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Science of Automotive

Deposition of the Coating

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Following pretreatment, or conversion coating, the vehicle body or part is immersed in the electrodeposition dip tank. The electroprimer contained in this tank is typically 77-84% water, 15-22% paint solids, and less than 1% solvent. Upon the application of an electric potential (i.e., voltage), a paint film containing 75-90% solids deposited onto the part or body.

During deposition, the exterior surfaces of the workpiece are coated first until the thickness of the applied film begins to act as a resistor. As this exterior surface resistivity begins to occur, remote interior surfaces draw increasing current, and deposition takes place on these surfaces. The process continues until all exterior and interior surfaces have been coated.

When deposition is completed according to immersion, or dwell time, the workpiece is removed from the dip tank. Adhered to the deposited coating is a high solids liquid referred to as "cream-coat." This material must be removed via post rinsing to achieve acceptable appearance of the applied coating. Also contained within the body is 1-2 gallons of paint that must be recovered and retained in the system for efficient paint utilization.



DuPont expresses appreciation to Xcel Industries for use of photograph.