Abstract:
Devices and methods for continuous cleaning of contaminant-coated hangers or racks by removing the overspray contaminant that is detrimental to the powder coating operation. Exemplary cleaning systems use radio frequency (RF) energy to heat the overspray coating and soften it. The coating is heated to an intermediate level that is less than the incineration point, wherein the coating would be reduced to ash.

Description:
[0001]     This application claims the priority of U.S. provisional patent application Ser. No. 60/709,576 filed Aug. 19, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates generally to systems and methods for removal of overspray residue, or other residue, from hangers used in in-line powder coating conveyor systems. In other aspects, the invention relates to the cleaning of component support racks.  
         [0004]     2. Description of the Related Art  
         [0005]     Powder coating is a process of coating an article, such as an automotive part or other metallic object, with a powdered paint coating and then curing the coating with heat to provide a desirable finish. Powdered paint is blown toward the article as a spray under pneumatic pressure. Electrostatic charge is used to cause the powdered paint particles to adhere to the article. A popular method of powder coating a large number of articles is an in-line conveyor-type powder coating system wherein hooks or hangers support the articles to be powder coated on a moving conveyor system. The articles move through spraying and curing stations to provide the desired finish upon the articles. Electrostatic charge is transmitted through the hangers to the article being supported and conveyed through the system.  
         [0006]     Effective powder coating requires that the support hanger be relatively free from overspray residue where electrical or ground contact is made between the support hanger and the part to be coated. Overspray residue build-up on the support hanger will significantly reduce the grounding needed to make the electrostatic attraction of the powder particles to the article effective. If the overspray residue is not removed, significant problems develop in the powder coating process. The powder is not sufficiently attracted to the article, and this may result in uneven coatings or high consumption of powder used to coat the articles. In some instances, improperly coated parts are scrapped because it is not economical to remove the coating from them and recoat them.  
         [0007]     To solve the problem of coating overspray, the hangers are typically removed from the conveyor line after a certain number of spray runs and then are placed in a burn-off oven to remove the overspray coating. However, this solution has significant drawbacks. Removing the hangers is time consuming and requires a significant number of replacement hangers. In addition, the cost of operating the burn-off oven is significant.  
         [0008]     Attempts have been made to develop “in-line” hanger cleaning systems wherein support hangers are cleaned of overspray without the necessity of removing them from the conveyor line. One such system is described in U.S. Pat. No. 6,520,097 issued to Shiveley. Shiveley describes an in-line conveyor-type powder coating system wherein hangers are cleaned by passing them through an in-line hanger heating station that heats the hangers with a high-intensity energy source to quickly bring the coating on the hangers to the coating incineration point. U.S. Pat. No. 5,617,800 issued to Moreschi et al. describes a similar system wherein the hangers are heated to a temperature sufficient to thermally decompose the paint particles to ash and gaseous combustion products. U.S. Pat. No. 3,830,196 issued to Guttman et al. also describes a similar in-line cleaning system in which hangers are passed through a heating oven to cause accumulated paint to be reduced to ash. The ash is then washed off by rinsing. In each of these in-line hanger cleaning systems, high energy thermal sources are used to heat the hangers to the point where the coating is incinerated to ash. Unfortunately, incinerating the coating overspray to the point where it is reduced to ash creates significant fumes, and it is necessary to provide elaborate venting for such fumes. The creation of these fumes causes safety concerns. The burn-off oven tempers (softens) the hook and reduces its load carrying capacity. Also, the expense associated with heating the hangers to a degree to cause the coating to be incinerated is significant.  
         [0009]     The problems associated with overspray on hangers extend as well to metal racks that are used to hold smaller components during the powder coating process. These metallic racks are typically hung from the hangers of the conveyor and must remain substantially free of coating residue in order to be properly grounded. Unfortunately, there is no effective technique for cleaning these racks other than use of a standard burn-off oven, which, as noted previously, is significantly costly in terms of fuel and labor costs.  
         [0010]     The present invention is directed to overcoming the problems of the prior art.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention provides improved devices and methods for continuous cleaning or contaminant-coated hangers or racks by removing the overspray contaminant that is detrimental to the powder coating operation. In a preferred embodiment described herein, an in-line cleaning system uses induction heating via radio frequency (RF) energy to induce eddy currents in the hanger to heat the overspray coating and soften it. The coating is heated to an intermediate level that is less than the incineration point, wherein the coating would be reduced to ash. Other heating sources will work, but are not preferred as they entail a greater cost.  
         [0012]     In a currently preferred embodiment, hanger guides are used to physically guide the hangers through the induction coils so that they remain substantially at a predetermined distance from the coil surface during conveyance. After the coating is softened by the heating, abrasive brushes or other tools are used to remove the softened coating.  
         [0013]     An alternative embodiment of the invention is also described wherein components-carrying racks can be cleaned of overspray using a conveyor system.  
         [0014]     The systems and methods of the present invention provide a number of advantages over conventional systems for cleaning support hangers. The in-line cleaning system of the present invention utilizes a reduced heating temperature for cleaning of the hangers. This results in significant savings in energy and cost. Also, the reduced heating temperature eliminates the concern of fumes created by the incineration process and does not detrimentally affect the metallurgy of the hanger. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     For detailed understanding of the invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which reference characters designate like or similar elements throughout the several figures of the drawings.  
         [0016]      FIG. 1  is a schematic illustration of an in-line conveyor-type powder coating arrangement that incorporates an exemplary hanger cleaning system constructed in accordance with the present invention.  
         [0017]      FIG. 2  is a side view showing components of the hanger cleaning system in greater detail.  
         [0018]      FIG. 3  is an isometric perspective view of portions of the hanger cleaning system shown in  FIG. 2 .  
         [0019]      FIG. 4  is an illustration of an exemplary hanger heating element used in the hanger heating system shown in  FIGS. 2 and 3 .  
         [0020]      FIG. 5  is an illustration of an alternative exemplary hanger heating element used in the hanger heating system shown in  FIGS. 2 and 3 .  
         [0021]      FIG. 6  is an illustration of an alternative embodiment of the present invention for cleaning disassembled rack components associated with an in-line powder coating process. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]      FIG. 1  depicts an exemplary in-line conveyor-type powder coating system  10  having an in-line moving conveyor  12  with belt or chain (not shown) that moves along a monorail  14  under the impetus of a prime mover (not shown), as is known in the art. Carriers  16  are suspended from the chain and carry removable hangers  18 , of a type known in the art for supporting articles  19  to be coated with paint. Although the monorail  14  is depicted in  FIG. 1  as being in a straight linear arrangement, it may in fact be arranged in a circular, oval, or other closed shape so that the carriers  16  are moved along a continuous track.  
         [0023]     The coating process equipment of the powder coating system  10  includes a powder spray station  20  and a curing station  22 , both of the variety known in the art for powder coating operations. As the structure and operation of these components are well known, they will not be described in any detail herein.  
         [0024]     In addition to the coating process equipment, the powder coating system  10  includes a hanger cleaning system  24  in accordance with the present invention. The structure and function of the hanger cleaning system will be described in greater detail shortly. In operation, movement of the hangers  18  and articles  19  is in the direction of arrow  26  in  FIG. 1 . The hangers  18  and articles  18  move first through the powder spray station  20 , where they are sprayed with powdered paint, which is electrostatically attracted to the articles  19  and hangers  18  via grounding of the hangers  18  through the monorail  14 . Upon exiting the spray station  20 , the hangers  18  now are coated, at least partially with overspray. Next, the articles  19  and hangers  18  are moved through the curing station  22  wherein the paint coating is cured onto both the articles  19  and hangers  18 . Articles  19  are then removed from the hangers  18 . The hangers  18  continue through the hanger cleaning system  24  wherein they are cleaned of the accumulated overspray. The hangers  18  are now available to be reused by the powder coating system  10 .  
         [0025]     In a currently preferred embodiment, the hanger cleaning system  24  includes a hanger heater  26  and a residue cleaner  28 . The hanger heater  26  preferably includes two shoes  30 ,  32  of a split induction coil, as depicted in  FIGS. 3 and 4 . During operation, the shoes  30 ,  32  are disposed on either side of the hanger  18  being heated. In an alternative embodiment, illustrated in  FIG. 5 , the hanger heater  26  comprises a single induction heating coil source  34 . Electrical lines  36  extend from the hanger heating sources to a power source  38  that is used to energize the hanger heater  26 . The hanger heater  26  is capable of heating the hangers  18  to a point wherein the outer 5-10 thousandths of an inch of the surface of the hangers  18  reaches a temperature in the currently preferred range from about 500° F. to about 750° F. This range of temperatures is sufficient to break the bond of the coating, or delaminate the coating, from the base metal surface of the hanger  18 . However, it is not high enough to incinerate the coating and reduce it to ash. For optimal heating, the hangers  18  should pass from about ⅛″ to about ⅜″ away from the heating source  34  or heating sources  30 ,  32  during operation of the system  10 . Preferably, each hanger  18  should pass adjacent the heating sources  30 ,  32  or heating source  34  for a period of time of about 4-8 seconds, although the specific length of time will vary somewhat depending upon the speed of the conveyor  12  and the size of the power source. To help accomplish this, it is currently preferred that the hanger cleaning system  24  incorporate a hanger alignment guide system  50 , as will be described. Suitable inductive coils for use as hanger heater  26  are available commercially from, for example, Inductoheat, Inc. of Madison Heights, Mich. The hanger heater  26  is preferably cooled by water pumped from a cooling heat exchanger (not shown).  
         [0026]     The residue cleaner  28  preferably comprises a pair of rotatable wire brush heads  40  that are each rotated by a rotary motor  42  (one shown in  FIG. 2 ). The brush heads  40  are located so that they will contact the outer surface of each of the hangers  18  as they pass adjacent the brush heads  40 , as  FIG. 3  illustrates. In an alternative embodiment, the residue cleaner  28  can comprise one or more stationary brushes that will contact the hangers  18  to help remove the delaminated coating. It is preferred that a residue collection bin  44  be located below the brush heads  40  to collect those deposits that are scraped away from the hangers  18  by the brush heads  40 .  
         [0027]     A vacuum system  46  with vacuum heads  48  may be located proximate the residue cleaner  28  to evacuate the residue removed from the hangers  18  by the residue cleaner  28 . The vacuum system  28  contains an appropriate cyclone separator and filters (not shown) of a type known in the art to remove the fumes. A suitable vacuum system for this application would be available commercially from, for example, Donaldson Torit, 100 North Central Expressway, Suite 800, Richardson, Tex. 75080.  
         [0028]     Hanger guide  50  is made up of a pair of moving friction belts  52  that will contact the lateral sides of the hangers  18  and physically move them past the induction coil hanger heater  26 . The hanger guide  50  centralizes and orients the hangers  18  so that they pass within a predetermined proximate distance of the hanger heater  26 . In a currently preferred embodiment, the hanger guide  50  locates the hangers  18  from about ⅛ inch to about ⅜ inch from the heating sources  30 ,  32 , or  34  for optimal effect. A frame  54  ( FIG. 2 ) is secured to the monorail  14  and serves to support and partially enclose many of the components of the hanger cleaning system  24 .  
         [0029]      FIG. 6  depicts an alternative embodiment of the present invention wherein a cleaning system  100  is used to clean the components  102  of a rack that is used to retain smaller components that are being coated with paint. The exemplary cleaning system  100  shown in  FIG. 6  includes a first conveyor  104  onto which rack components  102  to be cleaned are placed. It will be understood by those of skill in the art that the components  102  are portions of typically rectangular metallic support racks of a type known in the art which may be readily disassembled into component parts for cleaning. The components  102  will pass from the first conveyor  104  to a second conveyor  106  through an escapement or gate  108  that will help to orient the components  102  and regulate their entry onto the second conveyor  106  (i.e., the components  102  are passed onto the second conveyor  106  one at a time). The second conveyor  106  includes a component guide  109  with a converging throat that leads to component heater  110 . The component heater  110  is an induction coil-style heater of the same type as described previously for use with the hanger cleaning system  24  described earlier. The component heater  110  is powered by a suitable power supply  112 . Rotary abrasive brushes  114  are located downstream of the component heater  110 . A collection bin  116  is positioned at the end of the second conveyor  106  for collection of the cleaned components  102 .  
         [0030]     In operation, coating-contaminated components  102  are loaded onto the first conveyor  104  and pass through the gate  108  to the second conveyor  106 . The second conveyor  106  conveys the components  102  through the guide  109  and the component heater  110  whereupon the components  102  are heated to a point that is less than the incineration point wherein the coating would be reduced to ash. The heated components  102  then are conveyed through the abrasive brushes  114 , wherein they are cleaned of the heated coating.  
         [0031]     Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.