Coating apparatus – Projection or spray type – Applying solid particulate material
Reexamination Certificate
2000-04-14
2002-10-01
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
Applying solid particulate material
C118S326000, C118S064000, C118S634000, C118SDIG007, C454S050000, C052S309100
Reexamination Certificate
active
06458209
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to powder coating spray booths used for containing powder particles that do not adhere to articles intended to be coated. More specifically, the invention relates to a substantially non-conductive spray booth comprising a pair of self-supporting, one-piece, composite, seamless canopy booth halves.
BACKGROUND OF THE INVENTION
Powder spray booths for electrostatic powder coating operations are well known and are used for environmental purposes to contain oversprayed powder coating material that does not adhere to the target article. In addition, the booth facilitates collection of the oversprayed powder material which is often recycled back into the application system. In an electrostatic powder coating operation, the powder particles are charged, such as by one or more high voltage charging electrodes on an electrostatic powder spray application device, such as a spray gun, and the parts are grounded. The difference in potential creates an attraction of the powder particles to the surface of the parts. Typically, such target parts are overhead conveyed through the booth via one continuous slotted opening extending from one end of the booth through the ceiling and out the opposite end of the booth. The target parts are spray-coated therein as they pass at a controlled rate through the booth.
A powder coating booth and application system must be completely cleaned and purged of one color of powder coating material prior to a successive coating operation using a different powder color. Cleaning a powder coating spray booth can be a labor-intensive effort. In a production powder coating environment, minimizing the system down time to change from one color of powder coating material to another is a critical element in controlling operational costs. Powder material tends to get everywhere within the spray booth during a powder coating operation. During extended powder coating runs, the amount of oversprayed powder accumulated within the booth can impact color change time. Seams between booth panels and recessed ledges, such as where access doors or automatic or manual spray application devices may be located, are typically hard to clean areas and tend to hold concentrations of oversprayed powder coating material that could present a contamination risk after a color change. In addition to seams and ledges and other recesses within the booth, charged powder can adhere to booth interior surfaces.
In typical powder coating booth construction, an outer steel framework is provided for supporting individual panel members which form the roof, side and end walls of the booth. These panel members are known to be made of a thermoformed plastic, such as polypropylene, polyvinyl chloride (PVC), polyvinyl carbonate or polycarbonate. The floor may also be of thermoformed plastic or stainless steel construction. In other known embodiments, powder coating spray booths can have metallic walls, ceilings and vestibule ends, as well a metallic floor and exterior support framework.
U.S. Pat. No. 5,833,751 to Tucker is an example of a powder coating spray booth intended to reduce powder particle adhesion to the interior surfaces of the booth during an electrostatic powder spray operation. Tucker discloses a booth chamber comprising a pair of thermoformed plastic shells with smooth curvilinear interior surfaces that are intended to inhibit oversprayed powder particle adhesion. Two identical ends connect with the shells and an external support frame is disclosed, but not shown. Possible booth materials disclosed include polyvinyl carbonate and polycarbonate.
Known booth materials are available in limited sizes requiring some method of seaming to generate the overall size. These seams require much effort and cost to achieve a virtually uninterrupted, seamless surface.
In addition, known powder coating spray booths have numerous features that reduce operational efficiencies. These suboptimal features are evidenced during powder coating color changes between successive runs of different coating colors and during assembly and maintenance of the booth itself. Known powder coating spray booths use metallic external support frames and stainless steel or thermoplastic, floors, walls and ceilings. During an electrostatic powder spray coating operation, oversprayed powder material can actually be attracted and adhere to these booth interior surfaces. Higher concentrations of oversprayed powder coating material are typically seen in the immediate vicinity of the highly conductive steel frame members, which are typically grounded or are somewhat insulated from ground and could act as capacitors. Although thermoformed plastics are typically thought of as insulators, their insulative properties vary and powder particle adhesion can vary with the conductivity and resistivity of these materials. With age, conductivity of the thermoformed plastic materials can increase with corresponding increases in powder particle adhesion, as they can absorb moisture from the ambient air over time. Ultraviolet light is also known to change the physical properties of thermoplastics over time.
In addition, typical booths have numerous design features that act to increase accumulated oversprayed powder coating materials in the spray booth, thus increasing cleaning times during color change operations. In booths using panel members connected with each other and supported by an external frame, numerous seams exist throughout the booth interior that entrap oversprayed powder coating material, thereby making the booth harder to clean during a color change or routine booth maintenance. In addition to the seams, ledges are present in some powder coating spray booths on which spray gun application devices rest and are mounted, and where openings for doors and other access portals are reinforced and secured, for example. These ledges can either extend into the booth or, more typically, extend away from the inner surface of the booth. Even if otherwise angled or curved toward the floor from the typically vertical sidewalls, oversprayed powder coating material still tends to accumulate in these areas, thus making them more difficult to clean, as well.
In addition to the reduced spray booth operating efficiencies due to powder coating material adhesion as a result of electrostatics and booth design, booths constructed with frames and panel members and booths made of thermoformed plastics increase assembly and maintenance times, thus further reducing operational efficiencies. Known booths require external frames for structural support. Booths constructed of numerous individual wall and ceiling panel members must have their seams welded or otherwise sealed together. Installation of booths that require external frames for structural support of any kind increase booth installation time. Booths having multiple panels forming the walls, ceiling and floors further increase assembly time, and at best result in a semi-rigid enclosure that falls short of a preferred robust containment envelope that is suitable for industrial environments.
Maintenance of thermoformed plastic booths is also a concern and has a negative impact on efficient booth operations. With thermoformed plastic booth materials, workers and parts can accidentally nick and scratch the booth internal surfaces rather easily. These surface imperfections and discontinuities are hard to clean areas and act to entrap powder coating material therein. In addition to increased cleaning times, maintenance of the booth to remove the scratches and nicks are time-intensive at best, and results of repair activities cannot restore a surface to original condition. Both the ease at which thermoformed plastic booths can be scratched and the time involved in repairing them make thermoformed plastic booths less than ideal as a powder coating booth material.
It is desired, therefore, to provide a powder coating booth that overcomes these and other shortcomings.
SUMMARY OF THE INVENTION
The invention herein provides for an improved powder coating spray booth. In o
Calfee Halter & Griswold LLP
Crispino Richard
Nordson Corporation
Tadesse Yewebdar T
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