Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Reexamination Certificate
2000-03-10
2001-12-04
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
C118S500000, C118S504000, C427S458000, C427S471000
Reexamination Certificate
active
06325899
ABSTRACT:
BACKGROUND OF THE INVENTION
Electrostatic coating processes rely on a charge differential between an article to be coated and what is used to coat that article. In such processes, the article is typically grounded whereas the coating to be applied is endowed with a charge. When the article and coating are then brought into contact with one another, the result is that the coating adheres to the article. It is estimated that more than 10,000 facilities for accomplishing this exist in the U.S. alone.
Most such coating procedures and facilities employ a variety of steps, i.e., a cleaning step, a drying step, a coating step, and a heating step wherein the adhered coating is cured to afford a more desirable and permanent coat. These steps usually take place sequentially using batch operations commonly employed in the art, or else in specialized stations connected by a continuous conveyor line.
Conveyor lines can be of varying length depending on the facility. Articles to be coated are hung from these lines via spaced electroconductive racks or hangers that serve to ground articles attached thereto. Racks and hangers are popular that have the capacity to hang multiple articles. This is accomplished by multiple hooks, usually spot welded at set distances from one another on the same rack. Such rack and hook configurations vary widely in shape, size, and configuration to support different types and sizes of articles.
Once attached, the hangers or racks bearing grounded articles are conveyed through a coating station followed by a curing station. Once coating and curing are finished, the coated objects are removed and the process begins anew.
The hangers and racks of such systems, being expensive, are typically re-used. After passing through the coating station a number of times, that portion or portions of the hanger which contact the article gradually becomes fouled by the coating. The net effect is interference with grounding capacity, with consequent poor coating of the article, and an eventual possibility for spark or fire. This necessitates periodic replacing or cleaning of the racks or hangers, i.e., hooks, which is both time-consuming and expensive.
In the case of cleaning for re-use, conventional cleaning methods include chemical stripping, molten bath stripping, burning, and mechanical stripping, i.e., sandblasting, hammering, and filing. These processes reduce the useful life and capacity of racks, hangers, and hooks by compromising their structural integrity over time. For example, it is the Applicant's experience that hooks break off fairly regularly, thereby lessening the capacity and desirability of continuing with that rack. This necessitates, at considerable expense, either repair of the old rack or replacement with a new rack.
The art has thus far failed to provide a cost-effective alternative.
SUMMARY OF THE INVENTION
The invention provides a surprisingly efficient solution to the long-felt need described above.
It is an object of the invention to provide an electrically conductive intermediate, preferably a pliable one, at an interface or contact point between the hanger and article to be coated. This intermediate may be conveniently replaced or recycled at a comparatively small cost relative to existing procedures and implements.
In a first aspect, the invention features a system for extending the operating life of hangers or racks associated with electrostatic coating. This is accomplished by use of a relatively cheap, electrically conductive, and preferably pliable, intermediate that is suitable for grounding an article to be coated. The intermediate is interposed at a contact junction of the article and electroconductive hanger.
In preferred embodiments the intermediate slideably engages, wraps, or clamps to the hanger and may even adapt in shape or be engineered to accommodate the particular shape of a hook. In most preferred embodiments the article, via an orifice or recess, envelops at least a portion of the hook and intermediate attached thereto.
Various embodiments contemplate different conductive materials and configurations, including shape, of the intermediate. By way of materials, rubber, plastic, tape, and metalic foils all exist that are conductive and suitable, depending on the precise application. At present, most preferred is a silicone sleeve or cap having a hollow interior for receiving a hook portion of a hanger. The article to be coated then fits over or engages this enveloped portion of the hook, usually via an orifice of sufficient dimension.
Concentric “layers” of pliable sleeves are also envisioned for some coating applications wherein one sleeve is positioned over another for rapid exposure of fresh contact surfaces as appropriate. A spent layer is simply peeled away or cut off thereby exposing a fresh one. One such embodiment contemplates a tape made out of an electrically conductive material. Other embodiments contemplate a plurality of hollow tubes, one over the top of the next. These may be slit lengthwise and deposited one over the top of the next, or else constructed in multi-ply layers which are then curled to wrap or clamp to a hanger of interest. Other embodiments contemplate layers of metalic, electrically conductive foil wrapped about each hook. Of course, the diameter differential associated with this technique must accordingly be accommodated by the article.
In other embodiments, at least a portion of the hanger itself comprises a nonmetalic material such as a conductive silicone rubber or plastic. This new material can be conductively and integrally fixed during manufacture, e.g., by injection molding. Preferably, the material is pliable or bendable with the hands or other gentle means to quickly release or free unwanted deposits of coating that hinder contact and hence grounding ability. In such embodiments, the sleeve or intermediate is recyclable.
In still other embodiments, the sleeve intermediate is disposable. Of course, everything including hangers are disposable at a cost, but what distinguishes the present invention is the relatively low cost of the intermediate relative to the cost of replacing or recycling a hanger or rack. In embodiments where the intermediate is integrally a part of the hanger, the novelty resides in the hanger being easily cleaned relative to conventional hangers, e.g., metal ones, and more durable or receptive to cleanings.
In preferred embodiments, the intermediate bridges a hanger and an article to be coated. This bridge may occur in a variety of configurations as one of skill will appreciate. It may occur as described above, or else it may occur by a more comprehensive envelopment, not only of the hanger but also of the entire juncture, including a portion of the article itself. U.S. Pat. No. 5,897,709 issued to Torefors describes one such example. However, instead of a conductive bridge, Torefors specifies a non-conductive (“dielectric”) cover. The present invention, by contrast, serves a dual function in further providing a conductive bridge to facilitate grounding and suitable coating, while simultaneously preserving the operative part of the hanger or hook for future use.
In most preferred embodiments, the intermediate is made of a conductive material, preferably rubber, plastic, tape, foil, or grease that can be conveniently removed, disposed of, replaced, or recycled. Most preferably the intermediate has a resistance of less than 6 megaohms, more preferably one or less megaohms, more preferably still 0.5 megaohms, and most preferably about 0.1 megaohms or less.
Preferably such intermediates are also heat resistant to temperatures up to 600° F., but most preferably resistant in ranges of between about 250° F. and 450° F.
At present, the favorite known material for the intermediate is conductive silicone, which may be fashioned by mixing different conductive and nonconductive commercially available grades in certain proportions testable by one of skill in the using routine experimentation to arrive at a final suitable product. Alternatively, fully conductive commercially available c
Action Caps LLC
Brown Martin Haller & McClain LLP
Gorgos Kathryn
Tran Thao
LandOfFree
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