Apparatus and methods for in-line cleaning of contaminant-coated hangers

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

This application claims the priority of U.S. provisional patent application Ser. No. 60/709,576 filed Aug. 19, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

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.

2. Description of the Related Art

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.

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.

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.

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.

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.

The present invention is directed to overcoming the problems of the prior art.

SUMMARY OF THE INVENTION

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.

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.

An alternative embodiment of the invention is also described wherein components-carrying racks can be cleaned of overspray using a conveyor system.

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

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.

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.

FIG. 2 is a side view showing components of the hanger cleaning system in greater detail.

FIG. 3 is an isometric perspective view of portions of the hanger cleaning system shown in FIG. 2.

FIG. 4 is an illustration of an exemplary hanger heating element used in the hanger heating system shown in FIGS. 2 and 3.

FIG. 5 is an illustration of an alternative exemplary hanger heating element used in the hanger heating system shown in FIGS. 2 and 3.

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

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

Claims

1. An apparatus for removing powder coating residue from an object comprising:

a heater to heat powder coating residue coating the object to a temperature sufficient to soften the residue but not sufficient to incinerate the residue; and

a residue cleaner for removing softened residue from the object.

2. The apparatus of claim 1 wherein the heater heats the object such that an outer portion of the object is heated to a temperature within the range from about 500° F. to about 750° F.

3. The apparatus of claim 1 further comprising an in-line conveyor system to convey articles past the heater and the residue cleaner, the conveyor system comprising:

a moveable chain carried on a rail; and

a hanger retained upon the chain for removably supporting articles to be powder coated.

4. The apparatus of claim 1 wherein the residue cleaner comprises a brush.

5. The apparatus of claim 1 wherein the object to be cleaned comprises a hanger.

6. The apparatus of claim 1 wherein the heater comprises an induction coil unit.

7. A system for removing coating material from hangers suspended from an in-line conveyor system used to move articles through a zone for applying coating to the articles, the system comprising:

a hanger heater for heating a hanger to a temperature sufficient to heat coating material on the object to a temperature sufficient to soften the coating but not sufficient to incinerate the coating; and

a residue cleaner for physically removing heated coating material from the hanger.

8. The system of claim 7 wherein the hanger heater comprises an induction heating coil adapted to heat the hanger to a temperature such that an outer surface of the hanger reaches a temperature in the range from about 500° F. to about 750° F. to soften coating accumulated on the hanger but not incinerate it to ash.

9. The system of claim 7 wherein the residue cleaner comprises:

a rotatable wire brush head; and

a rotary motor for rotating the brush head.

10. The system of claim 7 further comprising a hanger guide to orient the hanger to pass within a predetermined distance of the hanger heater.

11. The system of claim 10 wherein the hanger guide comprises a moving friction belt.

12. The system of claim 10 wherein the predetermined distance is from about ⅛ inch to about ⅜ inch.

13. A method for removing coating material from hangers suspended from an in-line conveyor system used to move articles through a zone for applying coating to the articles, the method comprising the steps of:

heating a hanger to a temperature such that the outer surface of the hangers reaches a temperature in the range from about 500° F. to about 750° F. to soften coating accumulated on the hanger but not incinerate it to ash; and

removing the coating accumulated on the hanger.

14. The method of claim 13 wherein the step of heating the hanger further comprises heating the hanger until the outer 5-10 thousandths of an inch of the surface of the hanger reaches a temperature in the range from about 500° F. to about 750° F.

15. The method of claim 13 wherein the step of heating the hanger further comprises moving the hanger to a predetermined distance from a hanger heater that is in a range from about ¼ inch to about 1 inch.

16. The method of claim 15 wherein the hanger is moved to the predetermined distance for a predetermined period of time that is from about 4 to about 8 seconds.

17. The method of claim 16 wherein the step of heating the hanger further comprises contacting the hanger with a hanger guide to move the hanger to the predetermined distance for the predetermined period of time.