chapter  17
41 Pages

Automotive finishing and refinishing

The method by which the priming coat on vehicle body shells is applied in the factory is known as electro-deposition. A large dip tank containing about 2500 litres of a water-borne paint is included in the production line. An overhead conveyor carries the body shells from the pre-cleaning area to the dip tank. The paint is charged with electricity and the shell is earthed through the conveyor. The thinner of the paint, being water, acts as an electolyte; the paint solids, i.e. pigment and binder, are ionized and are attracted to the earthed car body. An even coating of paint is thus applied, even on thin metal edges. The thickness of the coating can be varied according to the electrical potential introduced. When the car body moves out of the tank, surplus paint drains out of it and the shell is then rinsed off under sprinklers, which does not affect the electro-deposited coating. The car body is then dried off and baked.