Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Patent
1980-12-24
1982-08-10
Newsome, John H.
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
118621, 118627, 361227, 427 33, B05D 104
Patent
active
043438288
DESCRIPTION:
BRIEF SUMMARY
Technical Field
This invention relates generally to spray painting systems and more particularly to spray painting systems utilizing electric fields for improved paint coverage.
BACKGROUND ART
Industry has long utilized various spray coating systems for the application to surfaces of coating materials such as paints, adhering powders and the like. Two great disadvantages are inherent to most of these systems. First, much of the material to be applied is wasted, owing to failure to reach the surface or adhere to the surface. Second, irregular surfaces were often not adequately covered; recesses, for example, have proven especially difficult to coat.
Various improvements of the basic spray system have been developed, most with the goal of decreasing the amount of coating material wasted and/or improving the evenness of coverage of the coating material. Possibly the most significant of these has been the use of electric fields for influencing the trajectory of particles of the coating material as they move in the direction of the surface to be coated. Such systems to date have depended upon the imposition of static electric fields, for example, between the element from which the coating material issues and the surface to be coated, to charge the particles of the coating material and to subsequently control their trajectories. These are known as electrostatic spray systems.
Prior electrostatic systems have been generally of three types. In the first, paint is sprayed past an electrode to which a D.C. voltage is applied. A portion of the paint particles accept a charge from the electrode and are then electrically attracted to an oppositely charged workpiece. In another, a conductive-paint system, having a bulk paint supply, paint pump and delivery conduits, is maintained at the electrostatic charging potential, as, for example, 50 kv to 100 kv. The charged paint system must be protected from access by the operator, complicating servicing of the supply, replenishment of paint and changing of paint color. Also, the electrical energy stored in the charged paint system presents a danger of fire or explosion in the event of a short circuit. The third system grounds the paint supply and spray gun while maintaining the article being coated at an electrical potential of the order of 100 kv. The paint particles are not electrically charged on formation at the gun and the higher efficiency of paint deposition associated with charging the paint particles is not achieved.
Electrostatic spray systems, though a significant improvement over electrically neutral systems, do not adequately coat many highly irregular surfaces. Many electrostatic spray coating operations rely on a final manually directed, non-electrostatic application of coating material to provide acceptable coverage of recessed areas of the surface being treated.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, an electrodynamic coating apparatus has first means for propelling a plurality of particles of a coating material toward a workpiece. A second means is provided for imparting a charge of time-varying magnitude to at least one of said workpiece and said particles.
In another aspect of the present invention, a method for coating a workpiece comprises the steps of charging a workpiece, spraying a coating material toward the workpiece, and exposing the coating material to a time varying electric field.
Spray coating systems typically suffer from uneven coating of the workpiece and wastage of coating material. In partial solution of these problems, the prior art positions an electrode proximate a nozzle from which coating material issues. This electrode is charged to a constant potential to establish an electric field for charging the particles of the coating material. A charge may also be imposed on the workpiece. The resulting electric field surrounding the workpiece controls the trajectories of the particles resulting in improved evenne
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patent: 2221338 (1940-11-01), Wintermote
patent: 2805642 (1957-09-01), Tuttle et al.
patent: 2894175 (1959-07-01), Lamm
patent: 3121024 (1964-02-01), Wampler et al.
patent: 3323934 (1967-06-01), Point
patent: 3900000 (1975-08-01), Gallen
patent: 3937401 (1976-02-01), Luderer et al.
patent: 4230068 (1980-10-01), Itoh et al.
A. Ser. No. 18,019--Bagby et al.--filed 3/6/79 now U.S. Pat. No. 4,258,655.
Lanchantin, Jr. Charles E.
Richards Thomas J.
Smead Robert G.
Caterpillar Tractor Co.
Newsome John H.
Phillips Richard F.
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