EP0359736B1 - Method of electrolytically pickling special steel - Google Patents
Method of electrolytically pickling special steel Download PDFInfo
- 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
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- European Patent Office
- Prior art keywords
- solution
- nano3
- naf
- special steel
- aqueous
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- 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.)
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- 238000000034 method Methods 0.000 title claims description 24
- 238000005554 pickling Methods 0.000 title claims description 20
- 229910000831 Steel Inorganic materials 0.000 title claims 5
- 239000010959 steel Substances 0.000 title claims 5
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 claims description 24
- 239000002253 acid Substances 0.000 claims description 18
- 239000000243 solution Substances 0.000 claims description 15
- 235000010344 sodium nitrate Nutrition 0.000 claims description 12
- 230000007935 neutral effect Effects 0.000 claims description 11
- 239000012266 salt solution Substances 0.000 claims description 7
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 6
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 6
- 239000007864 aqueous solution Substances 0.000 claims description 6
- 229910017604 nitric acid Inorganic materials 0.000 claims description 6
- 229910052938 sodium sulfate Inorganic materials 0.000 claims description 6
- 235000011152 sodium sulphate Nutrition 0.000 claims description 6
- 239000007832 Na2SO4 Substances 0.000 claims description 5
- 150000001450 anions Chemical class 0.000 claims description 3
- 239000007789 gas Substances 0.000 description 17
- 229910001220 stainless steel Inorganic materials 0.000 description 15
- 239000010935 stainless steel Substances 0.000 description 15
- GQPLMRYTRLFLPF-UHFFFAOYSA-N nitrous oxide Inorganic materials [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 description 12
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 3
- 150000007513 acids Chemical class 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000004202 carbamide Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 150000002222 fluorine compounds Chemical class 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 229910000000 metal hydroxide Inorganic materials 0.000 description 2
- 150000004692 metal hydroxides Chemical class 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 150000002823 nitrates Chemical class 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 150000001447 alkali salts Chemical class 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000010297 mechanical methods and process Methods 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- -1 potassium Chemical class 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000010802 sludge Substances 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
- 239000002562 thickening agent Substances 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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)
Description
Die Erfindung betrifft ein Verfahren zum elektrolytischen Beizen von Edelstahlband, insbesondere von Edelstahl-Warmband, bei welchem das Edelstahl-Warmband vorerst in einer wässrigen neutralen Lösung von Na₂SO₄ abwechselnd anodisch und kathodisch gebeizt wird.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.
Verfahren zum elektrolytischen Beizen von Edelstahl in verschiedenen Säuren, wie beispielsweise Schwefelsäure oder Salpetersäure, sind seit vielen Jahren bekannt und haben sich bereits weltweit durchgesetzt. Derartige Verfahren benötigen jedoch als nachfolgenden Schritt eine Behandlung in einer Mischsäure, wie beispielsweise einer Mischung von Salpetersäure und Flußsäure, um die chromverarmte Schicht an der Oberfläche zu entfernen. Ein seit längerer Zeit bekanntes Problem bei diesen Verfahren liegt nun darin, daß bei dieser Säurenachbehandlung gefährliche Gase,wie nitrose Gase, frei werden.Processes for the electrolytic pickling of stainless steel in various acids, such as sulfuric acid or nitric acid, have been known for many years and have already become established worldwide. However, as a subsequent step, such processes require treatment in a mixed acid, such as, for example, a mixture of nitric acid and hydrofluoric acid, in order to remove the chromium-depleted layer on the surface. A problem with these processes which has been known for a long time now lies in the fact that dangerous gases, such as nitrous gases, are released during this acid aftertreatment.
Infolgedessen wurden verschiedene Verfahren entwickelt, um diese nitrosen Gase durch Zusatz von Harnstoff oder Wasserstoffperoxid zur Mischsäure zu vermeiden.As a result, various methods have been developed to avoid these nitrous gases by adding urea or hydrogen peroxide to the mixed acid.
Des weiteren wurde versucht, den Edelstahl in einer wässrigen Neutralsalzlösung vorzubehandeln und anschließend mit Mischsäure fertigzubeizen. So beschreiben etwa die AT-PS 252 685 und die AT-PS 240 674 zweistufige elektrolytische Beizverfahren, wobei das erste Beizbad eine wässrige Lösung eines neutralen Alkalisalzes einer Mineralsäure, vorzugsweise Natriumsulfat ist. Anschließend folgt eine elektrolytische Beize in wässrigen Lösungen von Mineralsäuren, wofür Schwefel-, Salpeter-, Salz- oder Mischsäuren als Beispiele angegeben werden. In all diesen genannten Verfahren ist es jedoch nicht oder nur unzureichend gelungen, die Bildung giftiger Dämpfe, unter anderem nitroser Gase, wirksam zu verhindern.In addition, attempts were made to pretreat the stainless steel in an aqueous neutral salt solution and then to finish-pickle it with mixed acid. For example, 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.
Die Aufgabe der vorliegenden Erfindung liegt nun darin, ein Verfahren zu elektrolytischen Beizen von Edelstahlbändern zu schaffen, bei welchem in der Nachbehandlung die Bildung nitroser Gase vollständig vermieden wird, welches des weiteren mit einem geringen Kosten- und Arbeitsaufwand arbeitet und ein zunderfreies, hell glänzendes Edelstahlband liefert.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.
Diese Aufgabe wird bei einem Verfahren der eingangs genannten Art erfindungsgemäß dadurch gelöst, daß das Edelstahl-Warmband anschließend in einer wässrigen Neutralsalzlösung, welche die selben Anionen enthält wie die herkömmliche HNO₃/HF-Mischsäure, abwechselnd anodisch und kathodisch gebeizt wird, wobei nach einem weiteren Merkmal die wässrige Neutralsalzlösung eine Lösung von NaNO₃ und NaF ist.This object is achieved according to the invention in a method of the type mentioned at the outset in that the stainless steel hot strip is then alternately anodically and cathodically pickled in an 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.
Ein weiteres Merkmal des erfindungsgemäßen Verfahrens liegt darin, daß die Konzentration an NaNO₃ zwischen 100 und 400 g/l, vorzugsweise 200 bis 300 g/l und die Konzentration von NaF Zwischen 10 und 100 g/l, vorzugsweise zwischen 40 und 60 g/l beträgt.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.
Nach einem weiteren Merkmal des erfindungsgemäßen Verfahrens beträgt die Temperatur in der Lösung von NaNO₃ und NaF zwischen 20 und 90°C, vorzugsweise zwischen 60 und 80°C.According to a further feature of the method according to the invention, the temperature in the solution of NaNO₃ and NaF is between 20 and 90 ° C, preferably between 60 and 80 ° C.
Als weiteres Merkmal des erfindungsgemäßen Verfahrens ist vorgesehen, daß die anodische und die kathodische Stromdichte beim elektrolytischen Beizen in der Lösung von NaNO₃ und NaF zwischen 1 und 50 A/dm², vorzugsweise zwischen 10 und 30 A/dm² beträgt.As a further feature of the method according to the invention it is provided that 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.
Nachdem das verzunderte Edelstahlband in einer wässrigen Lösung von Na₂SO₄ abwechselnd anodisch und kathodisch gebeizt wurde, wird es gespült und mit Kunststoffbürsten gebürstet. Hierauf wird es zur Entfernung des restlichen anhaftenden Zunders in einer wässrigen Neutralsalzlösung, welche die selben Anionen enthält wie die herkömmliche Salpeter-Flußsäure-Mischung, abwechselnd anodisch und kathodisch gebeizt. Vorzugsweise wird zu diesem Zweck eine Lösung von NaNO₃ und NaF angesetzt. Nach der anschließenden Schlußspülung, welche ebenfalls eine mechanische Bandreinigung mit Bürsten enthält, erhält man ein zunderfreies, hell glänzendes Edelstahlband.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. After the subsequent final rinse, which also contains mechanical belt cleaning with brushes, a scale-free, bright, shiny stainless steel belt is obtained.
Die Neutralsalzlösung wird im allgemeinen durch Zugabe der jeweiligen Nitrate bzw. Fluoride in der gewünschten Menge in Wasser hergestellt. Jedoch sind auch andere Herstellwege möglich, insbesondere im Zuge von Versuchsanlagen kleiner Dimensionen, wo z.B. ein Neutralisieren von HNO₃/HF-Mischsäure mit Alkalilaugen erfolgen kann. Wirtschaftliche Überlegungen führen zur Verwendung der Natriumsalze, da diese preislich am günstigsten sind, doch ist die Verwendung von Nitraten und Fluoriden mit anderen Kationen, wie etwa Kalium, genausogut möglich.The neutral salt solution is generally prepared by adding the respective nitrates or fluorides in the desired amount in water. However, 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.
Durch die elektrolytische Beize mit NaNO₃ und NaF wird die Bildung von nitrosen Gasen vermieden, da das Edelstahlband nicht in Säure gebeizt wird, sondern die Säure nur dort, wo sie benötigt wird, durch Elektrolyse hergestellt wird.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.
Ein weiterer Vorteil dieses erfindungsgemäßen Verfahrens liegt darin, daß der gelöste Zunder nicht als Salz in Lösung geht und somit Säure verbraucht, sondern gleich als Hydroxid ausfällt.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.
Dieser beim Beizen entstehende Metallhydroxidschlamm wird durch mechanische Methoden, wie beispielsweise Filter, Eindicker oder Zentrifugen, von der Lösung abgetrennt. Damit wird nicht nur der Chemikalienverbrauch reduziert, sondern es entstehen auch leicht deponierbare Metallhydroxide.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.
Nachfolgend werden anhand von Ausführungsbeispielen weitere Einzelheiten bzw. Vorteile des vorliegenden erfindungsgemäßen Verfahrens beschrieben:Further details and advantages of the method according to the invention are described below using exemplary embodiments:
Ein Edelstahl-Warmband der Qualität AISI 304 wurde in einer kombinierten Glüh- und Beizlinie vor dem Beizen bestrahlt, um den Zunder an der Oberfläche teilweise zu entfernen und anschließend elektrolytisch in einer wässrigen Na₂SO₄-Lösung, einer Konzentration von 150 g/l mit 10 A/dm² abwechselnd anodisch und kathodisch gebeizt, wobei die Temperatur im Bereich zwischen 60 und 80°C gehalten wurde. Zum Vergleich mit dem erfindungsgemäßen Verfahren wurde das Edelstahlband zuerst auf rein chemische Weise im selben Temperaturbereich in einer wässrigen Lösung von 150 g/l HNO₃ und 25 g/l HF zur Entfernung der chromverarmten Schicht fertig gebeizt. Das Band war zunderfrei, doch entstanden beim Beizen in der Säure nitrose Gase in einer Konzentration von 500 - 800 ppm, die in der Abgasreinigungsanlage aus dem Abgas entfernt werden mußten.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. For comparison with the inventive method, 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.
Bei der gleichen Anlage und unveränderten Parametern wurde zur Verringerung der Emission an nitrosen Gasen dem zweiten Beizbad eine wässrige 10-20%ige Lösung von Harnstoff zugesetzt, wodurch die Konzentration an nitrosen Gasen von 500 - 800 ppm auf 100 - 150 ppm verringert wurde, aber nicht vollständig vermieden werden konnte.With the same system and unchanged parameters, 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.
Um ein Band nunmehr nach dem Verfahren gemäß der Erfindung behandeln zu können, wurde die Säure anschließend mit Natronlauge neutralisiert sodaß eine wässrige, neutrale Lösung mit einer Konzentration von 200 g/l NaNO₃ und 50 g/l NaF erhalten wurde. Der Beizbottich wurde mit Elektroden ausgestattet und diese an einen Gleichrichter angeschlossen. Bei gleicher Behandlungsgeschwindigkeit in der Anlage wurde bei einer Stromdichte von 20 A/dm² und in demselben Temperaturbereich wie in Beispiel 1 ebenfalls ein zunderfreies Band erhalten, es kam jedoch zu keiner Emission von nitrosen Gasen in der Absauganlage.In order to be able to treat a tape now by the process according to the invention, 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. At the same treatment speed in the plant, 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.
Die Versuche wurden mit identischen Parametern wie in den ersten drei Beispielen bei einem ferritischen Warmband der Qualität AISI 430 wiederholt. Beim Beizen mit Säure entstanden dabei 3000 -5000 ppm nitrose Gase, die durch Zugabe von Harnstoff auf 500 - 750 ppm reduziert werden konnten. Wurde dagegen die Nachbehandlung mit einer wässrigen NaNO₃- und NaF-Lösung durchgeführt, entstanden keine nitrogen Gase und das Edelstahlband war bei gleicher Behandlungslänge und Anlagengeschwindigkeit ebenfalls zunderfrei.The tests were repeated with identical parameters as in the first three examples with a ferritic hot strip of quality AISI 430. When pickling with acid, 3000 to 5000 ppm of nitrous gases were generated, which could be reduced to 500 to 750 ppm by adding urea. In contrast, if the aftertreatment was carried out with an aqueous NaNO₃ and NaF solution, none were formed nitrogen gases and the stainless steel strip were also scale-free with the same treatment length and line speed.
Beide Edelstahlbänder wurden im Kaltwalzwerk gewalzt, anschließend geglüht und nochmals gebeizt. Auch hier entstanden bei der Nachbehandlung in der NaNO₃-NaF-Lösung keine nitrosen Gase, während beim Beizen in Säure bei AISI 304 300 - 500 ppm und bei AISI 430 800 - 1000 ppm nitroser Gase im Abgas gemessen wurden.Both stainless steel strips were rolled in the cold rolling mill, then annealed and pickled again. Again, there were no nitrous gases in the aftertreatment in the NaNO₃-NaF solution, while when pickling in acid with AISI 304 300-500 ppm and with AISI 430 800-1000 ppm nitrous gases were measured in the exhaust gas.
Claims (5)
- A method of electrolytically pickling special steel strip, more particularly a special steel hot strip, in which the special steel hot strip is first alternately anodically and cathodically pickled in an aqueous neutral solution of Na₂SO₄, the concentration of Na₂SO₄ in the aqueous solution being between 50 and 300 g/l, preferably between 100 and 200 g/l, the temperature being between 20 and 90°C, preferably between 60 and 80°C, and the anodic and cathodic current density in the electrolytic pickling process being between 1 and 50 A/dm², preferably between 10 and 30 A/dm², characterised in that the special steel hot strip is then alternately anodically and cathodically pickled in an aqueous neutral salt solution which contains the same anions as the conventional HNO₃/HF mixed acid.
- A method according to claim 1, characterised in that the aqueous neutral salt solution is a solution of NaNO₃ and NaF.
- A method according to claim 2, characterised in that the concentration of NaNO₃ is between 100 and 400 g/l, preferably between 200 and 300 g/l, and the concentration of NaF is between 10 and 100 g/l, preferably between 40 and 60 g/l.
- A method according to claim 2, characterised in that the temperature in the NaNO₃/NaF solution is between 20 and 90°C, preferably between 60 and 80°C.
- A method according to claim 2, characterised in that the anodic and cathodic current density in the NaNO₃/NaF solution in the electrolytic pickling process is between 1 and 50 A/dm², preferably between 10 and 30 A/dm².
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT0225888A AT391486B (en) | 1988-09-14 | 1988-09-14 | METHOD FOR ELECTROLYTICALLY STICKING STAINLESS STEEL STRIP |
| AT2258/88 | 1988-09-14 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0359736A1 EP0359736A1 (en) | 1990-03-21 |
| EP0359736B1 true EP0359736B1 (en) | 1993-02-03 |
Family
ID=3530989
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP89890225A Expired - Lifetime EP0359736B1 (en) | 1988-09-14 | 1989-09-01 | Method of electrolytically pickling special steel |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US5022971A (en) |
| EP (1) | EP0359736B1 (en) |
| JP (1) | JPH0713320B2 (en) |
| KR (1) | KR950012425B1 (en) |
| AT (1) | AT391486B (en) |
| DE (1) | DE58903444D1 (en) |
| ES (1) | ES2039949T3 (en) |
| FI (1) | FI90093C (en) |
| ZA (1) | ZA896965B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0774480B2 (en) * | 1991-05-01 | 1995-08-09 | 中外炉工業株式会社 | Continuous annealing pickling equipment for stainless steel strip |
| AT399167B (en) * | 1991-06-10 | 1995-03-27 | Andritz Patentverwaltung | METHOD AND DEVICE FOR ELECTROLYTICALLY STICKING CONTINUOUSLY CONTINUOUS ELECTRICALLY CONDUCTIVE GOODS |
| ES2142018T3 (en) * | 1995-09-15 | 2000-04-01 | Mannesmann Ag | PROCEDURE AND INSTALLATION FOR THE TREATMENT OF PRODUCTS IN THE FORM OF STAINLESS STEEL STRAP. |
| 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 (en) * | 1998-12-22 | 2000-05-25 | Andritz Patentverwaltung | METHOD FOR STAINLESSING STAINLESS STEEL |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT1461B (en) * | 1899-06-12 | 1900-06-11 | Ver Elek Citaets Actien Ges | |
| AT213190B (en) * | 1958-12-23 | 1961-01-25 | Othmar Ing Ruthner | Process for pickling alloy steels |
| AT240674B (en) * | 1963-04-25 | 1965-06-10 | Othmar Ing Ruthner | Process for the electrolytic pickling of low-alloy and carbon steels |
| AT252685B (en) * | 1964-12-22 | 1967-03-10 | Ruthner Ind Planungs Ag | Process for pickling high-alloy steels and special alloys |
| AT252674B (en) * | 1965-04-09 | 1967-03-10 | Othmar Matzke | Suitable (load-bearing) rolling teeth to absorb the axle pressure |
| IT1047584B (en) * | 1975-09-26 | 1980-10-20 | Centro Speriment Metallurg | METHOD FOR IMPROVING THE SUSCETTI BILITA OF STEEL TO COATINGS |
| FR2431554A1 (en) * | 1978-07-20 | 1980-02-15 | Ruthner Industrieanlagen Ag | Electrolytic descaling of cold rolled stainless steel strip - which alternately forms the anode and cathode in both neutral sulphate bath and nitric acid bath |
| AT387406B (en) * | 1987-05-07 | 1989-01-25 | Andritz Ag Maschf | METHOD FOR ELECTROLYTICALLY STICKING CHROME-CONTAINING STAINLESS STEEL |
-
1988
- 1988-09-14 AT AT0225888A patent/AT391486B/en not_active IP Right Cessation
-
1989
- 1989-08-24 FI FI893978A patent/FI90093C/en not_active IP Right Cessation
- 1989-09-01 DE DE8989890225T patent/DE58903444D1/en not_active Expired - Fee Related
- 1989-09-01 EP EP89890225A patent/EP0359736B1/en not_active Expired - Lifetime
- 1989-09-01 ES ES198989890225T patent/ES2039949T3/en not_active Expired - Lifetime
- 1989-09-06 KR KR89012905A patent/KR950012425B1/en not_active IP Right Cessation
- 1989-09-08 JP JP1234527A patent/JPH0713320B2/en not_active Expired - Lifetime
- 1989-09-13 US US07/406,342 patent/US5022971A/en not_active Expired - Fee Related
- 1989-09-13 ZA ZA896965A patent/ZA896965B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE58903444D1 (en) | 1993-03-18 |
| FI90093C (en) | 1993-12-27 |
| JPH0713320B2 (en) | 1995-02-15 |
| KR950012425B1 (en) | 1995-10-17 |
| FI90093B (en) | 1993-09-15 |
| EP0359736A1 (en) | 1990-03-21 |
| FI893978A0 (en) | 1989-08-24 |
| JPH02107800A (en) | 1990-04-19 |
| FI893978A (en) | 1990-03-15 |
| US5022971A (en) | 1991-06-11 |
| ES2039949T3 (en) | 1993-10-01 |
| ZA896965B (en) | 1990-06-27 |
| ATA225888A (en) | 1990-04-15 |
| KR900004969A (en) | 1990-04-13 |
| AT391486B (en) | 1990-10-10 |
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