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US 5,843,240 AGranted
Process for stainless steel pickling and passivation without using nitric acid
AssigneeNovamax ITB s.r.l.
InventorsCesare Pedrazzini, Paolo Giordani
Life of this patent
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Abstract
Process for stainless steel pickling consisting in placing the material to be treated in a bath kept at a temperature ranging from 30.degree. C. to 70.degree. C. and containing: a) H.sub.2 SO.sub.4 b) Fe.sup.3+ c) HF d) emulsifiers, wetting agents, polishing agents, acid attack inhibitors; the bath being kept under agitation with: an air flow and continuously fed with a quantity of oxidizing agent adjusted to the bath redox potential to be kept at 250 mV min.
Claims7
Pickling process for chromium containing stainless steel comprising:
- placing the material to be treated in a bath kept at a temperature ranging from 30.degree. C. to 70.degree. C., said bath having the following optimal composition:
- (a) H.sub.2 SO.sub.4 from 30 to 150 g/l
- (b) Fe.sup.3+ at least 15 g/l
- (c) HF from 5 to 50 g/l
- (d) additives (emulsifiers, wetting agents, polishing agents) and acid attack inhibitors:
- approximately 1 g/l;
- keeping said bath under agitation by a continuous air flow or equivalent agitation means,
- feeding quantities of ingredients (a), (c), and (d) to said bath for maintaining said optimal composition in the bath and a bath pH not higher than 2.5, and an oxidizing agent quantity suitable for maintaining the bath redox potential at values of at least 200 mV, said oxidizing agent being selected from oxidized chlorine acids and salts thereof, peroxidized acids, such as persulphuric acid and salts thereof, alkaline permanganates.
5 more elements
Dependencies are inferred from the claim text.