Method for controlling supply of chromium in electrolysis process for producing chromium layer and electrolysis chamber therefor

Abstract

The invention relates to a method for controlling the supply of chromium in an electrolytic process for producing a chromium layer by means of a direct current and using an anode (44, 144, 244) and a cathode (48, 148, 248), comprising, in the event of forming a chromium layer during the electrolytic deposition of chromium: (E) applying a cathode voltage to a first additional electrode (54, 154, 254), the electrolyte (25, 125, 225) contains a passivation layer of chromium metal, whereby the passivation layer of the chromium metal is dissolved and the chromium metal begins to dissolve in the form of chromium (III) ions in the electrolyte (25, 125, 225); (F) after dissolution of the passivation layer, ending the supply of current to the first additional electrode (54, 154, 254) or cutting off the voltage at the first additional electrode (54, 154, 254); and (G) dissolving the chromium metal in the form of chromium (III) ions from the first additional electrode (54, 154, 254) by the action of the electrolyte (25, 125, 225) without current. Steps (E), (F) and (G) can be arbitrarily repeated a plurality of times by replenishing the chromium metal in the first additional electrode during step (G).

Description

Technical Field

[0001] The invention relates to a method for controlling the chromium supply in an electrolytic process for producing a chromium layer and to an electrolysis chamber therefor. Background Art

[0002] Electroplating processes for surface coating of objects have long been known in the prior art. The coated objects obtained have particularly advantageous surface properties, such as greater hardness, improved corrosion resistance, metallic appearance, gloss, etc. Metal is deposited on an object connected as cathode by means of direct current using an electroplating bath which contains the metal to be deposited as a salt in a solution. The object to be coated is therefore usually a metallic material or is subjected to additional metallization of the surface so that it becomes electrically conductive.

[0003] One metal used for this is chromium. Applying the chromium layer using an electroplating bath can serve decorative purposes to form a bright and highly reflective chromium layer. There is also the possibility of chrome-plating objects in technical applications, for example to increase wear resistance, improve wear stability and increase heat resistance and corrosion resistance. This is used, for example, for chrome-plating pistons, cylinders, bushings, bearings, etc.

[0004] It is known to use chromium (VI) salts such as CrO3 and sulfuric acid in electroplating baths. However, this has many disadvantages: the generation of gases, especially hydrogen and to a lesser extent also oxygen, thus leads to the formation of acidic, corrosive and sometimes toxic chromic acid mist. This requires intensive suction of the surface of the electroplating bath and the use of surfactants or wetting agents to contain the chromic acid mist that occurs. In addition, chromium (VI) electrolytes are highly toxic and carcinogenic. Therefore, it is better to use non-toxic electroplating baths containing chromium (III) salts.

[0005] When electroplating chromium using chromium(III) salts, it must be taken into account that the chromium layer can be deposited in a suitable layer thickness that is not too thin and the plant structure is not too complicated, so that industrial application is still feasible.

[0006] The precipitation of chromium from chromium (III) salts present in the electrolyte results in a reduction in the chromium (III) ion concentration in the electrolyte. However, Cr (III) can only be added in the form of chromium (III) salts, which leads to an undesirable gradual accumulation of anions present in the salts in the electrolyte. This requires regular dilution, subsequent addition of further components and therefore continuous checking and monitoring of the system.

[0007] In addition, it is not feasible to apply an anodic voltage or an anodic potential to a chromium metal anode, because chromium, as a very active metal, immediately forms an oxide layer on its surface, which makes the chromium passivated. When an anodic voltage is applied to such a passive chromium, only a small amount of chromium is dissolved. However, if a high anodic voltage is applied, chromium will dissolve in the form of chromium (VI) ions, which is not only carcinogenic, but also causes undesirable interference to the chromium (III) electrolyte and impairs the function of the electrolyte. Therefore, chromium is difficult to be continuously provided to the electrolyte by electrolysis as trivalent chromium.

[0008] The following solutions are known in the prior art:

[0009] According to EP 2 640 873 Al (WO 2012 / 067725 Al), a method for replenishing or increasing the chromium content of an electrolyte with trivalent chromium is described, wherein the method comprises the following steps:

[0010] a) immersing the chromium-containing electrode and the second electrode in an electrolyte containing trivalent chromium ions; and

[0011] b) applying a pulsed alternating current to the chromium electrode and the second electrode; wherein the chromium is dissolved from the chromium electrode by electrolysis in the form of trivalent chromium ions, and the chromium (III) content of the electrolyte in which the chromium electrode is immersed is replenished or accumulated again. The duration of each forward pulse and each reverse pulse is generally between about 0.1 and about 2 seconds. For example, a square waveform can be used as the waveform, wherein the duration of the alternating current pulse is about 400 ms cathode forward pulse and 400 ms anode reverse pulse. The disadvantage of this solution is that the technology is complex, wherein durable polarity conversion requires the use of expensive pulse rectifiers.

[0012] In addition, GB 414 939 discloses a method for electroplating chromium, in which direct current is conducted from the chromium anode to the cathode to be plated, and an alternating current is superimposed on the plating current to activate and dissolve the chromium from the anode. For example, FIG2 shows a circuit diagram of an arrangement that can be used when the alternating current is superimposed only at the anode. H is an auxiliary electrode, in which an alternating current generator WG is connected to the anode A and the auxiliary electrode H via a transformer T.

[0013] The object of the present invention is to avoid the disadvantages of the prior art and to provide a method or an electrolysis chamber which enables the supply of chromium metal to be controlled during electrolysis without causing an undesirable accumulation of anions and without the formation of chromium (VI) ions. The chromium layer provided should also meet the requirements imposed on chromium coatings, in particular on gravure cylinders. Summary of the invention

[0014] The described object is achieved according to the invention by the teaching of the following technical solutions. The teaching of the dependent technical solutions shows advantageous embodiments.

[0015] In particular, a method for controlling the chromium supply in an electrolytic process for producing a chromium layer is provided, wherein the chromium layer is produced by electrolytic deposition of chromium from an electrolyte by means of direct current and using an anode and a cathode, comprising the following steps:

[0016] (A) providing a first additional electrode which comprises chromium metal or consists of chromium metal;

[0017] (B) providing a second additional electrode in the form of an inert electrode,

[0018] (C) immersing two additional electrodes in an electrolyte containing at least one chromium (III) salt;

[0019] (D) coupling the first additional electrode and the second additional electrode together in a circuit separate from the cathode and the anode; and

[0020] In the case of formation of a chromium layer during electrolytic deposition of chromium:

[0021] (E) applying a cathodic voltage to the first additional electrode, thereby causing the passivation layer of the chromium metal to dissolve and the chromium metal to begin dissolving in the electrolyte in the form of chromium (III) ions;

[0022] (F) after the passivation layer is dissolved, ending the current supply to the first additional electrode or cutting off the voltage at the first additional electrode; and

[0023] (G) Chromium metal is dissolved from the first additional electrode in the form of chromium (III) ions by the action of the electrolyte in the absence of an electric current.

[0024] For example, when the object to be coated has been completely coated, the process can also be ended again in a targeted manner. According to one embodiment of the present invention, the process can be ended during step (G) by:

[0025] - applying an anodic voltage to the first additional electrode, or

[0026] - removing the first additional electrode from the electrolyte or pumping the electrolyte out of the electrolysis chamber so that the first additional electrode is in contact with the ambient air, or

[0027] The chromium metal of the first additional electrode is not replenished, so that the dissolution of the chromium metal in the form of chromium (III) ions from the first additional electrode by the action of the electrolyte in the absence of current ends once the chromium has completely dissolved.

[0028] The subject of the invention is also an electrolysis chamber for controlling the supply of chromium to an electrolyte, comprising

[0029] -anode;

[0030] -cathode;

[0031] - an electrolyte comprising at least one chromium(III) salt;

[0032] - The anode and cathode are immersed in an electrolyte;

[0033] a first circuit which connects the anode and the cathode and which enables the deposition of the chromium layer by electrolytic deposition of chromium from the electrolyte onto the cathode by means of direct current;

[0034] a first additional electrode comprising chromium metal or consisting of chromium metal;

[0035] - a second additional electrode in the form of an inert electrode,

[0036] - Two additional electrodes are immersed in the electrolyte;

[0037] - a second loop connecting the first additional electrode and the second additional electrode in a circuit separate from the cathode and the anode;

[0038] in

[0039] - applying a cathodic voltage to the first additional electrode so that the passive layer of chromium metal at the first additional electrode dissolves; or

[0040] - no voltage is applied to the first additional electrode, so that after the passivation layer has dissolved, chromium metal dissolves from the first additional electrode into the electrolyte in the form of chromium (III) ions in the absence of current; or

[0041] - applying an anode voltage to the first additional electrode so that a passivation layer is formed again at the first additional electrode.

[0042] The method according to the invention and the electrolysis cell according to the invention are therefore based on the chemical dissolution of chromium in the form of chromium(III) ions in an electrolyte, which is activated by the passage of an electric current, is continued in the absence of an electric current and, if necessary, can be terminated again by the passage of an electric current or in another way. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The depicted and other aspects, advantages and features according to the present invention will be described in more detail in the following paragraphs with reference to the accompanying drawings. In the accompanying drawings:

[0044] Figure 1 A flow chart is shown for illustrating an embodiment of the method according to the present invention;

[0045] Figure 2a shows a schematic diagram of an embodiment of an electrolysis chamber according to the invention during an electroplating phase, wherein a cathodic voltage is applied to the first additional electrode;

[0046] Figure 2b Shown with Figure 2a Schematic diagram of the same embodiment as in , wherein no voltage is applied to the first additional electrode;

[0047] Figure 2c Shown with Figure 2a Schematic diagram of the same embodiment as in , wherein the anode voltage is applied to the first additional electrode;

[0048] Figure 3a a schematic diagram according to an embodiment of the invention showing a loop comprising a first additional electrode, a second additional electrode and a third additional electrode, wherein a cathodic voltage is applied to the first additional electrode;

[0049] Figure 3b Shown with Figure 3a Schematic diagram of the same embodiment in which no voltage is applied to the additional electrode;

[0050] Figure 3c Shown with Figure 3a Schematic diagram of the same embodiment as in , wherein the anode voltage is applied to the first additional electrode;

[0051] Figure 4a A schematic diagram of an embodiment of the invention showing a circuit comprising cells of additional electrodes coupled together to illustrate the series connection, wherein a cathode voltage is applied to a first additional electrode;

[0052] Figure 4b Shown with Figure 4a Schematic diagram of the same embodiment in which no voltage is applied to the additional electrode;

[0053] Figure 4c Shown with Figure 4a Schematic diagram of the same embodiment as in , wherein the anode voltage is applied to the first additional electrode;

[0054] Figure 5a shows a schematic diagram of another embodiment of an electrolysis chamber according to the invention during an electroplating phase, wherein a cathodic voltage is applied to the first additional electrode;

[0055] Figure 5b Shown with Figure 5a Schematic diagram of the same embodiment in which no voltage is applied to the additional electrode;

[0056] Figure 5c Shown with Figure 5a Schematic diagram of the same embodiment as in , wherein the anode voltage is applied to the first additional electrode;

[0057] Figure 6ashows a schematic diagram of another embodiment of an electrolysis chamber according to the invention during an electroplating phase, wherein a cathodic voltage is applied to the first additional electrode;

[0058] Figure 6b Shown with Figure 6a a schematic diagram of the same embodiment as in , wherein no voltage is applied to the additional electrode; and

[0059] Figure 6c Shown with Figure 6a Schematic diagram of the same embodiment as in , wherein the anode voltage is applied to the first additional electrode;

[0060] Terms and Definitions

[0061] The term "electrolytic process" or "electrolysis" is understood to mean the deposition of a metal (here chromium) from a solution containing the corresponding metal ions using an electric current. It is used to produce a metal layer, in the present case chromium plating.

[0062] The terms "cathode voltage" or "cathode potential" are used synonymously and interchangeably in the present invention and are to be understood as a voltage applied to an electrode or an additional electrode such that the electrode or the additional electrode functions as a cathode.

[0063] The terms “anode voltage” or “anode potential” are also used synonymously and interchangeably in the present invention and are to be understood as applying a voltage to an electrode or an additional electrode such that the electrode or the additional electrode functions as an anode. DETAILED DESCRIPTION

[0064] The method according to the invention for controlling the chromium supply is carried out during the electrolytic process for producing the chromium layer. Therefore, the electrolytic process for producing the chromium layer is first described, since the method according to the invention is closely related to this:

[0065] The electrolytic deposition of the chromium layer is usually carried out in an electrolysis chamber filled with an electrolyte. Any vessel suitable to the person skilled in the art can be used as the container of the electrolysis chamber, such as vessels employed in particular in electroplating technology.

[0066] The object to be coated, for example a gravure printing cylinder, on which the chromium layer is to be deposited, is usually used as the cathode.

[0067] The anode can be an anode known to those skilled in the art. In particular, an inert electrode is used as the anode, which is composed of one or more conductive materials that are insoluble in the electrolyte. For example, the material acting as the insoluble anode or inert electrode is:

[0068] - Platinum-coated titanium,

[0069] - porous metal consisting of titanium, optionally coated with mixed oxides or with graphite,

[0070] - Carbon materials, such as graphite

[0071] - titanium coated with indium and / or tantalum,

[0072] - mixed metal oxides: in particular iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide or iridium-tantalum mixed oxide;

[0073] - mixed metal oxides, in which titanium is used as anode substrate, which is coated with platinum-, iridium-, tantalum- and / or palladium oxides;

[0074] - titanium, niobium or tantalum sheets coated with mixed metal oxides;

[0075] - titanium, tantalum or niobium coated with iridium-transition metal mixed oxides;

[0076] and its material combinations.

[0077] The shape of the anode can be adapted by a person skilled in the art to correspond to the respective purpose. The anode can be, for example, a flat material, a plate material, a sintered material or a porous material.

[0078] The anode and cathode are immersed in an electrolyte. Any electrolyte known to a person skilled in the art of electroplating technology can be considered as an electrolyte. When a direct voltage is applied to the two electrodes, the anode and the cathode, chromium (III) ions from the electrolyte are deposited on the object, the cathode. If the object is not metallically conductive, it can be made conductive by pretreatment.

[0079] As disclosed in WO 2008 / 014987 A2, the above setting can also be changed so that the electrolyte is separated into a cathode electrolyte (electrolyte in the cathode space) and an anode electrolyte (electrolyte in the anode space) by a semipermeable membrane in the electrolysis chamber. The cathode is immersed in the cathode electrolyte containing the chromium ions to be deposited as the object to be coated. When a voltage is applied, the current flows into the cathode electrolyte through the membrane via the anode electrolyte.

[0080] The anode system can also be a system in which the anode is in direct contact with the membrane, ie the anode is coated with the membrane. This is a so-called direct contact membrane anode, as known from DE 10 2010 055 143 A1.

[0081] The preparation of the chromium layer can be carried out at a temperature of 20° C. to 60° C., wherein the temperature of the electrolyte is adjusted by corresponding heating and cooling means. 2 The chromium layer was prepared at a current density of .

[0082] The electrolyte can be stirred or mixed during the immersion of the electrode in the electrolyte. In particular, a circulation can also be performed. Preferably, a circulation of five bath volumes, ie electrolyte volumes, per hour is performed.

[0083] The object to be coated can also be moved. When the gravure cylinder is to be coated, it can be moved, for example, at a rotation speed of 0.5 to 1.5 m / min.

[0084] In the method according to the invention, the chromium supply in the electrolytic process for producing the chromium layer can now be controlled. To this end, a first additional electrode (step (A)) and a second additional electrode (step (B)) are provided, both electrodes being immersed in an electrolyte (step (C)).

[0085] The first additional electrode comprises chromium metal or consists of chromium metal and is therefore also referred to herein as a “chromium electrode”. The first additional electrode or chromium electrode consists, for example, of a chromium molded part. The chrome moulding can be formed by a shaped part which can be held in a frame or support. The moulding can have a regular or irregular shape and can be smooth or porous. It can be, for example, a block, a fragment, a clot, a platelet, an ingot, a wire and / or a grid; powders should not be included. The frame or support is a material that is resistant to acidic electrolytes and can conduct current or not. Such a material that conducts current can be a metal, for example titanium. Such a material that does not conduct current is a plastic, for example polypropylene or polyvinyl chloride. If the frame or support does not conduct current, for example a conducting sheet is additionally installed in order to be able to supply current to the chrome moulding.

[0086] According to one embodiment, a chromium metal block, also referred to herein as a “chrome block”, is accommodated in a plastic frame as a chromium molded part.

[0087] The shape of the first additional electrode can be selected accordingly by a person skilled in the art. Important for the shape, especially for a molded body made of chromium metal, is that the larger surface area of ​​the chromium metal enables a higher dissolution rate in the electrolyte. A person skilled in the art can select a suitable shape from this.

[0088] In one embodiment, the surface area of ​​metallic chromium can be 1% to 50% or 1% to 100% of the surface area of ​​the first additional electrode. In this way, a particularly good dissolution of chromium and a supplementary supply of chromium (III) can be achieved.

[0089] The second additional electrode is an inert electrode composed of one or more conductive materials that are insoluble in the electrolyte. The material used for the inert electrode is not further limited as long as it has the characteristics described. For example, it is contemplated that the same material as the anode of the above-mentioned electrolytic process can be used for chromium coating.

[0090] The shape of the second additional electrode can be selected by a person skilled in the art according to structural conditions. The second additional electrode can be, for example, a flat material, a plate material, a sintered material or a porous material.

[0091] According to a preferred embodiment, the surface area of ​​the first additional electrode is selected to be exactly the same as the surface area of ​​the second additional electrode. In this case, it is expedient that the surface area of ​​the metallic chromium is 100% of the surface area of ​​the first additional electrode.

[0092] There are two separate circuits in the electrolysis chamber: In the first circuit, the anode and cathode are connected together so that the chromium (III) ions dissolved in the electrolyte are applied in the form of a chromium layer to the object connected as the cathode. Direct current is used and there is no polarity reversal between the anode and cathode. The anode always remains an anode and the cathode always remains a cathode.

[0093] In the second circuit, in one embodiment, the first additional electrode and the second additional electrode are connected together in a circuit separate from the cathode and the anode (step (D)). The first circuit of the anode and the cathode and the second circuit of the first additional electrode and the second additional electrode are not connected to each other, but are connected in a completely separate manner from each other. Therefore, the second circuit is controlled independently of the first circuit. In the second circuit, direct current is used, but the polarity is reversed after a certain time interval, which is significantly longer than the pulsed alternating current (for example, having a duration of 0.1 to 2 seconds). This makes it possible that first the first additional electrode works as a cathode and the second additional electrode works as an anode, and at a later point in time the first additional electrode works as an anode and the second additional electrode works as a cathode. This type of polarity reversal is known in the prior art, even in different contexts and for different purposes, so the technical implementation is easy for a person skilled in the art to achieve. For example, the polarity reversal can be achieved by a rectifier with a polarity inverter.

[0094] Since the second circuit operates independently of the first circuit, the second circuit can advantageously operate during the electrolytic deposition of chromium with the chromium layer formed. To this end, a cathodic voltage is first applied to the first additional electrode. The first additional electrode is thus the cathode and the second additional electrode is the anode. The cathodic voltage is also referred to here as the cathode potential and acts on the chromium metal in a reducing manner. As a result, the passivation layer that has formed on the surface of the chromium metal of the first additional electrode decomposes.

[0095] Although chromium is not actually as chemically inert as iron, its behavior is similar to that of noble metals when it comes to corrosion with respect to air and water. This is due to a very thin, almost invisible chromium oxide layer with a thickness of a few nanometers (about 50 atomic layers in the case of chromium-nickel-steel, about 5 atomic layers for pure chromium), which protects the metal from atmospheric and oxidative influences. The passivated layer also prevents diffusion into the metal, so that no further corrosion of the metal occurs. Therefore, the passivated layer is dissolved by applying a voltage to the cathode and the resulting reducing action.

[0096] Therefore, first a cathodic (i.e. reducing) voltage is applied to the first additional electrode (step (E)). Accordingly, the counter electrode, i.e. the second additional electrode, becomes an anode. The cathodic voltage reduces the passivation layer in the form of an existing chromium oxide layer already formed on the surface of the chromium metal. Here, the chromium oxide is reduced to metallic chromium (Cr2O3→Cr 金属 ). The cathode voltage or the cathode potential is selected such that the chromium oxide layer is decomposed. Thus, the reducing direct current dissolves the passivation layer and the chromium (III) ions begin to dissolve.

[0097] The cathode voltage can be adjusted, for example, in the range of 1.0 to 10.0 volts, preferably 2.0 to 9.0 volts, more preferably 2.5 to 8.5 volts, even more preferably 2.5 to 8.0 volts, most preferably 3.0 to 7.0 volts to decompose the passivation layer. The current density is, for example, 2.5 to 4 A / dm 2 In the range of 3.4A / dm 2 It has proven to be preferred that the current density is adjusted to be no higher than 4 A / dm 2 , since thereby no undesirable formation of chromium (VI) can occur in any case. Typically, the passivation layer can then be decomposed within about 5 to 60 seconds, preferably about 5 to 45 seconds, even more preferably about 5 to 30 seconds. However, this can also be exceeded or not exceeded in individual cases and depends on a number of process parameters, such as the adjusted pH value, the current density, the thickness of the chromium metal layer to be deposited, the temperature, the selected voltage and the type of additional electrode used. The given ranges serve only as a guide for the person skilled in the art, who can determine the optimum voltage level and duration for the cathode through-current at the first additional electrode for the respective application case based on a small number of experiments.

[0098] In the method according to the invention, the passivation layer which has already been produced as a side reaction at or on the chromium metal and which has a passivating effect can now be decomposed at the first additional electrode, thereby dissolving the chromium(III) ions without producing chromium(VI) ions. It has been shown that the decomposition of the passivation layer is a prerequisite for avoiding the formation of chromium(VI) ions during the electrolytic dissolution of chromium.

[0099] Only at very low pH values ​​of <0.5 is a purely chemical dissolution of chromium possible by acid, but this is unfavorable for the process conditions in the electroplating bath. According to the invention, the pH value in the electrolyte is generally in the range of 2.0 to 3.5, in particular 2.1 to 3.4, preferably 2.2 to 3.3, more preferably 2.3 to 3.2, even more preferably 2.4 to 3.1, very particularly preferably in the range of 2.5 to 3.0. Therefore, the pH value of the electrolyte, which is preferably used, alone is not sufficient to remove the passivation layer present on the chromium and is not sufficient to initiate chemical dissolution. For this reason, the dissolution of the chromium metal as chromium (III) ions is triggered and initiated to a certain extent by the application of the cathode voltage.

[0100] The dissolution of the passivation layer at the first additional electrode can be easily observed in a simple manner by the formation of small bubbles at the surface of the additional electrode. As soon as the chromium (III) ions dissolve in the electrolyte, hydrogen gas is formed, which becomes visible in the form of small bubbles. Therefore, it can be inferred in a simplified manner that the passivation layer is dissolved when small bubbles are formed over the entire surface of the chromium metal at the first additional electrode. As already explained, this occurs, for example, after about 5 to 30 seconds.

[0101] It has now been shown in a surprising manner in experiments that after a cathodic voltage has been applied to the first additional electrode as cathode and the passivation layer of the chromium metal has been dissolved, the dissolution reaction, which can be identified by the formation of hydrogen (bubbles), does not stop when the voltage is switched off, but continues in the absence of current. The dissolution of metallic chromium can therefore be observed. Without being limited to this, it is assumed that in the presence of chromium (III), chromium (II) is produced at the cathode during the reduction. This promotes the dissolution of metallic chromium. At the same time, it prevents the formation of chromium (VI) during oxidation, i.e. when the metallic chromium is dissolved during electrolysis, no chromium (VI) is produced.

[0102] Therefore, in the method according to the invention, after the dissolution of the passivation layer, the current supply to the first additional electrode is terminated (step (F)); the first additional electrode and the second additional electrode are then no longer under voltage. If the cathode voltage is maintained after the dissolution of the passivation layer, chromium (VI) ions can be formed, which should be avoided for the reasons already mentioned. The formation is inhibited by switching off the voltage.

[0103] The chromium metal is then dissolved from the first additional electrode in the form of chromium (III) ions by the action of the electrolyte in the absence of an electric current (step (G)). As soon as the chromium oxide layer is decomposed, the chromium is attacked by the acidic electrolyte and chemically dissolved. It is advantageous for this purpose if the electrolyte has an acidic pH value in the range of, for example, 2.0 to 3.5. In this pH range, the electrolyte is sufficiently acidic so that it dissolves the metal in the absence of an electric current after the dissolution of the passivation layer. By applying a relatively short cathodic current, the passivation layer is decomposed to such an extent that the acidic electrolyte can attack the elemental chromium of the first additional electrode. In the case of an electrolyte in a given pH range, after the decomposition of the passivation layer, the passivation of the chromium metal is not reconstructed, but the dissolution of the chromium continues until the dissolution process is interrupted or the chromium metal in the first additional electrode is exhausted and no longer replenished.

[0104] In one embodiment, during step (G), i.e., during the dissolution of chromium (III) ions into the electrolyte in the absence of current, the chromium metal in the first additional electrode is replenished, and then steps (E), (F) and (G) are performed sequentially as disclosed, preferably without intermediate steps. Thus, this embodiment includes

[0105] - replenishing the chromium metal in the first additional electrode during step (G);

[0106] (E) applying a cathodic voltage to the first additional electrode, thereby causing the passivation layer of the chromium metal to dissolve and the chromium metal to begin dissolving in the electrolyte in the form of chromium (III) ions;

[0107] (F) after the passivation layer is dissolved, ending the current supply to the first additional electrode or cutting off the voltage at the first additional electrode; and

[0108] (G) Chromium metal is dissolved from the first additional electrode in the form of chromium (III) ions in the absence of an electric current by the action of the electrolyte.

[0109] This process can be repeated as many times as desired, with chromium metal always being replenished and dissolved as chromium(III) ions for the chromium layer to be deposited.

[0110] In order to terminate the process, i.e. to stop the dissolution of chromium(III) ions into the electrolyte, there are several possibilities:

[0111] According to one embodiment, an anodic voltage is applied to the first additional electrode, whereby a passivation layer of chromium metal is formed again, and thereby the dissolution of chromium (III) ions in the electrolyte is terminated. Thus, by applying an anodic voltage (oxidation potential) to the first additional electrode, the dissolution of chromium in the electrolyte can be stopped at any desired time point. Accordingly, the second additional electrode preferably becomes a cathode as a counter electrode in the form of an inert electrode. This first causes the metallic chromium to dissolve in the form of chromium (III) for a short time, but in parallel with the dissolution of the Cr (III) ions, the aforementioned passivation layer made of Cr2O3 is formed again, because the chromium surface reacts with the oxygen contained in the water. The anodic voltage is selected here so that the passivation layer is constructed in the form of a chromium oxide layer. This can be observed in a simple way by the disappearance of the bubble formation at the surface of the additional electrode. As soon as the chromium (III) ions no longer dissolve into the electrolyte, hydrogen gas visible in the form of bubbles is no longer formed. It can therefore be inferred in a simplified manner that the passivation layer is formed again after the bubble formation disappears over the entire surface of the chromium metal at the first additional electrode.

[0112] For rebuilding the passivation layer, the anode voltage can be adjusted, for example, in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V. The current density is, for example, 2.5 to 4 A / dm 2 In the range of 3.4A / dm 2 The passivation layer is then typically regenerated within approximately 5 to 60 seconds, preferably approximately 5 to 45 seconds, even more preferably approximately 5 to 30 seconds. However, this may also be exceeded or not exceeded in individual cases and serves only as a guide for the person skilled in the art, who can determine the anodic voltage level and duration for the anodic through-current at the first additional electrode for the respective application case based on a small number of experiments.

[0113] To end the process, there is also the possibility of pumping the electrolyte out of the chamber. Another possibility is to remove the chromium electrode from the electrolyte so that it is exposed to the ambient air and thereby builds up the passivation layer again and ends the chemical reaction. Alternatively, the chromium metal in the existing first additional electrode can no longer be refilled, thereby allowing the chromium electrode to run dry.

[0114] Thus, in this process, chromium can be dissolved without current and can be started in any manner at a defined time by means of an applied direct current using two additional electrodes, continued by replenishing chromium metal as many times as desired, and ended again at a defined time. The method according to the invention is therefore based, according to this embodiment, on the chemical dissolution of chromium in the form of chromium (III) ions in an electrolyte, which is activated by a defined through current or a defined voltage, continued in the absence of current and ended by one of the aforementioned possibilities.

[0115] According to another embodiment, a third additional electrode is provided in addition to the first additional electrode and the second additional electrode. The third additional electrode is an inert electrode. Then according to one embodiment, the first additional electrode in the form of a chromium electrode, the second additional electrode and the third additional electrode are connected together in a second circuit to form one or more cells. Then the following cell is constructed:

[0116] Inert electrode-Chromium electrode-Inert electrode

[0117] (Second additional electrode) (First additional electrode) (Third additional electrode)

[0118] In other words, the first additional electrode is surrounded by the second additional electrode and the third additional electrode.

[0119] Two or more units consisting of additional electrodes can also be connected together, wherein in the case of two units the following sequence applies:

[0120] Inert electrode-chromium electrode-inert electrode-chromium electrode-inert electrode.

[0121] The cells are preferably connected in series, similar to a car battery. A series connection has the advantage that it enables a particularly space-saving arrangement of the cells. It also provides a higher solubility for chromium (III) ions.

[0122] The process with three or more additional electrodes is performed in a similar manner to the process with the first additional electrode and the second additional electrode already described in detail:

[0123] In order to dissolve the passivation layer at the chromium electrode, the inert electrode surrounding it is used as anode and the chromium electrode located in between is used as cathode. After the passivation layer has been dissolved, the chromium (III) ions from the chromium electrode are dissolved in the electrolyte without current. In order to continue the process, the chromium metal in the chromium electrode can be replenished again during the currentless dissolution. The process can then be continued by decomposing the passivation layer again and dissolving the chromium (III) ions again in the electrolyte. In each case, the chromium metal can be replenished again just before it is consumed. These process steps can be repeated as many times as required.

[0124] To rebuild the passive layer at the chromium electrode, the inert electrode is then connected as cathode and the chromium electrode is the anode. Alternatively, in step (G) the chromium electrode is removed from the electrolyte or the electrolyte is removed; in both cases, the passive layer rebuilds at the chromium electrode by contact with ambient air. There is also the possibility of no longer replenishing chromium metal in the chromium electrode, so that there is no longer any chromium metal replenishment.

[0125] exist Figure 1 In the embodiment of the method according to the present invention, a flowchart is shown:

[0126] During the electrolytic deposition of chromium at the cathode, the passivation layer at the first additional electrode or the chromium electrode is removed in step (E). After the passivation layer has dissolved, the current supply to the first additional electrode is terminated or the voltage is switched off (step (F)), and the chromium (III) ions are dissolved from the first additional electrode into the electrolyte in the absence of current (step (G)). The process can then be continued or terminated. Figure 1 It is shown in a diamond shape with "End process?" written inside. If the process is not ended ( Figure 1 If the "No" branch in the above is not reached, then one or more chromium electrodes can be supplemented with chromium metal (if necessary), and process steps (E) to (G) can be performed again. This can be repeated as many times as desired.

[0127] If the process should be terminated ( Figure 1 If the chromium electrode is not refilled, the passivation layer can be rebuilt by applying an anodic voltage to the chromium electrode or electrodes. Alternatively, the chromium metal in the first additional electrode can also no longer be refilled, allowing the chromium electrode to run empty. Another alternative to end the process is to pump the electrolyte out of the chamber or remove the chromium electrode from the electrolyte, so that the chromium electrode is exposed to air and the passivation layer is rebuilt and the chemical reaction ends.

[0128] The electrolyte used in the method according to the present invention is not particularly limited as long as it is suitable for electrolysis. Any electrolyte known to those skilled in the art can be used. The electrolyte contains water as a solvent. The electrolyte preferably has a pH value in the range of 2.0 to 3.5. In another embodiment, the electrolyte may also have a pH value in the range of 2.1 to 3.4, preferably 2.2 to 3.3, more preferably 2.3 to 3.2, even more preferably 2.4 to 3.1, very particularly preferably 2.5 to 3.0.

[0129] According to one embodiment, the electrolyte comprises:

[0130] (a) one or more chromium(III) salts,

[0131] (b) Compounds of formula (I)

[0132]

[0133] wherein R is selected from NH2, OH or SO3H, and / or salts thereof, especially for example Na + and / or K - a monovalent cation, or a salt of a divalent cation, wherein n represents an integer from 1 to 3,

[0134] (c) formic acid and / or its salts, especially for example Na + and / or K + monovalent cations, or salts of divalent cations and

[0135] (d) optionally one or more additives.

[0136] The component (a) of the electrolyte according to this embodiment is one or more chromium (III) salts. In the present invention, the term "chromium (III) salt" should be understood as any chromium (III) salt that can be used to deposit chromium as a metal layer on an object. The chromium (III) salt is selected from an inorganic or organic chromium (III) salt or a mixture thereof. Inorganic chromium (III) salts are, for example, selected from potassium chrome alum, ammonium chrome alum, chromium sulfate, chromium sulfate (hydroxy) (basic chromium sulfate), chromium sulfoacetate, chromium nitrate, chromium sulfamate (sulfamate), chromium chloride, chromium bromide, chromium iodide, chromium phosphate, chromium pyrophosphate (diphosphate), chromium phosphonate, and a mixture of two or more thereof, but not limited to the group thereof. Organic chromium (III) salts are, for example, selected from chromium citrate, chromium formate, chromium sulfoacetate, chromium oxalate, chromium methanesulfonate, chromium dimethanesulfonate, and a mixture of two or more thereof, but not limited to the group thereof. Inorganic and organic chromium (III) salts can also be used in the form of a mixture.

[0137] For example, it is expedient to select an amount of chromium(III) salt in the range of 0.25 mol / L to 2.0 mol / L with reference to the electrolyte. This amount range has proven to be particularly advantageous for producing chromium layers on metal objects by electrolytic deposition.

[0138] Component (b) of the electrolyte according to this embodiment is a compound of formula (I) and / or a salt thereof. Preferably, the compound of formula (I) is selected from glycine, glycolic acid, sulfoacetic acid, sodium sulfoacetate, potassium sulfoacetate or a mixture of at least two of these compounds.

[0139] With reference to the electrolyte, the amount of the compound of formula (I) in the electrolyte is preferably 0.5 mol / L to 1.5 mol / L. This can be used to adjust the pH value of the electrolyte.

[0140] According to this embodiment, formic acid is present in the electrolyte as a further component (c) which serves to remove the oxygen released from the chromium (III) salt by converting it into CO 2 and H 2 O. The amount of formic acid in the electrolyte is advantageously 1.0 mol / L to 3.0 mol / L, with reference to the electrolyte before chromium deposition. The mentioned amount range has proven to be particularly suitable for adjusting the pH value of the electrolyte.

[0141] Instead of formic acid or in addition to formic acid, salts thereof may also be used. Alkali metal and / or alkaline earth metal formates, in particular sodium formate, are mentioned by way of example.

[0142] Optionally, one or more additives may be employed as component (d) of the electrolyte. Any compound or mixture of compounds that can impart advantageous properties to the electroplating bath may be considered as an additive. Such compounds are known to those skilled in the art.

[0143] For example, the additive is selected from complexing agents, alkali metal or alkaline earth metal salts, wetting agents, catalysts or mixtures thereof.

[0144] The complexing agent is preferably a compound with a short alkyl chain (e.g. 1-5 carbon atoms) having 1 or 2 carboxyl groups or derivatives thereof or 1 or 2 sulfhydryl and / or sulfone groups. For example, the following compounds are used:

[0145]

[0146] in

[0147] R1 means C 1-5 -alkyl, especially CH3CH2-;

[0148] X represents one or more metal cations that balance the negative charge, such as Na + , K + ;in

[0149] n is an integer from 1 to 5, in particular 3.

[0150] The compound N,N-dimethyl-dithiocarbamoylpropylsulfonic acid sodium salt (DPS) is particularly preferred as complexing agent. The use of DPS can be advantageous since particularly good chromium layers can be obtained.

[0151] The wetting agent causes a reduction in the surface tension, so that the formed H2 bubbles can be separated from the cathode. The formation of pores in the chromium layer is thereby avoided and a more uniform chromium layer can be obtained. Preferred wetting agents are, for example, polyfluorinated mono- and / or di-alkyl phosphates and PEG (polyethylene glycol) derivatives of salts or esters of phosphoric acid, in particular PEGylated phosphates.

[0152] To increase the conductivity, sulfates or acetylsulphates, for example alkali metal or alkaline earth metal salts, in particular sodium sulfate, sodium sulfoacetate, potassium sulfate or magnesium sulfate, can be used.

[0153] The amount of sulfate or acetyl sulfate may be 5 mM to 30 mM, such as 10 mM to 20 mM.

[0154] The amount of additive present in the electrolyte may be 0.01 g / l to 2.0 g / l, with reference to the electrolyte. The resulting molar concentration, for example when using PEG 6000 as a wetting agent, is 0.001 mMol / L to 0.3 mMol / L.

[0155] As mentioned above, the pH value is preferably adjusted in the electrolyte to a value in the range of 2.0 to 3.5. The pH value can be adjusted, for example, by means of a compound of formula (I), formic acid and / or a salt thereof.

[0156] The electrolyte is substantially free of chromium (VI) ions, that is, only unavoidable chromium (VI) ion impurities are present in the electrolyte composition. In the method according to the invention, the content of chromium (VI) ions is below the detection limit.

[0157] According to one embodiment it can be preferred that the electrolyte does not contain any nitrogen-containing compounds. In this case, the chromium layer formed also does not contain any nitrogen-containing compounds, which results in the coating having particularly advantageous properties.

[0158] The subject of the invention is also an electrolysis chamber for controlling the supply of chromium to / in an electrolyte, comprising

[0159] -anode;

[0160] -cathode;

[0161] - an electrolyte comprising at least one chromium(III) salt;

[0162] - The anode and cathode are immersed in an electrolyte;

[0163] a first circuit which connects the anode and the cathode and which enables the deposition of the chromium layer by electrolytic deposition of chromium from the electrolyte onto the cathode by means of direct current;

[0164] a first additional electrode comprising chromium metal or consisting of chromium metal;

[0165] - a second additional electrode in the form of an inert electrode,

[0166] - Two additional electrodes are immersed in the electrolyte;

[0167] - a second loop connecting the first additional electrode and the second additional electrode in a circuit separate from the cathode and the anode.

[0168] The electrolysis chamber presents one of the following three states:

[0169] - applying a cathodic voltage to the first additional electrode so that the passive layer of chromium metal at the first additional electrode dissolves; or

[0170] - no voltage is applied to the first additional electrode, so that after the passivation layer has dissolved, chromium metal dissolves from the first additional electrode into the electrolyte in the form of chromium (III) ions in the absence of current; or

[0171] - applying an anode voltage to the first additional electrode so that a passivation layer is formed again at the first additional electrode.

[0172] As a container which can be used as an electrolysis chamber, any receptacle, vessel or tank which can be considered for use by a person skilled in the art, for example, which is commonly used in particular in electroplating technology, can be used.

[0173] The above statements concerning the method for controlling the chromium supply in an electrolytic process for producing a chromium layer apply equally to the electrolysis chamber and are therefore not repeated.

[0174] The electrolysis chamber can not only be one-piece, it can also be implemented as a two-piece: in one embodiment, the chrome plating bath can be located in a first chamber, in which a direct current flows between an anode and a cathode immersed in an electrolyte. In a second chamber that can be connected to the first chamber, a chromium electrode and an inert electrode are, for example, connected together, both electrodes being immersed in the electrolyte. Alternatively, one or more units consisting of an inert electrode-chromium electrode-inert electrode can also be connected together in the second chamber. The chrome plating of the object is carried out in the first chamber. In the second chamber, the electrolyte accumulates chromium (III) ions to a desired concentration and can then be returned to the chrome plating bath. Other embodiments are also feasible.

[0175] The process or electrolysis cell described is particularly useful for the treatment of Cr consumed in the electrolyte.3+ For example, the dissolution of chromium in the absence of an electric current is carried out over a period of time sufficient to bring the chromium content of the electrolyte to the desired level, which period of time may last from a few minutes to a few hours.

[0176] Alternatively, the equilibrium state is adjusted so that chromium (III) ions are continuously supplied to the coating bath and the coating bath operates continuously. The duration of the dissolution of chromium as chromium (III) ions is advantageously selected so that a constant concentration of chromium (III) ions is obtained in the electrolyte, in particular a stable equilibrium state between the supply and consumption of chromium (III) ions is obtained.

[0177] The chromium metal can preferably be replenished or refilled during this process. The replenishment of the chromium molded part of the first additional electrode is preferably carried out in step (G) by the action of the electrolyte during the dissolution of the chromium (III) ions in the absence of current. In this state, the filling can be carried out without any problems and the process is not interrupted in any additional way. It is understood that in the case of the refilled chromium molded part, the passivation layer must first be removed again as already described (step (E)), and then the chromium (III) ions are dissolved again in the electrolyte in the absence of current (steps (F) and (G)).

[0178] The invention also relates to a method for keeping the chromium (III) content in the electrolyte constant in the process disclosed herein by comparing the weight of chromium metal used in the first additional electrode with the weight of chromium metal consumed by the chromium layer and replenishing the chromium metal in the first additional electrode before the chromium (III) content in the electrolyte decreases. The chromium (III) content is controlled by measuring the weight of chromium metal present in the first additional electrode compared to the chromium metal consumed by the coating so that the chromium (III) content in the electrolyte can be kept constant. The weight measurement can be performed, for example, by a pressure sensor.

[0179] Supplying metallic chromium to the electrolyte makes it possible to keep the chromium (III) content approximately constant over a long period of time, for example from a few hours to a few months, while electrolysis is taking place, wherein chromium (III) ions are replenished to the electrolyte which is depleted in chromium (III). Keeping the chromium (III) content in the electrolyte constant is understood here to mean that the chromium (III) content preferably varies only by ±10%.

[0180] The subject matter of the invention also relates to the use of the method for producing a chromium layer on an object.

[0181] The invention likewise relates to the use of an electrolysis chamber for producing a chromium layer on an object.

[0182] The advantages of the present invention are extremely comprehensive:

[0183] The method according to the invention or the electrolysis chamber according to the invention is based on a technical embodiment that can be easily implemented by a person skilled in the art. It is not necessary to carry out continuous polarity reversal when using expensive pulse rectifiers. Instead, a simple rectifier with a polarity inverter can be used, wherein polarity reversal is only performed at the beginning and end of the dissolution of the chromium (III) ions.

[0184] Another great advantage is that the chromium (III) ions are dissolved without current after the passivation layer has been dissolved. For this reason, no additional energy needs to be used during the dissolution. This is particularly important for large industrial plants. This significantly reduces the energy costs of the process or the electrolysis chamber.

[0185] The method according to the invention also makes it possible to keep the chromium (III) content in the electrolyte constant, for example by relating the weight of chromium metal in the first additional electrode to the weight of chromium metal consumed by the coating and controlling it accordingly. It is thus possible to keep the chromium (III) content approximately constant over a long period of time, for example a few hours to a few months, during electrolysis, wherein chromium (III) ions are replenished to the electrolyte depleted in chromium (III). Keeping the chromium (III) content in the electrolyte constant is understood here to mean that the chromium (III) content preferably varies only by ±10%.

[0186] In the method according to the invention, the electrolytic deposition can also be advantageously carried out without the use of a semipermeable membrane. So far, semipermeable membranes have been used to separate the anode from the cathode so that no chromium (VI) is formed. This is not necessary for the implementation of the method according to the invention. In the method according to the invention and the electrolysis chamber provided, the formation of chromium (VI) is generally avoided during and after the electrolytic deposition of chromium. Chromium (VI) cannot be detected in the method according to the invention.

[0187] Chromium coating can thus be carried out in a simple, rapid and cost-effective manner even over a longer period of time.

[0188] According to one embodiment, it can be preferred that the electrolyte does not contain any nitrogen-containing compounds, so that the chromium layer formed also does not contain any nitrogen-containing compounds. This allows a coating with particularly advantageous properties.

[0189] For decorative purposes or for technical reasons, the chrome layer can be applied by electrolytic deposition of chrome. Examples of objects that are chrome-plated for technical reasons are rotationally symmetrical objects such as rods, pistons and cylinders, in particular gravure cylinders. The stamp used for gravure printing is called a gravure cylinder or gravure printing roller. The base cylinder is usually a steel tube core, which is first coated with copper in an electrolytic bath and then with chrome after the image data has been applied. This process is carried out by electroplating the gravure cylinder with chrome.

[0190] According to the invention, a chromium coating of particularly excellent quality is obtained, which surprisingly also meets the high requirements imposed on gravure cylinders. A smooth, homogeneous surface is obtained which is substantially free of pores, pits or depressions. The layer thickness of the chromium layer obtained can be thicker than the layers usually obtained in the prior art. Layer thicknesses of 100 μm or more can be obtained. In addition, chromium layers of high hardness, in particular more than 900 HV, can be produced. The chromium layers obtained are corrosion-resistant, wear-resistant, have favorable friction properties, and are heat-resistant and chemical-resistant; they are bright and highly reflective and are therefore also suitable for decorative purposes.

[0191] Embodiments of the present invention are described exemplarily below with reference to the accompanying drawings, which are schematically drawn and not to scale, so that exact geometric values ​​about the original dimensions cannot be assumed. The drawings of the present disclosure are an integral part of the specification and represent a part of the specification, and illustrate the embodiments of the present invention without being limited to the specific embodiments described. The drawings together with the specification are used to explain the present disclosure.

[0192] Figure 2a , Figure 2b and Figure 2c An embodiment of the process flow of the method according to the invention or the states of an electrolysis chamber in connection with an electrolytic process for electrolytically depositing a chromium layer for controlling the supply of chromium (III) ions by starting, continuing and ending the dissolution of chromium (III) ions is shown. Figure 2a , Figure 2b and Figure 2c Different states of the electrolysis chamber are thus shown, which illustrate the various steps of the method according to the invention according to one embodiment:

[0193] Figure 2a The electrolysis chamber 10 in the form of a bath arrangement is shown at a point in time during which a chromium layer is produced by electrolytically depositing chromium from an electrolyte 25 using an anode 44 and a cathode 48 by means of direct current. In the example shown, the cathode is a gravure cylinder 48, which is introduced into the bath arrangement, for example, by means of a crane (not shown). The gravure cylinder 48 is held by a support bridge 30 belonging to the support arrangement. The circumference of the gravure cylinder 48 is to be coated with chromium. Of course, another object, in particular a rotationally symmetrical object, can also be coated instead of the gravure cylinder 48 shown.

[0194] The electrolysis chamber 10 has a tank 15 in which a liquid electrolyte 25 is present, comprising the solvent water, which contains at least one Cr(III) salt: in the example shown, the electrolyte 25 has a pH value in the range of 2.0 to 3.5. According to one embodiment, the electrolyte has the following composition:

[0195] (a) one or more chromium(III) salts, as already explained in detail;

[0196] (b) Compounds of formula (I)

[0197]

[0198] wherein R is selected from NH2, OH or SO3H, and / or salts thereof, especially for example Na + and / or K + A monovalent cation, or a salt of a divalent cation, wherein n represents an integer from 1 to 3;

[0199] (c) formic acid and / or its salts, especially for example Na + and / or K + salts of monovalent or divalent cations and

[0200] (d) optionally one or more additives, as already described in detail.

[0201] Other compositions of the electrolyte are also possible.

[0202] A vertically movable anode device is also arranged in the cell 15, which is basically composed of an anode rail 42 and an anode basket 44 electrically and mechanically connected to the anode rail 42 and used as a metal holding device. The anode basket 44 can also be composed of a plurality of anode baskets or grids assembled together. The anode 44 represents an insoluble anode or an inert electrode and can, for example, include or consist of the following: platinum-plated titanium, carbon materials, such as graphite, titanium coated with indium and / or tantalum, and mixed metal oxides, such as iridium-ruthenium mixed oxides, iridium-ruthenium-titanium mixed oxides or iridium-tantalum mixed oxides; mixed metal oxides, in which titanium used as an anode substrate is coated with platinum-, iridium-, tantalum- and / or palladium oxides; titanium-, niobium- or tantalum sheets coated with mixed metal oxides; titanium, tantalum or niobium coated with iridium-transition metal mixed oxides; or porous metals composed of titanium, or porous metals composed of titanium, coated with mixed oxides, or coated with graphite and material combinations thereof.

[0203] For simplification and better representation, Figure 2a Only one of the supporting bridges 30 is shown in the figure. For example, the two supporting bridges 30 can be moved along the axial direction of the gravure cylinder 48 on a track (not shown) by means of a spindle or other suitable adjustment mechanism, so that they clamp the gravure cylinder 48 between them and hold it in a rotatable manner.

[0204] As in Figure 2a4, it can be seen that a portion of the cell 15 remains freely accessible at the top by means of the support bridge 30 supported on one side, so that the anode rail 42 extending there parallel to the axial direction of the gravure cylinder 48 can be freely moved vertically. The vertical movement of the anode rail 42 with the anode basket 48 is known to the person skilled in the art from the prior art and therefore does not require a detailed description and illustration.

[0205] Figure 2a The electrolysis chamber 10 is shown in the electroplating phase, in which the gravure cylinder 48 is almost completely immersed. In particular, an immersion depth of more than 65% can be achieved in the case of a large cylinder (circumference 1500 mm), and an immersion depth of up to about 80% can be achieved in the case of a smaller cylinder (circumference 800 mm).

[0206] For electroplating, ie for applying a chromium layer to the gravure cylinder 48 , the anode basket 44 has been pulled up laterally so that it surrounds the immersed gravure cylinder 48 with a large basket surface.

[0207] Anode 44 and cathode 48 thus form a first electrical circuit (not shown).

[0208] The first additional electrode 54 and the second additional electrode 56 are connected to each other in a second circuit that is coupled independently and separately from the first circuit such that there is no connection between the two circuits.

[0209] The first additional electrode 54 has chromium metal or consists of chromium metal and can therefore also be referred to as a "chromium electrode". This electrode consists, for example, of a chromium molded part 54a, which is held in a support, for example a frame or a basket. The molded part can have a regular or irregular shape and can be smooth or porous. For example, blocks, fragments, agglomerates, small plates, ingots, wires and grids are considered for this purpose, but not powders. The support is a material that is resistant to acidic electrolytes and can conduct current or not. Conductive materials are, for example, metals such as titanium. Non-conductive materials are, for example, plastics such as polypropylene, polyvinyl chloride. In the exemplary embodiment shown, the chromium metal block 54a is placed in a plastic frame, for example a polypropylene basket, and the chromium metal block is also particularly referred to as a chromium block.

[0210] The shape of the first additional electrode 54 is not further limited as long as it is suitable for the intended purpose. Suitable shapes are known to those skilled in the art.

[0211] The selected shape of the chromium metal moldings determines their surface area, wherein a larger surface area results in a higher dissolution rate in the electrolyte. A person skilled in the art can select a suitable shape from this.

[0212] The second additional electrode 56 is an inert electrode, which is made of one or more conductive materials and is insoluble in the electrolyte. The material used for the inert electrode is not further limited as long as it has the characteristics described. For example, it is conceivable to use the same material as the anode 44. The shape of the second additional electrode 56 can be selected by those skilled in the art according to the structural conditions. The second additional electrode 56 can be, for example, a flat material, a plate material, a sintered material or a porous material.

[0213] exist Figure 2a 1 shows the electrolysis chamber 10 at a point in time when a cathodic voltage is applied to the first additional electrode 54 using direct current, so that the passivation layer of the chromium metal at the first additional electrode 54 dissolves. This represents step (E) of the method according to the invention. Thus, the first additional electrode 54 is the cathode and the second additional electrode 56 is the anode. A power supply 58 provided with a rectifier and a polarity inverter (not shown) is used. The cathodic voltage has a reducing effect on the chromium metal mass 54a, and the passivation layer that has been formed on the surface of the chromium metal mass 54a of the first additional electrode 54 begins to decompose and dissolve.

[0214] The applied cathode voltage may be, for example, in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V. The current density is preferably in the range of 2.5 to 4 A / dm 2 In the range of 3.4A / dm 2 The passivation layer decomposes after 5 to 60 seconds, preferably 5 to 45 seconds, particularly preferably 5 to 30 seconds. Depending on the selected electrolysis conditions, in particular the pH value, the temperature, the selected voltage, the current density, the thickness of the chromium metal layer to be deposited and the type of additional electrode used, this duration can also be lowered or exceeded.

[0215] exist Figure 2b In FIG. 5 , the passivation layer has been decomposed at the first additional electrode 54 , wherein the dissolution of the passivation layer is indicated by the appearance of small bubbles 55 over the entire surface of the chromium metal at the first additional electrode 54 (hydrogen gas is formed due to the dissolution of chromium (III) ions).

[0216] Therefore, in Figure 2b The passivation layer has been dissolved and the power supply to the first additional electrode 54 and to the second additional electrode 56 is interrupted (step (F)). The voltage is cut off. Figure 2b5 is schematically shown in FIG. 5 by means of an open electric switch 59. The chromium metal is dissolved in the form of chromium (III) ions from the first additional electrode 54 in the absence of current by the action of the electrolyte 25, which has a pH value in the range of 2.0 to 3.5 (step (G)). The chromium metal block 54a is thus attacked by the acidic electrolyte and chemically dissolved. This occurs in the absence of current. The chromium (III) ions formed migrate in the electrolyte 25 toward the surface of the gravure cylinder 48 connected as cathode, where they are deposited in the form of a chromium coating.

[0217] The chromium metal in the first additional electrode (54) is thus reduced by the dissolution of the chromium (III) ions in the electrolyte. The chromium metal in the first additional electrode 54 can now be replenished during step (G), such as Figure 2b As shown. Steps (E), (F) and (G) of the method according to the invention are then repeated. This can be carried out as many times as desired. Thus, a continuous process is constructed to a certain extent, as shown below: Figure 2a → Figure 2b →Added→ Figure 2a → Figure 2b →Supplement→etc.

[0218] exist Figure 2c In the embodiment of the present invention, the dissolution of chromium (III) ions in the electrolyte is interrupted by applying an anodic voltage to the first additional electrode 54, whereby a passivation layer of chromium metal is formed again at the first additional electrode 54, and the dissolution of chromium (III) ions in the electrolyte 25 is terminated. The first additional electrode 54 shown then becomes the anode, and the second additional electrode 56 or the inert electrode becomes the cathode. Direct current flows again, but with the opposite polarity.

[0219] For example, from Figure 2a (the first additional electrode 54 is the cathode) to Figure 2c The polarity conversion (the first additional electrode 54 is the anode) can be achieved by a rectifier with a polarity inverter connected to the power supply 58.

[0220] exist Figure 2c In the exemplary case shown, the passivation layer has been completely formed again, and the bubbles 55 on the chromium metal surface, ie, on the chromium molding 54 a , have completely disappeared, since no more chromium(III) ions are dissolved into the electrolyte.

[0221] The applied anode voltage can be, for example, in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V. The current density is, for example, in the range of 2.5 to 4 A / dm 2 The range is preferably 3.4A / dm 2The passivation layer is built up after approximately 5 to 60 seconds, preferably approximately 5 to 45 seconds, particularly preferably approximately 5 to 30 seconds. Depending on the selected electrolysis conditions, in particular the pH value, the temperature, the selected voltage, the current density, the thickness of the chromium metal layer to be deposited and the type of additional electrode used, this duration can also be lower or higher.

[0222] Alternatively, the process can be terminated by removing the first additional electrode 54 from the electrolyte 25 during step (G) or pumping the electrolyte 25 out of the electrolysis chamber 10 (not shown), so that the first additional electrode 54, in particular the chromium molding 54a, comes into contact with the ambient air and thus forms a passivation layer. Alternatively, the chromium metal of the first additional electrode 54 can no longer be refilled, so that the dissolution of the chromium metal from the first additional electrode 54 in the form of chromium (III) ions by the action of the electrolyte in the absence of current ends as soon as the existing chromium metal is completely dissolved.

[0223] The formation of chromium (VI) ions could not be detected during the process.

[0224] exist Figure 3a to Figure 3c A further embodiment of the method according to the invention is schematically shown in FIG. 1 , in which a third additional electrode is present in addition to the first additional electrode and the second additional electrode. Like the second additional electrode, the third additional electrode is an inert electrode. There are coupled units of additional electrodes, which can, for example, replace Figure 2a The loop formed by the first additional electrode 54 and the second additional electrode 56 in the circuit. Figure 3a Two inert electrodes 56.1 and 56.2 are shown, which are also referred to herein as the second additional electrode and the third additional electrode. They surround the chromium electrode 54 to a certain extent, which is also referred to herein as the first additional electrode. In the embodiment shown, an anodic voltage is applied to the inert electrodes 56.1 and 56.2, and a cathodic voltage is applied to the chromium electrode 54. This is step (E), in which the passivation layer is dissolved.

[0225] exist Figure 3b It is shown in Figure 3a an embodiment, however, wherein no voltage is applied to the additional electrode (step (F)), and in Figure 3c A medium anode voltage is applied to the first additional electrode (ending the process during step (G)).

[0226] According to another embodiment of the invention, a third additional electrode ( Figure 3a , Figure 3b and Figure 3c ) can also be replaced by Figure 2a , Figure 2b and Figure 2c The second circuit in.

[0227] exist Figure 4a , Figure 4b and Figure 4c Schematically another embodiment of the method according to the invention is shown in FIG. 5 , in which the series connection of electrodes is to be described. Inert electrodes 56.1, 56.2, 56.3 and 56.4 are shown, which alternate with chromium electrodes 54.1, 54.2 and 54.3, respectively. Inert electrodes 56.1 and 56.4, respectively, represent edge electrodes, since they are located externally at the edge of the electrode. There are coupled units of additional electrodes, which can, for example, replace the chromium electrodes 54.1, 54.2 and 54.3, respectively. Figure 2a , Figure 2b and Figure 2c The first additional electrode 54 and the second additional electrode 56 form a second loop.

[0228] exist Figure 4a In the embodiment shown, an anodic voltage is applied to the inertial electrodes 56.1, 56.2, 56.3 and 56.4, respectively, and a cathodic voltage is applied to the chromium electrodes 54.1, 54.2 and 54.3, respectively. This is step (E), in which the passivation layer is dissolved.

[0229] exist Figure 4b It is shown in Figure 4a an embodiment, however, wherein no voltage is applied to the additional electrode (step (F)), and Figure 4c The middle anode voltage is applied to the first additional electrode, respectively (the process ends during step (G)).

[0230] exist Figure 5a , Figure 5b and Figure 5c Another embodiment of the present invention is shown in FIG. Figure 5a , Figure 5b and Figure 5c An embodiment of the process flow of the method according to the invention or the state of an electrolysis chamber in connection with an electrolytic process for electrolytically depositing a chromium layer for controlling the supply of chromium (III) ions by starting, continuing and ending the dissolution of chromium (III) ions is shown.

[0231] exist Figure 5a In the embodiment of the present invention, the cell of the electrolysis chamber 100 in the form of a bath device is divided into an upper cell 110 and a lower cell 120 arranged thereunder. In the upper cell 110 and in the lower cell 120 there is a liquid electrolyte 125, which is pumped from the lower cell 120 into the upper cell 110 by means of a pump 160 and flows back into the lower cell 120 again via an overflow 127 that can be moved vertically in at least two positions. Alternatively, two overflows that can be opened alternately can also be arranged at different heights.

[0232] If already in Figure 2a, Figure 2b and Figure 2c As explained in the case of FIG. 1 , a vertically movable anode device is arranged in the upper tank 110, which is basically composed of an anode rail 142 and an anode basket 144, which is electrically and mechanically connected to the anode rail 142 and serves as a metal holding device. The anode basket 144 can also be composed of a plurality of anode baskets or grids assembled together. The anode basket 144 is a part of an insoluble anode.

[0233] The cathode 148, here a gravure cylinder, is held on rails by two support bridges 130 (only one is shown) in a manner that it can be moved in the axial direction of the gravure cylinder 148 by means of suitable adjustment mechanisms, so that the gravure cylinder 148 is clamped between them and held in a rotatable manner. Thus, the upper half of the upper cell 110 is freely accessible, so that the anode rail 142 can be moved vertically.

[0234] The filling degree of the electrolyte 125 in the upper tank 110 , ie the height level of the electrolyte 125 , can be adjusted in a suitable manner by means of a vertically movable overflow 127 .

[0235] Figure 5a The electrolysis chamber 100 is shown in the electroplating phase, in which the gravure cylinder 148 is almost completely immersed. For electroplating, ie applying a chromium layer to the gravure cylinder 148 , the anode basket 144 has been pulled up laterally so that it surrounds the immersed gravure cylinder 148 with its large basket surface.

[0236] Thus, the cathode in the form of the gravure cylinder 148 and the anode 144 form a first circuit (not shown). In a second circuit, which operates independently of the first circuit, a first additional electrode 154 and a second additional electrode 156 are connected to each other in the lower cell 120 .

[0237] The first additional electrode 154 has chromium metal or is composed of chromium metal and is also referred to herein as a "chromium electrode". The structures of the chromium electrode 154 and the inert electrode 156 are as shown in Figure 2a As explained in the case of (here: chromium electrode 54 and inert electrode 56).

[0238] exist Figure 5a In the electrolysis chamber 100 shown, a cathode voltage is now first applied to the first additional electrode 154 using direct current, so that the passivation layer of the chromium metal at the first additional electrode 154 dissolves (step (E)). Therefore, the first additional electrode 154 is a cathode, and the second additional electrode 156 is an anode. For example, a rectifier with a polarity inverter (not shown) connected to a power source 158 is used. The cathode voltage has a reducing effect on the chromium metal block 154a, and the passivation layer that has been formed on the surface of the chromium metal block 154a of the first additional electrode 154 begins to decompose.

[0239] The applied cathode voltage may be, for example, in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V. The current density is, for example, in the range of 2.5 to 4 A / dm 2 The range is preferably 3.4A / dm 2 The passivation layer decomposes after approximately 5 to 60 seconds, preferably approximately 5 to 45 seconds, particularly preferably approximately 5 to 30 seconds. Depending on the selected electrolysis conditions, in particular the pH value, the temperature, the selected voltage, the current density, the thickness of the chromium metal layer to be deposited and the type of additional electrode used, this duration can also be lowered or exceeded.

[0240] exist Figure 5b The disappearance of the passivation layer at the first additional electrode 154 is shown by the appearance of small bubbles 155, which are caused by the dissolution of chromium (III) ions to form hydrogen. When the passivation layer is completely dissolved, small bubbles 155 are present here on the entire surface of the chromium metal at the first additional electrode 154.

[0241] Once the passivation layer is dissolved, the current supply to the first additional electrode 154 and the second additional electrode 156 is interrupted (step (F)). Figure 5b The circuit is schematically shown by means of an electric switch 159 which interrupts the current.

[0242] In the following, chromium metal is dissolved in the form of chromium (III) ions from the first additional electrode 154 in the lower cell 120 by the action of an electrolyte 125 in the absence of current (step (G)), wherein the electrolyte 125 has a pH value, for example, in the range of 2.0 to 3.5. The chromium metal block 154a is attacked by the acidic electrolyte and chemically dissolved. This occurs without supplying current to the additional electrodes 154, 156. The chromium (III) ions formed are distributed in the electrolyte 125, which is pumped from the lower cell 120 to the upper cell 110 by means of a pump 160 and flows back to the lower cell 120 again via an overflow 127 that can move vertically in at least two positions. The chromium (III) ions migrate via the electrolyte 125 toward the surface of the gravure cylinder 144 connected as a cathode and form a chromium coating there.

[0243] In order to reduce the amount of electrolyte in the upper cell 110, the upper cell 110 is gradually narrowed, for example, in the lower region. The gradual narrowing can be achieved by means of an additionally inserted plate 133 or by a corresponding adaptation of the wall of the upper cell 110. Blocks or boxes can also be used for displacement volume. The limitation or reduction of the volume of the upper cell 110 has the advantage that it is not necessary to pump excessive electrolyte 125 upward from the lower cell 120. Accordingly, there is no risk that the lower cell 120 is completely emptied and the pump 160 runs dry.

[0244] If necessary, during the execution of step (G) (according to Figure 5b ) replenishes the chromium metal of the first additional electrode 154, and the process can be continued accordingly, and steps (E), (F) and (G) can be repeated, so that the process flow is as follows: Figure 5a → Figure 5b →Added→ Figure 5a → Figure 5b →Supplement.

[0245] If the supply of chromium (III) ions to the electrolyte should be interrupted, an anodic voltage is applied to the first additional electrode 154, whereby a passivation layer of chromium metal is formed again at the first additional electrode 154 and the dissolution of chromium (III) ions in the electrolyte is terminated. Figure 5c . The first additional electrode 154 becomes the anode and the second additional electrode 156 or the inert electrode becomes the cathode. The direct current flows again but with the opposite polarity.

[0246] The applied cathode voltage may be, for example, in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V. The current density is, for example, in the range of 2.5 to 4 A / dm 2 The range is preferably 3.4A / dm 2 The passivation layer is built up after approximately 5 to 60 seconds, preferably approximately 5 to 45 seconds, particularly preferably approximately 5 to 30 seconds. Depending on the selected electrolysis conditions, in particular the pH value, the temperature, the selected voltage, the current density, the thickness of the chromium metal layer to be deposited and the type of additional electrode used, this duration can also be lower or higher.

[0247] For example, the polarity reversal (first additional electrode 154 as cathode and then as anode) can be achieved by a rectifier connected to the power source 158 with a polarity inverter.

[0248] When the passivation layer is completely formed again, bubbles 155 are no longer observable at the chromium metal surface of the first additional electrode 154 , since hydrogen is no longer formed and no chromium(III) ions are dissolved into the electrolyte 125 .

[0249] Alternatively, in order to terminate the process, the chromium metal in the first additional electrode 154 may not be replenished, so that once the existing chromium metal is completely dissolved, the dissolution of the chromium metal from the first additional electrode 154 in the form of chromium (III) ions by the action of the electrolyte 125 in the absence of current is terminated. Either the first additional electrode 154 is removed from the electrolyte 125, or the electrolyte 125 is pumped out of the electrolysis chamber 100 (not shown).

[0250] The formation of chromium (VI) ions could not be detected during the entire method run.

[0251] After the electroplating phase is over, the anode rail 142 is moved downwards with the anode basket 144 into the upper tank 110. At the same time or with a time delay, the overflow 127 is lowered so that the electrolyte 125 flows out into the lower tank 120 to a suitable height level. This allows a state to be achieved in which the anode basket 144 is still completely covered with the electrolyte 125, while the gravure cylinder 148 is completely free above the liquid level of the electrolyte 125 and can be easily lifted out there by a crane (not shown).

[0252] exist Figure 6a , Figure 6b and Figure 6c Another embodiment of the present invention is shown in the form of a schematic diagram. Figure 5a , Figure 5b and Figure 5c Unlike the embodiment of the present invention, a first cell 210 and a second cell 220 are arranged side by side instead of a lower cell and an upper cell. The two cells are connected to each other via a pipeline with a pump 260, so that the electrolyte 225 can be pumped from the first cell 210 into the second cell 220 by means of the pump 260 and can flow back into the first cell via an overflow (not shown). In other respects, the operating principle corresponds to Figure 5a , Figure 5b and Figure 5c , making it unnecessary to repeat the statement there.

[0253] Alternatively, in Figure 5a to Figure 5c and Figures 6a to 6c A third additional electrode (not shown) may be additionally provided as an inert electrode, wherein the second additional electrode (56, 156, 256) and the third additional electrode are as shown in Figure 3a to Figure 3c are arranged as shown in , so that the chromium electrode (54, 154, 254) is located between them.

[0254] According to another embodiment, a plurality of these units consisting of an inert electrode-chromium electrode-inert electrode can also be connected in series (e.g. Figures 4a to 4c shown), and can be replaced by Figure 5a to Figure 5c and Figures 6a to 6c The second circuit in.

[0255] With the method according to the invention and the electrolysis chamber according to the invention, it is therefore possible to obtain chromium layers having the desired properties, in particular on gravure cylinders, in a particularly advantageous manner.

[0256] The following examples are intended to further illustrate the present invention. They should not be construed as limiting the present invention.

[0257] Example

[0258] Example 1

[0259] An exemplary embodiment of the method according to the invention having steps (A) to (G) is carried out as follows:

[0260] An electrolyte having the following composition is provided:

[0261] -Chromium (III) sulfate (density = 1.26 g / mL; 3% Cr (III) → 37.8 g / L → 0.727 M) 18.6 L

[0262] -Sodium sulfoacetate (8.3 wt% → 104.6 g / L → 0.568 M) 6.27 kg

[0263] -Sodium formate (8 wt% → 100.8 g / L → 1.482 M) 6.05 kg

[0264] -Sodium sulfate, 1.7 wt% → 21.4 g / L → 17 mM) 1.29 kg

[0265] One liter of electrolyte was heated to 40° C. in a beaker with constant stirring, and the pH value was adjusted to 2.6. Then, two electrodes were introduced into the beaker in a manner parallel to and opposite to each other at a distance of 10 cm and connected to a DC power supply. One electrode was a mixed oxide coated (MMO) titanium-porous metal, which was used as an anode. The other electrode was a chromium plate, which was used as a cathode. The anode side or cathode side was selected so that the operating current density was about 4 A / dm at a current of 3 amperes. 2 The anode surface is chosen to be of the same size as the cathode surface.

[0266] A cathodic voltage is applied to dissolve the passivation layer at the chromium electrode (according to the invention: the first additional electrode).The other electrode is an inert electrode, which acts as an anode.

[0267] In the present example, after a short time of about 20 seconds, gas generation was observed at the chromium electrode and small bubbles rose to the surface. This means that the metallic chromium was dissolved in the form of chromium (III) ions. After the start of dissolution was observed, the current was turned off after 60 seconds in the present case, so that the anode and cathode were no longer loaded with direct current. It was found that the dissolution did not stop, but continued in the same way.

[0268] At 0, 2, 4 and 6 hours during the test, 1.0 mL samples were taken and the chromium content was determined. It was found that the amount of Cr(III) increased linearly over the observation period. Additionally, this was confirmed by weight measurement of the chromium electrode. The dissolved chromium species was only trivalent chromium. Hexavalent chromium (Cr(VI)) was not detected at any time point.

[0269] The dissolution in the absence of current is then stopped by removing the chromium electrode from the electrolyte. Alternatively, the electrolyte can also be removed from the beaker. The chromium electrode is thereby subjected to surface oxidation in ambient air and forms a passivation layer again. After the passivation layer has been built up, the chromium electrode is reinserted into the electrolyte (e.g. after a stay in ambient air of 30 seconds) and the dissolution process is no longer started.

[0270] To stop the dissolution in the absence of current, instead of removing the chromium electrode from the electrolyte, the polarity is changed, i.e. the chromium electrode is positively loaded for a short time until the hydrogen formation at the chromium electrode stops. The hydrogen generation stops after 60 seconds. After the visible gas formation ends, the power supply is turned off, thereby permanently stopping the dissolution of chromium.

[0271] Example 2

[0272] pH value variants

[0273] Example 1 was performed again, but the pH value was changed. In detail, under the same settings as in Example 1, the pH value was gradually reduced from 3.1 to 2.8, 2.6 and 2.4. In another test, the pH value was increased from 3.1 to 3.3 and 3.5. In both cases, the same results as described in Example 1 were obtained. However, at higher pH values, the chromium dissolution rate was lower.

[0274] Description of Reference Numerals

[0275] 10, 100, 200 electrolysis chamber

[0276] 15 Pool

[0277] 25, 125, 225 Electrolytes

[0278] 30, 130, 230 support bridge

[0279] 42, 142, 242 Anode rail

[0280] 44, 144, 244 Anode, anode basket

[0281] 48, 148, 248 cathode, gravure cylinder

[0282] 54, 54.1, 54.2, 54.3, 154, 254 First additional electrode, chromium electrode

[0283] 54a, 154a, 254a Chrome mouldings

[0284] 55, 55.1, 55.2, 55.3, 155, 255 Hydrogen bubbles

[0285] 56, 56.1, 156, 256 Second additional electrode

[0286] 56.2 Third additional electrode

[0287] 56.3, 56.4 Other additional electrodes

[0288] 58, 158, 258 Power Supply

[0289] 59, 159, 259 switch

[0290] 110 Upper Pool

[0291] 120 lower pool

[0292] 127 Overflow

[0293] 160, 260 pumps

[0294] 210 First Pool

[0295] 220 Second Pool

Claims

1. A method for controlling the supply of chromium in an electrolytic process for producing a chromium layer, wherein the chromium layer is produced by electrolytically depositing chromium from an electrolyte (25, 125, 225) by means of direct current and using an anode (44, 144, 244) and a cathode (48, 148, 248), comprising the following steps: (A) providing a first additional electrode (54, 154, 254) having or consisting of chromium metal; (B) providing a second additional electrode (56, 156, 256) in the form of an inert electrode, (C) immersing two additional electrodes (54, 56, 154, 156, 254, 256) in said electrolyte (25, 125, 225) containing at least one chromium (III) salt; (D) coupling the first additional electrode (54, 154, 254) and the second additional electrode (56, 156, 256) together in a circuit separate from the cathode (48, 148, 248) and the anode (44, 144, 244); and In the case of formation of a chromium layer during electrolytic deposition of chromium: (E) applying a cathodic voltage to the first additional electrode (54, 154, 254), thereby causing the passivation layer of the chromium metal to dissolve and the chromium metal to begin to dissolve in the electrolyte (25, 125, 225) in the form of chromium (III) ions; (F) after the passivation layer is dissolved, ending the current supply to the first additional electrode (54, 154, 254); and (G) The chromium metal is dissolved from the first additional electrode (54, 154, 254) in the form of chromium (III) ions by the action of the electrolyte (25, 125, 225) in the absence of an electric current.

2. The method according to claim 1, It is characterized in that The chromium metal in the first additional electrode (54, 154, 254) is replenished during step (G), and then steps (E), (F) and (G) of claim 1 are performed sequentially.

3. The method according to claim 1 or 2, It is characterized in that To terminate the process during step (G), - applying an anodic voltage to said first additional electrode (54, 154, 254), or - removing the first additional electrode (54, 154, 254) from the electrolyte (25, 125, 225), or - pumping the electrolyte out of the electrolysis chamber (10, 100, 200), or - not replenishing the chromium metal of the first additional electrode (54, 154, 254).

4. The method according to any one of the preceding claims 1 to 3, It is characterized in that In the electrolyte (25, 125, 225), the pH value is adjusted in the range of 2.0 to 3.5, in particular 2.1 to 3.4, preferably 2.2 to 3.3, more preferably 2.3 to 3.2, even more preferably 2.4 to 3.1, very particularly preferably 2.5 to 3.

0.

5. The method according to any one of the preceding claims 1 to 4, It is characterized in that One, two or more of the following conditions are met: - the cathode voltage is adjusted in step (E) to be in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V; - the anode voltage is adjusted to be in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V, to end the process in step (G); - the surface area of ​​the first additional electrode (54, 154, 254) is chosen to be exactly the same as the surface area of ​​the second additional electrode (56, 156, 256); - The current density is between 2.5 and 4 A / dm 2 In the range of 3.4A / dm 2 ; - by applying the cathodic voltage to the first additional electrode (54, 154, 254) in step (E), the passivation layer decomposes within 5 to 60 seconds, preferably within 5 to 45 seconds, particularly preferably within 5 to 30 seconds; - by applying the anodic voltage to the first additional electrode (54, 154, 254), the passivation layer is formed again within 5 to 60 seconds, preferably 5 to 45 seconds, particularly preferably 5 to 30 seconds, to end the process during step (G); and - the chromium metal of the first additional electrode (54, 154, 254) is present as a chromium moulding selected from blocks, fragments, agglomerates, plates, ingots, wires and grids held in a material resistant to an acidic electrolyte (25, 125, 225).

6. The method according to any one of the preceding claims 1 to 5, It is characterized in that A third additional electrode in the form of an inert electrode is provided, wherein the first additional electrode (54, 154, 254) in the form of a chromium electrode, the second additional electrode (56, 56.1, 156, 256) and the third additional electrode (56b) are connected together to form one or more units, wherein the units are selected from: inert electrode (56.1)-chromium electrode (54)-inert electrode (56.2), wherein a series connection is preferably adopted.

7. The method according to any one of the preceding claims 1 to 6, It is characterized in that The components of the electrolyte (25, 125, 225) are selected from: (a) one or more chromium(III) salts selected from inorganic and / or organic chromium(III) salts; (b) Compounds of formula (I) wherein R is selected from NH2, OH or SO3H, and n represents an integer from 1 to 3, and / or their salts, especially Na + and / or K + a monovalent cation, or a salt of a divalent cation; (c) formic acid and / or its salts, especially for example Na + and / or K + monovalent cations, or salts of divalent cations and (d) optionally one or more additives, in particular selected from complexing agents, alkali metal or alkaline earth metal salts, wetting agents, catalysts or mixtures thereof.

8. The method according to any one of the preceding claims 1 to 7, It is characterized in that The chromium (III) content in the electrolyte (25, 125, 225) is kept constant by comparing the weight of chromium metal used in the first additional electrode (54, 154, 254) with the weight of chromium metal depleted by the chromium layer and replenishing the chromium metal in the first additional electrode (54, 154, 254) before the chromium (III) content in the electrolyte (25, 125, 225) decreases.

9. An electrolysis chamber (10, 100, 200) for controlling the supply of chromium to an electrolyte (25, 125, 225), comprising - an anode (44, 144, 244); - cathode (48, 148, 248); - an electrolyte (25, 125, 225) containing at least one chromium (III) salt; - the anode (44, 144, 244) and the cathode (48, 148, 248) are immersed in the electrolyte (25, 125, 225); a first circuit connecting the anode (44, 144, 244) and the cathode (48, 148, 248) and carrying out the deposition of the chromium layer by electrolytic deposition of chromium from an electrolyte (25, 125, 225) on the cathode (48, 148, 248) by means of direct current; a first additional electrode (54, 154, 254) comprising chromium metal or consisting of chromium metal; - a second additional electrode (56, 156, 256) in the form of an inert electrode, - two additional electrodes (54, 56, 154, 156, 254, 256) are immersed in the electrolyte (25, 125, 225); a second loop connecting the first additional electrode (54, 154, 254) and the second additional electrode (56, 156, 256) in a circuit separate from the cathode (48, 148, 248) and the anode (44, 144, 244); in - applying a cathodic voltage to the first additional electrode (54, 154, 254) so ​​that the passivation layer of chromium metal at the first additional electrode (54, 154, 254) dissolves; or - no voltage is applied to the first additional electrode (54, 154, 254), so that after the dissolution of the passivation layer, chromium metal dissolves from the first additional electrode (54, 154, 254) into the electrolyte (25, 125, 225) in the form of chromium (III) ions in the absence of current; or - applying an anodic voltage to the first additional electrode (54, 154, 254), so that a passivation layer is formed again at the first additional electrode (54, 154, 254).

10. The electrolysis chamber (10, 100, 200) according to claim 9, It is characterized in that The electrolysis chamber (10, 100, 200) is formed by a cell (15), two cells arranged one above the other, in particular an upper cell (110) and a lower cell (120), or two cells arranged side by side, in particular a first cell (210) and a second cell (220).

11. The electrolysis chamber (10, 100, 200) according to claim 9 or 10, It is characterized in that Meet one, two or more of the following characteristics: - in the electrolyte (25, 125, 225), the pH value is in the range of 2.0 to 3.5, in particular 2.1 to 3.4, preferably 2.2 to 3.3, more preferably 2.3 to 3.2, even more preferably 2.4 to 3.1, very particularly preferably in the range of 2.5 to 3.0; the cathode voltage at the first additional electrode (54, 154, 254) is in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V, or the anode voltage at the first additional electrode (54, 154, 254) is in the range of 1.0 to 10.0 V, preferably 2.0 to 9.0 V, more preferably 2.5 to 8.5 V, even more preferably 2.5 to 8.0 V, very particularly preferably 3.0 to 7.0 V; - applying the cathodic voltage to the first additional electrode (54, 154, 254) for 5 to 60 seconds, preferably 5 to 45 seconds, particularly preferably 5 to 30 seconds, or applying the anodic voltage to the first additional electrode (54, 154, 254) for 5 to 60 seconds, preferably 5 to 45 seconds, particularly preferably 5 to 30 seconds; - the surface area of ​​the first additional electrode (54, 154, 254) is chosen to be exactly the same as the surface area of ​​the second additional electrode (56, 156, 256); - The current density is adjusted to 2.5 to 4 A / dm 2 In the range of 3.4A / dm 2 ; - said chromium metal of said first additional electrode (54, 154, 254) is present as a chromium moulding selected from blocks, fragments, agglomerates, plates, ingots, wires and grids held in a material resistant to an acidic electrolyte (25, 125, 225); and / or - The components of the electrolyte (25, 125, 225) are selected from: (a) one or more chromium(III) salts selected from inorganic and / or organic chromium(III) salts; (b) Compounds of formula (I) wherein R is selected from NH2, OH or SO3H, and n represents an integer from 1 to 3, and / or their salts, especially Na + and / or K + a monovalent cation, or a salt of a divalent cation; (c) formic acid and / or its salts, especially for example Na + and / or K + monovalent cations, or salts of divalent cations and (d) optionally one or more additives, in particular selected from complexing agents, alkali metal or alkaline earth metal salts, wetting agents, catalysts or mixtures thereof.

12. An electrolysis chamber according to any one of the preceding claims 9 to 11, It is characterized in that A third additional electrode in the form of an inert electrode is provided, wherein the first additional electrode (54, 154, 254) in the form of a chromium electrode, the second additional electrode (56, 56.1, 156, 256) and the third additional electrode (56b) are connected together to form one or more units, wherein the units are selected from: inert electrode (56.1) - chromium electrode (54) - inert electrode (56.2), wherein the units are preferably connected in series.

13. Use of the electrolysis chamber (10, 100, 200) according to any of the preceding claims 9 to 12 for producing chromium layers on rotationally symmetrical components, in particular gravure cylinders (48, 148, 248).

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