JPS6121319B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a horizontal fluid-supported electrolytic cell for electroplating strips and the like.

A vertical dipping method and a horizontal method are used to perform electroplating continuously. The superiority of electroplating methods is that they have equipment that can deposit metals at higher current densities and operate at lower voltages, and that they can provide products of superior quality. The strategy for increasing the current density is to increase the critical current density id, as shown by equation (1).

id=nFDC/δ...(1) id=Limiting current density (A/ ^cm2 ) n=Number of charges of metal ions F=Faraday's constant D=Diffusion coefficient of metal ions ( ^cm2 /sec) C=Metal ion concentration δ =Thickness of the diffusion layer To this end, increasing the concentration of metal ions, increasing the bath temperature, etc. can be proposed as measures to improve the solution surface.
On the other hand, it is known that the diffusion layer δ becomes smaller as the moving speed of the electrolytic surface plating solution increases, such as stirring or increasing the flow rate, so an electrolytic cell that can provide a uniform flow rate effect over the entire width of the strip is desirable. . or,
For low voltage operation, as expressed by equation (2),
Voltage increases due to strip resistance, liquid resistance, and gas accumulation must be considered.

V _T = Vd + Vs + Vl + Vg (2) V _T = Voltage between electrodes V _d = Decomposition voltage V _s = Voltage due to strip resistor Rs. Proportional to the effective length L from the conductor roll to the anode.

=I・Rs・L Vl=Voltage due to liquid resistance Re. Proportional to distance H between poles.

=I・Re・H Vg = voltage due to gas accumulation.

As is clear from equation (2) above, the key points of the Metsuki cell design to achieve low voltage operation are to shorten the distance between the electrodes as much as possible and to remove the oxygen gas generated at the anode from between the electrodes as quickly as possible. must be placed. It goes without saying that the arrangement of the conductor rolls and the plating bath and plating conditions with high conductivity should be adopted. Finally, the quality must not deteriorate compared to conventional low current density electrolysis within a critical current density.

Many technological developments have been made to improve electroplating methods and apparatuses in order to come as close as possible to the conditions described above. For example, special public service in the 1970s.
8020, in which the plating liquid is forced to circulate countercurrently in the direction of movement of the strip in a horizontal linear cell;
The method described in Japanese Patent Publication No. 46-7162, in which a strip is brought into contact with the surroundings of an energizing drum, and a curved anode is used close to the drum, and the method of plating through a slit or small hole provided in the anode, described in Japanese Patent Publication No. 54-138831. Method of plating while spraying liquid onto the strip, Tokkosho
45-7482, and another method using a jet flow (described in Metal Surface Technology 21, (3), 119 (1971)).

Each of these methods is an excellent storage method and has contributed to the development of high-efficiency cells. However, each of these has its own limitations and is difficult to meet as a highly efficient cell, which is required in recent years. For example, the 1980-8020 Special Publication Act (Iron and Steel Institute of Japan Lecture Conference Abstracts 1981-
Improvements to S334) have been proposed. But this
The ACIC method also has the problem that a uniform flow cannot be obtained, as will be described later. Also, Special Publication 1971-7162, Special Publication 1971-
Method 138831 is only for single-sided plating. Furthermore, the method disclosed in Japanese Patent Publication No. 45-7482 has limitations in supporting the strip and making the flow velocity distribution uniform in the width direction.

The present inventors have solved the problems with the conventional method described above, and have developed a method with a high current density of 200 A/dm ² and a distance between poles of 5 mm, which can cope with the recent increase in the electrical strength of electroplated steel sheets.
The purpose of this research was to provide a new high-efficiency electrolytic cell capable of close electrolysis, as well as to provide high-quality, inexpensive electroplated steel sheets. He invented and applied for a patent on an electrolytic method and device that maintains the plating solution between the electrodes by ejecting the liquid and at the same time supports it between the strip electrodes using the static pressure of the fluid generated at the time (Japanese Patent Laid-Open No. 56-127789 and 127799). This method and apparatus utilizes a pad with slits on the entire surface of the electrode itself, as shown in the specification and drawings.
Therefore, in the case of vertical electrolysis, the purpose of high efficiency electrolysis is fully achieved. However, if this prior invention is applied as is to a horizontal electrolytic cell, the plating liquid is likely to be confined within the slit because there is no free fall of the plating liquid, and the flow of the plating liquid becomes quite turbulent. Therefore, although the fluid supporting force for proximity is large, it is inferior in terms of ion supply and gas removal, and has the disadvantage that satisfactory results cannot always be obtained in achieving high current density.

In a horizontal electroplating device, the present invention provides a fluid pad in a part of the electrode, and uses the static pressure of the fluid pad to reduce the size of the catenary and support the strip. The present invention provides an ideal horizontal plating device that improves the flow of the plating liquid and enables stable supply of ions and rapid removal of gas.

As mentioned above, ACIC is currently the most excellent horizontal electrolytic cell. However, ACIC
However, there is a limit to how high efficiency can be achieved.

Below is the configuration and effects of the plating device of the present invention.
This will be explained in comparison with ACIC.

FIGS. 1 and 2 show basic cross-sectional structural diagrams of the present invention. In FIG. 1A, a box-shaped tank 2 containing an anode 1 is placed above and below a strip 3. A fluid pad 12 is introduced into the center of the box-shaped tank 2, and plating liquid is ejected from a header 10 toward the strip surface through a slit 16 provided on the surface of the fluid pad 12 facing the strip. The plating liquid flows out from the discharge ports 9 and 8, which are divided into the advancing direction of the strip (hereinafter referred to as parallel flow) and the direction opposite to the strip (hereinafter referred to as countercurrent flow). At the discharge ports 8 and 9, there are plated outflow rate control plates 11, which are moved up and down to control the gap with the strip and thereby control the flow rate. The plating liquid flowing out from the outflow ports 8 and 9 is stopped by the conductor roll 6 and back-up roll 7, is received in the receiving tank 4, enters the circulation tank (not shown) from the plating liquid outlet 5, and is sent to the header by a pump. Forced circulation to 10. Power is supplied from the conductor roll 6 to the strip and to the anode via the bus bar. The flow of liquid between the electrodes is illustrated using arrow symbols.

FIGS. 1B and 1C show an example of a cross-sectional view of the electrolytic cell of the present invention. In the same figure, B shows a cross-section taken along the line A-A' in Fig. A, and C shows a cross-section taken along the line B-B' in Fig. A. If necessary, the ends of the strips can also be provided with sealing mechanisms, for example edge masks 17 connected to horizontally movable supports 18. Further, when the edge mask 17 is not used or when the support 18 is accommodated within the tank, it is preferable that the side walls shown in FIG. 1B and C are integrated.

FIG. 2 is also a basic sectional structural diagram of the present invention.
In place of the plating liquid outflow control plate 11 shown in FIG. 1, liquid seal nozzles 13 are provided at the strip inlet 8 and the strip outlet 9. The liquid is supplied to the liquid seal nozzle 13 by branching from the liquid seal header 14 or the header 10. Additionally, as shown in the figure, a baffle plate 15 is installed to prevent the strip from coming into contact with the anode 1.
is attached to the anode.

FIG. 3 is a plan view of FIG. 2 viewed from the strip surface. The edge sealing mechanism 17 indicated by the dotted line is installed on both sides of the strip and has the effect of increasing the static pressure inside the electrolytic cell and making the flow velocity distribution uniform in the width direction of the strip. The sealing mechanism can also be accomplished by a liquid curtain or conventional edge mask, which moves across the width of the strip and brings it into close proximity to reduce plating edge overcoat and backing.

A slit 16 is provided in the fluid pad 12 . Naturally, the liquid seal nozzle is also provided with a slit 16'. The shape, gap, angle, etc. of the slit are determined by design according to the purpose, as will be described later. 1 and 2 show the basic configuration of the present invention, and the position and functional application of the fluid pads are naturally included in the present invention. For example, the present invention also includes an example in which the fluid pad 12 is made vertically movable independently from the box-shaped tank 2, a multiplicity of liquid seal nozzles 13, a mechanism for changing the spray angle of the slit, and a fluid pad used in the seal nozzle. This is an example.

Furthermore, the presence or absence of an edge seal mechanism, its structure and arrangement, the presence or absence of an edge mask 17, its structure, arrangement, and movement mechanism are also included in the horizontal fluid support electrolytic cell using the fluid pad of the present invention.

FIG. 4 shows an example of the configuration of the slit provided in the fluid pad. In both cases, static pressure is generated within the plane surrounded by the slit. A is a single slit structure, B is an example in which one or more slits are provided parallel to the direction of strip movement, and C, E, O, and F are inclined with respect to the direction of strip movement. , an example of giving a curve,
K and K are examples of double slits.

FIG. 5 is an example of a schematic cross-sectional view of the fluid pad portion viewed from the strip width direction. Naturally, it changes depending on the nozzle shape shown in FIG. Slit gap t
The angle θ, the distance between slits ls, etc. are determined according to the purpose. Further, the distance h between the strip and the fluid pad has an important relationship with the strip supporting force F, as will be described later. FIG. 6 is an example of a cross-sectional view of the fluid pad seen from the strip advancing direction, and A is a reverse funnel type bottom plate 19 of the fluid pad facing the strip.
A slit 16 is provided in the. A is an example of a box-shaped structure. Note that the anode plate 19 may be made of a conductive material, or may be made of an insulating material.
When used as an anode, from the viewpoint of preventing uneven plating, among the slit shapes shown in FIG. 4, inclined structures and curved structures are preferable. Inside the fluid pad 12, as shown in FIG. 6A, a baffle plate 20 may be provided to provide a uniform flow in order to obtain a well-balanced flow velocity from the slit 16.
In addition, the volume within the fluid pad is sufficient as long as it functions as a buffer tank for the liquid ejected from the slit, and there is no need for it to have a large structure (height).
A compact design is possible.

Next, the functions and effects of the electrolytic cell of the present invention will be explained in detail.

The present invention supports the strip by the static pressure created by the fluid pads described above and allows electrolysis at close interpolar distances. In addition, it is possible to control the flow velocity balance of parallel flow and countercurrent flow depending on the speed of the strip, which could not be controlled with known horizontal cells, and it is also a breakthrough that solves the problem of eliminating eddy current and enables high current density electrolysis. It is a typical electrolytic cell.

One of the challenges in the horizontal plating process is the strip catenary. The strip between the conductor rolls has a catenary with a large bow due to its own weight and the difference between the upper and lower liquid pools, and there is a limit to how close the poles can be brought together. The present invention solves this problem by using fluid support. FIG. 7 shows a diagram regarding the fluid support mechanism. Now, the fluid pads 12 are placed between the strips 3, and the plating liquid is jetted out from the slit 16 at the gap t at a flow rate U. Static pressures Pr and Pl develop between the fluid pad and the strip. This static pressure can be expressed by the following equation when the distance between the poles is h ₀ and the upper and lower poles are equal, and the density of the plating liquid is ρ.

Pr=Pl=ρU ² t・1/h ₀ Now, if the strip moves downward by △h (to the position of chain line 3a), Pr>Pl, and the difference △P between the upper and lower static pressures is calculated from the following equation. Proportional to △h △P=Pr−Pl=2ρU ² t・1/h ₀・△h △P=k・△h. That is, the larger Δh is, the more the strip is pushed back upward by a larger static force and is naturally centered.

Next, FIG. 8 shows the relationship between the displacement (catenary) of the strip and static pressure in the present invention shown in FIG. 2. A is a block diagram of the present invention in which the roll distance is 2500 mm, the strip tension is 0.72 Kg/mm ² , the thickness of the strip is 0.4 mm, and the width is 1000 mm. The fluid pad has a slit shape as shown in Figure 4A, and θ=90°, t= in Figure 5.
4 mm, ls = 200 mm, h = 10 mm, and the one shown in Figure 6 A was used. A known edge mask was used as the edge seal mechanism and was set 10 mm from the strip edge. Liquid seal nozzle slit is 1.5mm
The gap was used. In Figure 8 A, the central part between the electrodes is 0.
The catenary on the bottom side of the strip was measured using a displacement meter. Curve b shows the catenary caused by the weight of the strip, and curve a shows the catenary caused by the difference between the upper and lower liquid pools when water is ejected from a known electrolytic cell. As is clear from the figure, under such tension conditions, the catenary extends over 10 mm, making it impossible to bring the poles closer together. Curve c is a displacement curve obtained by ejecting plating liquid from liquid pad Q ₁ at a flow rate of 0.8 m ³ /min in the present invention. The static pressure distributions at the top and bottom of the strip at this time are shown in C _T (top) and C _B (bottom), respectively, in Figure 8C. The strip is centered in a W-shape and the catenary is kept below 4mm. Furthermore, liquid seal parts Q ₂ and Q ₃
When plating liquid is ejected at a flow rate of 0.1 m ³ /min and 0.2 m ³ /min, the static pressures are d _T (top) and d _B (bottom).
and the catenary of the _strip is less than 1 _mm when Q ₂ = Q ₃ = 0.1 m ³ /min (curve d in Figure 8), and when Q ₂ = Q ₃ = 0.2 m ³ /min. 0.5mm or less (No. 8
It can be suppressed to the curve e) in the figure. This is because Q ₂ and Q ₃ increase the overall static pressure within the electrolytic cell, increasing the centering effect.

FIG. 9 shows the electrolytic cell configuration of the ACIC communication example described above. In this system, the fluid supporting force at the center depends on the dynamic pressure ejected from the liquid discharge part 18, and the centering effect is weak. Also, if the strip tension is 1Kg/ ^mm2 , the maximum catenary will reach 15mm, and to make it 5mm, the tension must be 3 to 4Kg/mm2.
Must be mm ² .

As described in detail, the present invention is an epoch-making electrolytic cell in which the strip is centered by the static pressure of the fluid even under extremely small strip tension conditions. In particular, the mutual effect of liquid sealing of Q ₂ and Q ₃ is large, and improving static pressure in a non-contact state is extremely effective in suppressing catenary and is an epoch-making invention.

FIG. 10 shows measurement results corresponding to FIG. 8 without an edge mask. Curve a shows almost the same results, but there are differences in c and de. The catenary is smaller when Edgemask is installed. However, the centering effect of the strip is fully demonstrated even without the edge mask.

The functions and effects of the present invention for parallel flow and counterflow will be described in detail below.

The method disclosed in Japanese Patent Publication No. 50-8020 in which the plating liquid is forced to circulate countercurrently to the strip is effective in increasing the critical flow density. However, as the stripping speed increases, the flow within the electrolytic cell is likely to become turbulent due to the viscosity of the liquid, and gas removal and ion supply generated at the anode become problematic. Therefore, it is necessary to provide a large flow rate, and the limiting current density is also 50
~100A/ ^dm2 . Next, in the case of ACIC, there is a problem with the balance between parallel flow and countercurrent flow. That is, the parallel flow side has good ion supply and gas removal, but the relative velocity of the diffusion layer δ is low. Also, it is difficult to supply ions and remove gas on the counterflow side. ACIC is a special public corporation Showa 50-8020
Compared to this, there is a significant improvement effect, and the limiting current density also increases. However, the problem remains that gas removal is difficult due to turbulent flow and countercurrent flow, which depend on increasing the speed of the strip.

As mentioned above, the present invention reduces the number of catenaries in the strip to enable the electrodes to be brought closer to each other, and also solves the fluid problems of the conventional method by controlling the split flow of the electrolyte using a liquid seal mechanism. be able to.

FIG. 12 shows the relationship of the strip speed V on the flow velocity _UP of the parallel flow and the flow velocity _UR of the counterflow, measured by the current meter 21 installed in the electrolytic cell shown in FIG. 11. FIG. 12 P ₁ to P ₄ indicate parallel flow, and R ₁ 9R ₄ indicate counter flow. The flow velocity difference ΔU is the strip speed V=O
The liquid velocity flows U and V at 25, 50, 75, and 100 m/
This is the difference from the liquid flow rate U in minutes. [P ₁ and R ₁ ]
is the plating flow rate by dynamic pressure control without using a fluid pad.
The results for the case of 0.8 m ³ /min and [P ₂ and R ₂ ], [P ₃ and
R ₃ ], [P ₄ and R ₄ ] are the fluid pad flow rate Q ₁ = 0.8 m ³ /min using the fluid pad of the present invention, and the flow rates of the liquid seal are [Q ₂ = Q ₃ = 0] and [Q ₂ = Q ₃ = 0.1m ³ /min],
This is the flow velocity when [Q ₂ = Q ₃ = 0.2 m ³ /min].
As described above, in the present invention, a uniform flow velocity with little difference in flow velocity can be obtained between the parallel flow and the counterflow by the flow rate control by the flow dividing effect of the fluid pad and the liquid seal. In addition, in a fluid experiment in which the electrode was changed to a transparent acrylic plate, a tuft to observe the direction of flow was attached to the acrylic electrode surface, and when observed, uniform streamlines were observed that were divided into front and back sections in the longitudinal direction of the strip in both parallel and countercurrent flows. It was confirmed that Furthermore, it was confirmed that by controlling Q ₂ and Q ₃ with respect to V, a perfect distributed flow could be obtained.
For example, the strip speed is V=100
m/min, the fluid pad flow rate Q ₁ =0.8 m ³ /min, the liquid seal flow rate Q ₃ =0.2 m ³ /min, and Q ₃ =0 are obtained. or
A nearly perfect distributed flow can also be obtained by controlling Q ₂ and Q ₃ and adjusting the angle of the slit nozzle of the fluid pad. For example, when V=200 m/min, the angle θ of the slit 16 on the parallel flow side of the lower fluid pad 12 ⁱⁿ FIG _. minutes, Q ₂ = Q ₃ = 0.15
m ³ /min, and no gas accumulation occurs.

The effect of the distributed flow independent of the strip speed V in the present invention can be explained as follows. The fluid pad located in the center acts as a kind of wall due to its static pressure and blocks the plating liquid from being brought in by the strip. On the other hand, the removal of the plating liquid by the strip in parallel flow is controlled by a liquid curtain on the outlet side of the strip, and the flow rate on both sides sandwiching the fluid pad is divided, reducing the difference in flow velocity. In order to obtain a uniform flow velocity, it may be effective in some cases to position the fluid pad not at the center of the electrode 1, but to shift it back and forth from the center. Furthermore, as mentioned above, the slit angle θ is also effective.

The effects of the present invention on parallel flow and counterflow have been described above. Finally, FIG. 13 shows an example in which electrogalvanizing was performed using the electrolytic cell of the present invention under the conditions of [P ₄ and R ₄ ] in FIG. 12. strip speed 100
The relationship between current density in m/min and voltage between electrodes is shown.
In the figure, Vd is the decomposition voltage, and Vs is the voltage due to the strip resistor. H=5, H=7.5, H=10, and H=15 indicate the voltages when the distance between the electrodes is 5 mm, 7.5 mm, 10 mm, and 15 mm, respectively. The straight line was drawn by calculation, and the 〇, △, □, and ● marks near the straight line are actually measured values. Even at a current density of 200 A/dm ² , which was difficult with the conventional technology, the current density was almost linear, and no abnormal voltage increase due to gas accumulation was observed, and no plating loss occurred. Furthermore, since the catenary can be reduced due to the hydrostatic fluid support, the distance between the poles can be greatly shortened, making it possible to operate at a low voltage of 200 A/dm ² -12 V.

As described above in detail regarding the structure, fluid support, uniform flow rate effect, and plating of the electrolytic cell of the present invention, the present invention is an epoch-making invention that enables highly efficient electrolysis that could not be achieved with known techniques. .

[Brief explanation of the drawing]

FIG. 1A shows a sectional view of the electrolytic cell of the present invention. FIGS. 1B and 1C show cross-sectional views of the electrolytic cell of the present invention. FIG. 2 is a cross-sectional configuration diagram of the present invention in which the liquid seal nozzle 13 is arranged. FIG. 3 is a plan view seen from the strip surface of FIG. 2, and shows an example in which an edge mask 17 is attached. FIG. 4 is a plan view of the slit of the fluid pad 12. 5 and 6 are basic cross-sectional views of the fluid pad. FIG. 7 is a diagram showing an automatic strip centering mechanism using a fluid pad. FIG. 8 shows an embodiment of the invention. The catenary A and static pressure C of the strip are shown for the configuration A. FIG. 9 shows ACIC as a known example. FIG. 10 is a diagram of the catenary of the strip in an embodiment in which no edge mask is used, corresponding to FIG. 8. 11th
The figure shows an example in which the flow velocities of parallel flow and counterflow before and after the fluid pad ₁₂ were measured, and _{FIG . 12} shows the results _{. 4} ]
is the result of the present invention. Figure 13 is an example showing the relationship between current density and voltage when electrogalvanizing is performed under the conditions of [P ₄ , R ₄ ] in Figure 12. The straight lines are calculated values and are marked with 〇, △, □, and ●. is the measurement result. 1... Anode, 2... Box-shaped tank with a rectangular cross section, 3...
Strip, 4... Receiver, 5... Plating liquid outlet, 6... Conductor roll, 7... Backup roll, 8... Strip inlet (plating liquid discharge), 9... Strip outlet (plating liquid discharge) ,1
0...Plating liquid supply header, 11...Plating liquid outflow control plate, 12...Fluid pad, 13...Liquid seal nozzle, 14...Liquid seal header, 15
...Baffle plate, 16, 16'...Slit, 17...
... Edge mask, 18 ... Liquid discharge part, 19 ... Fluid pad bottom plate, 20 ... Baffle plate that provides uniform flow,
21... Velocity meter.

Claims (1)

[Scope of Claims] 1. In an electrolytic cell in which anodes made of an insoluble material are disposed facing each other on both upper and lower surfaces of a strip to be plated that passes horizontally, a hydrostatic fluid support pad is provided opposite to the strip surface, and a pad that supports the strip as it advances. 1. A strip horizontal fluid support electrolytic cell, characterized in that anodes are disposed on both sides of the strip, and an electrolyte outflow control mechanism is provided on the inlet and outlet sides of the anodes. 2. The horizontal fluid support electrolytic cell according to claim 1, wherein a hydrostatic fluid support pad is provided at the center of the electrolytic cell in the direction of strip movement. 3. Claim 1, wherein the electrolytic solution outflow amount control mechanism is a liquid sealing device having an electrolytic solution injection means.
Horizontal fluid-supported electrolytic cell as described in . 4. The horizontal fluid support electrolytic cell according to claim 1, 2 or 3, wherein an electrolyte sealing mechanism is provided near a position corresponding to the widthwise end of the strip. 5. The horizontal fluid support electrolytic cell according to claim 4, wherein the electrolyte sealing mechanism is an edge mask.