EP0359736B1 - Procédé pour le décapage d'acier spécial par voie électrolytique - Google Patents

Procédé pour le décapage d'acier spécial par voie électrolytique Download PDF

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Publication number
EP0359736B1
EP0359736B1 EP89890225A EP89890225A EP0359736B1 EP 0359736 B1 EP0359736 B1 EP 0359736B1 EP 89890225 A EP89890225 A EP 89890225A EP 89890225 A EP89890225 A EP 89890225A EP 0359736 B1 EP0359736 B1 EP 0359736B1
Authority
EP
European Patent Office
Prior art keywords
solution
nano3
naf
special steel
aqueous
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP89890225A
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German (de)
English (en)
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EP0359736A1 (fr
Inventor
Gerald Dipl.-Ing. Dr. Tech. Maresch
Ulrich Krupicka
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Andritz AG
Original Assignee
Andritz AG
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Publication date
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D1/00—Electroforming
    • C25D1/04—Wires; Strips; Foils
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
    • C25F1/02—Pickling; Descaling
    • C25F1/04—Pickling; Descaling in solution
    • C25F1/06—Iron or steel

Definitions

  • the invention relates to a method for the electrolytic pickling of stainless steel strip, in particular stainless steel hot strip, in which the stainless steel hot strip is initially anodically and cathodically pickled in an aqueous neutral solution of Na2SO4.
  • AT-PS 252 685 and AT-PS 240 674 describe two-stage electrolytic pickling processes, the first pickling bath being an aqueous solution of a neutral alkali salt of a mineral acid, preferably sodium sulfate. This is followed by electrolytic pickling in aqueous solutions of mineral acids, examples of which are sulfuric, nitric, hydrochloric or mixed acids. In all of the above-mentioned processes, however, it has not or only insufficiently been possible to effectively prevent the formation of toxic vapors, including nitrous gases.
  • the object of the present invention is to provide a method for electrolytic pickling of stainless steel strips, in which the formation of nitrous gases is completely avoided in the aftertreatment, which furthermore with a low cost and Workload works and delivers a scale-free, bright shiny stainless steel band.
  • aqueous neutral salt solution which contains the same anions as the conventional HNO3 / HF mixed acid, after another Characteristic the aqueous neutral salt solution is a solution of NaNO3 and NaF.
  • Another feature of the method according to the invention is that the concentration of NaNO3 between 100 and 400 g / l, preferably 200 to 300 g / l and the concentration of NaF between 10 and 100 g / l, preferably between 40 and 60 g / l is.
  • the temperature in the solution of NaNO3 and NaF is between 20 and 90 ° C, preferably between 60 and 80 ° C.
  • the anodic and cathodic current density during electrolytic pickling in the solution of NaNO3 and NaF is between 1 and 50 A / dm2, preferably between 10 and 30 A / dm2.
  • the scaled stainless steel strip After the scaled stainless steel strip has been alternately anodically and cathodically pickled in an aqueous solution of Na2SO4, it is rinsed and brushed with plastic brushes. Thereupon it is alternately anodically and cathodically pickled to remove the remaining adhering scale in an aqueous neutral salt solution which contains the same anions as the conventional nitric-hydrofluoric acid mixture.
  • a solution of NaNO3 and NaF is preferably prepared for this purpose.
  • the neutral salt solution is generally prepared by adding the respective nitrates or fluorides in the desired amount in water.
  • other manufacturing methods are also possible, especially in the course of small-scale test facilities, where e.g. a neutralization of HNO3 / HF mixed acid with alkali can be done.
  • Economic considerations lead to the use of sodium salts, since these are the cheapest in terms of price, but the use of nitrates and fluorides with other cations, such as potassium, is just as possible.
  • the electrolytic pickling with NaNO3 and NaF prevents the formation of nitrous gases, since the stainless steel strip is not pickled in acid, but the acid is only produced where it is needed by electrolysis.
  • Another advantage of this method according to the invention is that the dissolved scale does not dissolve as a salt and thus consumes acid, but instead precipitates out as a hydroxide.
  • This metal hydroxide sludge formed during pickling is separated from the solution by mechanical methods such as filters, thickeners or centrifuges. This not only reduces the consumption of chemicals, it also creates easily depositable metal hydroxides.
  • a stainless steel hot strip of quality AISI 304 was irradiated in a combined annealing and pickling line before pickling in order to partially remove the scale on the surface and then electrolytically in an aqueous Na2SO4 solution, a concentration of 150 g / l with 10 A / dm2 alternately anodically and cathodically pickled, keeping the temperature in the range between 60 and 80 ° C.
  • the stainless steel strip was first pickled in a purely chemical manner in the same temperature range in an aqueous solution of 150 g / l HNO3 and 25 g / l HF to remove the chromium-depleted layer.
  • the tape was scale-free, but when pickling in the acid nitrous gases were produced in a concentration of 500 - 800 ppm, which had to be removed from the exhaust gas in the exhaust gas cleaning system.
  • a 10-20% aqueous solution of urea was added to the second pickling bath to reduce the emission of nitrous gases, but the concentration of nitrous gases was reduced from 500-800 ppm to 100-150 ppm, but could not be completely avoided.
  • the acid was then neutralized with sodium hydroxide solution so that an aqueous, neutral solution with a concentration of 200 g / l NaNO3 and 50 g / l NaF was obtained.
  • the pickling tub was equipped with electrodes and these were connected to a rectifier.
  • a scale-free band was also obtained at a current density of 20 A / dm 2 and in the same temperature range as in Example 1, but there was no emission of nitrous gases in the suction plant.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Electroplating Methods And Accessories (AREA)

Claims (5)

  1. Procédé pour le décapage électrolytique de feuillard d'acier fin en particulier d'un feuillard d'acier fin à chaud, dans lequel le feuillard d'acier fin à chaud est en alternance décapé cathodiquement et anodiquement tout d'abord dans une solution aqueuse neutre de Na₂SO₄, la concentration de Na₂SO₄ étant de 50 à 300 g/l dans la solution aqueuse, de préférence entre 100 et 200 g/l, la température entre 20 et 90°C, de préférence entre 60 et 80°C et la densité de courant cathodique et anodique lors du décapage électrolytique entre 1 et 50 A/dm², de préférence entre 10 et 30 A/dm², caractérisé en ce que le feuillard d'acier fin à chaud est pour finir décapé en alternance cathodiquement et anodiquement dans une solution saline neutre aqueuse, contenant les mêmes anions que le mélange d'acide HNO₃/HF traditionnel.
  2. Procédé selon la revendication 1, caractérisé en ce que la solution saline neutre aqueuse est une solution de NaNO₃ et de NaF.
  3. Procédé selon la revendication 2, caractérisé en ce que la concentration en NaNO₃ s'élève entre 100 et 400 g/l, de préférence entre 200 et 300 g/l et la concentration de NaF entre 10 et 100 g/l, de préférence entre 40 et 60 g/l.
  4. Procédé selon la revendication 2, caractérisé en ce que la température dans la solution de NaNO₃/NaF se situe entre 20 et 90°C de préférence entre 60 et 80°C.
  5. Procédé selon la revendication 2, caractérisé en ce que la densité de courant anodique et cathodique lors du décapage électrolytique dans la solution de NaNO₃/NaF est entre 1 à 50 A/dm², de préférence de 10 à 30 A/dm².
EP89890225A 1988-09-14 1989-09-01 Procédé pour le décapage d'acier spécial par voie électrolytique Expired - Lifetime EP0359736B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AT0225888A AT391486B (de) 1988-09-14 1988-09-14 Verfahren zum elektrolytischen beizen von edelstahlband
AT2258/88 1988-09-14

Publications (2)

Publication Number Publication Date
EP0359736A1 EP0359736A1 (fr) 1990-03-21
EP0359736B1 true EP0359736B1 (fr) 1993-02-03

Family

ID=3530989

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89890225A Expired - Lifetime EP0359736B1 (fr) 1988-09-14 1989-09-01 Procédé pour le décapage d'acier spécial par voie électrolytique

Country Status (9)

Country Link
US (1) US5022971A (fr)
EP (1) EP0359736B1 (fr)
JP (1) JPH0713320B2 (fr)
KR (1) KR950012425B1 (fr)
AT (1) AT391486B (fr)
DE (1) DE58903444D1 (fr)
ES (1) ES2039949T3 (fr)
FI (1) FI90093C (fr)
ZA (1) ZA896965B (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0774480B2 (ja) * 1991-05-01 1995-08-09 中外炉工業株式会社 ステンレス鋼帯の連続焼鈍酸洗設備
AT399167B (de) * 1991-06-10 1995-03-27 Andritz Patentverwaltung Verfahren und vorrichtung zum elektrolytischen beizen von kontinuierlich durchlaufendem elektrisch leitendem gut
EP0763609B1 (fr) * 1995-09-15 1999-12-15 MANNESMANN Aktiengesellschaft Procédé et dispositif pour le traitement de produits sous forme de bande en acier inoxydable
US6096183A (en) * 1997-12-05 2000-08-01 Ak Steel Corporation Method of reducing defects caused by conductor roll surface anomalies using high volume bottom sprays
AT406486B (de) * 1998-12-22 2000-05-25 Andritz Patentverwaltung Verfahren zum beizen von edelstahl

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT1461B (fr) * 1899-06-12 1900-06-11 Ver Elek Citaets Actien Ges
AT213190B (de) * 1958-12-23 1961-01-25 Othmar Ing Ruthner Verfahren zum Beizen von legierten Stählen
AT240674B (de) * 1963-04-25 1965-06-10 Othmar Ing Ruthner Verfahren zum elektrolytischen Beizen von niedriglegierten und Kohlenstoffstählen
AT252685B (de) * 1964-12-22 1967-03-10 Ruthner Ind Planungs Ag Verfahren zum Beizen hochlegierter Stähle und Sonderlegierungen
AT252674B (de) * 1965-04-09 1967-03-10 Othmar Matzke Zur Aufnahme des Achsdruckes geeignete (lasttragende) Abrollverzahnung
IT1047584B (it) * 1975-09-26 1980-10-20 Centro Speriment Metallurg Metodo per migliorare la suscetti bilita dell acciaio ai rivestimenti
FR2431554A1 (fr) * 1978-07-20 1980-02-15 Ruthner Industrieanlagen Ag Procede pour le decapage electrolytique de bandes laf d'acier inoxydable
AT387406B (de) * 1987-05-07 1989-01-25 Andritz Ag Maschf Verfahren zum elektrolytischen beizen von chromhaeltigem edelstahl

Also Published As

Publication number Publication date
ATA225888A (de) 1990-04-15
KR900004969A (ko) 1990-04-13
FI893978A0 (fi) 1989-08-24
EP0359736A1 (fr) 1990-03-21
JPH0713320B2 (ja) 1995-02-15
FI90093B (fi) 1993-09-15
FI893978A (fi) 1990-03-15
KR950012425B1 (en) 1995-10-17
DE58903444D1 (de) 1993-03-18
ES2039949T3 (es) 1993-10-01
AT391486B (de) 1990-10-10
ZA896965B (en) 1990-06-27
FI90093C (fi) 1993-12-27
JPH02107800A (ja) 1990-04-19
US5022971A (en) 1991-06-11

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