Electrocoating Fasteners

Q. My company is looking into the possibility of installing an e-coat system for fasteners. What are the equipment and coating options for coating and curing fasteners? (September 2005 Clinic).

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A. Electrocoating of fasteners presents several challenges. While parts can be coated in baskets using monorail or square transfer systems by placing the parts in a “pile” or a single layer (much lower production level), problems include:

Parts stick together or exhibit variation in coating thickness if too many parts are in the “pile.”
Parts with internal threads can have typical “air pocket and puddle” problems.
Cleaning the baskets to ensure grounding contact with only a single or few layers of parts, due to the lack of weight of parts.
The problem of threaded parts was covered in my September 2002 Clinic. Problems of part sticking and cleaning of baskets can be improved by removing the baskets after the post rinse and dumping the parts onto a belt-type oven.

While any e-coat color and resin system can be used on fasteners as long as the fasteners are clean and can establish contact, black cathodic epoxy is the most popular e-coat material for automotive and other applications where corrosion protection is a prime consideration. No major automotive company has approved bulk coating at this time, but the coating and equipment suppliers are working on an acceptable combination. It is probable just a matter of time until it is developed.

Non-automotive parts are being coated and cured in new square transfer barrel-type systems. The parts are rotated throughout the pretreatment, coating and curing processes. The coatings being used have been developed to minimize damage of the coating during curing and provide some “healing” of contact marks.