JPH0434634B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides an edge mask device for preventing overcoating of the strip edge portion in a continuous electroplating device that continuously electroplats the surface of a metal strip such as a steel plate. Regarding.

BACKGROUND OF THE INVENTION Vertical and horizontal electroplating devices are known for continuous electroplating of metal strips, such as steel strips.

In either case, an electrode plate is provided opposite the surface of the metal strip to be plated as it travels through the plating tank, and the surface of the metal strip is continuously plated while passing through the tank.

The problem with electroplating both sides of a metal strip using such equipment is that the plating current concentrates at the edges of the metal strip.
An overcoat occurs in which the amount of plating on the edges is greater than on other parts. Furthermore, when electroplating one side of a metal strip, there is a problem in that in addition to overcoating the edges, the current flows around the unplated side as well, causing the plating to occur.

In this way, if an overcoat forms on the edges of the metal strip, a build-up phenomenon occurs in which the edges bulge when the metal strip is wound into a coil, and the plating films on the overcoat areas rub against each other, causing scratches. Problems such as poor welding strength of the overcoat portion during welding and poor appearance due to discoloration of the overcoat portion occur.

Edge masks and auxiliary electrodes made of insulators have been known as devices for preventing current from flowing into the overcoat or non-plated surface of the metal strip.

Among these, the auxiliary electrode is constructed as follows.

A short auxiliary electrode plate with a length similar to the length of the main electrode plate and a width is placed close to both edges of the metal strip moving in the electroplating tank, and a short auxiliary electrode plate is placed between the main electrode plate and the auxiliary electrode plate. By applying a voltage to the metal strip, the current concentrated at both edges of the metal strip is shunted to the auxiliary electrode plate. The overcoat thus formed on the edges of the metal strip,
and to prevent plating on the non-plated side in the case of single-sided plating.

On the other hand, an edge mask made of an insulator prevents current concentration on the edge portion by surrounding the edge portion of the metal strip with an insulator having a U-shaped cross section.

(Problems to be Solved by the Invention) According to the method using auxiliary electrodes, overcoating that occurs at the edges of the metal strip can be prevented, but conversely, the current at the edges is lower than that at the center, so A problem arises in which an undercoat occurs in which the amount of plating in some areas is less than in other areas.

Further, when overcoating is prevented using an insulating edge mask, the metal strip may be damaged or the edge mask may be damaged due to contact between the edge mask and the metal strip.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an edge mask device for a continuous electroplating device that is free from the risk of contact with and damage to metal strips and can easily set the mask strength to an appropriate level.

(Means for Solving the Problems) As a result of repeated research to achieve the above-mentioned object, the present inventor came up with the idea of applying a force (Lorentz force) toward the center of the strip by magnetic flux to the charges concentrated at the strip edge. I got it. If edge masking is performed using magnetic flux in this way, a sufficient masking effect can be obtained even if the magnetic poles that generate magnetic flux are placed apart from the strip. Further, the amount of magnetic flux can be easily controlled to an appropriate level by adjusting the amount of current in the coil that energizes the magnetic poles.

Thus, the gist of the present invention is that, in a continuous electroplating device for electroplating the surface of a running metal strip, a pair of magnetic poles that generate a magnetic velocity in a direction substantially perpendicular to the surface of the edge portion of the metal strip is connected to the metal strip. This is a magnetic flux type edge mask device for electroplating, in which an embedded metal strip is sandwiched between an electrode for electroplating or inside the electrode.

In addition, in order to perform edge masking efficiently, the magnetic pole must be made up of a plurality of segments divided in the width direction of the metal strip, and a magnetic pole drive means that independently magnetizes and energizes the segments, and a magnetic pole driving means that independently magnetizes and energizes the segments, and a It is preferable to include a control means that magnetizes and energizes only the segments near the metal strip edges according to the width to generate magnetic flux only near the edges.

(Function) Negative charges concentrated on the edge of the running metal strip are subjected to electromagnetic force (Lorentz force) in the direction toward the center of the strip from the magnetic flux perpendicular to the surface of the edge. (The polarity of the magnetic pole is determined by the Lorentz force that causes the moving negative charge to move toward the center of the strip.)
Select to receive from the generated magnetic flux. ) As a result, concentration of charge and current on the edge portion is prevented.

Furthermore, the efficiency of the edge mask can be increased by dividing the magnetic pole into segments and concentrating the magnetic flux only near the edges.

In addition, by controlling the magnetization segments of the segmented magnetic poles based on the sheet width of the metal strip and the meandering information of the metal strip in the plating bath, negative charges concentrated at the edges are more effectively directed toward the center of the steel sheet. This prevents overcoating on the edge of the steel plate.

The magnetic poles can be placed at a considerable distance from the metal strip with sufficient effect to prevent damage to the steel plate and damage to the edge mask.

(Example) Next, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a cross section of an embodiment (an example in which a magnetic pole is disposed between a steel plate and an electrode) in which a magnetic flux type edge mask device according to the present invention is used in a continuous electrogalvanizing apparatus for steel plates.

Continuous Electroplating Apparatus Electrodes 2 and 2' are installed in a plating tank so as to face both surfaces of a steel plate 1 running from the top to the bottom of the drawing. A negative voltage is applied to the steel plate 1 via a conductor roll (not shown), and a positive voltage is applied to the electrode 2. If the edge mask device is not operated at this time, negative charges will be concentrated at the edge portion of the steel plate 1 as a result of electric field concentration (see the minus sign in the figure).

The specific operating conditions and dimensions of this steel plate plating equipment are as follows, for example: Steel plate dimensions: thickness 0.9 mm, width 1200 mm Line speed: 180 m/min = 3 m/s Electrode dimensions: thickness 1800 mm, length 1000 mm Distance between electrode and steel plate: 20mm Plating liquid: ZnSO ₄ 400g/Na ₂ SO ₄ 70g/PH2~3 Liquid temperature 50~60℃ Plating weight: 50~150g/m ² Plating current density: 40~150A/dm ² Magnetic flux Type Edge Mask Device The edge mask device according to the present invention includes pairs 3 of a large number of magnetic pole segments divided in the width direction of a steel plate 1.
The magnetic pole segments 3a, 3a'; 3b, 3b' are installed between the steel plate 1 and the electrode 2 so as to sandwich the edges of the steel plate 1.

Each pole segment is independently magnetized and energized by a magnetizing current flowing through a coil (not shown). The magnetic pole segments are biased only to the pair of segments 3b and 3b' near the edge of the steel plate based on the width and meandering information of the steel plate 1, thereby generating concentrated magnetic flux at the edge.

FIG. 2 is an enlarged view of the vicinity of the edge in the chain line circle A in FIG.
shows the relationship between

As shown in Figure 3, the magnetic flux density B
A negative charge q(C) in a conductor moving at a speed v(m/S) in a magnetic field of (Wb/m ² ) has a Lorentz force f(N).
works according to the following formula: f = q・B・v(N) ...(1) Therefore, if the length of the conductor in the magnetic flux moving at the speed v (m/S) is l (m), then , the electromotive force e(v) generated at both ends of the conductor is given by the following formula: e=B・l・v(V)...(2) If the above formula (2) is applied to steel plate 1, Assuming that the moving speed is v (m/S), the magnetic flux density generated by the magnetic pole segments 3b and 3b' is B (Wb/m ² ), and the width of the steel plate 1 running within the magnetic flux is w (m), e=B・w /v (V) ...(3) An electromotive force is generated in the inner width direction of the steel plate 1.

Therefore, by generating a magnetic field with an appropriate magnetic flux density B according to the operating conditions, an optimal potential difference e is generated between the center and edge portions of the steel plate 1 according to equation (3), and thereby Concentration of negative charges on the edge portion can be eliminated.

The specific specifications and operating conditions of the edge mask device used in the plating device for which specific numerical examples of specifications are given above are as follows, for example: Number of segments: 20 per side vs. number of magnetized (energized) segments : 4 segments per side magnetic flux density: 10 Wb/m Distance between ² steel plates and magnetic poles: 15 mm (Effects of the invention) According to the present invention, magnetic flux can be generated intensively at the metal strip edge part, and the magnetic flux density can be reduced. Easily controlled to optimum strength. Therefore, the present invention has the following effects: It is possible to completely eliminate current concentration on edges and solve the problem of current flowing around to overcoat and non-plated surfaces.

There is no risk of undercoat.

The magnetic pole that generates the magnetic flux can be installed at a considerable distance from the metal strip and still produce a sufficient masking effect, so there is no risk of damage to the strip or damage to the masking device due to bumping. .

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a continuous plating device equipped with an edge mask device according to the present invention;
The figure is an enlarged view showing the part within circle A in Figure 1; and Figure 3 is a diagram showing a conductor moving between magnetic poles to explain the direction of force acting on a negative charge on a conductor moving in a magnetic flux. FIG. 1: Steel plate, 2, 2': Electrode, 3a, 3a'; 3b,
3b': magnetic pole segment.

Claims (1)

[Scope of Claims] 1. In a continuous electroplating device for electroplating the surface of a traveling metal strip, a pair of magnetic poles that generate magnetic velocity in a direction substantially perpendicular to the surface of the edge portion of the metal strip is electroplated with the metal strip. A magnetic edge mask device for electroplating, which comprises an embedded metal strip sandwiched between electrodes or inside the electrodes. 2. The magnetic pole consists of a plurality of segments divided in the width direction of the metal strip, and includes a magnetic pole drive means that independently magnetizes and energizes the segments, and a segment near the edge of the metal strip according to the width of the metal strip to be plated. 2. The magnetic flux type edge mask device for electroplating according to claim 1, further comprising a control means for magnetizing and energizing only the edge portion to generate magnetic flux only in the vicinity of the edge portion.