Steam Cleaning/Phosphating

Q. I am a manufacturing engineer for my company where we make a number of products used outdoors. One of the products is a structural steel frame fabricated from channel stock that serves as a base for some of our other products. Because of its large size, the frame will not fit through our phosphatizing pretreatment system.

Our present manufacturing procedure for these parts is: weld them together; coat them with a rust inhibiting oil; store them until they are needed; pretreat them with a cleaner/phosphate with a steam cleaner; and then dip them in a narrow paint tank. Unfortunately, we have been getting field complaints that the paint is peeling off in certain areas even before shipping. Apparently, this is because of insufficient degreasing and phosphating with the manually operated steam cleaner. As you know, this pretreatment process is difficult to control. Do you know of any better alternatives for our frame painting? F.E.

A. I agree with your assessment of your problem. There can be a lack of proper cleaning and phosphatizing using steam cleaners on complicated shaped parts. It is extremely difficult to spray the chemicals into channels and corners. Furthermore, even if your conveyorized phosphating line could handle these parts, spraying the chemicals onto all surfaces still could be a problem. The best way to pretreat these complicated shaped parts would be by immersion. I suggest a three-stage system that includes an alkaline cleaner, water rinse and phosphate. The system could use narrow tanks the same size and shape as your paint dip tank. The next best way to solve your problem would be using one tank containing a cleaner/phosphate chemical solution. Although not the best, it would still be better than using a steam cleaner on parts having complicated shapes.