Conveyors: fluid current – Load flow diverter – divider – or combiner
Reexamination Certificate
1999-09-22
2001-05-08
Ellis, Christopher P. (Department: 3651)
Conveyors: fluid current
Load flow diverter, divider, or combiner
C406S157000, C406S194000, C406S195000
Reexamination Certificate
active
06227769
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the application of powder coatings to substrates and, more particularly, to the application of a powder coating on the interior surface of a three-piece metal can with a high concentration of powder.
BACKGROUND OF THE INVENTION
The process of manufacturing three-piece metal cans typically involves forming a cylindrical can body from a sheet of precoated metal and then attaching two precoated lids to the opposite ends of the can body. In constructing a cylindrical can body, a sheet or blank of metal is formed around a mandrel or stubhorn. The edges of the sheet are either butted or overlapped and then secured together by welding. The welded seam is covered with a protective coating to protect the contents of the can, e.g. food, against metal contamination. The welded seams are coated with either a liquid or powder coating. If a powder coating is used, oversprayed powder is typically recovered from within the container bodies by a vacuum device.
After covering the seam with the protective coating, the can is subjected to heat for a preset period of time to cure the coating material. Where powder coating is used, it is important that a uniform layer of the powder coating, typically a dry resin powder, is deposited on the seam so that the powder melts and fuses to form a smooth adherent coating within the preset period of curing time. If the coating is too thick in some area, it might not completely fuse within the curing time and can later contaminate the contents of the can.
According to the prior art, a coating of liquid material is typically applied to the interior welded seam of a can body as disclosed, for example, in U.S. Pat. Nos. 3,526,027, 4,215,648, 4,259,923 and 4,346,667, with a coating gun attached directly to the end of the welding arm or stubhorn. Other patents which teach the application of coating powder onto a welded seam of a can body with a powder applicator that is secured to the end of the welding arm include U.S. Pat. Nos. 4,215,648, 4,259,923 and Re 33,394.
It is desirable to coat the entire interior of the can with powder to avoid solvent emissions given off from can blanks which are precoated. In addition, liquid coatings typically must be applied in thin layers requiring the application of two coats with a curing step after each coat. This process requires a high amount of energy utilization since two curing ovens, or two passes through a single curing oven, are required. Powder coatings, on the other hand, have no solvent emissions and can be uniformly applied and cured in one step as a thicker coating. Other advantages can also be obtained by coating the interior surface of cans on the welding arm of a can forming machine powder. Up to the present time, however, the industry has not satisfactorily developed commercially suitable equipment to powder coat cans at the end of a welding arm.
U.S. Pat. No. 4,343,436, describes applying a coating of powder to the interior of a hollow can with a spray gun mounted on the end of a welding arm so that a thicker coating is applied to the welded seam as compared to the remainder of the interior surface of the can. This concept, as disclosed in the U.S. Pat. No. 4,343,436, is deficient, for example, because it does not describe how the amount of air-entrained powder needed to coat the entire interior surface of the can be transferred through the narrow passage of the welding arm at satisfactory flow rates without excessive transport air which then has to be removed from the interior of the can.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an apparatus and method of applying a coating of powder on the interior surface of welded hollow can bodies to obviate the problems and limitations of the prior art systems.
It is a further object of the present invention to provide a method and apparatus of applying a stripe of coating powder on the welded seam areas of hollow can bodies to improve upon current powder stripe coating applications.
Yet another object of the present invention is to provide a method and apparatus for simultaneously applying a coating of powder having a first thickness on the longitudinally extending welded seam area and a second thickness less than the first thickness on the remainder of the interior surface of a hollow can or container body.
Still another object of the invention is to improve powder coating of a hollow can or container body with a spray gun mounted to the end of a welding arm by venting off air from a flow of air-entrained powder being transported through the welding arm so that the powder to air ratio of the air-entrained powder flowing into the welding arm is increased.
Another object of the invention is to further improve powder coating of a hollow container body with a spray gun mounted to the end of a welding arm by introducing compressed air into the flow of air-entrained powder exiting from the welding arm so that the velocity of the flow of the air-entrained powder being delivered to the spray gun is increased and a resulting suction force at the downstream end of the welding arm helps draw the air-entrained powder through the welding arm.
A further object of the invention is to introduce a flow of air into the air-entrained powder being delivered to the spray gun to mix the powder more evenly in the air and prevent the powder from concentrating on the bottom of the flow passage.
A still further object of the invention is to provide sufficient electrostatic charging power to ensure that the coating powder adheres to the interior of hollow container bodies being coated in a high speed welding and powder coating machine.
A yet further object of the invention is to provide a flow of cleaning air through the powder spray gun mounted to the end of a welding arm to prevent powder from collecting on the front surface of a nozzle assembly secured to the powder spray gun.
Still another object of the invention is to provide a powder gun assembly mounted to a welding arm wherein the gun assembly is shaped to enhance the attachment of coating powder to the interior surface of hollow container bodies.
Yet another object of the invention is to provide a powder gun assembly mounted to a welding arm wherein an offset nozzle deflector is assembled into the nozzle assembly of a powder coating gun so that the welded seam area is sprayed with more powder than the remainder of the interior surface of hollow container bodies.
An object of the invention is to provide a powder gun assembly mounted to a welding arm wherein a nozzle assembly for spray coating powder incorporates a powder deflector and air deflector assembly for directing a flow of air into the coating powder material being sprayed through the nozzle assembly for controlling the shape of the powder spray and for cleaning the front surface of the nozzle deflector from accumulated coating powder.
Still another object of the invention is to provide a powder gun assembly mounted to a welding arm wherein the gun assembly is effectively grounded through the welding arm to prevent the gun assembly from producing an electric arc.
Yet another object of the invention is to provide a collector hood in surrounding relation to two conveyors moving at different speeds and for collecting oversprayed powder escaping from between the hollow container bodies, vented off air and coating powder from a densifier, and from the powder coating gun when the container bodies are not moving past the coating gun.
According to the invention, a system and method for operating the system include electrostatically applying a coating of powder on at least a portion of the interior surface of hollow container bodies moving along a predetermined path in spaced relation to each other. A powder spray gun is mounted to the end of the welding arm of a can forming machine. The spray gun electrostatically charges air-entrained coating powder and sprays it through a nozzle into the hollow container bodies to coat the interior surface. The air-entrained coating powder is sup
Crum Gerald W.
Kakuta Wataru
Matsunaga Masafumi
Merk Raymond J.
Niemiec Ronald E.
Calfee Halter & Griswold LLP
Dillon, Jr. Joe
Ellis Christopher P.
Nordson Corporation
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