Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Controlling current distribution within bath
Patent
1991-08-06
1994-06-21
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Controlling current distribution within bath
205130, 205138, C25D 502, C25D 706
Patent
active
053226143
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a device and process for electrolytic deposition of metals on one or both sides of strips which form the cathode, preferably steel strips.
2. The Prior Art
In horizontal or vertical galvanic systems of this type, the deposition of metals from the electrolyte takes place on strips which form the cathode, which pass through two anodes which are parallel to one another and insoluble. An electrical charge, generally rectified, is applied to the two anodes, so that the metallic precipitation on the strip passing through takes place under the known suitable conditions. Such a system is known, for example, from DE-OS 35 10 592. Such and similar devices are also used, however, for one-sided coating of the strip passing through. One of the two parallel anodes is then removed from the device. Since systems generally have several pairs of anodes arranged one after the other, through which the strip passes, this results in long setup times of the system for one-sided coating. In addition, it is frequently found that in spite of the absence of the removed anode, partial coating takes place on the side of the strip which is not supposed to be coated.
Attempts have also already been made, in order to avoid such setup times, to have no current or voltage applied to one of the two anodes in each case. In operation, however, it turns out that in such a case, a disruptive metal precipitation on the anode takes place, both on the side of the strip which is not supposed to be coated, and in the lower anode region. Depending on the anode material, e.g. in the case of iridium dioxide coated anodes, this causes the surface to be passivated in the lower region and therefore to become unusable. The explanation must obviously be seen in the fact that a voltage drop from the entry point to the exit point of the segment of the strip to be coated takes place, so that potential differences between the anode, which actually has no current applied to it, and the strip segment opposite it occur, which are obviously sufficient to trigger deposition processes in the direction of the anode and/or the strip.
It has therefore already been proposed that the current-free anode be insulated from the strip segment by intermediate placement of an insulation, for example a thin plastic sheet. However, it is frequently not possible to place such insulation sheets in the very narrow gap between the strip and the anode. Furthermore, such a measure also requires significant setup times when switching from two-side coating operation to one-sided coating operation and vice versa.
SUMMARY OF THE INVENTION
The task of the invention consists of improving a device of the type stated and its method of control, in such a way that one-sided coating is made possible with simple means, without significant metal precipitation on the side of the strip which is not supposed to be coated, or on the anode.
The task of the invention is accomplished with a device in which the strips to be coated are guided in a slot between 2 anodes which are arranged parallel to one another and are insoluble. An electric charge can be applied to the anodes independently. One of the anodes is subdivided into several segments which are electrically insulated from one another. Different electrical charges can be applied to the several segments.
According to a preferred embodiment of the invention, the corresponding anode is subdivided into several segments of the same size, where the anode segments can be held in a holder, with clear segments or insulating pieces between them.
In one-sided coating operation, no current is applied to the anode, in known manner. Since the anode according to the invention is subdivided into relatively small segments in the direction of motion of the strip to be coated, only small voltage potentials relative to the strip to be coated can build up in these segments, which are small as compared with the overall length of the anode, and such potentials are not able to trigger deposition
REFERENCES:
patent: 3522166 (1970-07-01), Jones
patent: 3880725 (1975-04-01), Van Raalte et al.
patent: 3970537 (1976-07-01), Froman et al.
patent: 4240881 (1980-12-01), Stahya
patent: 4347115 (1982-08-01), Espenhahn et al.
patent: 4597837 (1986-07-01), Oda et al.
May Hans J.
Schnettler Roland
Leader William T.
Niebling John
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