Electrostatic coating

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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 workpiece by a powerful electrostatic charge.[1]

Process Characteristics

  • Uses a high voltage electrostatic charge which is applied to both the workpiece and the sprayer mechanism
  • Is incredibly efficient, using 95% of sprayed paint due to reduced over-spray and better wrap-around
  • Paint materials can be either powdered or liquid
  • Process can be either automatic or manual
  • Workpieces must be conductive
  • Workpieces are usually baked after coated.

Process

The workpiece travels down a conveyor belt towards a paint booth, where it is sprayed with electrostatically charged paint particles. Integrated into the 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 automatic 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. All hangers, conveyors, etc. must be cleaned often to ensure a good ground and prevent anyone in the area from getting a severe shock. 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. [2]

Workpiece Geometry

The geometry of the workpiece is limited only by the size of the paint booth. Using Electrostatic coating it is possible to apply paint in various thicknesses being limited only by the paints tendency to run and therefore ruin the coating if applied in too thick a manner. It is usually preferred to apply many thin coats as opposed to one thick coat.

Setup and Equipment

The workpiece may be delivered to the coating booth in any fashion, most commonly using either hands or pliers. After passing through the booth and getting coated the workpiece then either goes into a baking oven or out into the open air to allow the paint to cure on the part. Many different spray nozzles may be used depending on the desired paint consistency and the shape of the workpiece.

Typical Tools and Geometry Produced

There are a wide variety of spray nozzles available for use in electrostatic coating. The type of nozzle used will largely depend on the shape of workpiece to be painted and the consistency of the paint.

Example

Visit http://science.discovery.com/videos/how-its-made-shock-absorber.html to see how the process of Electrostatic Coating is used in the finishing process during their construction. Example is during the final minute of the video

References

  1. ↑ Manufacturing Processes Reference Guide, 1st ed. , Robert H. Todd, Dell K. Allen, and Leo Alting, 1994
  2. ↑ http://www.etfinancial.com/coatingsequip.htm
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