SE519159C2 - Method and apparatus for pickling - Google Patents

Abstract

Method and device for electrolytic, continuous treatment of a continuously formed material (1) of stainless steel, said material being made to run in an electrolyte (34) between electrodes (35, 36) lying in series, under the influence of a direct current with alternating polarity, every other electrode being anodic and every other being cathodic and every electrode being matched by an electrode of the same polarity on the opposite side of the material (1), an oxide surface layer being removed from the material in the method. According to the invention, said electrodes (35, 36) lying in series are partially, electrically insulated from each other in the electrolyte (34) by partial insulators (37) being arranged between after each other arranged electrodes of opposite polarity, preferably both on a first side and on a second side of the material (1).

Description

P1577 519 2159 of spinel type, this time with a thickness of about 10 micrometers. Since the oxide does not have the right stainless steel properties, it is also pickled away in the same way as in previous processes. After rinsing, the material has a matte, pickled surface. In some cases, e.g. when further forming operations are to be carried out, the pickled surface is an advantage, but a glossy surface is desired instead, which is then achieved by gloss annealing in a reducing atmosphere, followed by smooth rolling with only about 2% reduction of the material thickness. Blasting is not used on cold-rolled material, as it destroys the surface. Instead, so-called neolite treatment is used, which means an electrolytic treatment with direct current, usually in sodium sulphate, whereby chromium (III) is oxidized to chromium (VI) which is easily soluble.

SE 9800287-6 (= SE-511 777-C2) describes a method for, at a current density of 0.1 - 3 A / cm 2, electrolytically continuously treating a strand-shaped material of stainless steel, an oxidic surface layer having a thickness of at least 1 micrometer is removed from the material. In the method, in the same step, a selected surface conditioning effect is achieved, comprising producing a selected surface unit, the method being carried out using an electrolyte comprising sulfuric acid or salt thereof and / or phosphoric acid, or an electrolyte comprising nitric acid, and wherein the treatment step is performed in one or , series electrolysis cells, so that the material is caused to flow in the electrolyte between series electrodes, under the influence of a direct current of varying polarity, each other electrode being anodic and each other being cathodic and each electrode corresponding to an electrode of the same polarity on opposite side of the material.

However, a problem in electrolytic pickling where a strand-shaped material runs between electrodes of varying polarity has been found to be that only a small part of the applied current for the electrolysis passes through the strand-shaped material, with instead the main part of the current taking the path directly from cathode to anode via the electrolyte, ie without passing through the steel strip to be treated. It has been found that only 30% current efficiency is normally achieved, with the remainder being a loss due to short circuit between anodes and cathodes. This means that unnecessarily high voltages must be applied across the electrodes in order to achieve the desired pickling effect, which in turn means a considerable energy loss. Alternatively, the throughput speed of the strand-shaped material must be reduced in order to achieve the desired pickling effect, which means that the pickling step in the steel treatment line o fi a will constitute a bottleneck for production. It is known from U.S. Pat. No. 5,449,447 and U.S. Pat. Thanks to the device arrangement shown, an almost fi completely independent electrical insulation between anodes and cathodes is achieved, thus short-circuiting them between them. However, this is achieved at the cost of a very complicated set-up of apparatus, which thus involves a costly capital investment in completely new equipment, ie it cannot be achieved by rebuilding existing equipment for pickling. Maintenance should also be made more difficult and in addition fl the flexibility of the plant is low, e.g. in connection with the treatment of varying types of stranded materials with different amounts of oxide. The process shown is further primarily intended to constitute a pre-treatment step before a main treatment such as e.g. can consist of galvanizing.

US 5,840,173 discloses continuous pickling of stainless steel in connection with rolling.

The pickling takes place in hydrochloric acid, at a current density of 3-40 A / dmz and a temperature of 50-95 ° C, in a container containing individual compartments for alternating anode and cathode pairs. However, the writing does not go into more detail on why the cells / electrodes are arranged in this way, or on how the division is carried out in practice. Also US 5,804,056 shows continuous pickling of stainless steel in connection with rolling.

The pickling takes place in sulfuric acid and it is shown in Fig. 1A that a cell containing only three anode pairs is used, followed by a cell containing only one cathode pair. The publication does not go into detail about the reason for this configuration.

US 4,129,485 discloses continuous pickling of carbon steel in connection with a rolling line.

The pickling takes place with contact polarization of the strip and the strip is allowed to run through a number of treatment vessels which are alternately provided with cathodic and anodic electrodes, respectively. The conditions of the pickling are that the bath consists of NaCl, the temperature is 80-100 ° C and the current density is 0.5-1.0 A / cm 2.

A major problem with complete separation between different pickling vessels, each of which contains only one type of electrode, is that no, or at least deteriorated, equalization in the electrolyte is obtained between the different pickling vessels. The consequence of this is that elevated concentrations of e.g. iron ions and that elevated amounts of sludge build up in individual pickling tanks that make up the anode cell. The concentration of the active components in the electrolyte also becomes uneven between the different pickling agents. All this means that the pickling risks deteriorating sharply, despite the advantage achieved thanks to the electrical insulation.

Another problem when pickling stainless stranded materials, especially strip-shaped materials, is that the material is often in greater need of pickling on the underside than on the top. This places demands on different pickling on the underside and top of the belt, respectively, which can be difficult to achieve with the pickling equipment that is normally used today.

DESCRIPTION OF THE INVENTION The present invention aims to address the above problem complexes.

In particular, the invention aims to provide a method and device for pickling a stainless stranded material in connection with a production line for strip-shaped stainless material, which production line also comprises hot rolling and / or cold rolling of the strip. It is especially preferred that the pickling is adapted to be able to give a selected surface conditioning effect in the same step, comprising providing a selected surface unit.

The invention further aims in particular to provide a method and device for pickling a stainless strand-shaped material, said material being caused to run in an electrolyte between electrodes lying in series, under the influence of a direct current of varying polarity, each electrode being anodic and every other is cathodic and each electrode corresponds to an electrode of the same polarity on the opposite side of the material, an oxidic surface layer having a thickness of at least 1 micrometer being removed from the material and at the same time providing partial electrical insulation between successively arranged electrodes of opposite polarity , in that partial insulators are arranged between them, and wherein an electrically insulating effect of the insulators between the electrodes can be varied, at least on the first side of the material. Preferably, such insulators are arranged between each pair of electrodes arranged, preferably on both sides of the material, i.e. on a first side of the material and on a second side of the material. These insulators are preferably, at least on the first side of the material, displaceable for said variable insulating effect in the electrolyte between the electrodes arranged on said first side of the material. This also provides the conditions for a good, but variable, agitation in the electrolyte bath common to the entire pickling vessel to be achieved.

The term "displaceable" in this context means that the effective insulating surface of the insulator can be changed in the electrolyte bath. This can be accomplished in many different ways, as will be described in greater detail later. Typically, the position and surface of the insulator between the electrodes can be changed so that the electrodes are shielded differently from each other.

The insulating surface can, regardless of whether the insulator is fixed or displaceably arranged, be 20-95%, preferably 30-90% and even more preferably 40-85%, calculated on the total cross-sectional area in the electrolyte bath on one side of the strip.

The term "electrode" here refers, and hereinafter, to a single electrode or a bundle of electrodes, the latter variant being the most common in the industry and means that each electrode bundle in practice functions as an electrode in that an electrode bundle has a certain polarity (cathode or anode). The electrodes can e.g. be made of lead, titanium, stainless steel or Si steel.

In the context of the present invention, it has surprisingly been found that a very good improvement in current efficiency can also be obtained with an electrical insulation between electrodes of opposite polarity in the electrolyte, which insulation is not complete. This increased current efficiency can therefore be obtained at the same time as a good stirring in an electrolyte bath in a pickling vessel which is common to all electrode pairs. The reason why this is possible is that, in connection with the development of the invention, it has been found that the potential in the electrolyte falls exponentially with the distance to the electrode. Therefore, one can electrically shield / insulate electrodes of opposite polarity from each other in one and the same electrolyte bath, by introducing insulators which do not have to extend more than just past the electrodes, seen in their extent in the direction of the extruded material. As one gets closer to the string-shaped material, the potential has dropped so much that the current in any case prefers to seek its way into this material rather than taking the short-circuit path directly between the electrodes.

According to one aspect of the invention, said insulators are formed of an electrically insulating material, preferably selected from the group consisting of polymeric and ceramic materials, most preferably plastics, rubber, ceramics or plexiglass. Such insulators are arranged according to the invention between all or substantially all electrode pairs in the device.

The solution according to the invention has many advantages. The primary advantage is, as stated, that short circuits are largely prevented, whereby the power efficiency is improved, which in turn leads to an optimized pickling process with lower energy consumption and / or increased capacity. At the same time, a good stirring and concentration equalization is achieved in the electrolyte bath. According to the invention, these advantages can further be achieved with a relatively simple design in terms of apparatus which is also suitable for so-called "retro fi t", ie 15 rebuilding of existing equipment, with relatively small interventions. in the equipment. According to the invention, the electrical insulation and the concentration equalization in the electrolyte are also adjustable, thanks to displaceable insulators, which provides a valuable ill-flexibility in the system. For example, when it is desired to beta a steel strip with a strong but easily grazed oxide layer which gives rise to large sludge formation in the electrolyte, only a small shield between the electrodes and thus increased concentration equalization can be used, while, when it is desired to beta a steel strip with a smaller but difficult-to-pick oxide layer that does not give rise to so much sludge, can use a larger, perhaps almost complete, shielding between the electrodes.

The invention is advantageously used in connection with a pickling process of the type described in SE 9800287-6 (= SE-511 777-C2), which document is hereby incorporated by reference. This means that the pickling is carried out in such a way that in the same step a selected polishing effect of the steel can be achieved, instead of the conventional mat, pickled surface which is normally achieved during pickling. An electrolyte comprising sulfuric acid or salt thereof and / or phosphoric acid and optionally hydrochloric acid or salt thereof is preferably used. Most preferred ranges are 0-95% by volume of sulfuric acid and 5-100% by volume of phosphoric acid, but it should be understood that a large number of other variants are also possible, as described in SE 9800287-6. The electrolyte may also mainly comprise nitric acid, which, however, means a non-preferred negative environmental impact.

It should be understood, however, that the invention is not limited to the use of these electrolytes, but that it works well for all types of electrolytes.

According to a further aspect of the invention, the treatment time is 2 seconds - 5 minutes, preferably 10 seconds - 3 minutes and even more preferably 30 seconds - 2 minutes. Preferably the treatment time is 30 sec - 5 min, preferably 1 min ~ 3 min and even more preferably about 2 minutes when the starting material is hot rolled and annealed or 2 sec - 2 min, preferably 5 - 90 sec and even more preferably 10 - 60 sec when the starting material is cold-rolled and annealed, whereby the treatment can be carried out in one step or can be divided into two or two steps. The anodic current density during the electrolysis is 0.1 - 3 A / cm 2, preferably 0.3 - 2.5 A / cm 2 and even more preferably 0.5 - 2 A / cm 2 and the temperature is 50 - 100 ° C, preferably 60 - 90 ° C and even more preferably 65 - 80 ° C.

The stainless material that is pickled can Lex. be phenytic, martensitic, duplex, austenitic or superaustenitic. The composition of these stainless steels is defined in “Stainless Steel, The New European Standards”, 2nd Edition. 1997-02, 10 15 20 25 30 35 5197159 Pl577 Avesta Sheffield, but other types of stainless steels can also be treated according to the invention. .

According to a further aspect of the invention, the treatment according to the invention can be preceded and / or followed by a chemical surface treatment with mixed acid in one or more cells, preferably with nitric acid and hydrochloric acid.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail, with reference to the guras, of which: Fig. 1 schematically shows the current distribution in an electrolyzer according to the prior art without insulation between anode and cathode, Figs. Fig. 2 shows a preferred line for annealing with subsequent pickling according to the invention, Fig. 3 schematically shows a pickling vessel with lid, which comprises insulators according to the invention, Fig. 4 shows a cross section of a device according to a first preferred embodiment of the invention, Fig. 5 shows two further possible embodiments of the invention, Figs. 6-8 show the concentration of iron, chromium and nickel, respectively, at different degrees of insulation.

Fig. 9 shows the current in the band as a function of the total applied current, at different degrees of insulation.

DETAILED DESCRIPTION OF FIGURES Figure 1 shows the current distribution between anode 35 and cathode 36 in a laboratory-sized electrolytic cell in which a stainless steel strip 1 has been rigged. The arrangement shown is without suitable insulators, ie it is according to known technology. It is possible that the current, in the position between the anode and the cathode, goes directly between them, without taking the path via the band 1. This leads to a poor utilization of the current, i.e. a low current activity.

Figure 2 shows a production line for treatment of a hot or cold rolled strip material in stainless steel. In the following description of the figures, it is assumed that the starting material is a hot-rolled strip which thus has an oxide layer of the spinel type. The hot-rolled strip 1 is first laid on a so-called unwinding reel 2, after which it runs to a cap 3 and a welding device 4 which has the function of welding together a strip, at its end, starting at a new belt so that production can continue without any major stops for changing belts. This is followed by a stretching and switching plant 5 for stretching the belt and setting its line speed, which is preferably high. In the next step, the strip passes through an oven 6 with a temperature of about 1050-1150 ° C, the function of which is to soften the oxide on the surface of the strip. There follows a cooling stage 7 and a blaster 8 which has the purpose of cracking the oxide shell so that electrolyte, in a later stage, can penetrate into the chromium-depleted zone which lies inside the oxide shell. After the blasting 8 follows the step covered by the present invention, namely the pickling step which preferably also constitutes a combined polishing step. This step is here divided into three cells 9, 10, ll. In the cells there is an electrolyte as previously described, with the most preferred having the composition 5 mol / l sulfuric acid, 8-8.5 mol / l phosphoric acid and iron (triggered). The electrolysis in the cells is carried out with fi- partially and variably isolated cathodes and anodes, respectively, and with direct current at a preferred current density of 0, S-2 A / cm 2, a temperature of 70 ° C and a total time of about 2 minutes, whereby a glossy surface of the tape is obtained. The principle of how the electrolysis cells can be constructed is explained in more detail in Figures 3-5. After the treatment according to the invention in the cells 9, 10, 11, a rinsing equipment 12 for rinsing the belt and then a so-called reel 13 follows. The belt then possibly runs on to cold rolling.

The principle for treatment of a cold-rolled material is the same as that reported with reference to Figure 2. The difference is that a cold-rolled material is not blasted, as this destroys the surface of the strip, whereby instead a so-called neolite step can be used as pre-treatment before the pickling and polishing step. . The neolyte step may consist of an electrolytic cell with only slight agitation and which contains an electrolyte consisting of e.g. sodium sulfate. The neolyte step is performed with direct current with a current density of about 1-10 A / dmz. When treating a cold-rolled strip material, the oven also has a slightly different function, namely to stress-anneal the material.

The line described in Figure 2 can advantageously be designed as a so-called combination plant, whereby the strip material is caused to pass through the line twice, first in the hot-rolled state and then in the cold-rolled state.

Fig. 3 schematically shows the principle of the device according to the invention. A pickling vessel 9, 10, 11 is built up of a lower part with side walls 31 and bottom 32, and an upper part 33 which forms a lid. The tub houses an electrolyte bath 34 as previously described. The extruded steel material (strip) 1 runs into the tub and out of the same via seals (not shown) in the side walls 31 of the tub. is anodic 35 and every other is cathodic 36. In the upper part of the vessel there are also arranged electrodes 35, 36 in a corresponding manner, each electrode being corresponding to an electrode of the same polarity on the opposite side of the material. According to the invention, the electrode pairs are partially electrically insulated from each other in the electrolyte in that the electrodes 35, 36 of opposite polarity arranged between each other are arranged partial insulators 37, on both sides of the material. By the term "partial" is meant here that these insulators do not fi independently divide the tub into different, completely separated compartments, but that there remains a certain open cross-sectional area for an electrolyte fl fate between the different “rooms”. This electrolyte fate is usually achieved by means of a conventional pump device (not shown) circulating the electrolyte. The open cross-sectional area is suitably arranged in connection with the band 1, but it is also conceivable that in addition, or instead, a certain open cross-sectional area is arranged above the upper electrodes and / or below the lower electrodes, i.e. in connection with the bottom of the tub. 32.

A possible solution is e.g. that an open cross-sectional area is arranged adjacent to the band 1 at every other lower insulator 37, but that an open cross-sectional area is also arranged adjacent to the bottom 32 at the other insulator 37, so that the turbulence of the electrolyte is increased. Corresponding open cross-sectional area can of course also be arranged at every other insulator 37 over the upper electrodes.

Fig. 4 shows a cross section of a preferred device according to the invention, transverse to the passage direction of the belt 1, i.e. the belt 1 runs in and out of the plane of the paper in the figure, respectively. The insulator has a total height H2 which extends from the bottom 32 of the pickling vessel and up to the lid or to the liquid level. It is also conceivable that it ends a short distance below the liquid level, but always above the level of an upper electrode 35. The extent of the insulator from the bottom 32 of the tub and up to a center line of the band 1 is denoted H1. At the bottom, at the bottom of the tub, the insulator 37 has an opening which they have an open area hl> <bl, where bl is equal to or substantially equal to the total width B of the tub. a height h3 which is in principle equal to the thickness of the belt, which can be achieved e.g. by means of a rubber lip trailing towards the strip of the insulator, the proportion of insulating surface on the underside of the strip is defined as (1 - hl / H1) or h2 / H1, h2 constituting the effective height of the insulator on the underside of the strip. On the upper side of the strip, the insulating effect is in principle one hundred percent if H2 is greater than the liquid level, or partial if H2 is smaller than the liquid level, the proportion of insulating surface on the upper side of the strip in the latter case being calculated in the same way as on the lower side. The distance between the electrodes 35 in the electrode pair is denoted by 10 15 20 25 30 35 519 1159 P1577 h4, it being the case that h3 <h4, and that h4 is typically about 150-300 mm, preferably 200-250 mm. If h3 is greater than the thickness of the strip 1, this may be taken into account when calculating the proportion of insulating surface.

Figs. 3 and 4 do not show how the insulators can be designed for variable electrical insulating power. This is instead shown in principle in Fig. 5, which shows two variants of how the variable, partial, electrical insulation according to the invention can be solved practically. In the left part of the visas clock it is shown that the insulators can be constituted by rotatable rollers 37 ', which can be raised and lowered. This solution has the advantage that the belt 1, can rest on the rollers 37 'on its underside, so that the belt 1 can be moved closer to the electrodes 35, 36 on the underside, when these rollers 37' are lowered. In this way, the pickling can be strengthened on the underside of the belt. In this embodiment there is an open cross-sectional area, i.e. non-insulating, above and below the rollers 37 'on the upper side and lower side of the belt, respectively.

In the right-hand part of the figure, on the other hand, a partition wall 37 "'is arranged under the rollers 37' on the underside of the belt, which partition wall also constitutes an insulator. can be arranged so that an, possibly variable, open area is formed at the bottom 32 of the tub. On the upper side of the belt it is shown how a partition wall 37 " , as well as the partition 37 "'on the underside, can e.g. consists of a flexible rubber membrane, e.g. a rubber cloth.

Figs. 6-8 show, in curve form, the result of experimental experiments performed in laboratory equipment corresponding to that shown in Fig. 4, whereby the band was stationary while the electrolyte was subjected to agitation in anode and cathode cell, respectively.

Utilized electrolyte, temperature, current density, etc. were, as previously stated, preferred as preferred in connection with the invention.

Fig. 6 shows the concentration of iron ions in the whole vessel, as a function of the time for the electrolysis. Curve Fe; shows the concentration when there was no insulation, while curve Fega shows the concentration in the anode part of the tub when 70% insulation was present, curve Feh shows the concentration in the cathode part of the tub when 70% insulation was present, curve F e3, shows the concentration in the anode part of the tub when 100% insulation was present and curve Fegc shows the concentration in the cathode part of the vessel when 100% insulation was present.

Fig. 7 shows the concentration of chromium ions in the whole vessel when no insulation was present as curve Cr1, while curve Crza shows the concentration in the anode part of the vessel when 70% was present, curve Crgc shows the concentration in the cathode part of the vessel when 70% insulation was present, curve Crg. shows the concentration in the anode part of the vessel when 100% insulation was present and curve Crgc shows the concentration in the cathode part of the vessel when 100% insulation was present.

IFig. 8 shows the concentration of nickel ions in the whole vessel when no insulation was present as curve Nil, while curve Nig. shows the concentration in the anode part of the tub when 70% insulation was present, curve Nigc shows the concentration in the cathode part of the tub when 70% insulation was present, curve Nig, shows the concentration in the anode part of the tub when 100% insulation was present and curve Nigc shows the concentration in the cathode part of the tub when 100% insulation was available.

In all curves, it is clear that, with partial insulation, a significantly better equalization in concentration is obtained between the cathode and anode parts of the tub, respectively, compared with when 100% insulation is used. At the same time, the partial insulation gives a considerably improved current efficiency in the electrolysis compared to when no insulation is used at all, as shown in Fig. 9. Fig. 9 thus shows the current in the band as a function of the total current supplied to the electrolyte cell in the experiments 6-8. The best current efficiency is achieved with 100% insulation between the anode and cathode, but at the price of an insignificant concentration equalization between the anode and cathode part of the tub. At 70% insulation, a clearly improved current efficiency is achieved, at the same time as the concentration equalization is good. At 0% isolation, the current activity is very poor.

The invention is not limited by the embodiments described above, but can be varied within the scope of the following claims. The person skilled in the art realizes e.g. it is easy for further variants to be conceivable with regard to the practical design of the insulators, and that the variants shown here can also to some extent be combined with each other.

Claims (16)

10 15 20 25 30 35 51912159 P1577 PATENT REQUIREMENTS A method of electrolytically continuously treating a strand-shaped material (1) of stainless steel, said material being caused to run an electrolyte (34) between series electrodes (35, 36), under the influence of a direct current of varying polarity, wherein every other electrode is anodic and every other is cathodic and each electrode is represented by an electrode of the same polarity on the opposite side of the material (1), wherein during the method an oxidic surface layer with a thickness of at least 1 micrometer is removed from the material, series of electrodes (35, 36) are electrically insulated from each other in the electrolyte (34) by arranging insulators (37) between the electrodes arranged one after the other, preferably on both a first and a second side of the material (1), characterized in that the insulators (37) are partially electrically insulating in the electrolyte, and that an electrically insulating effect of the insulators (37) between electrodes ma (3 5, 36) can be varied, at least on the first side of the material (1). A method according to claim 1, characterized in that said electrodes (35, 36) are insulated to 20-95%, preferably 30-90% and even more preferably 40-85%, calculated on the total cross-sectional area of the electrolyte ( 34) on one side of the strap. Method according to claim 1 or 2, characterized in that said insulators (37), at least on the first side of the material (1), are displaceable for said variable electrically insulating effect in the electrolyte (34) between the electrodes (35, 36). ) which are arranged on the corresponding side of the material. Method according to any one of the preceding claims, characterized in that said insulators (37) are formed in an electrically insulating material, preferably selected from the group consisting of polymeric and ceramic materials, most preferably plastics, rubber, ceramics or plexiglass. A method according to any one of the preceding claims, characterized in that said electrolyte (34) comprises sulfuric acid or salt thereof and / or phosphoric acid, or comprises nitric acid, the electrolyte preferably further comprising hydrochloric acid or salt thereof. Method according to any one of the preceding claims, characterized in that said electrolyte (34) comprises sulfuric acid in a concentration of 2 - 12 mol / l, preferably PIS77 2 - 10 mol / l and even more preferably 2 - 6 mol / l and phosphoric acid in a concentration of 2 - 14 mol / l, preferably 4 - 12 mol / l and even more Preferably 4 - 9 mol / l. Method according to one of the preceding claims, characterized in that the method is carried out at a treatment time of 2 sec - 5 min, preferably 10 sec - 3 min and even more preferably 30 sec - 2 minutes, at a current density of 0.1 - 3 A / cm 2, preferably 0.3 - 2.5 A / cm 2 and even more preferably 0.5 - 2 A / cm 2, and a temperature of 50 - 100 ° C, preferably 60 - 90 ° C and even more preferably 65 - 80 ° C. Method according to any one of the preceding claims, characterized in that the treatment constitutes a sub-step (9, 10, 11) in a process line for the production of said extruded stainless steel materials, which process line also comprises hot rolling and annealing (6) and / or cold rolling and annealing (6). Device for electrolytic, continuous treatment of a strand-shaped material (1) of stainless steel, said device comprising a pickling vessel (31, 32) with lid (33) for an electrolyte bath (34), and electrodes (in series) , 36) arranged in this vessel with lid, which electrodes are arranged to have alternating polarity under the influence of a direct current, each other electrode being anodic and each other being cathodic and each electrode being represented by an electrode of the same polarity on the opposite side of the material ( 1), and wherein said electrodes (35, 36) lying in series are electrically isolated from each other in the electrolyte (34) in that the insulators (37) arranged between successive electrodes are arranged, preferably on both a first and a second side of the material (I), characterized in that the insulators (37) are partially electrically insulating in the electrolyte, and that the insulators (37), at least on the first side of matter alet (1), are arranged so that an electrically insulating effect between the electrodes (35, 36), of said insulators (37), is variable. Device according to claim 9, characterized in that said electrodes (35, 36) are insulated to 20-95%, preferably 30-90% and even more preferably 40-85%, calculated on the total cross-sectional area of the electrolyte (34) on one side of the band. Device according to claim 9 or 10, characterized in that the insulators (37), at least on the first side of the material (1), are arranged so that their effective insulating area between the electrodes (35, 36) is variable. 10 15 20 25 519 153 P1577 Device according to any one of claims 9-11, characterized in that said insulators (37), at least on the first side of the material (1), are slidably arranged for said variable electrically insulating effect in the electrolyte (34) between the electrodes (34). 3 5, 36). Device according to claim 12, characterized in that said insulators (37) are designed as partitions (37 ", 37" ') which are arranged in the lower part of the tub and / or at said lid (3 3), which partitions are slidable. in a direction perpendicular to the direction of passage of the material (1) in the device, said lid (33) preferably having passages for the partitions (37 "), so that these can be partially displaced out of the device or into the lid of the vessel. Device according to claim 9, characterized in that said insulators (3 7), on the other side of the material (1), are fixedly arranged at said cover (3 3). Device according to any one of claims 9-12, characterized in that said insulators (37) consist of rotatable rollers (37 '), at least on the first side of the material (1), which rollers are preferably so arranged on the first side of the material that this rests and rolls forward on them during the treatment process. Device according to any one of claims 9-15, characterized in that said insulators (37) are formed in an electrically insulating material, preferably selected from the group consisting of polymeric and ceramic materials, most preferably plastics, rubber, ceramics or plexiglass.