Patent Publication Number: US-3880744-A

Title: Apparatus for the electrochemical treatment of metal strip

Description:
United States Patent Idstein m 3,880,744 Apr. 29, 1975 APPARATUS FOR THE ELECTROCHEMICAL TREATMENT OF METAL STRIP Walter ldstein, Oestrich, Germany Kalle Aktiengesellschait, Wiesbaden-Biebrich, Germany July 11, 1973 Inventor:  
 Assignee:  
 Filed:  
 Appl. No.:  
 Foreign Application Priority Data July 13, 1972 Germany 2234365 US. Cl. 204/206; 204/28; 204/207;  
  204/275 Int. Cl C23b 5/68 Field of Search 204/28, 206, 207. 275  
 References Cited UNITED STATES PATENTS 6/1926 Taylor 204/28 X 2.930.739 3/1960 Burnham 204/28 Primary E.\&#39;aminer lohn H.. Mack Assistant Examiner--W. 1. Solomon Attorney, Agent, or Firm-James E. Bryan [57] ABSTRACT This invention relates to an apparatus for the electrochemical treatment of metal strip, which comprises an electrolyte bath means having at least two compartments and provided with at least one electrode, guide means for guiding the strip through the electrolyte bath means, at least one duct means through which. in operation, the strip travels past the electrode. and means for maintaining different liquid levels in different compartments.  
 3 Claims, 2 Drawing Figures IIIIIIIIIIII/IIIIII II I I I I I APPARATUS FOR THE ELECTROCHEMICAL TREATMENT OF METALSTRIP The invention relates to an apparatus forthe electrochemical treatment of metal strip.  
 Metals may be electrochemically treated in order to remove some of the metal and thus to modify. and in particular, toroughen the surfaceuThe treatment also maybe carried out for the purpose of producing an oxide layer or of removing a metal coating layer.  
  When the metal to be treated is in the form ofendless elements. e.g. wires or strips. the treatment is preferably carried out by passing the elements continuously through the treatment bath.  
  It has been proposed, for example in German Offenlegungsschrift No. 1,621,115, to pass an aluminum strip through a succession of different electrochemical treatment baths in which the strip is first roughened electrolytically and then anodically oxidized The strip is passed through the various baths with the aid of guide rollers.  
  French Pat. No. 1,424,643. discloses an apparatus for the anodic treatment of aluminum strip in which the strip. passes horizontally through the treatment bath without the aid of guide rollers. and is led through inlet and outlet orifices in each of the side walls&#39;of the bath container, these orifices being fitted with sealing means to prevent the escape of liquid. The bath liquid is circulated by means of a pump in such a manner that a very turbulent flow is maintained between the strip and the electrode. This ensures a very rapid exchange of electrolyte at the surface of the strip and the rapid dissipa-&#39; tion of heat. Under these conditions it is possible to operate at high current densities and. therefore, to pass the strip through the bath at high speeds.  
 A disadvantage of this apparatus resides in the use of rubber sealing elements. which have an abrasive effect at the points where the strip enters and leaves the bath. The sealing means easily may lead to scratching of the surface of the strip, particularly when it has been electrochemically treated. Furthermore. the method of circulating the electrolyte as described in the French patent. supra. does not ensure that all theliquid in the bath is thoroughly mixed in the best possible manner.  
  Although, on account of the corrosive action of many baths. it is often desirable not to have guide rollers in the liquid. their use does provide considerable advan tages in those cases in which there is no risk of any significant corrosion. They permit the use of considerably shorter electrolyte baths and thus of apparatus occupying less space. Furthermore. no sealing elements having an abrasive action are required.  
  On the other hand it is difficult. when the strip is passed around a guide roller, to produce and maintain an even turbulent flow of the bath along the surface of the strip in a simple manner.  
  To achieve the highest possible flow velocities, it usually has been the practice to pump the liquid under pressure into the gap between the strip and the electrode, as indicated, for example, in the French patent. supra. and German Offenlegungsschrift No. 1,521,068.  
  It now has been found that when external pressure is used for this purpose this results practically always in surfaces that are not free from flow patterns or other irregularities attributable to an uneven flow of the electrolyte. It is apparently not possible, particularly when treating strip of very great width. toobtain under such conditions a completely unidirectional flow and a completely uniform velocity of flow over the entire width of the strip.  
  The present invention provides apparatus for electrochemical treatment of metal strip. which comprises an electrolyte bath having at least two compartments and is provided with at least one electrode, guide means for guiding the stripthrough the electrolyte bath, at least one duct throughwhich, in operation, the strip travels past the. or each, electrode, opposite ends of the. or each. duct being in different compartments of the electrolyte bath, and means for maintaining different liquid levels in different compartments whereby, in operation, the opposite ends of the, or each, duct are in compartments with different liquid levels.  
  The means for guiding the strip through the apparatus preferably comprises one or more guide rollers.  
  The differing liquid levels in the separated parts of the liquid-containingspace may be maintained by providing means for drawing the liquid by suction from one of the parts and pumping it back into the other part. 1  
  Using the apparatus of the invention. a unidirectional electrolyte flow between the strip and the counterelectrode may beobtained which is of high velocity and uniform over the entire width of the strip.  
  In one form of construction of the apparatus. the ends of the flow duct are at different levels. i.e., the duct is inclined at an acute angle to the vertical or even may be vertical. This enables shorter electrolyte baths and therefore space-saving complete installations to be used.  
  With particular advantage, two such flow ducts may be provided in one apparatus, these being disposed above a guide roller and in the path of travel of the strip. one upstream and the other downstream of the .guide roller. In this arrangement, the two ducts preferathe electrolyte bath. In this way it becomes possible for the strip to be threaded into the apparatus while not in the usually corrosive electrolyte, at the commencement of operations, or for any troubles occurring during operation to be readily eliminated without the need for draining the electrolyte from the bath.  
  Another form of construction of the apparatus has at least two guide rollers in the electrolyte bath. between which rollers the flow duct is disposed substantially horizontally. In this case. the liquid is forced to flow through the duct by the fact of the duct forming the only connection between the separated parts of the liquid-containing space.  
  In the apparatus of the invention. the liquid is always caused to flow simply by the difference between the hydrostatic pressures at the beginning and end of the flow duct. Thus. extremely simple means may be used for maintaining, between the surface of the strip to be treated and the electrode disposed opposite thereto, a vigorous turbulent flow which is uniform over the entire width of the chamber and which is so even that flow patterns are not formed on the treated surface. If the metal strip is to be electrochemically treated on one side only, it is advantageous to move it along close to that side-wall of the duct opposite to the electrode.  
  In the apparatus of the invention, metal strips may be electrochemically treated in various ways. Thus. for example. the surface of a strip can be cleaned. descaled or roughened by means of treatments using direct current or alternating current. It is also possible to carry out anodic oxidation or to galvanize the strip.  
  The strip may constitute the counter-electrode to the electrode or electrodes, or may form the central conductor between two electrodes of different voltage.  
  The latter system may be used in particular in the case of treatment using alternating current, but it also may be employed in direct-current treatment. In this case the strip forms the anode to one of the electrodes and the cathode to the other.  
  The apparatus permits work to be carried out with very high current densities, which are preferably within the approximate range of from 2 to 150 A/dm depending upon the type of treatment. In electrochemical etching it is preferred to use a current density ranging from approximately to 120 A/dm&#34;. With such current densities, treatment times of approximately 10 seconds to 2 minutes generally may be achieved.  
  The velocity of flow of the electrolyte in the gap between the strip and the electrode is adjusted to suit the required current density. The flow velocity may be adjusted by varying the difference between the level of the electrolyte in the separated parts of the liquidcontaining space and, optionally, by varying the distance between the side walls of the flow duct, i.e.. normally the distance between the strip and the electrode.  
  The apparatus is mainly designed for and suited to the electrochemical treatment of one side of metal strips. In principle it is also possible to carry out treatment of both sides of the strip by inserting a further electrode in that wall of the flow duct opposite the rear side of the strip and by passing the strip through the duct at a corresponding distance from this wall. In the treatment of one side of the strip. for which it is preferred to use the apparatus. the strip is generally passed at so small a distance from the rear wall that it almost touches it. In this mode of operation the rear side of the strip remains practically unchanged apart from narrow marginal zones. The distance between the strip and the electrode is usually in the order of magnitude of l to 5 cm.  
  The apparatus advantageously may be composed of a plurality of the above-described basic units and one electrolyte bath. Washing stations advantageously may be provided between these basic units in order to remove from the strip any adhering liquid picked up during treatment. Similarly. chemical etching or pickling units may be provided upstream of. downstream of. or between the electrochemical treatment stations. An example of the combination of a plurality of electrochemical treatment stages in a continuous installation is the electrochemical roughening and subsequent anodic oxidation of aluminum strip. Similarly. etching and galvanizing treatment of aluminum. copper. steel or other metal strip may be carried out in a number of successive stations using apparatus according to the invention.  
  The invention will now be explained in greater detail. by way of example only. with reference to the accompanying drawings, in which:  
 FIG. 1 shows a section through the basic unit of one form of construction of the apparatus of the invention, and  
 FIG. 2 illustrates another form of construction of the apparatus of the invention.  
  Referring to FIG. 1, a metal strip 1 is passed over the rollers 9, l0 and 11 and through a bath 2 containing electrolyte 3. Above the guide roller 10. the path of travel of the strip is surrounded by two flow ducts 5 and 5&#34; which are of shallow rectangular cross-section and are formed by outer walls 4&#39; and 4&#34; and electrodes 7&#39; and 7&#34;. constituting inner walls, and of end walls (not shown) disposed forwardly and rearwardly of the plane of the drawing.  
  Together with non-conductive wall parts which are contiguous with them at the top and bottom. the electrodes 7 and 7&#34; form a chamber 6 which is separated from the main liquid-containing space of the electrolyte bath 2 and communicates with this space only by way of the slots 8&#39; and 8 below the electrodes 7&#39; and 7&#34; respectively.  
  A guide roll 9 for the strip 1 is connected to the cathode. and the electrodes 7&#39; and 7&#34; are connected to the anode of a current source.  
  A suction pipe 12 extends into the chamber 6 to a point adjacent to its base. The suction pipe is connected at its other end to a suction pump 13 from which a pipe 16 leads back into the main liquidcontaining space of the electrolyte bath 2 by way of a throttle valve 15. A cooler 17 for removing excess heat is fitted near the point at which the pipe 16 enters the bath.  
  During operation of the apparatus. the strip 1 is passed at the required speed through the electrolyte. The liquid flows uninterruptedly downwards through the ducts 5 and 5&#34; and between the surface of the strip and the electrodes 7&#39; and 7&#34; respectively. It flows through the slots 8&#39; and 8&#34; into the chamber 6 and is there continuously drawn off by suction through the pipe 12 and with the aid of the pump 13. The suction force is regulated by means of the throttle valve 15 which is controlled by an adjustable level probe 14.  
  The entire part of the apparatus consisting of the guide rollers 9, l0 and 11, the chamber 6, the flow ducts 5&#39; and 5&#34;. and the suction means is connected to form a single unit and can be raised from the electrolyte bath 2.  
  FIG. 2 shows in a simplified form a further construction of apparatus in accordance with the invention. Here the strip is passed over two guide rollers 10 and 10a which are disposed at the ends of an elongate electrolyte trough 2. The trough contains two basic units each having two flow passages. The main liquidcontaining space of the trough 2 is separated by a partition 18 which is so fitted as to leave only a narrow gap, through which the strip can pass, above the bottom of the vat. In the left-hand half of the vat is a separated chamber 6 in which the liquid level is lower than in the main liquid-containing space. The level of the liquid&#39;in the chamber 6 is kept constant by means of the overflow 19 through which the liquid flows, by way of a discharge pipe, not shown. and into a reservoir from which his pumped back into the electrolyte trough.  
  The electrolyte flows from the main liquid-containing space through the flow ducts 5 and 5 between the strip 1 and the electrodes 7&#39; and 7&#34;. and into the chamber 6.  
  The basic unit shown in the right-hand half of the electrolyte vat 2 consists of the same elements as the unit on the left-hand side. The related reference numerals are in each case followed by a small letter a for the purpose of differentiation.  
 The electrodes can be connected to suit the required results. In the drawings the electrodes 7&#39; and 7&#34;a are connected to the negative pole and the electrodes 7&#34; and Tax to the positive pole of a direct-current source. In this case, the strip acts as a central conductor between the oppositely poled electrodes 7&#39; and 7&#34;. and Ta and 7&#34;a, respectively.  
  It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.  
 What is claimed is:  
  1. An apparatus for the electrochemical treatment of metal strip which comprises an electrolyte bath means having two compartments, one compartment being the main compartment and the other being a common compartment, and provided with two electrodes. a guide roller for guiding the strip through the electrolyte bath means. two duct means arranged in a V-form above the guide roller. one upstream and one downstream of the guide roller in the path of travel of the strip, through which duct means. in operation. the strip travels past the electrodes in a straight line toward said guide roller and in a straight line from said guide roller,  
 means connecting the lower ends of the two duct means to the common compartment separate from the main compartment of the electrolyte bath to which the upper endsof the duct means are connected, and means for maintaining a liquid level in the common compartment lower than that in the main compartment.  
  2. An apparatus as claimed in claim 1 in which the common compartment to which the lower ends of the duct means are connected lies between the two duct means, and including means whereby the part of the apparatus comprising the duct means, the said common compartment and the guide roller may be raised from the main compartment of the electrolyte bath.  
  3. An apparatus as claimed in claim 1 wherein the distance between the electrode and the path of travel of the strip is in the range of about 1 to 5 cm.  
  l l= l= l l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,880,744 DATED April 29, 1975 INVENTOR(S) 1 Walter Idstein It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below; I  
 Item should read HOECHST AKTIENGESELLSCHAPT,  
 Frankfurt/Main, Germany Signed and Sealed this twenty-ninth Day Of July 1975 [SEAL] RUTH C. MASON C. MARSHALL DANN Arresting ()jficer (&#39;mnmissium&#39;r oflarents and Trademarks