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Evaluation of strip solution life

I'm doing a project on evaluation the stripping solution for EN plating jigs... now we use nitric acid... I want to know how often we should change the solution bath.

Cindy [last name deleted for privacy by Editor]
- Singapore
1999

Cindy, this is normally an economics question. As you dissolve metal you get into a rate or kinetics of the reaction that can be equated to a solubility product or Ksp equation. The more that you change the amount of the "product side" the faster the rate slows down. Economics is when the cost of a slow strip equals the cost of getting rid of the old strip, it is time to change. Most people will add a little more acid and when a small acid add does not help, they dump it. The reality of it is the floor boss gets so ---- mad at the slowness of the operation that he dumps it. On a relative few strips, you can get into a situation where it pits the base metal as well as strips the nickel. If you are stripping off of stainless steel, and you can stand the NO2 formed, nitric is the cheapest way to go. On other metals, I would look into the B-9 family of strippers from Metalx (Ronatec.us) [a finishing.com supporting advertiser]. Good product and good company.

James Watts
- Navarre, Florida
1999

Thanks, but I still want to know whether the over etch of stainless steel jig in EN plating is good or not. because use Nitric acid have slow strip rate and have passivation effect, but when we add in H2O2 (hydrogen peroxide, the stripping rate increase, but the effect of passivation decreased, is it good for the next step EN plating? Same question for the EN stainless steel bath, whether the passivation effect quite important for the stainless steel bath, or just etch off the nickel layer?

Cindy [last name deleted for privacy by Editor]
- Singapore
1999

By jig, I assume that you mean rack or fixturing device to hold a part or parts. Since a normal jig would go thru the activation steps for plating, passivation or no passivation should not make any significant difference. Since you have not stated what your metal being plated is or what your process is, we can only guess. A passivated tank does not immediately plate because it has not been activated. Over etching is not good for the jig for several reasons and normally would try to be avoided. Nitric acid is an oxidizing acid. Peroxide is an oxidizer also, so while it may increase the strip rate, I would not expect it to decrease the passivation (but I do not know). Passivation for the jig is normally irrelevant. Passivation of a stainless steel EN tank is very important.

James Watts
- Navarre, Florida
1999

Thanks again. Yah, My jigs are stainless steel... and now I think longer time to strip and make them well passivated, and later have better resistant to EN plated. am I right?

Cindy [last name deleted for privacy by Editor]
- Singapore
1999

Cindy, you missed the point stated above. When you run your parts thru cleaning and activating, you are activating (etch) your SS jigs as well. This is destroying any passivation or at a minimum, significantly reducing it. If you do not want your jigs to plate, mask off more of it, so you do not have much more than a decent sized area for the point of contact. If you have lots of racks, a slow strip rate is fine. If you need the racks turned around for another load, a long strip time is costing you money. A gross excess of racks also costs you money. Plating is a series of tradeoffs. There is no perfect answer, just what ever is best for your operation.

James Watts
- Navarre, Florida
1999

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2001

I need information about the mechanism of passivation in H2O2, grade PA, and about HNO3 too. I working in my thesis. Its is one alternative work for substitute the HNO3. I need bibliography about.

Please, help me!

This is important ... Thank you!

P.S.: The material which used is stainless steel AISI 304.

Carlos Roberto de Arajo
- Minas Gerais, Brazil