plating, anodizing, & finishing Q&As since 1989
Steel pickling and side effects
I use non-pickled steel to manufacture parts for automobiles. In the process, I TIG weld to the steel, and grind the weld flush for a flat surface finish. The grinding discs become clogged and become ineffective rather quickly due to the finish on the steel. I have submerged the steel parts in a muriatic acid/water solution, which removes the finish on the steel, but then requires several rinses in water, then a final soak in an oil solution to prevent rust.
My problems are: 1. The vapors cause rust throughout my building on the surface of any steel.(never had the problem before bringing in the muriatic acid solution) I have a small quantity, maybe 25 gallons in a covered container. 2. to purchase "only" pickled steel for the quantities I use has not worked out over the years, so I need to pickle the steel in only the parts that need it. How can I do this more effectively without the rust problem in the vapors. 3. After a period of time, the muriatic acid/water solution starts to form green crystals and becomes ineffective in removing the surface finish of the steel. Can I add something to the mix to get more life out of it. I use close to a five to one ratio water to acid to make the solution, which seems to work best. More or less acid is used depending on the result of the steel bath. My main aim is to have less waste of grinding disks by using pickled steel, but to have less problems in the process I am using.
- Weymouth, Massachusetts, USA
Many companies use sulfuric acid (which still has problems but not as much as HCl) for pickling. There are also some new technologies that are coming out that work well if you can run at higher temperatures.
Stellar Solutions, Inc.
Usage of pickled and oiled H.R coils could be the solution to your problem, but you said you had difficulties with this type of product. I have experience in pickling of h.r.products and also similar situation as yours in some other context.
Batch pickling of the components is the only solution. Batch pickling is carried by having a acidproof container which can withstand temp. of 60 to 70 degrees C and also the hydrochloric acid.
Hydrochloric acid of conc.8 to 10% in water heated to 60 to 70 degrees C, would be sufficient. Dip the H.R. components in the tank for 3 to 5 mins time. There are commercially available inhibitors to be added to the bath to avoid overpickling.
Later, the components are to be rinsed with water, and preferably with D.M.water. If you are required to stock the components from further rusting, temporary rust preventive oils are available. I do not know whether, usage of mineral based oils is allowed in your process.
Word of caution: HCl is corrosive and has to be handled safely.
- SURAT, GUJARAT, India.