Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2002-04-09
2003-11-11
Carrillo, Sharidan (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S002000, C134S009000, C134S015000, C134S019000, C134S025500, C134S026000, C134S028000, C134S030000, C134S034000, C134S035000, C134S036000, C134S041000, C134S042000, C510S258000, C510S367000, C252S186270, C252S186280, C252S186410
Reexamination Certificate
active
06645306
ABSTRACT:
FIELD OF INVENTION
This invention relates to a process for pickling ferrous alloy steels (stainless steels). More particularly, this invention relates to a process for pickling hot rolled and annealed stainless steel strip using a pickling solution comprising hydrogen peroxide.
BACKGROUND
The annealing of stainless steel strip can result in the formation of oxides on the surface of the steel. These oxides, comprised of iron, chromium, nickel and other associated metal oxides, must be removed prior to utilizing the steel. However, the oxides of stainless steel are resistant to most of the common acid treatments. These oxides adhere tightly to the base metal, thus requiring mechanical scale cracking such as shot blasting, roll bending or leveling of the steel strip or electrolytic and/or molten salt bath treatment in order to either loosen these oxides or make the surface more porous prior to pickling. Traditionally, the oxides on the surface of the stainless steel have been removed, or “pickled off,” using nitric acid in combination with hydrofluoric acid.
There is a desire for a method of pickling stainless steels that eliminates the use of nitric acid.
SUMMARY OF THE INVENTION
The present invention relates to a process for pickling hot rolled, hot rolled & annealed, and cold rolled & annealed stainless steel strip in a continuous fashion. The process comprises immersing the stainless steel strip in a pre-pickling tank comprising a solution of sulfuric acid and hydrofluoric acid. The strip is then immersed in a pickling tank comprising a solution of sulfuric acid, hydrofluoric acid and hydrogen peroxide. In one embodiment, the pre-pickling tank (Tank
1
in
FIG. 1
) contains from about 90 g/l to about 200 g/l sulfuric acid and from about 10 g/l to about 60 g/l hydrofluoric acid. The solution in the pre-pickling tank is maintained at a temperature of from about 54° C. to about 77° C. The pickling tank (Tank
3
in
FIG. 1
) is comprised of a mixture of stabilized hydrogen peroxide, sulfuric acid, and hydrofluoric acid. In a specific embodiment, the pickling tank (Tank
3
in
FIG. 1
) is comprised of a mixture of stabilized hydrogen peroxide in a concentration of about 5 g/l to about 50 g/l, sulfuric acid in a concentration of about 20 g/l to about 60 g/l, and hydrofluoric acid in a concentration of about 2 g/l to about 50 g/l. In another embodiment, the concentration of stabilized hydrogen peroxide is from about 20 g/L to about 40 g/L. In a preferred embodiment, the concentration of stabilized hydrogen peroxide is from about 25 g/L to about 35 g/L. In another embodiment, the concentration of hydrogen peroxide is from about 5 g/L to less than 10 g/L. The solution in the pickling tank is maintained at a temperature of from about 20° C. to about 60° C. and is preferably at a temperature of from about 35 ° C. to about 50° C.
Prior to immersing the steel strip in the pickling tank, the strip may be scrubbed, preferably using a scrubber-brush machine. In addition, the strip may also be immersed in a de-smutting tank immediately prior to being scrubbed. The de-smutting tank contains a solution comprising hydrogen peroxide, sulfuric acid and hydrofluoric acid, which is the overflow pickle solution form the pickling tank that is channeled back into the de-smutting tank.
In a separate embodiment, a filtration device and a heat exchanger are external to and coupled to the pickling tank. The filtration system device and heat exchanger are arranged in a re-circulating loop so that at any time, a portion of the solution from the pickling tank is routed through the filtration system device and heat exchanger. The resulting solution is deposited back into the pickling tank through at least one nozzle located inside the pickling tank.
REFERENCES:
patent: 2347742 (1944-05-01), Keene et al.
patent: 3489652 (1970-01-01), Dell et al.
patent: 3649194 (1972-03-01), Glanville
patent: 3864271 (1975-02-01), Stalter
patent: 3903244 (1975-09-01), Winkley
patent: 3905907 (1975-09-01), Shiga
patent: 4002489 (1977-01-01), Hedqvist et al.
patent: 4022703 (1977-05-01), Bakes et al.
patent: 4051057 (1977-09-01), Ericson et al.
patent: 4459216 (1984-07-01), Nakazato et al.
patent: 4754803 (1988-07-01), Escobar, Jr. et al.
patent: 4946520 (1990-08-01), Escobar, Jr. et al.
patent: 5100500 (1992-03-01), Dastolfo
patent: 5154774 (1992-10-01), Bousquet et al.
patent: 5164016 (1992-11-01), Henriet
patent: 5248386 (1993-09-01), Dastolfo, Jr. et al.
patent: 5292374 (1994-03-01), Maresch et al.
patent: 5354383 (1994-10-01), Bianchi
patent: 5417775 (1995-05-01), Pedrazzini
patent: 5538152 (1996-07-01), Fontana
patent: 5702534 (1997-12-01), Rodabaugh et al.
patent: 5743968 (1998-04-01), Leeker et al.
patent: 5785765 (1998-07-01), Zavattoni
patent: 5810939 (1998-09-01), Angel et al.
patent: 5821212 (1998-10-01), Peterson
patent: 5843240 (1998-12-01), Pedrazzini et al.
patent: 5904157 (1999-05-01), Meseha et al.
patent: 5908511 (1999-06-01), Bianchi
patent: 5958147 (1999-09-01), Berglind et al.
patent: 5992196 (1999-11-01), Giraud et al.
patent: 6068001 (2000-05-01), Pedrazzini et al.
patent: 6174383 (2001-01-01), Angel et al.
patent: 6210491 (2001-04-01), Colgan et al.
patent: 6540931 (2003-04-01), Faw et al.
patent: 2002/0148484 (2002-10-01), Cole et al.
patent: 2002/0174880 (2002-11-01), Madi et al.
patent: 582121 (1994-02-01), None
patent: 910356 (1962-11-01), None
patent: 55018552 (1980-02-01), None
patent: 55050468 (1980-04-01), None
patent: 61049706 (1986-03-01), None
patent: A-2122087 (1990-05-01), None
patent: 11269677 (1999-10-01), None
patent: WO 02/081777 (2002-10-01), None
Leeker Jerald W.
Madi Vijay N.
Van Scoy Clayton A.
AK Steel Corporation
Carrillo Sharidan
Frost Brown Todd LLC
LandOfFree
Hydrogen peroxide pickling scheme for stainless steel grades does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydrogen peroxide pickling scheme for stainless steel grades, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrogen peroxide pickling scheme for stainless steel grades will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3144481