, issued to Takahashi et al. on Jul. 4, 1989, and U.S. Pat. No. 6,139,708, issued to Nonomura et al. on Oct. 31, 2000.  
      However, attention has been recently directed to the use of conveyor systems upon which are loaded parts. The parts are then carried through and out of an electrocoating tank. An example of this approach includes U.S. Pat. No. 5,810,987, issued to Opitz on Sep. 22, 1998.  
      While the above-noted approaches represent improvements in the state of the art, there still remains room for improved electrocoating techniques.  
     SUMMARY OF THE PRESENT INVENTION  
      The present invention discloses a method and apparatus for the electrocoating of relatively small components. The apparatus may be generally defined as a coating process unit. The coating process unit is comprised of three component parts, which are defined as the process tank, the transfer system, and the electrode system. Each of the three component parts is integrated with a support structure. The process tank is a fluid-tight, open-top receptacle that holds the coating solution through which the parts are passed. The transfer system generally includes a conveyor chain and transfer media connected to the conveyor chain. The conveyor chain may be electrically insulated. The transfer media connects to the conveyor chain to form the continuing moving support surface on which the parts are loaded, coated and unloaded. The transfer media includes a support surface and electrical contact. The electrode system includes both an electrode and an electrode contact of opposite polarity.  
      The method of the invention generally includes the preparation of the parts to be coated (by cleaning and, preferably, by phosphating), the introduction of the components onto the transfer media (the conveyor), the movement of the transfer media and its accompanying parts to be coated through the coating-filled process tank, the subjecting of the prepared parts to an electrically charged coating solution while in the process tank, and the conveyed removal of the parts to a post treatment and/or curing area as required. During the coating operation, the conductive portions of the transfer media are coated simultaneously with the parts. Accordingly, following the unloading of the coated parts, the top surface of the transfer media is cleaned to remove the deposited but uncured coating. This step helps to provide positive electrical contact of the parts and, thus, optimal coating results.  
      The present invention finds broad utility in a variety of painting and coating applications, particularly where small parts are presently being manually fixtured for coating. For example, the present invention would be desirable in painting small parts, i.e. fasteners, clamps, brackets, etc. The coating apparatus of the present invention finds particular application in the painting of small parts, which require a uniform film of highly corrosion resistant coating applied over irregularly-shaped items.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will be more fully understood by reference to the following detailed description of the preferred embodiments of the present invention when read in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout the views, and in which:  
       FIG. 1  is an elevational side view of the present invention, illustrated in partial shadow lines, and showing the primary components of the bulk electrocoating apparatus;  
       FIG. 2  is a top plan view of the present invention, illustrated in partial shadow lines; and  
       FIG. 3  is an elevational end view of the input end of the present invention, illustrated in partial shadow lines.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The drawings disclose the preferred embodiment of the present invention. While the configurations according to the illustrated embodiment are preferred, it is envisioned that alternate configurations of the present invention may be adopted without deviating from the invention as portrayed. The preferred embodiment is discussed hereafter.  
      Referring primarily to  FIG. 1 , a side elevational view of the present coating apparatus, generally illustrated as  9 , is shown. The apparatus  9  includes a parts input end  10 , an output end  11 , a support portion  12  and a coating portion  14 . The support portion  12  may be defined by a frame arrangement (as shown) or may be of any other supportive configuration (a cast cement base, for example).  
      The coating portion  14  includes a coating or process tank  16 , a transfer system, generally illustrated as  18 , an electrode  20 , and an opposite polarity electrode contact  21 . The electrode  20 , and the electrode contact  21 , are supplied D.C. power by a rectifier  25  or other appropriate external D.C. power source.  
      The electrode network composed of the electrodes  20  and  21  forms a plane that is substantially parallel to both the opposing electrode and the transfer media  26 . These electrodes  20  and  21  may be a single unit or multiple units. The use of multiple units will allow the use of multiple D.C. sources for multiple voltage potentials or differently sized electrodes for multiple current densities. The electrodes are mounted in an easily removed assembly, which includes an insulating grid  23  below the electrode to prevent accidental short circuits should parts stack excessively on the transfer media  26 . This design allows very close proximity of the electrode to the parts which reduces the required voltage and improves the overall coating efficiency. As illustrated in  FIG. 2 , the electrodes are shown as bare conductive plates, although it is to be understood that other electrode configurations, such as tubular flushable electrodes, may be used.  
      The process tank  16  is a fluid-tight, open-top receptacle that holds the coating solution through which the parts are passed. The solution level  22  in the process tank must be maintained to fully submerge the electrodes and the parts as they pass through the solution.  
      The electrocoating solution and permeate will be supplied to the process tank  16  from a fluid control module (not shown) of the conventional type which will condition the solutions to maintain the coating bath within the coating manufacturer&#39;s specifications. The holding capacity of the fluid control module shall be sufficient to allow complete draining of the process tank  16  for easy maintenance. The preferred arrangement would elevate the process tank sufficiently high to allow gravity drainage to the fluid control module. The fluid control module and its component parts may be configured as needed with respect to holding and transfer capacities.  
      A watertight pan  17  is provided below the process tank  16  to rinse the coating, by immersion, that may adhere to the conveyor chains  24 ,  24 ′ and the transfer media  26 . Fresh permeate solution is continuously supplied to this pan from the fluid control module through header  63  and is overflowed back to the fluid control module through header  64 . This arrangement facilitates cleaning of the transfer media  26  and conveyor chains  24  and  24 ′, reduces paint waste and prevents air drying of the coating on the transfer media  26 , hence increases the efficiency of the coating process.  
      The transfer system  18  includes a pair of spaced apart, parallel conveyor chains  24 ,  24 ′ (the latter shown in  FIG. 3 ) and a transfer media  26  suspended by the conveyor chains  24 ,  24 ′. (Because the conveyor chains  24 ,  24 ′ are identical, and because reference is being made primarily to  FIG. 1  wherein only conveyor chain  24  is shown, the present discussion will focus only on the conveyor chain  24 . However, it is to be understood that the discussion is to have equal application to the conveyor chain  24 ′.)  
      The conveyor chain  24  may be metal or may be composed of a non-conducting material. Alternatively, a metal chain may be modified by having some of its metal links replaced with insulated connectors  15 ,  15 ′ at selected intervals along the length of the chain  24 . The purpose for this modification is to electrically insulate or to isolate certain segments of the conveyor chain  24  as may be desired. In addition, this arrangement allows for electrical contact to be made at the parts input end  10  of the system, thereby insuring “live entry” of the parts; and reduces the possibility of stray current loops at the load and unload areas.  
      The conveyor chain  24  is carried on the apparatus  9  by way of a series of sprockets that support, drive, and guide the chain  24 . These elements have like counterparts on the opposite (that is, unseen) side of the apparatus  9 , and, accordingly, it is to be understood that while only the sprockets on the side shown in the view of  FIG. 1  will be discussed, each of these elements has a counterpart.  
      Included in this array is an outer input end upper idler sprocket  27  that is fixed to an outer input end upper idle shaft  28 , an inner input end upper idler sprocket  30  that is fixed to an inner input end upper idle shaft  32 , an inner output end upper idler sprocket  33  that is fixed to an inner output end upper idle shaft  35 , a drive sprocket  34  that is fixed to a drive shaft  36 , and a drive  38 . The drive  38  can be of any standard industrial type that is known to those skilled in the art for such operations. However, for maximum operational flexibility a variable speed conveyor drive is recommended. In addition, an input end lower idler sprocket  40  is fixed to an input end lower idler sprocket shaft  42 , and an output end lower idler sprocket  44  is fixed to an output end lower idler sprocket shaft  46 . Of course, a greater or lesser number of sprockets and associated shafts may be used as required for complete operation of the apparatus  9 . Sprockets and shafts can be replaced by skids, slides, guides or pulleys, etc. Guidance for the conveyor chain  24  in the coating portion  14 , is provided by an input end idler sprocket  52  and shaft  53  and an output end idler sprocket  54  and shaft  55 .  
      As noted above, connected between the conveyor chains  24 ,  24 ′ is the transfer media  26  (shown in  FIG. 3 ). The transfer media  26  comprises a plurality of non-insulated conductive media segments  70  attached to the conductive contact bars  71  provided. The transfer media  26  is secured in place by fastening a mating hold down bar  72  to the contact bar. The conductive segments make sliding electrical contact with the electrode contact  21  through the contact bars  71  as the conductive segments pass over the electrode  21 . Accordingly, at least some of the segmented media are in contact with the electrode contact  21  at all times as the segmented media take turns passing over the electrode contact  21 . This arrangement also provides continuous cleaning of the electrical contact.  
      The combination of the conveyor chains  24 ,  24 ′ and transfer media  26  form a continuous moving support surface onto which the parts to be coated are loaded, coated, and unloaded. Edge guards  19 ,  19 ′ may be provided to contain the small parts on the transfer media  26 . These edge guards may be affixed to the transfer media  26 , the conveyor chains  24 ,  24 ′ or the tank  16  walls. By providing the transfer media  26  as a plurality of individual segments, repair and replacement of worn segments may be made individually, thus avoiding the need to replace the entire medium.  
      To create the desired electrical potential of the transfer media  26 , one electrode  20  is situated above the transfer media  26  and the other electrode  21  (opposite polarity) contacts the transfer media  26 . Of course, the charge of the electrodes may be reversed and the positioning of the electrodes may be re-arranged, as long as the transfer media  26  is positioned between the electrodes to create the required potential to accomplish electrocoating. Preferably, the transfer media is at ground potential (for safety) regardless of anodic or cathodic operation.  
      As noted above, a conventional fluid control module provides the conditioned electrocoating solution. The coating solution is conveyed into the apparatus  9  by way of an array of eductors strategically disposed within the tank  16 . With particular reference to  FIG. 1 , the eductors are provided as a first row of coating eductors  56  (upper),  57  (lower) and a second row of coating eductors  58  (upper),  59  (lower) and are fluidly connected by way of a common line  60  which is connected to the fluid control module (not shown). These eductors provide a continuous feed of coating to the tank  16  so as to maintain the minimum required coating liquid level  22 . The coating bath solution is overflowed back to the fluid control module through header  62 . They also provide continuous circulation of the electrocoating bath, thereby reducing the settling of coating solids, excessive foam generation, or localized temperature variations.  
      In operation, the parts to be coated must be externally pretreated (not shown) followed by a thorough rinsing in deionized water immediately before the coating process. The cleaned parts are then randomly loaded (manually or automatically) on the input end  10  of the transfer media  26 . The parts may either be loaded while the transfer media  26  is moving or may be loaded while the media  26  is stationary. In either event, the parts are transported by the transfer media  26  through an optional dual air knife  66  to remove excess deionized water and then through the electrocoating bath and eventually resurface at the output end  11  of the apparatus  9 . After the parts resurface, the coated articles, the returning portion of the conveyor chain  24 , and the transfer media  26  pass through a dual permeate spray from header  61  (supplied by the fluid control module), an air knife  67  to remove any excess liquid, and an optional deionized water spray from header  68 . The coated parts are then off-loaded for post treatment and/or curing.  
      The apparatus also provides a method of maintaining optimal coating of the parts by utilizing a method for cleaning the conductive portions of the transfer media  26 . Following the unloading of the coated parts, the top surface of the transfer media is cleaned by a rotating brush  48  or alternative method to remove the deposited, but uncured coating. This may be done in conjunction with a permeate spray  65  and an air knife  69 . By maintaining the transfer media in a properly cleaned condition, electrical contact between the individual parts and transfer media  26  is improved, thereby assuring consistent application.  
      A timer or trip mechanism [neither shown] may be provided to automatically rinse the conveyor chain  24  and the transfer media  26  for a timed system shutdown.  
      Those skilled in the art can now understand from the foregoing description that the broad aspects of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and the following claims.