Removing Anti-Corrosion Compound

Q. My company manufactures industrial grade mixing and blending equipment. We are currently applying a petroleum-based anti-corrosion compound between the flat machined mating surfaces of steel castings during our assembly procedure. We do this to eliminate corrosion of these surfaces when they are exposed to severe environmental conditions. The compound is low enough in viscosity that when the machined surfaces of the castings are bolted together, the flatness tolerance between the two plates is not lost. Our problem is that the compound eventually seeps out onto the other surfaces intended to be painted after assembly. We use solvent-soaked rags to clean the anti-corrosion compound from the surfaces to be painted. We have been experiencing paint adhesion failures in these areas. What can we do to solve this problem? S.O.

 

A. It is well know that solvent wiping is not always a good pre-paint cleaning method. If you must solvent wipe, use clean rags and change the rags and solvent often. If the casting surface is rough it may be necessary to use a stiff brush to assist contaminant removal. If the surface is very porous, it may be impossible to remove the contaminant by this method.

It appears to me that your paint adhesion problem is caused by and aggravated by the petroleum-based anti-corrosion compound that continues to seep out from between the mating surfaces while solvent wiping. The solvent, which is drawn into the mating surface by capillary action, dilutes and reduces the viscosity of the anti-corrosion compound and causes more of the contaminant to seep out onto the surface to be painted. To eliminate this problem, it may be necessary to use a steam jenny to apply cleaner/phosphate chemicals to the assembly surfaces. On the other hand, masking the machined surfaces and painting the outside surfaces prior to application of the anti-corrosion compound and final assembly may provide a better solution to the problem.