KR900008255B1 - Counter flow device for electroplating apparatus - Google Patents

Abstract

Rotating drum electroplating device with counter flow of electrolyte and strip to be plated includes a bottom nozzle whose opening is opposite to the entering direction of the strip, and a top nozzle whose tip is immersed in the proximity of the surface of the electrolyte where the strip leaves the electrolyte.

Description

Backflow mechanism of electroplating device

1A is a center cross-sectional view of a conventional radial cell plating apparatus.

FIG. 1B is a sectional view of the plating apparatus taken along line IB-IB in FIG. 1A.

2 is a graph comparing the relationship between the critical current density and the speed of the metal strip in downpass and uppass states.

3A is a graph illustrating Zn and Fe distribution in the depth direction of a Zn-Fe alloy plating layer plated by the prior art.

3b is a graph illustrating the distribution of Zn and Fe in a plated layer plated according to the present invention.

4 illustrates an arrangement of a base nozzle according to the present invention.

Figure 5 illustrates an arrangement of the top nozzle according to the present invention.

Figure 6a is a cross sectional view of a radial cell type bath in accordance with the present invention taken along the direction of travel of the strip.

FIG. 6B is a sectional view of the plating bath of FIG. 6A taken along the axis of the drum. FIG.

FIG. 6C is a sectional view of the plating bath taken along the line VIC-VIC in FIG. 6A.

FIG. 7A is a partial sectional view showing a modification of the base nozzle according to the present invention; FIG.

FIG. 7B is a cross sectional view taken along the line VIIB-VIIB in FIG. 7A;

FIG. 8 shows a plating liquid circulation system when using the base nozzle shown in FIG.

9 is a graph showing the relationship between the strip speed and the critical current density depending on the flow rate of the plating liquid between the electrodes.

FIG. 10 is a comparative graph showing the Fe distribution in the depth direction of the alloy plating layer depending on the spray angle θ of the plating liquid at the nozzle. FIG.

11a and 11b are schematic views for explaining the plating conversion of one side and both sides.

12 is a view for explaining the contraction of the top nozzle in the subsequent stage plating bath as an embodiment of the present invention.

13A is a cross-sectional view of the base nozzle capable of changing the spraying direction according to the present invention.

13B is a cross sectional view taken along the line XIIIB-XIIIB in FIG. 13A.

* Explanation of symbols for main parts of the drawings

1 strip 2 plating bath

3: Rotary Drum 4: Roll

5: anode 6, 7: nozzle

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backflow mechanism for an electroplating apparatus of a metal strip, particularly a backflow mechanism for an electroplating apparatus having a radial cell type plating bath capable of plating a metal strip traveling through a bath at a low current density at a high current density.

The radial cell plating apparatus is equipped with a large diameter rotary drum with approximately half of itself submerged in the plating solution or electrolyte. The metal strip contacts approximately half of the drum circumferential surface and passes approximately in synchronism with the rotation of the drum, during which it flows through the plating liquid between the strip and the anode spaced apart by a radial flow gap from the strip. Current is generated.

Such a plating apparatus is advantageously used to plate only one side of the strip because of its inherent structure, and high speed plating can be performed at high power by minimizing the gap between the anode and the strip as much as possible to avoid unnecessary consumption of plating power. Will be.

There are generally two cases in such electroplating systems, one using insoluble electrodes for the anode and the other using soluble electrodes composed mainly of the same metal as the plating material. In particular, the latter case using a soluble electrode is suitable for obtaining a thick plated layer with high power since it has the advantage that the plated metal is easily replenished and little gas is generated at the positive surface.

In the plating system used up to now, as shown in FIGS. 1A and 1B, the metal is sprayed upward from the inlet 2 'of the base of the plating tank 2 toward the rotary drum 3 to the strip 1 so that the metal The gap is provided between the strip 1 and the pair of anodes 5. The metal strip 1 is transported along the rotary drum 3 in contact with the outer surface of the rotary drum 3. The pair of anodes 5 are arcuate in cross section and are arranged side by side facing each other in the direction of movement of the strip and in the lower half of the circumferential surface of the drum 3.

Thus, the plating liquid flows in the opposite direction to the movement of the strip on the inlet side of the strip (hereinafter referred to as downpass) but on the outlet side of the strip in the same direction as the movement of the strip (hereinafter referred to as uppass). It has been thought that high current density is desirable in electroplating because the required plating is obtained at higher plating speeds or smaller plating apparatuses, however, if the current density is too high above the limit, a treelike electric deposit will occur. deposits often occur on the surface of metal strips, particularly at the edges of the strip, often resulting in defects such as "burns" or "black spots" due to excessive concentration of current.

Such critical current density varies with plating conditions such as the composition and temperature of the plating liquid, among which the relative speed between the strip and the plating liquid greatly affects the critical current density.

As a result, in the conventional radial cell type plating bath or plating tank as shown in FIG. 1, the relative speed between the metal strip and the plating liquid becomes much smaller in the above-mentioned "uppass" in which the strip and the plating liquid move in the same direction. In particular, the low speed of movement of the strip makes the critical current density even smaller, thereby increasing the tendency to generate "carburism" at the edge of the strip. As shown in FIG. 2, which illustrates an example of the relationship between the critical current density and the speed of the metal strip, a "carburet" occurred in the "uppass" even under favorable conditions for plating in the "downpass". Therefore, it was necessary to lower the speed of the metal strip further in order to reduce all supply currents and to avoid burns. In other words, disadvantageous operations were forced to plate the metal strips.

In recent years, the demand for corrosion resistance has become even more severe, and various types of alloy plating have actually been used instead of the single metal plating used up to now. For plating, the use of multi-metal alloys such as Zn-Ni-Co, Zn-Ni-Cr, as well as binary alloys such as Zn-Ni, Zn-Fe, etc. has been studied.

In plating using this alloy, deposits of alloying components are sensitively affected by the plating conditions. In other words, variations in current density and flow rate of the electrolyte greatly affect the composition of the alloy to be plated. In FIG. 3A illustrating an example of Zn and Fe distribution by IMMA (Ion Mass Micro Analysis) of a Zn-Fe alloy plating layer plated by a radial cell type plating apparatus used so far, the Fe and Zn contents are either thick or It can be seen that the depth varies considerably. In this case, unstable black band forms occur on the surface of the strip, possibly due to the irregular flow rate of the electrolyte, which significantly deteriorates the appearance of the metal strip.

SUMMARY OF THE INVENTION The main object of the present invention is to provide a backflow mechanism for a radial cell type electroplating apparatus, which backflow mechanism eliminates defects in the plated layer generated by the conventional apparatus and ensures that the plated layer obtains a good plating layer even at a low running speed of the strip therein. So that the instrument is used for the use of the substance.

This object can be achieved by a backflow mechanism of the plating apparatus, which comprises a rotary drum, wherein approximately half is immersed in the bath's plating liquid, wherein the drum is plated with a metal strip passing in synchronization with the rotation of the rotary drum. The anodes are spaced apart by a radial gap from the strip in order to allow current to flow between the strip and the anode, and the backflow mechanism according to the present invention is arranged at the base of the bath and at the same time the introduction of the strip A base nozzle having nozzle openings extending in a direction substantially opposite to the direction, and a top nozzle submerged near the surface of the plating liquid at a tip end of the nozzle opening where the strip leaves the plating liquid.

The top and base nozzles can inject the plating liquid from this opening between the strip and the anode at a linear speed of 0.2 to 2 m / sec. In particular, the top and base nozzles have a spraying direction of the plating liquid relative to the tangent of the rotary drum. It is preferably arranged so as to be inclined at an angle within 10 degrees.

Furthermore, the depth at which the tip end of the top nozzle is immersed in the plating liquid should be deeper than 15 mm from the surface of the plating liquid at rest. As the jet flow moves from the nozzle, the surface of the plating bath is lowered by about 10 mm from the stationary plating liquid to contain air. To avoid this, the tip end of the top nozzle should be locked to a depth of at least 15 mm from the surface of the plating bath at rest.

In addition, in the direction of movement of the strip, the overlapping lengths of the edges of the anodes and the top and base nozzles are 10 mm or less at the top nozzle and 2 mm or less at the base nozzle. This feature is particularly important in the radial cell type plating apparatus of a soluble anode having a plurality of anodes having an arcuate cross section disposed on a locked bus bar in order to be able to move radially as the anodes are consumed.

With the above arrangement of the invention, the plating liquid is forced in a direction opposite to the direction of movement of the strip in which the exit direction of the strip as well as the direction of introduction of the strip into the plating liquid within the current flow gap between the metal strip and the arcuate electrodes is present. By circulating, all of the conventional disadvantages are eliminated.

Figure 3b illustrates the content of Fe and Zn distribution in the Zn-Fe alloy coating layer plated with the backflow mechanism according to the present invention by ion mass micro analysis (IMMA). It can be seen from Fig. 3b that the distribution of Fe and Zn is quite uniform according to the present invention.

The invention will be more clearly understood by reference to the following detailed description and claims in conjunction with the accompanying drawings.

3 and 5 illustrate examples of the base nozzle 6 and the top nozzle 7 according to the invention, respectively. 6a, 6b and 6c exemplarily illustrate a radial cell type plating tank or plating bath having a backflow mechanism in accordance with the invention in which the circulation system is improved by using the nozzles shown in FIGS. 4 and 5.

Each nozzle 6 or 7 has at its tip end a conduit 6a or 7a having an opening facing in the direction opposite to the direction of movement of the strip 1. This conduit 6a or 7a is in communication with a plene chamber or header connected to the pump for circulating the plating liquid or electrolyte. Reference numeral 6c or 7c denotes a reinforcing rib. The top nozzle 7 shown in FIG. 5 is an example of a nozzle having one coupling 7d in order to install the nozzle detachably.

6A, 6B and 6C, the circulating plating liquid or electrolyte is introduced into the plating liquid circulation piping 8 and 9 having the sleeve joints 10 and 11 in order to maintain a predetermined pressure in the headers 6b and 7b. By receiving the force in the direction of the arrows α and β, the plating liquid from the top, the openings of the base nozzles 6 and 7 is transferred to the strips shown by arrows r in both the downpass and uppath of the strip 1. Reverse flow in the direction of movement. The surface level of the plating liquid in the plating liquid tank 2 is kept constant with the aid of an overflow weir 12 into which the overflowed solution is introduced into the circulation pump.

7a and 7b illustrate one variant of the base nozzle 6 in which the new plating liquid is circulated into the downpass in the same way as in the top nozzle 7 so that the solution passed through the uppass is passed to the base nozzle. Prevent mixing with fresh solution sprayed in (6).

That is, the conduit 6a and the header 6b of the base nozzle 6 are divided into upstream and downstream portions by the partition 6d. The downstream portion is formed as a suction port 6c which communicates with the return pipe 8 'along the uppath so that the passage solution can be discharged without mixing with the fresh solution. Reference numerals 13 in FIGS. 7A and 7B are separators, such as soft brushes or sponges, arranged on top of the partition 6d and are in intimate contact with the strip 1 between the uppass and the downpass.

The base nozzle 6 of this type serves to flow the plating liquid in the same way as in the upper nozzle 7 and also to serve to effectively remove the gas during the uppass, and the gas is an arcuate cross section anode 5 Is generated in large quantities when insoluble.

FIG. 8 shows a schematic diagram of the operation of a radial cell plating tank having a backflow mechanism using the base nozzle 6 described in FIGS. 7A and 7B.

9 illustrates the effect of strip speed on the critical current density A / dm ² . In this experiment, the composition of the plating bath is typical, such as 200 g / l ZnCl ₂ and 300 g / l KCl. The plating liquid is fed through the top, base nozzles 6 and 7 at flow rates of 0.1, 0.2, 1 and 2 m / sec at a temperature of 50 ° C. As the ordinate represents the critical current density, the area of the intersegment of the flow velocity of the plating liquid as a parameter indicates a forbidden area in which "carburism" tends to occur.

If the flow rate of the plating liquid is 0.2 m / sec or less, the desire to perform plating with high efficiency at a higher current density cannot be fulfilled. On the other hand, if the circulation plating liquid flows at a speed higher than 2 m / sec, an excessively large capacity pump is required, which is disadvantageous in terms of installation cost. Therefore, the flow rate of the plating liquid is preferably 0.2 to 2 m / sec.

Next, Zn-Fe alloy plating aimed at a Fe content of 20% is performed to obtain a plating layer of 20 g / m ² under the following plating conditions.

Composition of plating bath: ZnCl ₂ 200g / l, KCl 300g / l, FeCl ₂ 4H ₂ O 100g / l

Plating bath temperature: 50 ℃

Current density: 100A / dm ²

The Fe content of the obtained alloy layer is measured in the thickness direction according to IMMA. As shown in FIG. 10 to illustrate the measurement result, when the spray angle θ of the plating liquid at the top, the base nozzles 6 and 7 is more than ± 10 ° with respect to the tangent to the rotary drum 3, the surface layer and the base wire are separated. The Fe content in the alloy plating layer of is significantly reduced to 20% or less, so that a uniform alloy composition cannot be obtained. In contrast, a substantially uniform alloy composition can be obtained with an injection angle within ± 10 °.

If a soluble electrode is used in either case, a plurality of anodes having an arcuate cross section are placed side by side above and downstream of the base nozzle sandwiched therebetween, with locked bus bars 21 (Fig. 6a). It is arranged above and also slightly inclined with respect to the generator of the rotary drum in the plating bath so that the anodes can be moved radially in accordance with the consumption of the anodes to maintain the spacing between the electrodes to an appropriate value. In this case, since the anodes having an arcuate cross section are slightly inclined with respect to the horizontal line, if the overlap between the anode and the tip end of the nozzle (symbols 22 and 23 in the fourth and fifth degrees) is too large, the anode portion is the anode portion. It is wrapped by a nozzle to block backflow through it to prevent it from dissolving. Thus, these anode portions remain undissolved and are likely to be in accidental contact with the nozzles as they extend beyond the normal anode surface. In a preferred embodiment of the invention, the overlap length of the nozzles in the direction of movement of the strip is 10 mm or less for the top nozzle and 5 mm or less for the base nozzle.

In addition, a so-called basket system can also be used in some cases, in which a basket is mainly composed of metal nets, which contain soluble metal in granular or lump form. In this case, the space between the electrodes need not be fixed because the basket can be fixed. The basket is sometimes used as a safety measure for the top, base nozzle.

During plating using the radial cell plating bath, two baths are often used integrally. Referring to FIGS. 11A and 11B to illustrate the same thing as the one example, the deflector rolls 4 ', 4 "running straight on as shown in FIG. 11A, or as shown in FIG. 11B. And 4 "), it is necessary to select either of the two-sided plating which bypasses. While the one-side plating changes to double-sided plating, the moving direction of the strip is reversed in the plating bath 2 on the downstream side, and the spraying direction of the base nozzle 6 'is reversed so that the upper nozzle 7 in FIG. It is necessary to change ') to (7 "). Such a change is difficult.

In order to avoid such a difficult operation for the top nozzle 7 ', the support 14 of the intermediate deflector roll 4, as shown in FIG. 12, partially illustrating one example of a plating bath on the downstream side. In the ground of the bracket, a hawk-like bracket 15 is fixed. In the web of the bracket, a long groove is formed in the web of the bracket to support the head nozzle 7 'and the support 17 supporting the head 7b'. Guided along 16) to move forward and backward. As observed in FIG. 12, one of the right or left top nozzles is used along the direction of movement of the strip. Other unused nozzles naturally enter the non-operational position represented by the phantom line in FIG.

For the base nozzle 6 ', as shown in Figs. 13A and 13B, the head 6b' is provided with two nozzle openings A and B respectively directed in the downpass and uppass directions, between them. A swingable flap 18 is suspended to selectively switch between the positions of the solid and imaginary lines, thereby easily reversing the spraying direction of the plating liquid to cope with difficult problems. In Fig. 13B, reference numeral 19 denotes a pivot axis for the flap 18 and reference numeral 20 denotes a conversion lever.

As can be seen from the above description, the backflow mechanism according to the invention comprises a top, base nozzle suitably arranged to generate a constant backflow over the entire gap between the metal strip and the electrodes, thereby increasing the critical current density significantly. In the case of alloy plating, it is advantageous to realize uniform plating.

While the invention has been particularly shown and described with reference to the preferred embodiments, it will be apparent to those skilled in the art that other changes in the foregoing contents, forms or details may be made without departing from the spirit and scope of the invention. Will be understood.

Claims (9)

A rotary drum immersed in about half the plating liquid in the plating bath and a metal strip which is plated and passed in synchronization with the rotation of the rotary drum around the drum, and radially from the strip so that current flows between the strip and the anode. A backflow mechanism for a plating apparatus including anodes spaced apart by a gap, comprising: a base nozzle disposed at the base of the plating bath and having a nozzle opening in a direction substantially opposite to the introduction direction of the strip; And a top nozzle in a displaced position, the top end having a nozzle opening, the tip end of which is immersed near the surface of the plating liquid. 2. The backflow mechanism of an electroplating apparatus according to claim 1, wherein the upper and base nozzles can inject a plating liquid from the opening portion between the strip and the anode at a linear speed of 0.2 to 2 m / sec. 2. The backflow mechanism of an electroplating apparatus according to claim 1, wherein the upper and base nozzles are arranged to allow the spraying direction of the plating liquid to be inclined at an angle within 10 degrees with respect to the tangent of the rotary drum. 2. The backflow mechanism of an electroplating apparatus according to claim 1, wherein the locking depth of the tip end of the upper nozzle in the plating liquid is 15 mm or more from the surface of the plating liquid in the stationary state. 2. The backflow of the electroplating apparatus according to claim 1, wherein an overlapping length of the edge of the anode, the upper end and the base nozzle in the moving direction of the strip is within 10 mm for the upper nozzle and 2 mm for the base nozzle. Instrument. The method of claim 1, wherein the base nozzle includes a conduit and a header divided into an upstream portion and a downstream portion by a partition wall; The downstream portion has a suction port connected to the return pipe for discharging the plating liquid sprayed from the upper nozzle and is formed along the moving direction of the strip, and flows toward the base nozzle without mixing with the new plating liquid sprayed from the base nozzle. Backflow mechanism of electroplating apparatus. 7. The base nozzle of claim 6, wherein the base nozzle comprises a separator disposed at the top of the partition between the upstream and downstream portions to make intimate contact with the strip, and the separator is made of a soft material such as a brush, sponge material, or the like. Backflow mechanism for electroplating apparatus, characterized in that made. 2. The buried portion according to claim 1, wherein in the case of integrating the two plating baths, the web is formed into grooves as guide means between the two rotary drums of the plating bath and from above the lower side of the support for the deflector roll. The bracket is fixed and each support for transporting the upper nozzles along with their headers along their grooves is retractable from the respective rotary drum, so that one of the top nozzles is adapted to the change in the direction of movement of the strip. Therefore, the backflow mechanism of the electroplating apparatus, characterized in that when not in use is retracted to the non-operational position. 2. The nozzle of claim 1, wherein the base nozzle comprises: two nozzle openings facing in opposite directions; A rotatable flap suspended between the two nozzle openings and selectively switched to block either one of the two nozzle openings in accordance with a change in the direction of movement of the strip; Backflow mechanism of the electroplating apparatus, characterized in that it has a.

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