JP3911227B2 - How to extend the life of electroplated electrodes - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for extending the life of an electroplating electrode suitable for a continuous plating line such as a steel plate.
[0002]
[Prior art]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-200377
In order to perform continuous plating on a metal strip such as a steel plate, a plating line in which a large number of paths are provided in series inside a plating tank is used. Each pass is provided with an electroplating electrode, and the metal strip is electroplated in each pass while running in a zigzag manner in a vertical or horizontal direction between a conductor roll and a turn roll.
[0004]
A total current is used to control the basis weight in such a plating line. The total current is an integrated value of currents supplied from the electroplating electrodes of each path while the metal strip travels through all paths in the plating line. This total current is calculated based on the required basis weight, plate width, plating efficiency, and line speed, and is distributed to each path. The total current is proportional to the basis weight, the plate width, and the line speed. For example, when the line speed decreases, the total current decreases.
[0005]
By the way, the electroplating electrode has an optimum current density, and if it is out of this range, the plating efficiency is lowered. For this reason, conventionally, when the total current of the plating line is reduced due to a decrease in the weight per unit area or the line speed, instead of reducing the energization amount of all the paths uniformly, by reducing the number of passes to be used, The optimum current density of the electroplated electrode of the energized path is maintained.
[0006]
FIG. 1 is an explanatory diagram showing this relationship. The straight line OA indicates the current density of the electroplating electrode of each pass when using 3 passes, and falls within the optimum current density range when the line speed (or the total current proportional thereto) is in the AB section. ing. However, if the line speed is further decreased from B, the plating efficiency is lowered below the optimum current density range. Therefore, energization to one path is stopped and the two-path use indicated by the straight line OC is switched. When the line speed further falls below D, the operation is switched to one-pass use indicated by the straight line OE in order to secure the optimum current density range.
[0007]
The above-described prior art has a great effect in maintaining high plating efficiency of the energized electrode. However, with a specific electrode, energization and de-energization are repeated according to changes in the total current, and it has been found that there are the following problems.
[0008]
For example, a plating solution containing fluoride and having a pH of about 1 is used for chromium plating of a steel sheet, and a PbO ₂ electrode is used for the electroplating electrode as shown in Patent Document 1 described above. As shown in the Plube curve (pH-potential diagram) in FIG. ₂ , the PbO ₂ state is stable in the plating solution at pH 1 when the potential is 1.5 V or higher, but Pb ² when the potential is −0.35 to 1.5 V. ^{The +} state becomes stable, and when the potential is −0.35 V or less, the Pb state is stable. That is, the PbO ₂ electrode becomes unstable when the potential is near zero.
[0009]
Therefore, since the potential during energization is 1.8 to 2.0 V, the electroplating electrode is stable in the state of PbO _2. However, when the energization is stopped and the potential becomes 0 V or less, the state of Pb ²⁺ becomes stable and the plating is performed. It reacts with the chromium ions in the liquid to produce insoluble matter of PbCrO ₄ while the energization is stopped. When energized again, a stable layer of PbO ₂ is formed again under the PbCrO ₄ layer, and the PbCrO ₄ is peeled off to generate sludge. When the energization and the energization stop are repeated in this way, the PbO ₂ electrode is gradually consumed and must be replaced in a short period of time.
[0010]
The above-mentioned problems are common not only to PbO ₂ electrodes but also to electroplated electrodes made of materials that exhibit unstable characteristics when the potential is 0 or less on the Plube curve (pH-potential diagram). Examples include an IrO ₂ electrode in a tin plating solution or a zinc plating solution. As shown by the Plube curve in FIG. 3, the IrO ₂ electrode also has a different stable state during energization and deenergization in the plating solution having a low pH, and becomes unstable during deenergization.
[0011]
[Problems to be solved by the invention]
The present invention solves the above-mentioned conventional problems, prevents the generation of sludge in the electroplating electrode installed in the plating line where the total current changes, and can greatly extend the service life of the electroplating electrode. The present invention has been made to provide a method for extending the life of an electroplated electrode.
[0012]
[Means for Solving the Problems]
The method for extending the life of an electroplated electrode according to the invention of claim 1 made to solve the above-mentioned problem is that a plating line comprising a plurality of passes in which PbO ₂ electrodes are arranged in a chromium plating solution, Even when the total current of the plating line decreases due to a decrease in the line speed, the current is distributed to each path so that the minimum energization current necessary to stabilize the electrode in any path is secured. To do. According to a second aspect of the present invention, there is provided a method for extending the life of an electroplating electrode in a plating line comprising a large number of passes in which an IrO ₂ electrode is disposed in a tin plating solution or a zinc plating solution. Even when the total current of the line decreases, the current distribution to each path is performed so that the minimum energization current necessary for stabilizing the electrode in any path is secured.
[0013]
According to the present invention, when the total current of the plating line is reduced due to a decrease in the basis weight or the line speed, it is not necessary to reduce the number of used paths and stop energization of a specific path as in the past. The current distribution to each path is performed so that the minimum energization current necessary for stabilizing the electrode is secured. As described above, in the present invention, even when the total current is decreased, the potential of the electroplating electrode in all passes is kept high by supplying the current for electrode protection. As a result, the electrode is not chemically unstable, the generation of sludge can be prevented, and the service life of the electroplated electrode can be greatly extended.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention are shown below.
FIG. 4 is a diagram showing a plating line composed of 10 passes. A metal strip such as a steel plate is zigzag-shaped between the conductor roll 1 and the turn roll 2 and continuously electroplated through each pass. Is to be given. Although FIG. 4 shows the case of the saddle path, the same applies to the case of the horizontal path. The electroplating electrode 3 is disposed in each pass, and the material thereof is unstable as described above, such as Pb, PbO ₂ used for chrome plating, tin plating, or the like. IrO ₂ used for galvanizing. In addition, examples of the electrode material include Pt, Ta, IrO ₂ —Ta ₂ O ₅ , and examples of the electrode base material include Ti, Zr, Nb, Ta, and the like.
[0015]
The controller 4 distributes the energization amount to the electroplating electrode 3 in each pass. The controller 4 calculates the total current based on the required weight per unit area, the plate width, the plating efficiency, and the line speed, and energizes all the paths during high-speed plate passing with a large total current. At this time, the electroplating electrode 3 of any path is within the range of the optimum current density. Thus, the present invention is not different from the conventional method at the time of high-speed feeding with a large total current.
[0016]
However, when the total current of the plating line is reduced due to a decrease in the basis weight or the line speed, the number of passes used in the conventional method is reduced and a path that completely stops energization is generated. Current distribution to each path is performed so that the minimum energization current necessary for the electrodes to be stable is secured even in the path.
[0017]
For example, when the total current of the 10-pass plating line should be reduced to 40% of the rating, the conventional method maintains the energization amount to the 1st to 4th passes at 100%, and the 5th to 10th. By setting the energization amount to the path to 0, the total current is reduced to the target value of 40%. That is, (1 × 4 + 0 × 6) /1×10=0.4. As a result, the optimum current density is ensured in the first to fourth passes and high plating efficiency is maintained. However, in the fifth to tenth passes where the energization is stopped, the electrode wears out as described above.
[0018]
On the other hand, in the present invention, for example, when the total current of the plating line of 10 passes should be reduced to 40% of the rating, the energization amount to the first to fourth passes is reduced to 85%, for example. The energization amount to the 5th to 10th paths is set to 10% necessary for stabilizing the electrodes. That is, (0.85 × 4 + 0.1 × 6) /1×10=0.4. As described above, in the present invention, a predetermined minimum energization current necessary for the electrode to be stabilized in any path is ensured, and a current for electrode protection is also supplied to the path that has been stopped in the past so that all the current is supplied. Keep the potential of the electroplating electrode in the pass high. As a result, the stability of the electrode is maintained, the generation of sludge and the like are prevented, and the service life of the electroplated electrode can be greatly extended.
[0019]
The magnitude of the protective current required for this varies depending on the type of electrode and the composition of the plating bath, but can be obtained by drawing an anodic polarization curve. For example, in the case of a PbO ₂ electrode used in a chromium plating bath having a specific composition, it is 1.0 A / dm ² . As described above, according to the present invention, since the current for electrode protection is also supplied to the path where the energization is conventionally stopped, the plating efficiency of the entire plating line may be slightly lower than the conventional method. However, the effect of extending the service life of the electroplated electrode is more than that.
[0020]
Specifically, according to the present invention, the service life of the electroplating electrode can be increased to more than 10 times that of the conventional one, and the amount of sludge generated from the plating line can be greatly reduced to 3% of the conventional one. It was. This also reduces the burden on the environment, and its significance is significant.
[0021]
【The invention's effect】
As described above, according to the method for extending the life of an electroplated electrode of the present invention, the electroplated electrode that is repeatedly energized and de-energized is protected by a protective current, and the service life of the electroplated electrode is greatly extended. In addition, there are effects such as prevention of sludge generation.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the number of used paths and current density.
FIG. 2 is a Plube curve (pH-potential diagram) of a PbO ₂ electrode.
FIG. 3 is a Prube curve (pH-potential diagram) of an IrO ₂ electrode.
FIG. 4 is an explanatory diagram of a plating line.
[Explanation of symbols]
1 Conductor roll 2 Turn roll 3 Electroplating electrode 4 Controller

Claims (2)

In a plating line consisting of a large number of passes in which PbO ₂ electrodes are arranged in a chromium plating solution, the electrode stabilizes in any pass even when the total current of the plating line is reduced due to a decrease in the basis weight or line speed . A method for extending the life of an electroplated electrode, characterized in that current distribution to each path is performed so that a minimum energization current necessary for the operation is ensured. In a plating line consisting of a large number of passes in which IrO ₂ electrodes are arranged in a tin plating solution or a zinc plating solution, when the total current of the plating line is reduced due to a decrease in the basis weight or the line speed, the electrode is in any pass. A method for extending the life of an electroplated electrode, wherein current distribution to each path is performed so that a minimum energization current necessary for stabilization is secured.

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