Phosphating on Differing Surfaces

Question:

Is a smooth surface better for phosphating or a rough one? We are thinking of moving to a steel media in our mass-finishing equipment instead of the ceramic media we are using now. There is no question the steel media provides for a better finish but will it affect the phosphating process negatively? T.T.

Answer:

I assume you are painting your parts following the phosphate process. In general, a rough surface is thought to be better for paint adhesion. The phosphating process should not be significantly impacted by it. The primary result of moving to the new mass-finishing media could be an increase in sludge and chemical usage in the phosphate step. This would be attributable to the increased total surface area the chemical is working on. Even though the apparent surface area is the same, the microscopic surface area could be much greater if the surface is significantly rougher. The increase in chemical usage may then also generate an increase in bath sludge. Carryover of steel media into this step could also produce the same effects.