EP0244417B1 - Verfahren zum beitzen von eisen- und stahlgegenständen - Google Patents

Verfahren zum beitzen von eisen- und stahlgegenständen Download PDF

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Publication number
EP0244417B1
EP0244417B1 EP19860902076 EP86902076A EP0244417B1 EP 0244417 B1 EP0244417 B1 EP 0244417B1 EP 19860902076 EP19860902076 EP 19860902076 EP 86902076 A EP86902076 A EP 86902076A EP 0244417 B1 EP0244417 B1 EP 0244417B1
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EP
European Patent Office
Prior art keywords
pickling
solution
iron
proportion
acid
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Expired
Application number
EP19860902076
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English (en)
French (fr)
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EP0244417A1 (de
Inventor
Harry Ericson
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KORROSIONSFORSKNING AB
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KORROSIONSFORSKNING AB
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/36—Regeneration of waste pickling liquors
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/08—Iron or steel

Definitions

  • This invention relates to methods for pickling iron or steel objects, before a subsequent surface treatment or a mechanical processing.
  • the surface coating Before the mechanical processing of objects of iron or steel, e.g. by drawing, milling or pressing, or before application of any anti-corrosive film, the surface coating usually must be removed.
  • This coating can comprise various oxides, e.g. rust, being formed by chemical corrosion.
  • Other coatings can consist of scale from a preliminary heat treatment or rolling skin from a preliminary rolling. These different coatings are normally removed by pickling in acid baths.
  • sulphuric acid or hydrochloric acid is used for pickling carbon steel or cast iron.
  • the former is less expensive to buy, but the hydrochloric acid presents several technical advantages, often making the total economy for this acid the most profitable.
  • a pickling bath intended for pickling with hydrochloric acid normally comprise about 200 g HCI per liter.
  • iron is solved as Fe 2+ .
  • the proportion of iron in the pickling bath rises gradually until it, after some use, reaches about 80-85 g per liter pickling solution.
  • the proportion of acid in the pickling bath is now about 80-100 g per liter pickling solution.
  • the pickling continues very slowly during these circumstances making it necessary to exchange the pickling solution for regenerating or dumping. In total, 7-8 kg of hydrochloric acid is used per kg of dissolved iron.
  • the depositing or regenerating of used pickling solution is very important from various points of view. Partly because these pickling baths constitute a dangerous waste, which has to be destructed before deposition. Partly because the pickling bath has a significant value with respect to the content of remaining free acid, solved iron and a corresponding amount of negative ions.
  • the hyrochloric solution can be regenerated through a roasting process within an oil-burning oven. Thereby the solved iron forms iron oxide and hydrogen chlorine. The latter is absorbed while the pickling acid is recovered.
  • One disadvantage with this process is that a certain amount of hydrogen chlorine is lost because also the remaining free acid goes into the oven.
  • the pickling solution It is also possible to regenerate the pickling solution through electrolysis.
  • the iron in the solution will be deposited at the cathode of the electrolytic cell.
  • the electrolyte (the pickling solution) must form an almost neutral solution of ferrous chloride in order to enable the electrolysis. Since the pickling solution, however, contains a comparatively large proportion of remaining acid, there will mainly be development of hydrogen gas at the cathode, i.e. the deposition of metal will be small in relation to used electric energy.
  • the solution can be neutralized by evaporation and crystallization of iron chloride and separation of remaining surplus acid, which can be returned to the pickling process.
  • an electrolytic cell for recovery of pickling acid must have a ion-exchange membranes as a partition between anode and cathode, so that the acid formed at the anode will not prevent the deposition of metal at the cathode.
  • a useful pickling solution may comprise between 100-200 g free hydrochloric acid per liter solution with between 0-80 g Fe2+ and usually attacks the base metal furiously.
  • objects of iron or steel with scales normally comprising Fe 2 0 3 -FeO-oxides
  • pittings occur. This happens because the surface of the base metal usually is rather small compared to the oxide surface, i.e. the cathode, wherein the oxide has the high electric potential in relation to the iron within said solution and is cathodic in relation to the base metal, which becomes the dissolving electrode, because of its anodic potential.
  • the scales are not dissolved in the acid, but rather “explodes” away from its surface, because the acid penetrates below the scale and lifts it away. The consequence is severe pittings on the base metal, because of the anodic current density (corrosive current) is very high.
  • the proportion of acid in the solution declines, the difference of potential also declines and thereby the pickling effect of the solution.
  • the Fe 3 0 4 - oxide is deposited as a sludge on the bottom of the pickling bath. The proportion of iron rises during conventional pickling, while the proportion of acid declines. At the beginning of the process the difference of potential between the iron oxides is at least 1000 mV.
  • the base metal Fe then acts as anode, meaning that the iron oxides form Fe°-.Fe 2 '.
  • the surface of the metal is therefore pitted when it is exposed by fractures and pores in the oxide coating. It is normal to use an inhibitor or restrainer in the pickling bath to reduce the pitting damage on the base metal.
  • DE-3 141 949 discloses a method for regeneration of an etch bath which is used for etching of a metal foil. Such methods are used in the industry for manufacture of printed circuit cards.
  • the dissolved copper has a substantial metal value which allows for the use of energy consuming regeneration methods.
  • the regeneration takes place in an electrolytic cell having diaphragms, at a temperature of between 50 and 95°C, and with a current density of between 20 and 60 AJdm 2. For a current of 8 volts, the energy consumption will then be between 160 and 480 Watt/dm 2. This prior art method is not applicable for large scale pickling processes.
  • the object of the present invention is to provide a method for pickling objects of iron and steel, which enables a continuous regenerating of the pickling solution, at a high level of electrolytic efficiency, wherein the pickling can be performed in a closed process having as residual products pickled objects of iron and steel and pure electrolytic iron corresponding to the amount of dissolved iron.
  • the method according to the present invention is characterized in that the objects are transported into a pickling solution having a temperature above 25°C and containing ferrous chloride and a low proportion of free hydrochloride acid, and that said solution is continuously regenerated in a circulation system with electrolytic cells, which are connected to a source of direct-current, in order to deposit iron electrolytically and recover free acid.
  • the pickling fluid contains at least 300 g FeC1 2 per liter and no more than 50 g of free acid reckoned as HCI per liter.
  • the electrolytic cells are electrically connected in series with the source of direct-current and in parallel with the flow of pickling solution in said circulation system.
  • the proportion of ferrous chloride sinks no more than 10 g per liter solution during its passage through any of the electrolytic cells, and the current intensity at each of their respective cathode is especially between 0.2-10 A per dm 2 of cathodic surface.
  • a solution for pickling objects of iron or steel, before a subsequent surface treatment or mechanical processing comprising: FeC1 2 , Fe 2 and HCI, preferably contains the following proportions: FeC1 2 between 250 and 450 g/l, Fe 2 between 110 and 200 g/I and HCI between 5 and 50 g/I.
  • the figure shows a pilot plant for pickling of cast iron and hot rolled objects before hot zinc coating.
  • a tank containing pickling solution is generally denoted 10.
  • Objects represented by the arrow 11 are transported down into the solution after a preliminary degreasing and rinsing.
  • Pickled objects are represented by the arrow 12.
  • the pickling solution is continuously pumped, by means of a pump 13, from the tank 10, into five electrolytic cells 14, connected in parallel with the flow from the pump 13, and returns to the tank 10 by means of a return pump 15.
  • the electrolytic cells are electrically connected in series to the positive and negative terminals 16 and 17, respectively, of a direct-current source.
  • Each electrolytic cell 14 conventionally comprises one anode 18 and one cathode 19.
  • the cathode plates 19 are made of 0.1 mm thin stainless, acid resistant sheet.
  • the cathodes are changed regularly in the cells 14. By bending the sheets, the electrolytic iron can easily be removed from said sheets.
  • the pickling solution circulates through the cell system during the electrolysis at a rate of about 30 liter per minute. This implies that the difference in concentration of iron in the solution leaving vs. entering the tank is between 2.0-2.5 g/l. In the present case, when the dissolving rate of iron in the pickling solution is 10 kg/h, 40% of the acid is recovered.
  • the above described method radically alters the properties of the pickling solution.
  • the iron oxides Fe 3 0 4 becomes the dissolving electrode and the base metal is not attacked by pitting.
  • the sludge of iron oxides is completely dissolved leaving no remains at the bottom of the tank.
  • the objects are cleaned with no trace of dirt film.
  • the surrounding pickling solution is strongly reducing at the conditions according to the invention.
  • the very high electrolytic efficiency during the process according to the invention results from the relation between the overpotential of the hydrogen towards the cathode and the dissolving potential of the iron.
  • the overpotential of hydrogen is preferably as high as possible, since the electrolytic efficiency declines with a rising proportion of free acid in the solution.
  • the regenerating cells can be built as a modular system, which can be adapted to most existing pickling plants, while changing from a conventional process to the pickling process according to the invention.
  • the above mentioned dimensions, rates and values can obviously be varied within the scope of the following claims.
  • the method according to the invention can be used in combination with conventional pickling methods.
  • An activator can be added to the above described pickling solution, comprising a surface active agent with a high affinity to the base metal surface, to facilitate the penetration of the pickling fluid beneath the scales.
  • the electrolytic current between terminals 16, 17 can be pulsed at low frequency, giving a lower electrolytic polarization and therefore a higher electrolytic efficiency.
  • the pickling effect of the solution according to the invention can be even more improved by addition of any of the salts: magnesium chloride, calcium chloride or aluminium chloride.
  • This increases the overpotential at any given proportion of free acid and therefore the electrolytic efficiency.
  • An additive of 50 g/I MgCI 2 reduces tensile stress at the iron deposited at the cathode, so that a ductile film of iron is formed.
  • the iron can be plated to form any desired thickness. The growth is about 1 pm/min at a current density of 5 Aldm 2 and 90% electrolytic efficiency.
  • This addition of magnesium chloride also improves the pickling process.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Electrolytic Production Of Metals (AREA)

Claims (6)

1. Verfahren zum Beizen von Eisen- oder Strahlgegenständen vor einer nachfolgenden Oberflächenbehandlung oder einer mechanischen Bearbeitung, dadurch gekennzeichnet, daß die Gegenstände (11) in eine Beizlösung transportiert werden, die eine Temperatur oberhalb von 25°C besitzt und Ferrochlorid FeCl2, Fe und einen freien Chlorwasserstoff HCI enthält, wobei der Anteil an FeC12 zwischen 250 und 450 g/l liegt, wobei der Anteil an Fe zwischen 110 und 200 g/l beträgt, und wobei der Anteil an HCI zwischen 5 und 50 g/l liegt, daß die Lösung kontinuierlich in einem Umlaufsystem mit elektrolytischen Zellen (14) regeneriert wird, welche elektrisch in Reihe mit einer Gleichstromquelle (16, 17) geschaltet sind, um elektrolytisch Eisen niederzuschlagen und freie Salzsäure ohne das Vorhandensein irgendeines Diaphragmas zu gewinnen, und daß die eletrolytischen Zellen (14) parallel zu der Strömung der Beizlösung in dem Umwälzsystem geschaltet sind.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Beizlösung wenigsten 300 g Eisenchlorid pro Liter enthält.
3. Verfahren nach einem der Ansprüche 1o der 2, dadurch gekennzeichnet, daß der Anteil an Eisenchlorid auf nicht mehr als 10 g/1 Lösung während dessen Durchtritt durch irgendeine der elektrolytischen Zellen verringert wird.
4. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, daß die Stromstärke an jeder Kathode (19) in den elektrolytischen Zellen (14) zwischen 0,2-10 A pro dm2 Kathodenfläche beträgt.
5. Lösung zum Beizen von Eisen- oder Stahlgegenständen vor einer nachfolgenden Oberflächenwandlung oder einer mechanischen Bearbeitung, bestehend aus: FeC12, Fe und HCI, dadurch gekennzeichnet, daß der Anteil an FeCl2 in der Lösung zwichen 250 und 450 g/1 liegt, daß der Anteil an Fe in der Lösung zwischen 110 und 200 g/l beträgt, und daß der Anteil an freier Säure, HCI, zwischen 5 und 50 g/l liegt.
6. Lösung nach Anspruch 5, dadurch gekennzeichnet, daß sie ein Magnesium- oder Calciumchlorid enthält, um den Beizvorgang zu verbessern, die elektrolytische Effizienz zu erhöhen und die Zugspannung bei dem auf der Kathode niedergeschlagenen Eisen zu verringern.
EP19860902076 1985-03-19 1986-03-17 Verfahren zum beitzen von eisen- und stahlgegenständen Expired EP0244417B1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86902076T ATE52545T1 (de) 1985-03-19 1986-03-17 Verfahren zum beitzen von eisen- und stahlgegenstaenden.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE8501329 1985-03-19
SE8501329A SE452481B (sv) 1985-03-19 1985-03-19 Forfarande for regenerering av betbad samt regenererbar losning for betning av jern- och stalforemal

Publications (2)

Publication Number Publication Date
EP0244417A1 EP0244417A1 (de) 1987-11-11
EP0244417B1 true EP0244417B1 (de) 1990-05-09

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Application Number Title Priority Date Filing Date
EP19860902076 Expired EP0244417B1 (de) 1985-03-19 1986-03-17 Verfahren zum beitzen von eisen- und stahlgegenständen

Country Status (6)

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EP (1) EP0244417B1 (de)
JP (1) JPS62502268A (de)
CA (1) CA1256357A (de)
DE (1) DE3671042D1 (de)
SE (1) SE452481B (de)
WO (1) WO1986005523A1 (de)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0762575A (ja) * 1993-08-27 1995-03-07 Unitika Ltd 浴液の浄化設備および浄化方法
NL9302035A (nl) * 1993-11-24 1995-06-16 Piet De Vries Beitswerkwijze en een inrichting daarvoor.

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE637287C (de) * 1935-01-20 1936-10-24 Georg Agde Dr Verfahren zur Wiederauffrischung von 3 wertige Eisensalze enthaltenden Beizloesungen
US2423385A (en) * 1944-07-27 1947-07-01 Chemical Foundation Inc Process of pickling and of recovering pickling agent
US4113588A (en) * 1976-03-09 1978-09-12 Solex Research Corporation Of Japan Process for recovery of waste H2 SO4 and HCl
ATE7050T1 (de) * 1980-01-18 1984-04-15 Boliden Aktiebolag Verfahren zur regenerierung von beizloesungen.
CS218296B1 (en) * 1980-10-30 1983-02-25 Antonin Stehlik Method of continuous regeneration of the iron trichloride solution

Also Published As

Publication number Publication date
SE8501329D0 (sv) 1985-03-19
DE3671042D1 (de) 1990-06-13
CA1256357A (en) 1989-06-27
SE8501329L (sv) 1986-09-20
EP0244417A1 (de) 1987-11-11
WO1986005523A1 (en) 1986-09-25
SE452481B (sv) 1987-11-30
JPS62502268A (ja) 1987-09-03

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