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Preparing steel for painting (descaling)

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I have started a small (Me!) company making steel furniture and other items (park benches, tables, etc.). I usually finish with a primer, then Rustoleum. Most of the items are made from hot roll, and some involve smithing. I've been de-scaling the steel using muriatic acid [linked by editor to product info at Amazon], then rinsing with a hard stream of water. I can't seem to avoid getting some oxidation during the drying process. here's my questions:

1. How important is the de-scaling? how clean does the metal need to be ? Am I going about it the right way?
2. Is that little surface rust acceptable, or is there an easy way to eliminate it? (I can't always reach the parts with a wire brush, and that's unproductive)
3. How does large scale industry do it? how clean is their metal before powder coating, for example?
4. Are there different kinds of primers?

The stuff I'm making is looking good, I just need some guidance about how neurotic to be with the metal preparation. Thanks in advance for those of you willing to share your expertise.

Art Thompson
Art Works

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Art:

Descaling hot rolled steel is very important, because the heat scale does not provide a very good adhesive surface for the coating. You are only missing one thing. A short term corrosion inhibitor for the rinse water. Once you have removed the scale, the surface of the steel is very active and will begin to corrode almost instantly, because you have left the surface acidic.

There are two ways to go here: You can phosphatize the surface with an iron phosphate solution with the pressure washer, or apply an alkaline rust preventative mixed with the rinse water to prevent flash rusting while the parts dry.

Both ways are being used by industrial plants that paints very large items from heavy equipment to dumpsters. Any of the pretreatment suppliers here on finishing.com or the corporate members of the Chemical Coaters Association could help you with your process.

Craig Burkart - Naperville, Illinois

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A cheap alternative to a phosphate system is to rather use a mixture of sulphuric and phosphoric acid to remove the scale.

A thin layer of iron phosphate on the surface provides short term protection.

Laurence van Niekerk

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