Painting Aluminum and Brass Castings

Q. I am the Manager of Quality at our plant. We produce brass and aluminum castings used as nozzles. valves, hose and hydrant connections, etc. These products are used by the fire protection industry for indoor applications. Because of possible rough handling, the coating for these products must be durable.
Occasionally, we have small orders for parts that must be painted red. The parts are rough castings of brass and aluminum, and the paint is applied with a brush. However, our problem is that we cannot find a paint that will adhere to the castings.
My question is, can I buy a brush-on paint that I can use in a one-step operation (bucket to casting) with the following qualifications? It must be fast drying (45 min to 1 hour) and brushable (1–2 inch wide). It should have a fair to medium luster. Most importantly, it must adhere to brass and aluminum. I would appreciate and information you can give me on this problem. J. F.

A. The most important thing for you to remember is surface preparation. These castings must be free from loose dirt, corrosion products and oily soils before painting to ensure adhesion. You may be able to coat them immediately after casting before any corrosion products form on the surface. Otherwise they must be degreased, deoxidized, dried and air-blown to remove any of the aforementioned contaminants. If the surface is not properly prepared, the best paint in the world will not adhere.

There are several paints suitable for your application. These include epoxies, polyurethanes and modified versions of both such as acrylic urethanes. The most durable of these are two-component materials that have a limited pot life. This means you must mix only what you can use during the coating’s pot life.