JPH0130919B2 - - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to electroplating apparatus, and more particularly to horizontal continuous electroplating apparatus for continuously running metal strips.

(Prior Art) In recent years, the production volume of galvanized steel sheets has been increasing, especially with the expansion of their uses, and many improvements have been made to the production technology. Therefore, many proposals have been made regarding continuous electroplating of metal strips as one of the production means and devices for the same.

For example, in Japanese Patent Publication No. 50-8020, a jet cell method was proposed, in which the plating tank is configured in a cylindrical shape, and the plating liquid is forced to circulate in countercurrent to the metal strip running inside the tank. . This method is used for both double-sided plating and single-sided plating, but a jet plating method is proposed in Japanese Patent Publication No. 14759/1983 for use exclusively with single-sided plating. This is a method in which only one side of the metal strip is plated while a plating liquid is jetted from an electrode placed close to one side of the metal strip. The other side of the metal strip is supported by a support roll.

Furthermore, a fluid cushion pad system has been proposed in Japanese Patent Application Laid-Open No. 136796/1983. This method is a combination of the jet cell method and the jet plating method described above, and plating is performed while jetting plating liquid from both the upper and lower surfaces of the metal strip, and the plating liquid is jetted out at the middle part of the pair of energized rolls. The current also supports the metal strip.

(Disadvantages of the prior art) Plating metal strips requires economic efficiency that enables continuous processing at high speed, and it is also necessary to perform plating under as constant conditions as possible in order to achieve high quality plating. It is desirable that the It goes without saying that the composition of the plating solution must always be kept constant, and in particular, it is desirable that the distance between the electrodes be kept as small as possible and always constant.

Conventionally, in horizontal plating tanks, the metal strip hangs down due to its own weight, so the gravity acting on the metal strip and the tension in the plating tank (usually 0.5 to 5 kg/
mm ² ), it is inevitable that the metal strip running in the plating bath will be located between the pair of energized rolls and have a catenary curved longitudinal cross-sectional shape.

The maximum amount of deflection of the metal strip at this time, that is, the amount of catenary at the center of both current-carrying rolls, is expressed by the following equation.

h (catenary amount) = k (l ² /T) where, l: distance between the supporting points of both energized rolls (mm) T: strip tension (Kg/mm ² ) k: proportionality constant Therefore, the distance between the poles and the strip Since the distance is large on the top surface and small on the bottom surface, the current distribution on the top surface side becomes more uneven than that on the bottom surface, and the voltage on the top surface side becomes larger than that on the bottom surface. Also, if the plating liquid is injected in such a state,
This causes a difference in flow velocity between the upper and lower surfaces, which, together with the above-mentioned difference in the distance between the poles, results in significantly uneven plating quality on the upper and lower surfaces of the strip.

Furthermore, due to the vibration and flapping of the strip, contact accidents between the anode provided on the bottom surface and the strip frequently occur, making close electrolysis impossible. It is necessary to increase the power consumption, and as long as such operation is carried out, power saving cannot be achieved.

Moreover, even though they do not contact each other, the distance between the anode on the bottom surface and the strip becomes partially close, so there are localized areas with a high density of H ₂ and O ₂ gas bubbles. The unevenly attached gas bubbles make the current distribution even more uneven, leading to variations in the quality of the alloy plating (composition, precipitated phase), and in extreme cases, pin holes and uneven plating, which can damage the product value. There is.

In the jet cell method described above, it is inevitable that the metal strip running inside the cylindrical plating bath will have a catenary curve shape. In addition, even with the jet plating method, since it is a non-immersion type, the plating liquid that is ejected from the anode surface toward the plating surface will then overflow from the plating surface to the surrounding area.
It is necessary to flow a large flow rate of plating liquid to fill the space between the electrode and the strip, which not only requires a large-capacity circulation pump, but also the flow rate necessary to stabilize the quality of the alloy plating. A problem arises in that the flow rate and the flow rate for liquid filling become unbalanced. Furthermore, especially in the case of plating liquid containing Fe ions (Fe plating, Fe-Zn plating, Fe-Ni plating, Fe-Mn plating, etc.), a large amount of overflowing plating liquid becomes droplets (splash) and falls. Therefore, it reacts with oxygen in the air to form (4Fe ²⁺ +O ₂
+4H ⁺ →4Fe ³ +2H ₂ O), it is oxidized in the air and is consumed, resulting in significant fluctuations in the composition of the plating bath. This problem is particularly serious when the strip width is narrower than the nozzle width, and large variations in the plating solution composition are unavoidable. In the case of a non-immersion type jet cell, the disadvantage is that the pressure near the discharge nozzle becomes partially negative, air is drawn in from the surroundings as bubbles, and air oxidation from Fe ²⁺ to Fe ³⁺ is significantly accelerated. It is compared to the type. Similarly, in the case of the above-mentioned fluid cushion nozzle method, when manufacturing alloy electroplating, the flow conditions differ between the upstream side (countercurrent direction) and the downstream side (forward flow direction), so the alloy composition and precipitated phase are not uniform. This results in uniform plating. That is, in order to improve the gas removal performance on the upstream side, it is necessary to flow at a higher flow rate than on the downstream side, and the relative liquid flow rate will be different between the upstream side and the downstream side. Controlling such a liquid flow rate is quite difficult in actual operation.

(Related Invention) The applicant of this patent previously proposed in Japanese Patent Application No. 58-59194 that the central portion of each insoluble anode arranged facing each other at a distance on the upper and lower surfaces of a metal strip was divided, and a pair of upper and lower platings were placed at the central portion of each insoluble anode. We proposed a two-stage countercurrent plating device equipped with a liquid injection nozzle. With such a device, the flow of the plating liquid sent countercurrently becomes more uniform, the change in the inter-electrode distance over time due to non-uniform dissolution of the anode is reduced, and the strip running speed can be further increased. I can do it. However, this method is also not completely satisfactory, and the problem has been damage to the nozzle caused by the strip coming into contact with the upper surface of the two-stage counterflow nozzle (lower side).

(Object of the invention) The object of the invention is to provide high quality plating, especially stable alloy plating (e.g. Zn-Fe, Zn-Ni, Zn-
Ni−Cr, Zn−Mn, Zn−Cr, Fe−Mn, Zn−Fe
-Ni, etc.) at high current density and efficiently.

Another object of the invention is to provide an apparatus for continuous electroplating of metal strips in which the distance between the poles can be kept more precisely and constant.

(Summary of the Invention) Here, the present invention provides a horizontal continuous metal strip comprising an insoluble anode disposed facing away from a metal strip running in the horizontal direction, and a pair of front and rear energized rolls in contact with the metal strip. The electroplating device includes: an intermediate support roll provided at an intermediate position between the pair of current-carrying rolls; the insoluble anodes disposed in pairs above and below between the intermediate support roll and each of the current-carrying rolls; and The metal strip is provided near the downstream end in the running direction of the metal strip of at least one conduit surrounded by an insoluble anode and the metal strip running in the horizontal direction. The device comprises at least one plating liquid blowing nozzle which is open to the metal strip and has a discharge angle of 60 degrees or less between the metal strip and the plating liquid blowing flow.

Aspects of the Invention To further explain the invention with reference to the accompanying drawings, FIGS. 1a and 1b show in schematic cross-section an apparatus 1 for continuous electroplating of metal strips according to the invention, in which The metal strip 2, which is continuously running in the horizontal direction as shown by the arrow, is fed to a horizontal electroplating tank 3, which is a horizontal plating tank.

In the case of Fig. 1a, this continuous electroplating device 1
The structure includes energizing rolls 4, 4 (shown with diagonal lines in the figure), a pair of intermediate support rolls 5 disposed approximately in the center between them, and a metal strip in front and behind the intermediate support rolls 5. The metal strip 2 is made up of a pair of upper and lower insoluble anodes 6, 6 which are spaced apart from each other, and the metal strip 2 is electroplated while continuously traveling between these insoluble anodes. In the illustrated example, a pair of jet nozzles 7, 7, 8, 8 for plating liquid are formed on both upper and lower surfaces of the continuously running metal strip 2, and the jet nozzles 7, 7, 8, 8 are arranged in a pair at the upper and lower sides of the insoluble anodes 6, 6 and upstream of the exit-side energizing roll. They are provided at adjacent portions, and eject plating liquid countercurrently to the metal strip. Normally, both sides of the metal strip are provided with an appropriate plating liquid sealing mechanism, such as a known edge masking device (not shown), so each of these members seals a type of plating liquid on the upper and lower surfaces of the metal strip. A conduit 9 is formed into which the plating liquid is forced in countercurrent direction to the metal strip. The entire apparatus including the insoluble anode 6 is immersed in the plating bath of the plating tank 3, and the plating liquid from the jet nozzles 7 and 8 is forced into the plating tank via the circulation tank 10 in the illustrated example. is circulating. Dam rolls 11 are provided at the inlet and outlet of the plating tank 3, respectively.

FIG. 1b shows the dam roll 11 in the case of FIG. 1a.
This shows an example in which a dam roll plate 12 is provided in place of the dam roll plate 12, and the same members are indicated by the same reference numerals. Figure 1b
In this case, the plating tank 3 is divided into two by providing the dam roll plate 12 also in the downstream adjacent region of the intermediate support roll 5.

In this way, for example, in either case of FIG. can be prevented.

Note that when the plating liquid sealing mechanism described above is provided, for example, a known edge masking device (not shown), it is possible to not only substantially prevent the plating liquid from going around to the opposite side of the strip, but also to prevent the plating liquid from going around to the opposite side of the strip. By providing it at both ends of the strip, the plating liquid conduit consisting of the metal strip surface and the insoluble anode is closed from the surroundings, thereby making it possible to change the composition of the plating bath in contact with the plating surface. can be held constant. By forming the plating liquid pipeline in which only the inlet and exit of the plating liquid are open, and by making the entire plating device an immersion type, it is possible to stably obtain even more uniform electroplating. . Sealing of the plating liquid in the running direction of the strip may be accomplished by any suitable device known in the art, such as the above-mentioned dam roll or dam seal plate.

The intermediate support roll may be of any type, structure, or mechanism as long as it functions to mechanically fix the position of the strip during running. The most common type is a pinch roll type or an offset roll type, but in that case, a multi-stage roll type or a combination of rolls of different diameters with upper and lower rolls may also be used. Furthermore, rolls partially divided into rectangular roll bodies may be combined.

Note that it is sufficient to provide the intermediate support roll only on the lower surface side of the metal strip, especially from the viewpoint of catenary prevention.

It is desirable that the discharge angle (θ) between the strip and the plating liquid blowing flow be as low as possible, close to parallel flow (θ = 0°), in order to ensure uniform fluidity of the plating liquid. Considering the wear and tear caused by contact with the nozzle tip and the installation space, the practical angle is about 15 to 60 degrees. If this discharge angle exceeds 60 degrees, the flow velocity distribution of the plating liquid to be blown tends to become non-uniform. In this case, it is advantageous to form the tip of the nozzle into a curved shape similar to the beak of a waterfowl.

The discharge tip of the nozzle is generally slit-shaped with a rectangular cross section, but the cross-section of the slit-shaped nozzle may have a gradual opening interval. Alternatively, a nozzle with many small circular slots may be used as long as it can achieve a uniform liquid flow velocity distribution in the width direction of the plate.

The pass line along which the metal strip runs must not only be completely horizontal, but also within ±
Even if the range is tilted by about 10 degrees, it still falls within the scope of the horizontal plating tank, ie, the horizontal continuous plating device, referred to in the present invention.

Furthermore, the countercurrent property between the running direction of the strip and the flow direction of the plating liquid does not only occur when the two are completely parallel, but also when, for example, the flow of the plating liquid deviates by a small angle outward or inward. too,
The present invention falls within the category of counter flow with respect to the direction of strip movement.

As described above, one feature of the present invention is that in an immersion type plating tank, an intermediate support roll is provided approximately in the center between the front and rear pairs of energized rolls, and this configuration is adopted. The following effects can be seen depending on:

The amount of strip catenaries, which is the biggest drawback of horizontal plating tanks, is reduced.

Reliability is increased because the pass line position control is displacement control rather than a pressure control method like the fluid pad.

Unlike the fluid cushion pad method,
Since the nozzle/header pressure is not high, there is little power loss in the plating liquid supply pump.

When the dimensions of the metal strip to be processed are changed, troubles such as unstable vibrations and poking of the tip of the coil do not occur when the metal strip passes through a width transition area where the width changes greatly.

Since the above-mentioned effects can be obtained, the overall effect is that proximity electrolysis is possible,
There is almost no difference in the quality of the alloy plating on the top and bottom surfaces.

Furthermore, another feature of the present invention is that a plating liquid blower is provided near the downstream end of the conduit in the running direction of the metal strip into the conduit formed by the insoluble anodes and the metal strip before and after the intermediate support roll. The plating liquid is forcibly injected from the plating nozzle in a direction countercurrent to the running direction of the metal strip.
By adopting such a configuration, the following effects can be obtained in addition to the above-mentioned effects.

Since there is no forward flow only in the countercurrent direction, the self-stabilizing effect of the relative flow velocity due to mutual interference between the countercurrent blowing and the strip viscosity works, contributing to uniformity of the alloy plating quality.

Since the countercurrent blowing electrode length is shortened, gas removal performance is improved. In the case of the present invention, the electrode length can be approximately half that of the jet cell method described above. Therefore, the quality of the resulting alloy plating is stabilized.

In this regard, in a preferred embodiment of the present invention:
As alluded to above, if appropriate, sealing mechanisms may be provided along both sides of the metal strip, which would provide further improvements.
This sealing mechanism is already well known in the art, for example as an edge masking device, so no further mention is necessary.

In addition, in the present invention, the amount of catenary can be reduced as much as possible by providing the intermediate support roll, but the effect of using the intermediate support roll is not limited to this, and the plating process in the immersion type plating tank is Coupled with the adoption of countercurrent injection of liquid, many more excellent effects are brought about as described above.

Next, the effects obtained by the apparatus according to the present invention will be explained in more detail based on some specific examples.

(1) Catenary correction effect: Figure 2 shows the inside of a cell when a steel strip with a thickness of 0.8 mm and a width of 300 mm is plated in a horizontal plating tank similar to the one shown in Figure 1 at a line speed of 150 m/min. 3 is a graph showing the results of measuring how far the position of the strip deviates from the pass line. Examples according to the present invention are indicated by ● in the figure. As is clear from the illustrated results, according to the present invention, since the strip position is fixed by displacement control using intermediate support rolls, there is no need for complicated flow rate control compared to the conventional method, and the operation is extremely stable. and has high reliability. In other words, a steady-state catenary was obtained.

This method also mechanically pinches the strip when it passes the width transition part of the strip (the welded part of the front and rear coils), so it does not cause the unstable vibrations seen when using the fluid cushion pad method (indicated by ○ in the figure). there is no problem.

In addition, when using the jet cell method (in the figure,
According to the present invention, the distance between the fulcrums is halved, so that the flapping vibration of the strip due to fluctuations in the tension in the cell during running and unbalanced fluctuations in the flow rate of the upper and lower nozzles, which can be seen in
It is approximately 1/4 times, which is a significant decrease. Therefore, the distance between the electrodes, which was 25 to 50 m/m in the jet cell method, can be significantly shortened to 5 to 15 m/m according to the present invention.

(2) Gas bubble removal property: Using the same equipment as shown in Figure 1a,
Electric Zn-
Ni alloy plating (Zn ² 40g/, Ni ²⁺ 70g/,
(NH ₄ ) ₂ SO ₄ 100 g/PH2) was carried out while changing the current density, and the plating voltage at that time was measured. The electrode length was measured in the case of 3 m (jet cell method...indicated by ○ in the figure) and in the case of the two-stage countercurrent method in which the electrode was divided into front and back sections of 1.5 m (in the case of the present invention...indicated by ● in the figure). The results are shown graphically in FIG.

From the results shown, it can be seen that the gas bubble removal efficiency of the device according to the present invention is considerably improved compared to that of the so-called jet cell method, as can be seen from the small voltage rise.

(3) Stability of alloy electroplating quality: Using a steel strip with a thickness of 0.6 mm and a width of 600 mm, a horizontal water plate similar to that shown in Fig. 1 is used, and the line speed can be varied between 0 and 200 m/min. In a flow model experimental tank, the flow velocity between the electrodes was actually measured using a hot wire anemometer, a pitot tube, etc. in the case of no countercurrent blowing and the case of discharging at a blowing flow rate of 125 m/min.

The results are summarized in a graph in Figure 4.

As is clear from the illustrated results, when countercurrent blowing is performed according to the present invention (in the figure,
(shown as a solid line), Couette with strip running
Because the flow and the Poiseuille flow caused by the blowing interfere with each other in a complicated manner, as the line speed increases, the influence of the flow due to strip running becomes stronger. For this reason, as can be seen from Figure 4, the relative liquid flow velocity seen from the strip movement coordinate system tends to be relatively stable even when the line speed changes, and this is important for uniformity of alloy plating quality. is ideal.

When countercurrent blowing is performed in this way, the relative flow velocity is high, so mass transfer is good, the limiting current density is high, and burnt-like or powdery plating does not occur. Moreover, even if there are fluctuations in line speed during operation,
It can be seen that the relative flow velocity is stable, and therefore, the blowing method can always expect uniform mass transfer.

Next, a thin steel plate coil with a plate thickness of 0.3 m/m and a plate width of 200 mm was used to construct a two-stage counter-flow type horizontal tank (counter-current blowing 2 m ³ /min) and a fluid cushion according to the present invention shown in Fig. 1. Padded method (Unexamined Japanese Patent Application No. 58-136746) (Qc
= 2.0m ³ /min, Qc = ^{0.3m 3} /min), Zn-Fe
A series of alloy electroplating was produced. Electrolysis conditions are (Fe ²⁺ )/(Zn ²⁺ ) concentration molar ratio 1.0 to 2.5, bath temperature 50
~60℃, PH1.5~2.5, current density 50~150A/ ^dm2
Then, Zn--Fe plating was carried out with a plating deposition amount of 20 g/m ² by changing the line speed and the number of cells. The powdering resistance and the blister width under the electrodeposited coating were evaluated for each of the obtained plated steel sheets in the following manner. The results are summarized in a graph in FIG.

(i) Powdering resistance (alloy plating film processability)
Test method: Attach sellotape to the plated surface of a test piece with a width of 50 mm and a length of 200 mm, and place it along a round bar with a diameter of 10 mm.
Perform a 180° internal bend. Thereafter, the test piece is bent back and the tape is removed. At this time, the powdering resistance was evaluated according to the following grading based on the amount of plating powder that adhered to the tape surface.

○: Hardly any △: Slightly thin and fine plating powder adhesion ●: Dense, large plating powder adhesion (2) Test method for blister width under electrodeposition coating: Phosphate-based chemical conversion treatment and electrodeposition coating for automobile bodies After applying 20 μm of salt water spray test 500
Corrosion resistance after painting was evaluated based on the corrosion status of the cross cut portion after a period of time.

As is clear from the illustrated results, in the low speed, high current density region, powdering resistance (plating film workability) is poor, while in the high speed, low current density region, the η phase is easily precipitated and mixed. Blister corrosion is likely to occur at the cross-cut area of the paint film.

The range of good Zn--Fe alloy electroplating performance is wider in the case of the present invention than in the case of the fluid cushion pad method. This is considered to be because the liquid flow condition between the electrodes is more stable and uniform in the present invention.

[Brief explanation of drawings]

Figures 1a and b are schematic cross-sectional views of a horizontal continuous electroplating device according to the present invention; Figure 2 plots the amount of catenary in several methods versus the distance between energized rolls in a horizontal plating tank. Figure 3 is a graph showing the relationship between plating tank voltage and plating current density in order to compare the gas bubble removal performance in horizontal plating tanks; A graph showing the relationship between relative plating liquid speed and line speed to compare the stabilizing effect; and Figure 5 shows the relationship between plating current density and line speed to explain the effective area of plating quality. It is a graph. 1: continuous electroplating device, 2: metal strip, 3: plating tank, 4: energizing roll, 5: support roll, 6, 6': insoluble anode, 7, 8: spout nozzle, 9: plating liquid conduit.

Claims (1)

[Scope of Claims] 1. A horizontal continuous electroplating device for metal strips, comprising: an insoluble anode disposed facing away from a metal strip running in the horizontal direction; and a pair of front and rear current-carrying rolls in contact with the metal strip; an intermediate support roll provided at an intermediate position between the pair of energizing rolls; an insoluble anode disposed in a pair of upper and lower positions between the intermediate support roll and each of the energizing rolls; and a horizontal direction with respect to the insoluble anode. provided near the downstream end in the running direction of the metal strip of at least one conduit surrounded by the metal strip running in the pipe, and opening in a countercurrent direction to the running direction of the metal strip toward the conduit; and at least one plating liquid injection nozzle in which the discharge angle between the metal strip and the plating liquid injection flow is within 60 degrees.