Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Patent
1993-09-07
1996-12-10
Beck, Shrive
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
427483, 118621, 118627, B05D 104, B05B 5025
Patent
active
055828752
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
The present invention relates to a process and an apparatus for insulating a paint supply during electrostatic painting. More particularly, the present invention relates to a process and apparatus for preventing electrical continuity in a stream of electrically conductive paint, such as water-based or aqueous paint during electrostatic painting.
In conventional electrostatic painting, oil-based paint is used to achieve painting efficiency. In conventional electrostatic painting an electrode applies a charge to a paint drop as it exits a paint spraying nozzle, enabling the droplet to adhere to a painted surface at a lower potential. Conductive paints prevent the application of a charge to an exiting droplet by forming a conductive path from the paint spraying nozzle back to a paint supply which shorts a charge-applying electrode. Oil-based paint is well suited for electrostatic painting because it is nonconductive and therefore incapable of forming a conductive path. Yet, oil-based paint causes air pollution. Additionally, oil based paint is toxic and flammable. Current fire laws restrict its use.
Water-based paint is less toxic and less flammable than oil-based paint. Because water-based paint is electrically conductive (due to the ions naturally present in water), a paint supply stream drips through a paint spraying nozzle to prevent continuity.
Japanese Examined Patent Publication No. 56-3108 discloses a method for insulating an aqueous paint in electrostatic coating. The method for insulating the paint includes pumping an aqueous conductive paint into an insulated, sealed chamber. Paint enters the insulated, sealed chamber through a hole in the top and drops on top of a dome-shaped ceiling member. Paint flows from a raised center of the ceiling member to a lower edge and falls over a hole in the edge. Paint drops fall downward through holes in a series of circular dropping plates. Optimally, paint drips downwardly without touching an inner wall of the chamber.
However, as dripping paint enters a lower region of the chamber, the possibility that paint will adhere to an inner wall of the chamber increases. Once paint sticks to the inner wall, the inner wall becomes electrically conductive. A high voltage applied to a tip of a paint spraying nozzle charges the paint stuck on the inner wall. The charged paint adhering to the inner wall attracts oppositely-charged drops of paint to the inner wall. Paint eventually covers the entire inner wall of the chamber, creating a conductive path from the paint spraying nozzle to a paint supply. The conductive path shorts the electrode and prevents electrostatic painting.
The present inventor has discovered a method and apparatus that avoids the problems of conventional electrostatic painting.
OBJECTS AND SUMMARY OF THE INVENTION
It is a main object of this invention to provide an apparatus and a process for insulating an electrically conductive paint such as an aqueous paint during electrostatic painting.
According to an embodiment of the present invention, a process for preventing electrical continuity in a stream of a conductive paint in an electrostatic painting, includes: pumping a stream of a conductive paint into an insulating chamber, dividing the stream into a plurality of radial substreams, dripping the paint downward through the chamber, bleeding a charge forming on paint adhering to an inner wall of the insulating chamber through the inner wall to a grounding electrode having a lower electric potential than that of the inner wall.
The process of preventing electrical continuity in the paint stream includes vertically stacking a plurality of containers to form the insulating chamber, forming openings in lower ends of each container, dripping the paint straight down through the openings, and attaching a grounding electrode on an outer wall of each container.
According to a further aspect of the present invention, an apparatus for preventing electrical continuity in a stream of conductive paint in electrostatic painting, includes: a storage conta
REFERENCES:
patent: 3893620 (1975-07-01), Rokadia
patent: 3934055 (1976-01-01), Tamny
patent: 4879137 (1989-11-01), Behr et al.
patent: 4892750 (1990-01-01), Soshi et al.
patent: 4995560 (1991-02-01), Lasley et al.
Beck Shrive
Parker Fred J.
Yugenkaisya Kotogawa Kenzai Kogyosho
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