Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1992-05-06
1993-06-29
Niebling, John
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
2041813, C25D 1300
Patent
active
052231046
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates generally to a method for painting an engine by the electrocoating process, and more particularly to such a process in which preselected components of the engine are coated with an electrically nonconductive ceramic material prior to assembly and painting.
BACKGROUND ART
Electrocoating is a well known process for painting electrically charged articles by immersion in a bath of paint having an electrical charge of opposite polarity to that of the article. In this painting process up to 90%, or more, of the paint adheres to the workpiece. Also, paint coatings applied by the electrocoating process have very uniform film properties, and the thickness of the paint film is accurately controllable. Further, there are virtually no runs, sags, or tears in the paint film.
However, for a number of reasons, the electrocoating process has not heretofore been used to paint assembled engines even though that process is especially effective for completely coating a workpiece having sharp edges, points, and hidden or otherwise inaccessible outer surfaces. First, there are surfaces on an assembled engine, such as exhaust manifolds and turbocharger housings, that become very hot during engine operation. If these surfaces are coated with paint, the paint will burn off during operation, producing smoke and undesirable fumes. To avoid paint burnoff it is necessary to carefully mask the surfaces that are subsequently subjected to high operating temperatures prior to the painting operation or, alternatively, strip the surfaces after painting. Both of these operations are labor intensive and difficult to control.
Submersion of the workpiece in a fluid paint bath, an integral step in the electrocute process, makes the requirements for effective masking or subsequent stripping more difficult. Furthermore, paint applied by the electrocoat process has excellent penetrating ability and can readily flow past gaskets, seals, bearings and temporary covers over openings on the engine. This, of course, is very undesirable and can seriously damage the engine.
The present invention is directed to overcoming the problems set forth above. It is desirable to have an effective, economical process for painting an assembled engine. It is also desirable to have such a process wherein preselected portions of the assembled engine are not coated with paint in the course of carrying out the paint process, and further, that paint not enter into the internal cavities and passageways of the engine.
DISCLOSURE OF THE INVENTION
In accordance with one aspect of the present invention, a method for painting an engine having internal cavities and passageways includes coating the outer surface of a preselected component of the engine with an electrically nonconductive ceramic material prior to assembly. The engine is then assembled and, after assembly, has both electrically conductive and electrically nonconductive outer surfaces. A flow of gas is directed into the internal cavities and passageways of the engine and the pressure of the gas in those internal cavities and passageways is maintained at a preselected value. The engine is cleaned and immersed in an electrically charged paint bath. The engine is then connected to a source of electrical charge having a polarity opposite that of the paint. The charged engine is maintained in the oppositely charged paint bath for a length of time sufficient to form a film of paint, having a thickness of at least about 0.013 mm (0.0005 in), on the electrically conductive outer surfaces of the engine. The engine is then removed from the paint bath, the source of electrical charge on the engine is disconnected, and the engine is rinsed. In the rinsing operation, substantially all paint is removed from the electrically nonconductive outer surfaces of the engine. Pressure is released from the internal cavities and passageways of the engine, and the paint film formed on the electrically conductive outer surfaces of the engine is cured.
Other features of the method for painting an eng
REFERENCES:
patent: 3616392 (1971-10-01), Haney
patent: 4074010 (1978-02-01), Knight
patent: 4808441 (1989-02-01), Chattha et al.
Biehler Deane I.
Gephart Harry N.
Gilbert William H.
Grassi John A.
Caterpillar Inc.
Mayekar Kishor
McFall Robert A.
Niebling John
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