Electrostatic coating

Electrostatic coating is a manufacturing process that employs charged particles to more efficiently paint a workpiece. Paint, in the form of either powdered particles or atomized liquid, is initially projected towards a conductive workpiece using normal spraying methods, and is then accelerated toward the work piece by a powerful electrostatic charge.

An addition to the electrostatic coating (or e-coating) process is dipping electrically conductive parts into a tank of paint that is then electrostatically charged. The ionic bond of the paint to the metal creates the paint coating, in which its thickness is directly proportional to the length of time the parts are left in the tank and the time the charge remains active. Once the parts are removed from the paint tank, they are rinsed off to remove any residual paint that is not ionically bonded, leaving a thin film of electrostatically bonded paint on the surface of the part.

The workpiece travels down a conveyor belt towards a paint booth, or paint tank, where it is sprayed with, or dipped into, electrostatically charged paint particles. Integrated into a powder paint booth is a powder recovery unit, which recovers between 95% and 100% of the paint over-spray coatings. After the workpiece is coated, it continues on the conveyor belt to an oven, where the paint is cured. The benefits to the process of electrostatic coating is the ability to recover the little over-spray and having the process automated which will cut costs. The reason for the little over spray is the paint particles that do not hit the piece will turn in the air and go back to the piece. There are also some drawbacks to the process: everything in the area of the coating must be grounded to prevent static buildup and can easily arc, damaging the hanging devices and/or the locations where the hanging devices rest on the conveyor. All hangers, conveyors, etc. must be cleaned often to ensure a good ground and prevent anyone in the area from getting a severe shock. In an airborne system, any recesses on the piece that is being coated can be missed because the electrostatic paint is more attracted to corners and sharp edges; this means that another process for coating can be a better option if the piece has recesses. In the dipping process, air entrapment can occur in blind holes and deep recesses, so the positioning of the part as it enters the paint tank is critical in removing any trapped air that will restrict paint coverage.

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Wikipedia