Armco Inc.

Armco Steel Company, L.p.

Ronald D Rodabaugh

Jerald W Leeker

Franklin E Rower

Joyce C Neidringhaus

A process for removing scale from stainless steel using an aqueous solution containing hydrogen peroxide and an inorganic acid, i.e., hydrochloric or sulfuric acid. A hot rolled or annealed stainless steel strip (10) covered with scale is immersed into hot inorganic acid contained within pickling tanks (12) and (14). Thereafter, the strip may have residual amounts of tightly adherent scale (11). This scale is activated by a solution containing the inorganic acid and hydrogen peroxide applied to the strip such as by a spray header (16) extending completely transversely across and positioned above the strip and another spray header (18) extending completely transversely across and positioned below the strip. It may be desirable to pass the activated strip through the hot inorganic acid again and reactivate the strip at very high line speeds to insure complete removal of scale from the strip. Any hydrogen peroxide spray dripping from the strip is collected on a catch pan (30) and flowed into a tank (28). Preferably, the collected spent aqueous solution containing the inorganic acid and spent hydrogen peroxide is disposed in the pickling tanks. The aqueous solution aids in the removal of any residual scale and smut remaining on the strip thereby improving the cleanliness of the pickled strip.

Hydrogen peroxide pickling of stainless steel

A process for removing scale from stainless steel using an aqueous solution containing hydrogen peroxide. A hot rolled or annealed stainless steel strip (10) covered with scale is immersed into hot sulfuric acid contained within tanks (12) and (14). Thereafter, the strip may have residual amounts of tightly adherent scale (11). This scale is activated by the aqueous solution containing hydrogen peroxide applied to the strip such as by a spray header (16) extending completely transversely across and positioned above the strip and another spray header (18) extending completely transversely across and positioned below the strip. Any peroxide spray dripping from the, strip is collected on a catch pan (30) and flowed into a tank (28). Preferably, the peroxide solution is a dilute concentration of the acid in tanks (12) and (14). The hydrochloric acid removes smut from the strip formed by the sulfuric acid to improve the cleanliness of the pickled strip.

Acid concentrations are determined by the method and apparatus, particularly HCl acid for picking ferrous material. Specific gravity measurements are made on acid samples, diluted acid samples and water. Conductivity measurements are conducted on the diluted acid samples. The water dilution minimizes the influence of the metal salt in the sample to improve the conductivity measurements. The system calculates the acid concentration by a series of approximations using the conductivity data and the acid concentration - conductivity relationships to provide an accurate acid concentration which is easily automated by computer.

Method and apparatus for determining acid concentration

Caustic dezincing galvanized steel scrap. A dezincing plant includes a plurality of tanks interconnected in series with steel scrap sequentially being moved through each of the tanks. The tanks contain a caustic leaching solution including an oxidant with the leaching solution being circulated through each of the tanks in a direction opposite to the movement of the scrap. Fresh scrap initially is exposed to a partially depleted leaching solution with the oxidant concentration of the leaching solution increasing as the scrap moves through the series of tanks. Leaching solution depleted of its oxidant is transferred to an electrolytic cell where zinc is removed and plated as metallic zinc powder onto a cathode. The leaching solution is recycled by removing zinc. The chemistry of the leaching solution is controlled so that sufficient free caustic is present to prevent passivating zinc coating on the scrap. Oxidant is added to the recycled solution and the caustic concentration is adjusted, if necessary, to have a total caustic concentration of at least 5 M and the recycled solution is returned to the last tank. Compressed scrap bales are dezinced and ready for use as a melting furnace charge material.

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Middletown, OH, United States of America

Ronald D Rodabaugh