Centrifugal Coating

Q. I am the manager of finishing operations. My plant produces a number of small parts, such as mounting clips and angles, that need to be cleaned and painted. They range in size from 1 ? 1 ? 1 inch to 1 ½ ? 3 ? 8 inches. Most of these parts have flat surfaces.

Since the parts must have high corrosion resistance, they are zinc phosphated before painting. However, coating appearance is not critical. We spend a lot of time racking parts by hand, after which they are pretreated on a six stage zinc phosphate line and painted by spraying. We have heard the terms “centrifuging” and “tumbling” finishing and wonder if these are possible processes for us to use on our products. What is your opinion? J.L.

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A. Centrifugal coating is an excellent way to finish large numbers of small parts. A centrifugal coater is simply a wire or perforated metal basket, for holding parts, which is suspended above a tub of paint. In practice, the tub is raised, or the basket is lowered so the paint covers the parts. The basket is then raised above the level of the paint and spun at high speed, causing the excess paint to be flung centrifugally off the parts onto the sides of the tub allowing the liquid to drain down into the bottom.

I suggest you rack and spray paint your larger parts and centrifugally paint the smaller parts. For convenience, you may want to pretreat the smaller parts by sending them through your phosphatizer in baskets.

An excellent alternative to the centrifugal painting process is barrel finishing the small parts in an electrocoating line. Since your present process is very labor intensive, the savings will pay for a small electrocoating line in a short time.