Title of Invention

AN APPARATUS FOR THE ELECTROGALVANIC METAL COATING OF STRIPS

Abstract

An apparatus for the electrogalvanic metal coating of strips which travel through an acid electrolyte enriched with metal includes at least one insoluble anode provided parallel to the strip, wherein the current flows to the strip switched as the cathode, and wherein metal is deposited from the electrolyte on the surface of the strip. Each anode is divided into anode strips parallel to the travel direction of the strip, wherein the anode strips are insulated relative to each other and each anode strip is individually supplied with current.

Full Text

The present invention relates to an arrangement for the electrogalvanic metal coating of strips which travel through an acid electrolyte enriched with metal. The arrangement includes at least one insoluble anode arranged parallel to the strip, wherein the current flows to the strip switched as the cathode, and wherein metal is deposited from the electrolyte on the surface of the strip. Cold-rolled strip of normal carbon steel must tie provided with a protective layer in order to prevent corrosion or at least significantly delay the corrosion. The type of protective layer depends on the intended use and the economical feasibili ty . Plants for applying such zinc layers on one side or both sides of the strip in thicknesses of about 2.5 to 15 micrometers are known in the art. The anodes are arranged parallel to the strip at as small a distance as possible of between 5 and 30 mm. The space between each anode and the strip is filled with an acid electrolyte which is enriched with metal, i.e., zinc . During coating, the current flows from the anodes to the strip which is switched as the cathode and the zinc is deposited on the surface of the strip. In these conventional arrangements, there are problems when coating on one side as well as when coating on both sides. The current flux density increases toward the edges of the strip. Consequently, an extremely high current density occurs at o"-- strip edges which leads to an increased depositing of zinc Therefore, the thickness of the zinc layer in the edge region of the strip is about 2 to 3 times greater than in the middle o* strip. c. Aside from the wasted metal and energy, this results in problems when coiling the strip and in the subsequent processing steps. For this reason, the edges of the strips must, be trimmed over a great width prior to coiling which leads to a significant material loss as well as additional work. If such an arrangement is to be used to coat the strip only on one side, there are additional problems. If the anode of the .. strip which is not be coated is completely removed or is replaced -by a dummy anode, for example, a plastic plate, not only the edges of the side to be coated are galvanized, but because the current flows around the edge, the edges of the side not be coated are also galvanized. edges into the U-shaped sections. Accordingly, it is necessary that the U-shaped sections always very exactly follow the strip travel. This requires a strip edge position measurement and complicated edge mask drives with complicated measuring and regulating technology. Another disadvantage of the edge masks is the fact that they are susceptible to trouble. For example, when the strip edges are not smooth or when width variations of the strip occur suddenly, the edge masks may be damaged. Expensive idle times and repairs are the consequence. Finally, the edge masks require a minimum n; stance between the anodes in order to be able to construct the edge masks with sufficient stability. ('/ In addition, the edge masks do not solve the problem that the coating thickness over the width of the strip is a direct reflection of the transverse section of the strip. For example, if the strip has a transverse arc or other non-planarities or inclined positions between the anodes, this results in a nonuniform coating thickness. In order to prevent this undesired effect, the prior art provides for expensive stretching and straightening plants arranged upstream of the coating processes. SUMMARY OF THE INVENTION Therefore, starting from the above-described prior art, it is the object of the present invention to provide an arrangement for the electrogalvanic metal coating of the above-described type in which edge build-ups of the deposited metal are safely prevented and, simultaneously, the disadvantages of the arrangements with edge masks are avoided. In particular, a uniform metal coating is to be ensured independently of any possible non-planarities of the strip, a removal of the anode on a sxde not to be coated is to be rendered superfluous and no moveable parts should be required in the anode area. In accordance with the present invent ion, in an arrangement of the above-described type, each anode is divided into anode strips parallel to the travel direction of the strip, wherein t.h." anode strips are insulated relative to each other and each strip is individually supplied with current. The arrangement according to the present invention makes it possible, in dependence on the respective width of the strip to be coated, to supply only those anode st.i. i.ps with current which are located opposite the strip. For this purpose, the actual strip position can be determined by means of the strip position measuring system which is already present; , The arrangement according to the present invention makes ir especially also possible to coat non-planar strips in an advantageous manner by switching off the current supply of individual anode strips which are closer to the.' strip surface than intended in accordance with the average value of the distances. Although the strip continues to be coated because of the dispersion effect of the adjacent anode strips, this takes place to a lesser extent. To an even lesser extent, this is also true for the strip which is next to the strip adjacent the anode strip. Consequently, switching-of t of individual anode strips has the consequence that the coating becomes more uniform. When the anode strips are insulated relative to each other by means of insulating materials arranged between the anode strips, and the insulating materials protrude at least above the surface of each anode facing the strip into the electrolyte, a current transfer from an anode strip supplied with current with an anode strip not supplied with current is effectively prevented. This also has an advantageous effect particularly in the strip edge areas because the current flux is directed toward the strip surface and high current density concentrations which are usual in the prior art are prevented. If the anode strips are sufficiently narrow, it is possible by selecting a cover of the top or bottom of the strip edges with current - supplied anode sti i.ps t.o coin, roi the layer thickness :.or example, such that the thickness decte^8r; i.uwaia the strip edge.. is uniform or increases toward the strip edge. it the anode strips are sufficiently narrow, the insulating strips protruding with the strip which may occur in the event of extremely non-planar strips or when the tension in the strip decreases. Accordingly, this embodiment of the invention safely prevents strip contacts which occur in conventional arrangements under current and lead to high short circuit currents and to significant damage of the anode surface. In order to eliminate this risk even more effectively, the insulating strips are preferably manufactured of wear-resistant and non-breakable material. Another significant advantage of the insulating strips protruding above the surface of each anode is the fact that the electrolyte is guided parallel with or against the strip travel direction. The uniform t. low speed adjusted over the sti ip width has the result of a more uniform metal deposition than in Alternatively, the thickness cf the coating can be controlled by dividing the anode strips of each anode several times over its length .and by supplying each anode strip portion preferably through a switch individually with current. For example, if the anode strip is divided four times, each anode strip can be supplied with 0%y 25%, 50%, 75% and 100% current. intensity. Consequently, a percentage adequate layer build-up is produced on the strip in the area of this portion of the anode strip. The various .features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to t:he drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

Documents:

883-mas-1998-abstract.pdf

883-mas-1998-claims duplicate.pdf

883-mas-1998-claims original.pdf

883-mas-1998-correspondence others.pdf

883-mas-1998-correspondence po.pdf

883-mas-1998-desription complete duplicate.pdf

883-mas-1998-desription complete original.pdf

883-mas-1998-drawings.pdf

883-mas-1998-form 1.pdf

883-mas-1998-form 26.pdf

883-mas-1998-form 3.pdf

883-mas-1998-other documents.pdf