APPARATUS FOR PLATING METAL STRIP IN ELECTROLYTIC CELL

Abstract: An apparatus for plating a metal strip (4) in an electrolytic cell (1) is provided with a supporting roll (3). The support roll is disposed apart from the deflector rolls (2a, 2b) by a pre­ determined distance and supports the metal strip in such a way that the catenary of the metal strip can be reduced. The distance is determined so that the catenary is 0.04 or less times of the distance between upper (5a,6a) and lower (5b,6b) electrodes in the electrolytic cell. When the metal strip is a steel plate having a density of 7.85 × 10⁻⁶ (kg/mm³), the pre­ determined distance (mm) between the axis of the deflector roll and that of the supporting roll is subject to the following formula: in which the distance between the upper and lower electro­ des is ΔD (mm), the thickness of the metal strip being t (mm), the width thereof being W (mm) and the tension applied to the metal strip being T (kg).

Description: BACKGROUND OF THE INVENTION [FIELD OF THE INVENTION] The present invention relates generally to an apparatus for plating a metal strip in an electrolytic cell. More specifically the invention relates to an apparatus for plating a metal strip, which apparatus can generate a deposit of consistent thickness on the surface of the metal strip. [DESCRIPTION OF THE PRIOR ART] In a horizontal pass-line type of apparatus for simultaneously plating the upper and lower surface of a metal strip, deflector rolls have been generally used near the opposing inside walls in a plating bath in order to deflect the flow direction of the metal strip fed from a point outside of the plating bath. However, when the distance between the deflectors is relatively large, the metal strip will be warped across its width and may have a large catenary longitudinally, so that the distance between the metal strip and electrodes of the apparatus is not constant. In this condition, when the metal strip is plated in the plating bath, a deposit of uneven thickness tends to occur on the surfaces of the metal strip. Therefore, a conventional apparatus is provided with deflector rolls as well as snubber rolls or presser rolls. which clamp the metal strip, so as to decrease the warp in the lateral and longitudinal catenary of the metal strip. However, since the deflector rolls and snubber rolls in the aforementioned apparatus rotate so that one presses against another under a predetermined pressure in the electrolytic solution, there is a problem in that the rolls do not tend to clamp only the metal strip but also foreign matters, such as sluges and slimes. in the plating bath, thereby marring the metal strip. It is also known from FR-A-889.657 to provide a support roll between the deflector rolls. SUMMARY OF THE INVENTION It is therefore a principal object of the present invention to eliminate the aforementioned problems in conventional apparatus for plating a metal strip in an electrolytic cell and provide a process which can generate a deposit of even thickness on the surface of the metal strip. In order to accomplish the aforementioned and other specific objects, a process for plating a metal strip, according to the present invention, is provided with at least one support roll between the deflector rolls. This support roll is disposed at a predetermined distance from the deflector rolls and/or the other support rolls so that the distance between the metal strip and electrodes of the apparatus is substantially constant. These objects are achieved by a process according to claim 1. Additional features of the invention are provided in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention. The drawings are not intended to imply limitation of the invention to this specific embodiment, but are for explanation and understanding only. In the drawings: Fig. 1 is a schematic diagram of a preferred embodiment of an apparatus for plating a metal strip in an electrolytic cell according to the present invention. Fig. 2 is a schematic diagram of another preferred embodiment using a long plating bath. Fig. 3 is a graph showing the thickness of the deposit relative to the position of the metal strip according to an apparatus of the present invention and prior art. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, particularly to Fig. 1, the preferred embodiment of an apparatus for plating a metal strip, according to the present invention, can plate a metal strip 4 in a processing bath 1, such as a plating bath. The processing bath 1 is filled out with electrolytic solution 9. The processing bath 1 is provided with deflector rolls 2a and 2b near its opposing inside walls. The metal strip 4 is deflected by means of the deflector rolls 2a and 2b so as to be essentially horizontal between the deflector rolls 2a and 2b in the processing bath 1. Two pair of electrodes 5a, 5b and 6a, 6b are provided between the deflector rolls 2a and 2b in series. The electrode 5a is essentially parallel to the electrode 5b and the electrode 6a is essentially parallel to the electrode 6b, so that the metal strip 4 can be disposed between the electrodes 5a and 5b and between the electrodes 6a and 6b. The electrodes 5a, 5b, 6a and 6b are connected to bus bars 7a, 7b, 8a and 8b, through which electric currents flow for the electrodes 5a, 5b, 6a and 6b. and suspended by the bus bars 7a, 7b, 8a and 8b. According to the preferred embodiment of the present invention, a support roll 3 is provided between two pair of electrodes 5a, 5b and 6a, 6b, said support roll 3 disposed at a predetermined distance from the deflector rolls and supports the metal strip 4. The metal strip 4 is supported by the support roll 3 so as to be essentially horizontal, thus the longitudinal catenary and warpage in the lateral axis of the metal strip 4 can be reduced. It is described below how to determine the optimum distance between the axis of the deflector roll 2a or 2b and that of the support roll 3 in the processing bath 1. When the metal strip 4 runs in the processing bath 1 by means of the deflector rolls 2 so that the metal strip 4 has a predetermined tension T (kg), the catenary Δh₁ (mm) of the metal strip 4 between the deflector roll 2a or 2b and the support roll 3 can be expressed as follows: wherein w denotes the unit weight (kg/mm) of the metal strip 4, and ℓ is the length of a pass, that is, the distance (mm) between the deflector roll 2a or 2b and the support roll 3, which supports the metal strip 4 passing through the space between the electrodes 5a and 5b and between the electrodes 6a and 6b. Furthermore, the relationship between the catenary Δh₁ and the thickness distribution of the deposit on the surface of the metal strip 4 was tested by using a pilot arrangement. As a result, a deposit of essentially uniform thickness across the lateral axis of deposit on the surface of the metal strip 4 was obtained when the relationship between the catenary Δh₁ and the distance ΔD between the electrodes was expressed by the following formula: Therefore, if at least one support roll is provided between the deflector rolls so as to be disposed at a predetermined distance from the deflector rolls 2a and 2b and/or the other support rolls, a deposit of essentially uniform thickness across the lateral axis of deposit on the surface of the metal strip 4 may be obtained. The distance is preferably determined so that the catenary Δh₁ is equal to or less than 0.04 x ΔD. The length of a pass ℓ can be obtained from this result and the expression (1). If the width of the metal strip 4 is labelled with W (mm), its thickness labelled with t (mm) and its density labelled with γ (kg/mm³), the unit weight w can be expressed by following formula: w = γ x W x t (3) In addition, the following formula can be obtained from the formulae (1) and (3). Therefore, from the formulae (2) and (4), the following formula can be obtained : If the metal strip 4 is a steel plate, γ = 7.85 x 10⁻⁶ (kg/mm³). Therefore, the pass length ℓ (mm) can be obtained from the formula (5) as follows: If the pass length ℓ is determined as the formula (6), a deposit of uniform thickness can be generated on the surface of the metal strip 4. A metal strip was plated by electrolytic Ni-plating by using an apparatus for plating according to the present invention shown in Fig. 1. As shown in Fig. 3, the thickness of the deposit was essentially equal near the center and edges on the surface of the metal strip 4. The unit weight of the deposit was 0.06 g/m² near the center and edges on the surface of the metal strip and its scattering was lower than ±5%. Furthermore, the thickness of the deposit on the surface of the metal strip is similar to the aforementioned results with respect to longitudinal direction. According to another preferred embodiment of the present invention, a plurality of support rolls 3 can also be used in the apparatus for plating a metal strip as shown in Fig. 2. In this case, the distance between the axes of the support rolls is preferably similar to ℓ shown in formula (6).

Claims: A process for plating a metal strip in an electrolytic cell comprising the steps of: introducing the metal strip (4) into a processing bath (1) which extends in a direction of a longitudinal axis of the metal strip (4) and which contains electrolytic solution therein : holding the metal strip in said processing bath at a predetermined position by means of a holding arrangement including first and second deflector rolls (2a,2b) and a first supporting roll, (3), said first and second deflector rolls (2a,2b) being arranged in said processing bath (1) at locations neighboring both ends thereof, each of the first and second deflector rolls extending in a direction perpendicular to said axis of the metal strip and being used for guiding and deflecting said metal strip (4) so as to apply downward force to the upper surface thereof, said first supporting roll (3) being arranged in said processing bath between said first and second deflector rolls so as to extend in a direction essentially parallel to the axes of the first and second deflector rolls (2a,2b) and being used for supporting said metal strip (4) thereon so as to cooperate with said first and second deflector rolls (2a,2b) to reduce the catenary of said metal strip (4), said first supporting roll (3) being disposed such that distance ℓ between the adjacent rolls including said first and second deflector rolls (2a,2b) and said first supporting roll (3) being respectively subject to the following formula : in which D (mm) is a distance between the upper (5a,6a) and lower (5b,6b) electrodes, t (mm) being a thickness of the metal strip, w (mm) being a width of the metal strip, γ (kg/mm³) being a density of the metal strip and T (kg) being a tension applied to the metal strip; electroplating the metal strip between upper (5a,6a) and lower (5b,6b) electrodes arranged in said processing bath, said upper and lower electrodes extending essentially parallel to each other and separated from each other by a predetermined distance, and taking the metal strip out of said processing bath. A process as set forth in claim 1, wherein said holding arrangement further includes a second supporting roll arranged in said processing bath between said first and second deflector rolls, said second supporting roll extending in a direction essentially parallel to the axes of the first and second deflector rolls and being used for supporting said metal strip thereon so as to cooperate with said first and second deflector rolls and said first supporting roll to reduce the catenary of said metal strip, said second supporting roll being disposed such that distances ℓ between adjacent rolls including said first and second deflector rolls and said first and second supporting rolls are respectively subject to said formula. A process as set forth in claim 1, wherein said holding arrangement further includes a plurality of supporting rolls arranged in said processing bath between said first and second deflector rolls, each of said plurality of supporting rolls extending in a direction essentially parallel to the axes of the first and second deflector rolls and being used for supporting said metal strip thereon so as to cooperate with said first and second deflector rolls and said first supporting roll to reduce the catenary of said metal strip, said plurality of supporting rolls being disposed such that distances ℓ between adjacent rolls including said first and second deflector rolls and said plurality of supporting rolls are respectively subject to said formula. A process as set forth in any one of claims 1 to 3, wherein said metal strip is a steel plate having a density γ of 7.85 x 10⁻⁶(kg/mm³) and said distances ℓ between said adjacent rolls are respectively subject to the following formula : in which D (mm) is a distance between said upper and lower electrodes, W (mm) being a width of the metal strip and T (kg) being a tension applied to the metal strip.

Inventors: MORI, TADAKUNI KAWASAKI STEEL CORP., SHISMOYAMA YUJI@KAWASAKI STEEL CORP., UKENA, TOSHIMICHI KAWASAKI STEEL CORP., YAMAGUCHI, YASUHIRO KAWASAKI STEEL CORP., YASUNAGA, HISAO KAWASAKI STEEL CORP., Shismoyama YujiµKawasaki Steel Corp.
Applicants: KAWASAKI STEEL CORPORATION
Application year: 1986
Main classification: C25D7
IPC codes: C25D7