Cleaning Lime from Forged Steel

Question:

At our plant we electrocoat forged steel parts. We are having problems removing the lime from the parts. Is adding a pickle stage the answer? D.P.

Answer:

A good, basic cleaning process (including the acid) may improve the cleanliness of the parts. A strong, alkaline cleaning stage would be a good start. This would help in removal of lubricants, fatty oils and metal soaps that all may be present on the forging. An acid cleaning stage would also be beneficial for removal of residual contaminants. Depending on the degree of contaminants remaining, a relatively weak phosphoric acid may be adequate (10-20% by volume, heated to 120-160F). If there is still significant residue on the part, a stronger mineral acid will be needed in order to pickle the part. A treatment with sulfuric acid (5-10% by volume, ambient to 120F) should remove any remaining residue. Thorough rinsing will need to be done after each process step. If parts are not going directly into the electrocoat, a rust inhibitor will likely be required to provide short-term rust protection.

Additionally, I would consult with your electrocoat paint supplier, since they should also have knowledge of the pretreatment steps necessary in order to obtain an adequate coating. They may also supply pretreatment chemicals that would improve the process. Always be careful when handling concentrated acids and follow the recommendations on the Material Safety Data Sheet provided.