GB2093863A

GB2093863A - Method for electroplating steel strip and electroplating apparatus

Info

Publication number: GB2093863A
Application number: GB8205487A
Authority: GB
Original assignee: Nippon Kokan Ltd
Current assignee: JFE Engineering Corp
Priority date: 1981-02-24
Filing date: 1982-02-24
Publication date: 1982-09-08
Also published as: FR2500490B1; GB2093863B; AU8053282A; DE3206457A1; DE3206457C2; AU530006B2; FR2500490A1

Abstract

Disclosed is a method for electroplating a steel strip (13) by arranging a plurality of electrode rows (18a, 18b, 19a, 19b) each consisting of a plurality of electrodes (18, 19) disposed adjacent to each other along the direction of width of said steel strip (13) in opposition to said strip (13) travelling in an electrolytic cell (12) holding an electrolytic solution (11), so that a metal constituting said electrodes (18, 19) may be electroplated on said steel strip (13), comprising the steps of intermittently or continuously transferring said electrodes (18, 19) of said electrode rows (18a, 18b, 19a, 19b) in a direction perpendicularly to the direction of travel of said steel strip (13) at a speed so that a distribution of a deposition amount of the metal of said electrodes (18, 19) along the direction of width of said steel strip (13) may be kept within an allowable tolerance, a width of said electrode rows (18a, 18b, 19a, 19b) being greater than the width of said steel strip (13); and unloading said electrode (18, 19) from one end of one of said electrode rows (18a, 18b, 19a, 19b) transferred by said transferring step and loading said electrode (18, 19) to the other end of said one electrode row (18a, 18b, 19a, 19b) or to an end of another of said electrode rows (19a, 19b). <IMAGE>

Description

SPECIFICATION Method for electroplating steel strip and electroplating apparatus The present invention relates to a method for electroplating a metal strip in a soluble anode system using zinc, tin or other metals as an electrode material, and an apparatus for the same.

According to the electroplating method of a steel strip in a soluble anode system, electrodes of a metal for electroplating are arranged in an electrolytic solution in opposition to one or both surfaces of a steel strip. A current is flown using the electrodes as an anode and the steel strip as a cathode, so that the metal of the electrodes may be deposited on the steel strip by electrolysis.

Apparatuses for practicing such electroplating method include those of horizontal type, vertical type and radial type.

In a horizontal type electroplating apparatus, as shown in Figs. 1 A and 1 B, a plurality of electrode rows 2, each consisting of a plurality of electrodes arranged horizontally and perpendicularly to the direction of travel of a steel strip 1, are disposed below and above the steel strip 1 travelling horizontally within an electrolytic solution 4. Each electrode row is immersed in the electrolytic solution 4 and is connected to busbars 3.

In a vertical type electroplating apparatus, as shown in Fig. 2, electrode rows 2, each consisting of a plurality of electrodes arranged horizontally and perpendicularly to the direction of travel of the steel strip 1, are arranged at the input side and the output side of a sink roll 6 in opposition to both surfaces of the steel strip 1 which is transferred in a U-shaped form by vertically arranged conductor rolls 5 and the sink roll 6.

In a radial type electroplating apparatus, as shown in Fig. 3, two electrode rows 2, each consisting of a plurality of electrodes arranged perpendicularly to the direction of travel of the steel strip 1 are arranged in opposition to both surfaces of the steel strip 1 which is curved in an arc shape by a conductor roll 7.

In these horizontal type and vertical type electroplating apparatuses, the width of the electrode row 2 is set to be narrower than that of the steep strip 1 by a predetermined amount. This is for the purpose of avoiding the problems to be described below when the width of the electrode row 2 is greater than or excessively smaller than that of the steel strip 1.

When the width of the electrode row 2 is greater than that of the steel strip 1, problems (1) and (2) to be described below occur: (1) As shown in Fig. 4A, the current from the electrodes 2 is concentrated at the edge portions of the steel strip 1, 50 that the metal film formed at these edge portions becomes thicker.

(2) As shown in Fig. 4B, since the thickness of only electrodes 8a opposed to the steel strip 1 decreases, it is impossible to keep the gap between the steel strip 1 and the electrodes constant (this is because the electrode rows cannot be brought closer to each other since electrodes 8b at the ends of the electrode row 2 contact each other). When this happens, the voltage must be increased, so that the power consumption increases.

On the other hand, if the width of the electrode row is excessively smaller than that of the steel strip, problem (3) to be described below occurs.

(3) As may be seen from the distribution of the deposition amount shown in Fig. 5, a metal deposited on the portions a little inside of both edges of the strip has a smaller amount than at the central portion of said strip. This results in irregular distribution of the deposition amount along the direction of width of the strip.

For the reasons (1), (2) and (3) described above, the width of the electrode row is conventionally adjusted according to changes in the strip width. According to the method for this adjustment, as the strip width decreases, the electrodes at the ends of the electrode rows are unloaded. However, this adjustment method presents following problems (4) to (7): (4) The lower electrode row of horizontal type apparatus and the electrode rows of the vertical type apparatus are respectively arranged below the steel strip and the conductor roll. Therefore, the accessibility for unloading the electrodes at the ends of the electrode rows for the purpose of decreasing the width of the electrode row is poor.

(5) The thickness of the individually unloaded electrodes is not so small as to justify disposal but is not uniform. If these electrodes are disposed, the use efficiency of the electrodes is degraded. On the other hand, if these electrodes are to be put to use again, they must first be stored in great quantity and must then be grouped into electrode rows of substantially the same thickness.

(6) As may be seen from the graph shown in Fig. 6, even if the width (line s) of the steel strip decreases linearly, the width (stepped line e) of the electrode row decreases in a stepped manner.

Therefore, the difference between the width of the electrode row and that of the steel strip becomes maximum when the electrodes at the ends of the electrode row are unloaded. Then, the width of the electrode row becomes too small as compared with the strip width. This results in the nonuniformity of the deposition amount of the metal as shown in Fig. 5. In order to prevent this, the width of each electrode constituting the electrode row may be decreased. However, this results in a greater frequency of unloading of electrodes, which is not preferable.

(7) In the horizontal type apparatus, as shown in Fig. 7, the busbar 3 for energizing the electrode row 2 arranged below the steel strip 1 is in direct opposition with the steel 1 in the electrolytic solution.

Therefore, the current flows from the busbar 3 to the steel strip 1, and the busbar 3 is electrolytically corroded. This electrolytic corrosion of the busbar 3 is notable when a chloride bath is used as an electrolytic solution.

Problems (4) to (7) described above may be solved by increasing the width of the electrode row in excess of the strip width. However, when this measure is taken, problems (1 ) and (2) as described above occur. In order to solve problem (1), a method is developed according to which an edge mask is arranged in the vicinity of the edge of the steel strip 1 in order to avoid the current concentration at the strip edge. However, even when this measure is taken, problem (2) still remain unsolved.

In order to solve problem (2), the electrode transfer method is known which is conventionally adopted in tin plating. According to this method of electroplating, as shown in Figs. 8A and 8B, electrodes 8 of sequentially varied thicknesses are arranged on inclined busbars 3, so that a constant gap is kept between the steel strip 1 and the respective electrode 8. When the thickness of each electrode is decreased by a thickness corresponding to the thickness difference between the adjacent electrodes, the electrode row 3 is displaced in the direction indicated by the arrow for a distance corresponding to the width of one electrode. Then, the electrode of least thickness is unloaded from the left in the direction indicated by the arrow, and a new electrode is loaded from the right.According to this method, the gap between the electrodes 8 and the steel plate 1 may be kept constant. However, if the width of the electrode row 2 is smaller than the width of the steel strip 1, problems (4) to (7) with the conventional adjustment method cannot be solved. This method especially suffers from the fatal disadvantage of low use efficiency of the electrodes.

Thickness tw (in mm) of the electrode unloaded for treating a steel strip of a given width W (in mm) is given as: tw=TW(T t)lmax where T is the thickness (in mm) of an electrode which is loaded anew; t is the width (in mm) of the electrode which is unloaded when the width of the steel strip is Wmax; and Wmax is the maximum width in mm of the steel strip used in the treatment line.

The use efficiency w of the electrode is given as: tw = (T - tw)/T = (WAWmax)(T - t)/T (T - t)/r corresponds to the use efficiency of the electrodes when a steel strip of the maximum thickness is used. (T - t)T is thus the maximum use efficiency amax. Therefore, = W/\AImax amax On the other hand, the minimum use efficiency amin is given as: amin = Wmin/Wmax amax where Wmin is the minimum width of the steel strip to be used in the treatment line.

In the case of tin plating wherein there is only a small difference between the maximum width and the minimum width of the strip, the minimum use efficiency does not become very low. However, in the case of zinc plating of a steel plate having a maximum width of 1,819 and 1,219 mm and a minimum width of 900 to 610 mm, the minimum use efficiency decreases to 1/2 to 1/3 the maximum use efficiency. According to the electrode transfer method described above, the unloaded electrode of greatest thickness is smaller than the thickness of the electrode which is loaded anew, the used electrodes may not be used again and all of them must be disposed. This results in a low use efficiency.

As an improvement over the method shown in Figs. 8A and 8B, a method is proposed which is adopted in the radial type apparatus. According to this method, as shown in Fig. 9, the width of the electrode row 2 is made greater than the strip width and the edge mask 9 is used. Although problems (4) to (7) of the conventional adjustment method are solved, problem (5), that is, the decrease in the use efficiency of the electrodes, and the fact that the electrodes cannot be used again, is not solved.

Furthermore, as shown in Fig. 9, the electrodes 8 which are not opposed to the steel strip 1 are in the stepped form. Therefore, it is impossible to arrange the edge masks 9 as shown in Fig. 9 and then to displace them to the right or left in accordance with the shift of the steel strip 1.

It is object of the present invention to provide a method for electroplating a steel strip, which solves the problems as described above.

It is another object of the present invention to provide an electroplating apparatus which is suitable for practicising the electroplating method as described above.

According to an aspect of the present invention, there is provided a method for electroplating a steel strip by arranging a plurality of electrode rows each consisting of a plurality of electrodes disposed adjacent to each other along the direction of width of said steel strip in opposition to said strip travelling in an electrolytic cell holding an electrolytic solution, so that a metal constituting said electrodes may be electroplated on said steel strip, comprising the steps of intermittently or continuously transferring said electrodes of said electrode rows in a direction perpendicularly to the direction of travel of said steel strip at a speed so that a distribution of a deposition amount of the metal of said electrodes along the direction of width of said steel strip may be kept within an allowable tolerance, a width of said electrode rows being greater than the width of said steel strip; and unloading said electrode from one end of one of said electrode rows transferred by said transferring step and loading said electrode to the other end of said one electrode row or to an end of another of said electrode rows.

According to another aspect of the prevent invention, there is also provided an electroplating apparatus having an electrolytic cell holding an electrolytic solution in which a steel strip travels, a plurality of electrode rows each of which consists of a plurality of electrodes arranged adjacent to each other along the direction of width of said steel strip and which are arranged along the direction of travel of said steel strip in opposition to a surface of said steel strip to be treated, and a plurality of vertically movable busbars which are arranged along the direction of width of said steel strip and which support said electrode rows, further comprising means for reciprocally moving said busbars along the direction of width of said steel strip so as to transfer said electrodes, electrode-gripping means which are arranged at both sides of said steel strip and movable along the direction of travel of said steel strip and which are provided with a vertically movable electrode-gripping member, and stoppers which are arranged at intervals at the sides of each of said electrode rows and which prevent transfer of said electrodes in excess of a predetermined distance to shift the positions of said electrodes relative to said busbars.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 A is a front view of a conventional parallel type electroplating apparatus; Fig. 1 B is a plan view of the apparatus shown in Fig. 1; Fig. 2 is a front view of a conventional vertical type electroplating apparatus; Fig. 3 is a front view of a conventional radial type electroplating apparatus; Figs. 4A and 4B are views for explanation of problems with the conventional electroplating method; Fig. 5 is a graph showing the relationship between the strip width and the deposition amount of the metal according to the conventional electroplating method; Figs. 6 and 7 are views for explanation of problems with the conventional method for adjusting the width of the electrode row;; Figs. 8A, 8B and 9 are views for explanation of conventional, improved electroplating methods; Fig. 10 is a front view showing an apparatus which is used in an electroplating method according to an embodiment of the present invention; Fig. 11 is a plan view of the apparatus shown in Fig. 10; Fig. 12 is a sectional view of the apparatus shown in Fig. 10 along the line A-A thereof; Figs. 13 to 1 5 are views showing the methods for unloading and loading the electrodes according to the present invention; Fig. 1 6 shows the positional relationship between the steel strip and the electrodes in an experiment conducted according to the present invention;; Figs. 1 7 and 18 are graphs showing the results obtained in the experiment shown in Fig. 1 6.

Figs. 1 9 and 20 are graphs showing the distribution of the deposition amount of zinc in the experiment according to the present invention; Fig. 21 is a plan view of an electroplating apparatus according to an embodiment of the present invention; Fig. 22 is a sectional view of the apparatus shown in Fig. 21 along the line B-B thereof; Fig. 23 is a sectional view of the apparatus shown in Fig. 21 along the line C-C thereof; and Figs. 24 and 25 are views showing the transfer procedure of the electrodes in the apparatus shown in Fig. 21.

The preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

Fig. 10 is a front view showing an example of an electroplating apparatus used for practicing the method according to the present invention. Fig. 1-1 is a plan view of Fig. 10 while Fig. 1 2 is a sectional view along the line A-A of Fig. 10. In this apparatus, a steel strip 13 is made to pass through an electrolytic cell 12 holding an electrolytic solution 11. The steel strip 13 is electroplated using soluble anodes.The steel strip 1 3 is horizontally transferred by a conductor roll 1 5, a back-up roll 16, and dam rolls 1 7. Upper electrode rows 1 spa and 1 sub, and lower 1 9a and 1 9b are arranged along the direction of travel of the steel strip 13 to be in opposition with the upper and lower surfaces, respectively, of the steel strip 1 3 travelling in the electrolytic cell 12. The upper and lower electrode rows 1 spa, 1 sub, 1 9a and 1 9b consist of a plurality of electrodes 18 and 19 which are arranged perpendicularly to the direction of travel of the steel strip 1 3, and define a soluble anode system.These electrode rows 1 spa and 1 8b are electrically connected to upper busbars 20, while the lower electrode rows 1 9a and 1 9b are electrically connected to lower busbars 21. Push rods 22 are arranged at one side surface of the upper and lower electrode rows for moving them. The push rods 22 are mounted to hydraulic cylinders 27 supported by a frame 26. An electrode-loading carrier 23a and an electrode-unloading carrier 23b are arranged at the respective side surfaces of each of upper and lower electrode rows. These carriers 23a and 23b are suspended from hoists 25a and 25b are travelling on two rails 24 (only one shown in Fig. 10).

In order to practice the method of the present invention, as shown in Figs. 11 and 12, a number of electrodes are arranged on the busbars 20 and 21 so that the width of the upper and lower electrode rows 18 and 1 9 may be greater than the width of the steel strip 1. Upon operation of the hydraulic cylinders 27, the push rods 22 urge the side surfaces of the electrodes 18 and 1 9. Then, the electrodes are moved in the direction which is substantially perpendicular to the running direction of the steel strip 1. Thus, the electrodes are sequentially unloaded from one ends of the electrode rows and are loaded on the other ends of the same electrode rows or to the ends of other electrode rows. The transfer of the electrodes may be performed by a belt conveyor or the like in place of the hydraulic cylinders 27 and the push rods 22.

According to the method of the present invention, the transfer of the electrodes is performed intermittently or continuously at a speed so that the distribution of the deposition amount of the metal in the direction of width of the steel strip 1 may fall within a predetermined range. More specifically, the transfer speed v (m/hr) is within the range defined by relations (1) and (2) below: V > [60 E DA W(1002A)]/(20ApK D) (1)

where p is the density of deposited metal (g/cm3); K, the electroplating constant of the metal (A min/g); D, the distance between the steel strip and the electrode end at the loading side of the electrode row (mm); A, the allowable tolerance of the deposition amount in the direction of width of the steel strip (%); E, the electrolytic efficiency; DA, the current density (A/dm2); and W, the width of the steep strip (m).

Relation (1) as given above is applicable to the case as shown in Fig. 13 wherein the transfer direction (indicated by the solid arrow) is the same for all electrode rows.

On the other hand, relation (1) as given above is applicable to the case shown in Figs. 14 and 15 wherein the transfer direction (indicated by the solid arrow) alternately becomes opposite. Fig. 14 shows a case wherein the electrode unloaded from the last electrode row is loaded to the first electrode row. Fig. 1 5 shows a case wherein the electrode unloaded from the last electrode row has reached a thickness which allows no further use and must be disposed.

Relations (1) and (2) above are obtained in the manner to be described below.

The amount of metal consumed per hour Ch (g/hr) in the electroplating process of the steel strip is given as: Ch = C.W.S.60 (3) where C is the deposition amount of the metal per square meter of one surface of the steel strip (g/m2); S, the running speed of the steel strip (m/min); and W, the width of the steel strip. The volume of the metal consumed per hour V (cm3/hr) is expressed by relation (4) below: V=Ch/p (4) where p is the density of the metal (g/cm3).

The surface area SA (cm2) of one surface of the electrode is expressed by relation (5) below: SA=W' L 104 (5) where L is the length of the electrode (m).

The running speed S of the steel strip is expressed by relation (6) below: S=(L.DA)/(K/E.C).10 (6) where E is the electrolytic efficiency and K is the electroplating constnt (A min/g).

From relations (3) to (6) given above, the reduction in the thickness of the electrode Ti (cm/hr) is expressed by relation (7) below: Ti =V/SA= (C W S 60)l(p W L - 104) = (e.60.DA)/(# .K .10 (7) Let v denote the transfer speed in m/hr of the electrode, and the difference d(mm) between the thickness of the unloaded electrode and the newly loaded electrode is given by relation (8) below: d=Ti-W/v- 10 =(E60DAW)AP K.v K v . 10) (8) Therefore, v=(E60DW)/(pKd10) W)/(# .K . d . 10) (9) The difference d between the thicknesses of the electrode and the deposition amount of the metal in the direction of width of the steel strip were found to hold relations (10) and (11) below from the experiments: (C1-C2)/C1 =d/(D+d) (10) (C1 - CcVC1 = [d/(2D + d)]2 (11) where C1 is the metal deposition amount (g/m2) on the steel strip at the electrode loading side; C2, the metal deposition amount (g/m2) on the steel strip at the electrode unloading side; Cc, the metal deposition amount (g/m2) on the central portion of the steep strip along the direction of width thereof; and D, the distance (mm) between the electrode and the steel strip at the electrode loading side.

Relation (10) given above was obtained by varying the average current density DA, the distance D between the steel strip and the electrode, the difference d between the thickness of the electrodes, and the width W of the steel strip, in a plating bath which held zinc sulfate and in which were arranged a steel strip 1 3 and zinc electrodes 1 8. Fig. 1 7 shows an example of the deposition amount distribution of zinc when DA = 60 A/dm2, D = 25 mm, d= 10 mm, and W = 1,200 mm.

Relation (11 above was obtained when electroplating was performed under various conditions with the right and left sides of the steel strip reversed after performing electroplating with the arrangement of the steel strip 13 and the zinc electrodes 18 shown in Fig. 1 6. Fig.18 shows an example of the deposition amount distribution of zinc when electroplating was performed for 12.5 seconds under the conditions of DA = 60 A/dm2, D = 25 mm, d = 25 mm, and W = 1,200 mm, and when electroplating was performed again for another 12.5 seconds with the right and left sides of the steel strip reversed.

If the allowable tolerance of the deposition amount is represented by #A (%), the transfer speed of the electrodes which allows electroplating with the deposition amount falling within the allowable tolerance may be obtained by relations (1) or (2) from relations (9) and (10) or from relations (9) and (11).

If the transfer direction of the electrode is the same for all electrode rows as shown in Fig. 1 3, from relation (10), we obtain: 2A/100 > (C1 - C2)/C1 = d(D + d) d( [2A/(100-2A)]. D (12) From relations (9) and (12), we obtain: v # [E . 60 . DA .W(100-2A)]/(# . K .D . 2A . 10) (1) If the transfer direction of the electrode alternatively becomes opposite for the respective electrode rows as shown in Figs. 14 and 15, we obtain from relation (11): 2A/1 00 > (C1 - Cc)/Ci = [d/(2D + d)j2

From relations (9) and (13), we obtain:

According to the method of the present invention, the electrodes are transferred at a transfer speed which satisfies relation (1) or (2). The electroplating is performed under this condition, and the unloaded electrodes are repeatedly loaded on the same or other electrode rows until their thickness reaches a predetermined value.This is because the difference d between the thickness of the loaded electrode and that of the unloaded electrode is extremely small as may be seen from relations (10) and (11) above, and the unloaded electrode may be directly used as the electrode to be newly loaded without any problem.

In the embodiment described above, the electrodes are arranged to oppose both surfaces of the steel strip. However, the electrodes may be arranged to oppose only one surface of the steel strip.

The present invention will now be described by way of examples.

EXAMPLE 1 Using the apparatus shown in Fig.10, the electrode row had a length of 700 mm and a width of 1,500 mm. Twelve such electrode rows were arranged along the running direction of the steel strip and were plated with zinc in a zinc sulfate bath. The obtained result is shown in Fig. 1 9. The electrode transfer conditions and the running conditions of the steel strip were: W = 1 ,200 mm, S = 60 m/min, D = 25 mm, and DA = 60 A/dm2. In order to obtain the deposition amount within the allowable tolerance A < *15%, v must be equal to or larger than 20 mm/hr.In Fig. 19, a line a1 corresponds to the case when v = 100 mm/hr, and line a2 corresponds to the case when v = 50 mm/hr, It is seen from Fig. 1 9 that the deposition amount within the allowable tolerance may be obtained according to the present invention.

EXAMPLE2 Electroplating was performed in the similar manner to that in Example 1 except that W = 600 mm, S = 50 m/min, D = 30 mm, and DA = 100 A/dm2. The obtained result is shown in Fig. 20. In this case, in order to obtain the deposition amount within the allowable tolerance A, equal to or less than 1 5%, v must be equal to or greater than 14 mm/hr. In Fig. 20, line b1 corresponds to the case when v = 100 mm/hr, and line b2 corresponds to the case when v = 50 mm/hr.

As may be seen from Fig. 20, the deposition amount within the allowable tolerance may be obtained according to the present invention.

Thus, according to the present invention, by making the width of the electrode row greater than the width of the steel strip, the position from which the electrode is unloaded or through which the electrode is loaded may be set at a position outside the steel strip and rolls. In this manner, the unloading or loading operation becomes extremely easy. Furthermore, since this unloading or loading operation may be performed without stopping the treatment line, the working efficiency is improved.

Since the busbars are all covered by the electrodes, they are not subjected to corrosion. For this reason, a chloride bath may be used which allows easy conduction of electricity while it may allow easy corrosion of busbars. Since the electrodes are transferred at more than a predetermined speed, the consumed amount of the unloaded electrodes is small and the unloaded electrodes may be loaded again. Consequently, the use efficiency may be improved and the deposition amount distribution may be kept to fall within a predetermined range.

A description will now be made on an apparatus for practicing the electroplating method of the present invention as described above.

Fig. 21 is a plan view of an electroplating apparatus which is suitable for the method of the present invention. Fig. 22 is a sectional view along the line B-B of Fig. 21, while Fig. 23 is a sectional view along the line C-C of Fig. 21. The main construction of the electroplating apparatus of this embodiment is substantially the same as that shown in Figs. 10 and 11. Therefore, the detailed description of the main construction will be omitted. The mechanism for the transfer, loading and unloading of the electrodes will mainly be described.

At both sides of the electrolytic cell 12, jacks 31 for vertically moving the upper busbars 20 are arranged for each of the electrode rows 1 8a and 1 8b. A roller 33 for supporting a busbar-connecting member 32 for connecting a pair of busbars 20 is mounted on the top of each jack 31. A jack 31 of this construction is also incorporated for vertically moving the lower busbars 21. In the apparatus shown in Figs. 21 to 23, a total of eight jacks 31 are included. By these jacks 31, the levels of the respective electrode rows 18a, 18b, 19a and 1 9b are individually adjusted. These jacks 31 are, therefore, incorporated for the purpose of keeping optimum the gap between the steel strip 13 and the electrode rows 18a, 18b. 19a and 1 9b which are gradually consumed.At the part of the electrolytic cell 12 through which extends the lower busbar 21 is arranged a bellows 34 for prevention of leakage of the electrolytic solution. An outer cell 35 is arranged to surround the electrolytic cell 12 so as to recover the electrolytic solution which overflows from the electrolytic cell 12 or leaks from sealed parts of the dam roll 17.

At the side of each electrode row is incorporated means for reciprocating the busbars 20 and 21 in the direction perpendicular to the running direction of the steel strip 13. This means respectively comprises a base 36, hydraulic cylinders 37 which are respectively pivoted to the upper end and lower portions of the side surface of the base 36, and rods 38 which are mounted to the front ends of the hydraulic cylinders 37. The busbar-connecting members 32 are pivoted to the rods 38. As has been described above, since the busbar-connecting members 32 are supported by the rollers 33 of the jacks 31, the busbars 20 and 21 supporting the electrode rows 18a, 18b, 19a and 1 9b may be smoothly reciprocated upon operation of the hydraulic cylinders 37. Stoppers 39 are arranged at predetermined intervals on both sides of the respective electrode rows.

Above one side of the electrolytic cell 12 is arranged an electrode-gripping means, movable along the longitudinal direction of the electrolytic cell 1 2. This means will now be described. A main body 41 overrides a rail 43 which is arranged along the lontitudinal direction of the electrolytic cell 12 and travels on the rail 43 through rollers 44a, 44, and 44c which roll over three surfaces of the rail 43. A rack 45 is mounted on the top surface of the rail 43 and engages with a pinion 47 which is mounted on the main body 41. The main body 41 is made to travel upon rotation of the pinion 47 by a motor 46. An electrode-gripping member 50 is vertically movably mounted to the main body 41.The electrodegripping member 50 comprises an arm 51 a which is mounted to its lower end, two vertically movable upright bars 51 on the backs of which are mounted racks 51 b, and grips 53 which are vertically moved by cylinders 52 which are, in turn, respectively fixed to these upright bars 51. The upright bars 51 are vertically moved by a pinion 55 which is driven by a motor 54. The electrode-gripping means of the same construction is also incorporated at the upper portion on the other side of the electrolytic cell 1 2.

The transfer operation of the electrodes in the apparatus of the construction as described above will now be described with reference to Figs. 24 and 25. Fig. 24 shows the transfer operation for the front electrode rows 18a and 1 9a; while Fig. 25 shows the transfer operation for the rear electrode rows 18b and 19b.

Stage I shown in Figs. 24 and 25 illustrates the normal state after loading and unloading of the electrodes 18 and 1 9. The electrodes 18 and 1 9 are loaded or unloaded at the parts at both ends of the respective electrode rows indicated by broken lines. At both sides of the electrode which is to be loaded or unloaded is incorporated a gap g so as to prevent its contact with the adjacent electrodes or stoppers during loading or unloading. Let a denote the width of the electrodes 1 8 and 19 and n the number of the electrodes 18 and 19, and the width na of the electrode row during the normal state must be wider than the maximum width of the steel strip 13 by a distance corresponding to 4g.Although the stopper 39 must be incorporated at least at the loading side of the electrode row, it is also incorporated at the unloading side as indicated by the broken line so that the excessive transfer of the electrodes by erroneous operation is prevented and the damage to the electrode-gripping means is also prevented.

Under this state, the electrode to be loaded is first transferred by the electrode-gripping means and is stopped at a predetermined position. The loading or unloading of the electrodes of the front electrode rows 18a and 1 9a will be described with reference to Fig. 24. In stage II, the electrode-gripping member 50, gripping an electrode 61 a to be loaded, is lowered (step 1). A grip 53 of the electrode-gripping member 50 is released immediately before the upper electrode contacts the busbars 20 (step 2). The upright bar 51 is further lowered. The downward movement of the electrode-gripping member 50 is stopped after completely handling the upper and lower electrodes 61 a to the busbars 20 and 21.

In stage Ill, the busbars 20 are drawn toward the stoppers 39 by a distance corresponding to (a + 2g) to bring the electrode 61 a in contact with the stopper 39 (step 3). Then, the gap g between the electrode 61 a to be loaded and the adjacent electrode is eliminated, and the positions of the electrode rows 18a and 1 9b relative to the busbars 20 and 21 are shifted by a distance corresponding to the width a of one electrode. In this condition, the electrode-gripping member at the unloading side is lowered (step 4), and is made to wait at the unloading ready position.

In stage IV, the busbars 20 and 21 are fed toward the unloading side by a distance corresponding to (a + 3g) (step 5), and the respective electrodes are transferred, so that the electrode 61 b to be unloaded comes to the unloading ready position of the electrode-gripping member 50. The electrodegripping member 50 at the loading side is raised (step 6). In stage V, the electrode-gripping member 50 at the unloading side is raised. Then, the arm 51 a at the lower end of the member 51 contacts the lower electrodes, and a load cell or the like detects that a load is exerted on the member 51. Thereafter, the member 51 is raised by a distance corresponding to a sum of several millimeters and the gap between the upper and lower electrodes, and the member 50 is then stopped (step 7). The grip 53 is lowered to grip the upper and lower electrodes (step 8).

In stage VI, the busbars 20 and 21 are drawn toward the loading side by a distance corresponding to the gap g (step 9) to define the gap g between the electrode 61 b and the adjacent electrode. The electrode-gripping member 50 for unloading is then raised to prevent the interference by the adjacent electrode during unloading of the electrode 61b (step 10).

In this manner, in the front electrode rows 18a and 19a, the electrodes 61 a are loaded, the electrodes 61 b are unloaded, and the line is restored to the normal state.

The procedure for the loading and unloading of the electrode in the rear electrode rows 1 8b and 1 9b will now be described with reference to Fig. 25. The electrodes 61 b unloaded from the front electrode rows 18a and 1 9b are transferred along the longitudinal direction of the electyrolytic cell 1 2 in the condition that they are gripped by the electrode-gripping member 50 for unloading. These electrodes 61 b are stopped at a predetermined position at the loading side. The loading and unloading of the electrodes are performed in the same manner as described with reference to Fig. 24.In this manner, the electrodes 1 6c unloaded from the rear electrode rows 18b and 1 9b are loaded to the loading sides ot the next electrode rows in the state indicated by stage li shown in Fig. 24. Similar operations are repeated up to the final electrode rows. If the electrodes are used in rotation within the same electrode row, one supplementary electrode is prepared for each of the upper and lower electrode rows, and the loading and unloading of the electrodes may then be performed in a manner similar to that described above.

According to the electroplating apparatus of the present invention, the loading and unloading of the electrode may be performed while the electrodes remain energized and without requiring interruption of the electroplating operation. Furthermore, since the operations of the means for reciprocating the busbars and the electrode-gripping means are simple repetitive operations, they may be performed by robots, so that all the operations may be automated except for the feeding and positioning of the unused electrodes and recovery of the disposed electrodes.

Claims

1. A method for electroplating a steel strip by arranging a plurality of electrode rows each consisting of a plurality of electrodes disposed adjacent to each other along the direction of width of said steel strip in opposition to said strip travelling in an electrolytic cell holding an electrolytic solution, so that a metal constituting said electrodes may be electroplated on said steel strip, comprising the steps of intermittently or continuously transferring said electrodes of said electrode rows in a direction perpendicularly to the direction of travel of said steel strip at a speed so that a distribution of a deposition amount of the metal of said electrodes along the direction of width of said steel strip may be kept within an allowable tolerance, a width of said electrode rows being greater than the width of said steel strip; and unloading said electrode from one end of one of said electrode rows transferred by said transferring step and loading said electrode to the other end of said one electrode row or to an end of another of said electrode rows.

2. A method according to claim 1, wherein a plurality of pairs of said electrode rows are arranged so that one and the other of each of said plurality of pairs of said electrode rows are respectively arranged to oppose both surfaces of said steel strip.

3. A method according to claim 1, wherein a transfer direction of said electrodes is the same for all of said electrode rows.

4. A method according to claim 3, wherein a transfer speed v (m/hr) of said electrode satisfies the relation: v 1 [60 E D, W(2 00 -- 2A)120 A p K D) where p is a density of deposited metal (g/cm3); K is an electroplating constant of the metal (A min/g); D is a distance between said steel strip and said electrode end at the loading side of said electrode row (mm); A is an allowable tolerance of the deposition amount in the direction of width of said steel strip (%); E is an electrolytic efficiency; DA is a current density (A/dm2); and W is the width of said steel strip (m).

5. A method according to claim 1, wherein a transfer direction of said electrodes alternately becomes opposite for said electrode rows.

6. A method according to claim 5, wherein a transfer speed v (m/hr) of said electrode satisfies the relation:

where p is a density of deposited metal (g/cm3); K is an electroplating constant of the metal (A min/g); D is a distance between said steel strip and said electrode end at the loading side of said electrode row (mm); A is an allowable tolerance of the deposition amount in the direction of width of said steel strip (%); E is an electrolytic efficiency; DA is a current density (A/dm2); and W is the width of said steel strip (m).

7. A method according to any one of claims 1 to 6, wherein electroplating is performed by placing said electrode rows on busbars connected to a power source and by energizing said electrode rows.

8. A method according to any one of claims 1 to 6, wherein said step of transferring said electrodes comprises pushing said electrode rows by push rods which are arranged at sides of said electrode rows.

9. A method according to claim 7, wherein-said step of transferring said electrodes comprises transferring said busbars.

1 0. An electroplating apparatus having an electrolytic cell holding an electrolytic solution in which a steel strip travels, a plurality of electrode rows each of which consists of a plurality of electrodes arranged adjacent to each other along the direction of width of said steel strip and which are arranged along the direction of travel of said steel strip in opposition to a surface of said steel strip to be treated, and a plurality of vertically movable busbars which are arranged along the direction of width of said steel strip and which support said electrode rows, further comprising means for reciprocally moving said busbars along the direction of width of said steel strip so as to transfer said electrodes, electrodegripping means which are arranged at both sides of said steel strip and movable along the direction of travel of said steel strip and which are provided with a vertically movable electrode-gripping member, and stoppers which are arranged at intervals at the sides of each of said electrode rows and which prevent transfer of said electrodes in excess of a predetermined distance to shift the positions of said electrodes relative to said busbars.

11. An apparatus according to claim 10, wherein a plurality of pairs of said electrode rows are arranged so that one and the other of each of said plurality of pairs of said electrode rows are respectively arranged to oppose both surfaces of said steel strip.

1 2. An apparatus according to claim 10 or 11, wherein said busbars are supported by rollers which are mounted to front ends of jacks.

1 3. An apparatus according to claim 10 or 11, wherein said electrode-gripping member comprises a vertically movable upright bar which has, at a lower end thereof, an arm for placing said electrode thereon, and a vertically movable grip for gripping said electrode in cooperation with said arm.

1 4. A method for electroplating steel strip and electroplating apparatus, substantially as hereinbefore described with reference to the accompanying drawings.