US3471375A - Process and apparatus for continuous anodic treatment - Google Patents

Abstract

An aluminium rod, wire or strip 12 is continuously anodized to produce a porous oxide film thereon by successively moving it through an electrolytic cleaning cell 10 and anodizing cell 11, wherein there is maintained in contact with the electrolyte an anode for cell 10, e.g. consisting of upper and lower lead anodes 14, 15, and a cathode for cell 11, e.g. consisting of upper stainless steel cathode 18 and preferably a lower graphite electrode 19, the cleaning and anodizing cells being in open communication with one another through a connecting zone so dimensioned that leakage current is less than a quarter of the total current, the electrolyte being maintained in turbulent flow lengthwise of the moving aluminium e.g. by re-circulating the electrolyte collected from <PICT:1087256/C6-C7/1> pipes 51, 52 at the strip-inlet end of the anodizing cell to the strip-outlet end through pipes 67, 68 using pump 117, and D.C. 135 being passed between the anodes and (one or both) cathodes through the electrolyte and strip 12 at a current density of at least 100 A.S.F. of aluminium surface exposed in the anodizing cell 11. The electrolyte in the anodizing cell may be separated into two parts by the strip (as shown), one part contacting the cathode 18 and the other part contacting an anode 19 (switch contact 139) whereby oxide film is formed on one side only of the strip. Alternatively both parts may contact cathodes (switch contact 143), preferably the potential of the two cathodes 18, 19 being at different values (switch contact 144 connecting cathode 19 through a variable resistor 145) whereby oxide films of different thickness are formed on the two sides of the strip.

Description

Oct. 7, 1969 w. E. COOKE ET AL PROCESS AND APPARATUS FOR CONTINUOUS ANODIC TREATMENT 5 Sheets-Sheet l Filed Aug. 18. 1964 Worf/ey Oct. 7, 1969 W. E. COOKE ET AL PROCESS AND APPARATUS FOR CONTINUOUS ANODIC TREATMENT 5 Sheets-Sheet 2 Filed Aug. 18, 1964 Oct. 7, 1969 w. E. COOKE ET AL 3,471,375

PROCESS AND APPARATUS FOR CONTINUOUS ANODIC TREATMENT Filed Aug. 18, 1964 5 Sheets-Sheet 3 QQ QQ bm MN /n ven fors Pau/ Sm/'fs Jacques Franco/s C/e S. AMM/MJ A Harney Oct. 7, 1969 wv, E, COOKE ET AL Y 3,471,375

Paocss ANU APPARATUS Foa CONTINUOUS ANoDIc TREATMENT Filed Aug. 18, 1964 5 sheets-sheet 4 i /nvenfors W////0m Err/as. 60o/re Pau/ .Sm/fs Jacques Franco/s Cfe' A//Ofney Oct. 7, 1969 w, E, COOKE ET Al. 3,471,375

PRUczss ANT APPARATUS FOR CONTINUOUS ANoDTc TREATMENT .filed Aug. 18, 1964 5 sheets-sheet 5 United States Patent O 3,471,375 PROCESS AND APPARATUS FOR CONTINUOUS ANODIC TREATMENT William Ernest Cooke, Paul Smits, and Jacques Franois Ct, Kingston, Ontario, Canada, assignors to Aluminium Laboratories Limited, Montreal, Quebec, Cauada, a corporation of Canada Filed Aug. 18, 1964, Ser. No. 390,367 Int. Cl. C23b 9/02, 5/58; B011: 3/00 U.S. Cl. 204-28 21 Claims ABSTRACT F THE DISCLOSURE In procedure and apparatus for continuous anodizing of work such as aluminum strip or wire, the work traverses an elongated vessel passing successive electrodes, advantageously in the wall, from which current passes at high -density through the electrolyte to the work and then from the work through the electrolyte to the other electrode, the electrodes being mutually spaced lengthwise of the work path so that leakage current through the electrolyte itself between the electrodes is relatively Very small, while the vessel is of full cross-section throughout the entire path. With recirculation, the electrolyte travels continuously and preferably with turbulence from one end of the vessel to the other, the structure of the apparatus providing sealed ingress and egress of the work while guiding the electrolyte into and out of its path, and the section of the vessel intermediate the electrodes being of insulating material. Exceptionally high current, high speed operation is obtainable with minimum of electrical loss and especially with optimum avoidance of overheating and breakage of the work.

This invention relates to the production of anodic coatings or films on aluminum, the term aluminum being employed to include aluminum base alloys which, like pure aluminum, are susceptible of being anodized to produce porous type oxide films. More particularly, the invention is directed to apparatus and procedure for continuous anodizing of extended aluminum articles, meaning sheet, strip, wire, rod or the like, being articles that are greatly elongated and may therefore be caused to traverse continuously one or more baths wherein anodizing or other treatment is performed. In a further sense, the present improvements are concerned with processes for continuous electrolytic treatment of elongated aluminum members, including both anodic and other operations, a particular aim being to afford an improved method of performing a combination of treatments, including anodizing treatment, on the passing member, while advancing the latter at a relatively rapid rate of travel.

In another sense, the invention is an improvement of certain procedure, of a prior and related invention, wherein an elongated aluminum article, such as strip or wire, is continously advanced through cathodic cleaning and anodizing stages while subjecting the moving article in each stage to turbulent ow of the electrolyte. In previous examples of practice of that basic method, a strip or the like advanced in succession through cathodic cleaning and anodizing compartments, traverses a narrow orifice in a wall between them, which is designed to prevent appreciable connection or intermediate flow of electrolyte.

Where the anodizing current or a substantial part of it is carried through the strip or wire (such current entering and leaving through the electrolyte in the respective compartments), one function of the partition and its restrictive orifice has been to avoid current by-pass or short-circuit in the liquid, i.e. in that an undesirably large current would have been expected to pass from the elec- ICC trodes in one compartment to those in the other directly through a continuing body of electrolyte between them. In this connection, it should be appreciated that the potential difference between the electrodes is relatively high in anodizing operations, in contrast to other types of electrochemical work. Thus the voltage requirements for anodizing are always in excess of 10 or 15 volts, or at least about 15 volts and above, where as the voltages applied -for other electrolytic treatments such as pickling and plating are customarily much lower than the values just indicated. Indeed in high speed continuous anodizing, the required voltages are of the order of 20 volts and upwards, which has led to the employment of diaphragm arrangements, with narrow orifices, as explained above, for the purpose of avoiding unduly severe leakage currents.

While satisfactory, high speed anodizing operations have been achieved with the forms of treatment described above, and while the employment of turbulently owing electrolyte, e.g. on both sides of the strip, is of basic advantage in permitting high current densities without burning or otherwise impairing the anodic coating as it forms, an important object of the present invention is to afford improved ways of performing the basic process as just described.

Still further objects are to simplify and expedite continuous anodizing procedures, and to provide for such operations with a minimum of equipment and indeed with apparatus of relatively simple and economic character.

Another object is to alford improved means and arrangements of anodizing apparatus, capable of effective and reliable use in high speed operation.

To these and other ends, an important aspect of the invention is predicated on the discovery that cathodic cleaning or similar action on the passing strip, and the desired anodizing treatment, can effectively be achieved by moving the strip or other work continuously through a single electrolyte-filled region, i.e. a region preferably so arranged that electrolyte is moved continuously through it, e.g. in the desired turbulent manner, from one end to the other, and without intermediate apertures or provisions for separately handling the electrolyte in localities of different treatment. In a more general sense, whether cathodic cleaning is actually needed or not, the invention contemplates a single tank operation whereby anodizing current may be conducted to the passing article, and then from the latter as anode, for the production of the anodic coating, to suitable electrode means. The operation thus involves effectively making contact with the strip by liquid engagement alone while providing, if desired, for anodizing both sides of the article and for doing so in a better way.

Thus in presently preferred embodiments of the new method, the strip or the like is advanced continuously lengthwise through an elongated treatment region, lled with moving electrolyte, where in one portion of such region current is conducted from local electrode means through the liquid to the strip, and in another portion, spaced from the rst, the anodic treatment is eifectuated by flow of such current from the strip to similarly local electrode means.

It has been found that even though the cross-section of the electrolyte-filled region may be substantially the same throughout its length, operation in the manner described is entirely feasible, without economically undesirable losses due to by-pass of electrolytic current through the electrolyte. Indeed circumstances can preferably lbe such that the by-pass of current is only a very low fraction of the total current (even with relatively short spacing between the localities of successive treatments), while a full circulation of the same electrolytic liquid is attained throughout the entire length of the cell.

A particular feature is that the cross-sectional area of the liquid filled cell assembly through which the elongated work travels longitudinally, or at least the connecting region between the treatment zones, is selected so that it is sufliciently small to allow by-pass of only the desired minor fraction of current (e.g. less than one-fourth of the total), and yet sufiiciently large that adequate control of electrolyte temperature and concentration is possible, as by rapid flow of such electrolyte along and in contact with the surface of the work. Specifically, it has been found that these criteria can be achieved in a satisfactory manner and within practical dimensional limits, in coaction with provision for the desired temperature-controlling ffow of electrolyte from one end to the other of the entire cell or system.

Among Various advantages of the present procedure and the apparatus for carrying it out are the facts that: the metal of the article is continuously exposed to a substantial -volume of electrolyte through all areas, between as well as along the areas of the successive treatments; there is a gradual transition of polarity of the aluminum article from negative to positive; there is no need for an orifice or other special structure between successive regions of treatment; and the apparatus may be of the simplest form, with a corresponding minimum of external piping, temperature control, pumping and related instrumentalities in the electrolyte circulating system.

The elimination of a central orifice or other region closely confining the strip or wire in effect increases the current-carrying capacity of the latter, whereby maximum current densities are attainable in anodizing and correspondingly high speeds of operation can be achieved. In prior practice, utilizing such an orifice between the cathodic cleaning and anodizing tanks, it has been found that an increase of the current beyond a determinable value often actually results in breakage of the wire or strip as it traverses the orifice. Excess heating effect in even a short orilice region can sometimes damage or break the wire or strip, there being (as explained above) no substantial cooling by electrolyte tiow at this point. These hazards or limitations are greatly overcome by the present invention, allowing turbulent flow of electrolyte at all localities throughout the tank.

Expressed in another way, an important aspect of the invention is specific to high speed anodizing with a flowing electrolyte. The advantages of the operation in an essentially single tank or channel, without a diaphragm or orifice arrangement separating the regions of electrodes of different polarity, are notably significant in continuous high speed treatment. The flow of current required for the anodizing function is then unusually large, to obtain the desired high current densities, yet in comparison the leakage or by-pass current of the present process is small, even for rather short distances of separation between the electrode areas. The latter current is governed by the voltage rather than the absolute value of anodizing current, and the voltage, although high in comparison with some other electrochemical operations, does not increase in proportion to the anodizing current, hence the by-pass current becomes very minor relative to the large magnitude of that required to form the anodic coating, and may be, for example, not more than several percent of the total current.

At the same time, the absence of a diaphragm or partition enables full temperature control, e.g. cooling, to be achieved by rapid, turbulent flow of electrolyte at all localities of the moving aluminum strip or the like, including especially the region between the electrode zones, which is the place of maximum current tlow in the metal of the strip and thus of maximum heating effect. By omitting an orifice or restricted area there, the danger of breakage or damage to the strip by insuicient cooling in this critical region is obviated or greatly reduced. Hence there is a special relation of the present process and system to the attainment of safe and dependable anodizing operation at very high speeds, in that the invention permits elfective cooling for the sake of safety to the work at high current values, and also takes advantage of those high current values in the sense that the by-pass or leakage current through the unobstructed mid-region is then very minor (and thus inconsequential as a factor of loss) in relation to the total current.

The operation, moreover, is greatly simplified in requiring only a single stream of electrolyte for both electrode zones (and the central zone) in sequence. These several aspects of the process thus complement each other in an unusual way, for the promotion of improved or higher speed operation in the special field of rapid continuous anodizing as described.

v For accomplishment of one or more of the foregoing and other objects, certain examples of the process and apparatus are set forth hereinbelow and illustrated in the accompanying drawings, wherein:

FIG. 1 is a schematic view of an anodic treatment operation in accordance with the basic principles of the invention;

FIG. 2 is a simplified perspective view of a presently preferred form of apparatus utilizing the invention;

FIG. 3 is a longitudinal vertical section of the cathodictreatment part of the apparatus, as on line 3 3 of FIG. 2;

FIG. 4 is a horizontal section taken on line 4-4 of FIG. 3;

FIG. 5 is an enlarged, perspective, exploded view, with certain portions broken away, of the electrolyte discharge header and an accompanying portion of the cathodic treatment tank or vessel, seen as if looking toward the region of the line 5 5 in FIG. 3;

FIG. 6 is a longitudinal, central, vertical section, essentially on line 6-6 of FIG. 2, showing the anodizing chamber and electrolyte inlet headers and distribution means; and

FIG. 7 is a transverse vertical section on line 7-7 of FIG. 6.

Referring first to FIG. 1, for illustration of the principles of the new procedure, the strip 10 of aluminum is continuously withdrawn from a supply reel or coil 11, as by being wound on a take-up reel 12, remotely located therefrom and appropriately driven by conventional means, not shown. The strip 10 is advanced continuously lengthwise through a treatment vessel 14 having a cathodic cleaning compartment 15 and an anodizing compartment 16, separated by an intermediate transfer region 17, all of these regions having substantially the same crosssection, as for fiow of electrolyte above and below the strip.

Although in some situations, the electrolyte ow may be concurrent, a preferred countercurrent arrangement is illustrated in all of the drawings. Thus there is an appropriate electrolyte inlet header or distribution chamber 20 at the strip exit end, having suitable piping 21, 22 for supply of rapidly fiowing aqueous electrolyte above and below the strip. A similar outlet header or distribution chamber 23 is located at the strip entrance, i.e. the lefthand end of the apparatus of the diagram, with associated llquid discharge pipes 24, 25. Suitable seals are included for entrance and exit of the strip respectively at the distribution chambers 23 and 20, e.g. pairs of heavy, selfclosing flaps or the like 26, 27, of natural or synthetic rubber or other elastic material.

At the cathodic cleaning region 15, there are suitable electrodes, such as the upper and lower fiat plates 28, 29 disposed to be parallel with the passing strip, and similar electrode plates 30, 31 at the anodizing region. The tank is completed in the transfer region 17 by appropriately insulated wall structure enclosing the vessel and separating the two sets of electrodes, such structure including upper and lower walls 32, 33, which with the two sets of electrode plaies constitute the entirety of the horizontal portions of the enclosure above and below the passing strip. As will be noted, the strip may traverse additional treating stations either before or after its travel through the successive regions 15, 17 and 16, one such operation being illustrated as the rinse tank 35. Other such operations, not shown, might include washing, ahead of the tank 14, and also beyond the tank 35, such steps as further rinsing, sealing and drying.

It will now be seen that if the electrodes 28, 29 are connected to the positive terminal of a source of direct current, and the electrodes 30, 31 to the negative terminal of such source, and if electrolyte is caused to flow through the entire vessel from the header 20 to the header 23, filling all of the space in a turbulent manner, a sequence of electrolytic treatments is performed on the strip as it travels through, i.e. a cathodic cleaning operation in the region and anodic coating operation in the region 16. With a suitable cross-section of the tank, preferably of limited size as is desirable for electrolytic efliciency while permitting sufficient electrolyte circulation, and with sutiicient length of the intermediate, insulated region 17, high intensity anodizing is readily achieved, with correspondingly high values of current density. At the same time it is found that by-passed current through the electrolyte at the region 17 is small relative to the stated high anodizing current, and in consequence `a high speed of operation is safely and simply achieved.

lIn the given example of the method, current thus enters the liquid, i.e. the electrolyte, from both of the plates 28, 29, and is conducted through the liquid to the strip 10, through which the current iiows to the anodizing region 16, where such current then travels from the strip 10, again through the liquid, to the exposed upper andv lower electrodes 30, 31. The desired cooling or temperalture-controlling flow of electrolyte occurs uniformly throughout the entirety of strip travel, i.e. in all areas of anodizing action and indeed throughout all regions where electric current is being carried in the strip, including a locality -of maximum current ow therein at the region 17. Thus full cooling or temperature control effect is maintained at all surfaces of the strip, yet there is need only for one system of electrolyte circulation, correspondingly having a single place of electrolyte feed and a single place of discharge, i.e. respectively at the outermost ends of the tank.

The equipment may embody any suitable materials of construction, the electrodes 28 and 29 being conveniently of lead, although other materials such as graphite can be used. Likewise the electrodes 30, 31 of the anodizing zone may be appropriate as cathodes for the anodic treatment there, e.g. being members of stainless steel, or indeed other materials, such as other steel, lead, graphite or the like. The tank housing or wall at the central region 17 is preferably of insulating character, e.g. suitable plastic or resin filled with asbestos fiber, glass fiber or other reinforcing material. The end housings 36, 37 for chambers 23 and 20 respectively, may also be of insulating material where various types of electrical circuits are to be accommodated, although simple metal construction may sometimes be employed where the upper and lower electrodes in each pair are always electrically connected so as to have the same polarity.

The improved procedure and apparatus are adapted to a variety of types of anodizing treatment, with or without the combination of a irst cathodic cleaning, and may utilize direct current, alternating current, or equivalent special current supplies such as alternating current superimposed on direct current, periodically reversed current, or periodically interrupted direct current. For simple illustration of various types of treatment eifectuated with D.C., FIG. 1 shows a set `of connections wherein a conductor 38 extends from the upper electrode 28 to the positive terminal 39 of a suitable source of D.C., having its other terminal 40 connected through the conductor 41 to the upper electrode plate 30. The lower electrode plate 29 of the cleaning compartment extends to a switch arm 42 adapted to engage either of two switch contact localities 43, 44, the latter being connected to the conductor 38 and thus to the positive current supply terminal. The lower electrode 31 of the anodizing section is similarly connected to a switch arm 45 which may engage either a switch point 46 that extends to the electrode 29 and switch arm 42, or a switch point 47 which runs to the conductor 41 and the negative source terminal 40, or a still further switch point 48, where connection is made through a variable resistor 49, again to the negative terminal 40.

For cathodic cleaning of both sides of the passing strip 10 and anodizing operation likewise on both sides, the switch arm 42 is placed -on contact 44 and arm 45 on contact 47 whereby the positive terminal extends to both the cleaning electrodes 28, 39 and current returns to the negative terminal from both of the electrodes 30, 31 of the anodizing section. In this instance, the entire current travels through the strip as explained above, except, of course, for the small proportion of current that is by-passed. If cathodic cleaning is not of consequence, it may in some instances be feasible to dispose the switch arm 42 on the open contact 43, so that current only flows into the strip from the electrolyte above it, and the electrode 28. If it is desired to anodize only one side of the strip, for example the upper side, one set of connections involves the arm 42 on open point 43 and arm 45 on the switch point 46; the positive terminal of the source is then connected only to the upper electrode 28, and the negative terminal 40 extends only to the upper electrode 30, neither of the lower electrodes being then energized and the entire electrolytic action, both cleaning in the section 15 and anodizing in the section 16 being essentially limited to the upper face of the passing article 10. Alternatively, if the switch arm 42 is placed on contact 44 and the arm 45 again on contact 46, the anodizing action is still limited to the upper surface of the strip (by current flow from the strip as anode to the upper electrode 30), but current flows into the strip from both of the electrodes 28, 29 and also from the lower electrode 31 of the anodizing region, i.e. traversing the electrolyte in each locality. This arrangement has some advantage in reducing the amount of current that actually travels along the strip itself, i.e. between the regions 15 and 16.

Finally, in further accordance with arrangements contemplated in a prior invention here applicable, so-called differential anodizing may be eiiected by placing the switch arm 45 on the contact 48 and placing the arm 42 on either of the contacts 43, 44, i.e. utilizing the latter if `effective cathodic cleaning is desired for both sides of the strip. In such cases, and in proportion to the adjustment of the resistor 49, the current flow from the strip as anode in the section 16 is effected at different current densities at opposite sides of the strip, for example to achieve different thicknesses or other properties of the applied anodic ilm. Such operation is desirable and economical where a heavy protective coating is needed on one face of the sheet 10, while only a thin or less rugged coating will suffice for the opposite face.

As explained, the described system takes advantage of the principle of liquid contact, avoiding any direct mechanical engagement for electrical connection to the work, yet affords rapid continuous anodizing treatment. Only a single circulation of electrolyte is needed throughout the entire system, and effects due to overheating, abrasion or other action of an orifice region intermediate successive electrolytic treating or contact zones are avoided. Turbulent flow of electrolyte, with full cooling effect, is possible throughout the entire length of the work, whether strip, wire or other shape, at all localities where it is carrying current, indeed usually very heavy current. In consequence a simple and reliable operation is achieved for high speed anodizing.

FIGS. 2 to 7 inclusive illustrate, in somewhat simplilied form, a specific system of apparatus, having certain further features of novelty and advantage, for carrying out the basic operations as described above. As seen in FIG. 2, a continuous aluminum article, such as the strip 10, is advanced continuously lengthwise, for example in ilat horizontal position, through an elongated vessel consisting, in sequence, of a first or cathodic cleaning section 50 and a second or anodizing section 51, the rst section 50 including also a separating portion 52 as explained below. Again, for circulation of electrolyte countercurrent to the strip advance, a liquid distribution header 54 is provided at the righthand, strip-exit end of the anodizing section 51, while a liquid discharge header 55 is located at the strip-entrance end of the cathodic section 50. Liquid leaves the outlet header 55 through a pair of downwardly extending ducts 56, 57, being received by an electrolyte reservoir 58, which may also include suitable temperature control means, with associated cooling means; the control and cooling means may consist of instrumentalities conventional for such operation on flowing liquids and are therefore not here illustrated in detail.

From the reservoir 58, electrolyte is withdrawn at a suitable rate through the pipe 59, by a pump 60, and is delivered through a further pipe 61 in branching ducts 62, 63 to upper and lower parts of the inlet header 54, whereby the liquid is delivered for turbulent flow along the interior of the chambers 51, 50 and in contact with both upper and lower surfaces of the passing strip 10. The electrolyte is preferably an aqueous solution, eg, of sulfuric acid, having a suitable concentration as in the range of to 50% by weight, one convenient formulation being a sulfuric acid solution.

As shown in FIGS. 3, 4 and 5, the main body of the cathodic cleaning or contact section advantageously comprises a monolithic structure of asbestosfilled resin or equivalent, strong plastic or other electrical insulating material having an upper wall 65, a lower wall 66 parallel thereto, and side walls 67 and 68. This housing is of the general conguration of a flattened tube of rectangular cross-section having open ends provided with attachment anges 69, 70. The upper wall or top has a row of transverse internal recesses or sockets 71, each extending entirely across the housing, being closed at one end by the wall 67 and opening through the other wall 68, each such recess being shaped to accommodate a slab 72 of lead or other suitable conductive material to serve as part of the electrode system for the upper region of the cathodic cleaning zone. As will be noted, the recesses 71 are open at their lower sides, but have undercut areas forwardly and rearwardly in the direction of strip travel so as to provide shoulders or flanges 74 to retain the electrode slabs 72 in place. By providing a plurality of such recesses or sockets 71, each filled with an electrode slab 72, in parallel array along the upper wall 65, an effectively extended electrode structure is achieved. For instance, seven (7) such electrode slabs may be provided, although for simplicity the drawing illustrates lesser numbers, as with the housing broken away in FIG. 3.

A similar system of identical recesses or sockets 75 and electrode slabs 76 (of lead or the like), with corresponding retaining shoulders 78, are provided in the lower wall or bottom 66 of the housing 50. Hence the strip 10, as it moves through the cathodic cleaning zone 50, travels with its upper and lower faces respectively in parallel to, and spaced shortly from, the exposed surfaces of the upper and lower electrode slabs 72, 76.

Where the recesses 71, 75 traverse the housing side wall 68 (such wall being vertically enlarged and transversely thickened for reinforcing purposes), the electrode slabs 72, 76 project through the wall as shown in FIGS. 4 and 5 and permit ready attachment of electrical connectors of suitable sort, not shown. The electrode elements may be appropriately sealed with respect to the housing, as by sealing rings 80 around their necks, and plates 81 fitted against the sealing rings, the plates being secured by bolts or the like, not shown. For clarity, the plates 81 are omitted in FIG. 5, and only shown at some of the localities of the electrode necks in FIG. 2.

This electrode structure for the cathode cleaning section 50 permits a fully enclosed and sealed housing, to contain the liquid, and at the same time affords ready removal and replacement of the electrode members 72, 76 whenever necessary. For such replacement, the sealing plates 81 are removed, and the slabs or elements 72, 76 withdrawn endwise from their sockets, replacement being effected in similar, reverse manner.

The housing structure 50 also includes a portion 52, extending beyond the upper and lower arrays of electrode slabs, in the direction of the travel of the strip 10, and terminating with the attachment flange 70. This section 52 is in effect simply a attened tubular passage, conveniently having the same internal dimensions and cross-section as the cavity of the electrode region. Being made of insulating material, section 52 serves to separate the first region of liquid electrical contact from the following anodizing region 51, being found, as explained above, to afford sufficient length of electrical path so as to minimize or inhibit objectionable by-pass of current.

The anodizing section 51, as shown in FIGS. 2, 6 and 7, comprises again a shallow, rectangular tube or box-like structure constituted by an upper plate 83, a lower plate 84 and coextensive side walls 85, 86, this assembly being provided with attachment flanges 87, 88 at its respective open ends. Thus the flange 87 is secured to the flange 70 of the first section 50 so that the internal channel of the latter communicates squarely with the identically dimensioned channel in the section 51. The upper and lower walls or plates 83, 84 advantageously constitute electrodes for the anodizing section, current here flowing from the strip 10 to these electrodes for anodizing respectively the upper and lower surfaces of the strip. These members 83, 84 may be made of suitable material, such as stainless steel, other types of steel, or indeed any conductive material appropriate for the selected electrode situation in anodizing operation. While in cases where the plates 83, 84 are of different polarity or otherwise of differing electrical situation, the side walls or rails 85, 86 should be 0f insulating material, they are shown in FIG. 7 as made of metal, eg. stainless steel, for apparatus employed in twoside anodizing with the same electrical connection of both electrodes 83, 84.

If desired to prevent accidental, mechanical contact of the passing strip with the exposed face of either electrode,

insulating shield structure 88a may be secured against the exposed face of each electrode. Each shield 88a consists essentially of an open frame of thin insulating material, having longitudinal members 89 at the sides and transverse members 90 at widely spaced localities, whereby the mechanical separating function is achieved without appreciably covering the electrode 83 or 84 with respect to its electrical function. Likewise if desired, long channelshaped members 91, 92 may be mounted within the section 51 so that their channel recesses provide loose guides for the strip 10, these guides being shown in FIG. 7 and one of them, guide 92, being fragmentarily indicated in FIG. 6, it being understood that when used they conveniently extend the length of section 51. In many cases these guards or guides are unnecessary, but they may have the special function of avoiding over-anodizing adjacent the edges of the strip, if there is a tendency of such action.

Referring to FIGS. 2 and 6, one arrangement of a liquid inlet header 54, for flowing electrolyte, is shown in simplied and somewhat schematic manner, as comprising a box-like metal structure providing upper and lower transverse chambers 94, 95, communicating at their ends respectively (i.e. at one side of the assembly as seen in FIG. 2) with the ducts 62 and 63. Curved baffle structures 96, 97, respectively below the chamber 94 and above the chamber 95, guide the liquid downwardly or upwardly and then horizontally into the anodizing section or chamber S1, these baffles being arranged to provide an entrance cavity 98 which is conveniently congruent in cross-section with the channel of the section 51. The flange 88 is suitably bolted to the rear wall 99 of the header 54.

The guided path for the liquid may be further defined, as by appropriate baffles or blocks 100, 101 of reinforced resin or like material, these blocks being fitted in the front wall 102 of the header S4 and being also shaped to define an exit slot 103 for the strip 10, as well as having sloping surfaces 104, 105, respectively, to coact with the baflles 96, 97 in constituting the inlet liquid passages, With some undercut or bevel adjacent the strip path, as shown.

Although various sealing or other means may be employed to effectuate passage of the strip from the apparatus while preventing or inhibiting escape of liquid electrolyte, the device shown includes a simple pair of flexible, stiflly elastic members 106, 107, arranged as closure lips across the exit slot and bearing resiliently on the strip as it leaves. From the header 54, through the guided paths therein as explained above, the liquid flows rapidly and preferably with considerable turbulence, along the entire length of the sections 51 and S0, filling these sections completely with liquid at all times and making flowing, turbulent contact throughout both upper and lower faces of the strip. At the liquid discharge header 55 (see FIGS. 2, 3, 4 and 5), the flowing electrolyte is diverted to discharge through the ducts 56, 57 for ultimate return in the liquid flow circuit as explained above.

The discharge header 5S includes a generally box-like structure having an attachment flange 110 which is appropriately secured, in sealed relation, to the corresponding flange 69 of the first liquid -contact section 50. The structure 55, conveniently of metal in the apparatus shown, includes a pair of vertically spaced horizontal guide plates 111, 112, between which the strip passes as it enters the system, with some clearance. Above the upper plate 111, a pair of rearwardly and sidewise curving walls 113, 114 are disposed in a plow-like configuration generally designated 115. These plow faces 113, 114 thus cooperate with the roof 116 of the header box and the upper guide plate 111, to direct flow of liquid from above the strip along streamlined paths into the discharge ducts 56 and 57 at the sides. An identical plow structure 117 below the guide plate 112 coacts with the bottom wall 118 of the header box to form similar deflecting channels for the lower part of the liquid, i.e. below the strip. In aid of these deflecting functions, the plates 111, 112 have shallow V-shaped edge contours, providing each with an apex 119 which extends into the flaring mouth 120 of the cathode cleaning section or channel 50. Likewise each plow structure 115, 117 may have a downwardly sloping front wall, as at 121 for the plow 115, likewise fitting into the mouth 120 of the section 50. Hence the rapidly flowing liquid issuing through the flange 69 and the mouth 120, is in effect diverted above and below the strip, and sidewise at each locality, into the outlet ducts 56 and 57.

As seen in FIG. 3 the entering strip 10 passes through a liquid shield structure consisting of a drip or splash pan 123 and a cover 124, at the rear of the header assembly 55, and enters the space between the guide plates 111 and 112 through a pair of stiflly elastic horizontal lips 125, 126 that bear on the strip in the same manner as the members 106, 107 (FIG. 6), being sloped toward the strip in the direction of its travel. These members 125, 126, like the members 106, 107, may be made of rubber or similar synthetic material, appropriate for resiliently engaging the strip in sealing effect, it being further understood that equivalent or other means may be employed, as may be known for admitting passages of a traveling article into and out of the side wall of a liquid filled vessel.

For simplicity, the apparatus of FIGS. 2 to 7 inclusive has been shown as designed for two-side anodizing of a strip or equivalent elongated Work, with cathodic cleaning being effected on both sides of the strip as it traverses the first section 50. Thus as illustrated in FIG. 2, a suitable D C. source 130, which may have conventional control and regulating means for current or voltage as desired (not shown) has its positive terminal connected through suitable bus and conductor structure 131 to the electrodes 72, 76 of the cleaning section 50, while the negative terminal of the source 130, again through appropriate bus and conductor structure 132, is connected to the electrodes 83, 84 of the anodizing section 51, e.g. by appropriate connection to one side (or if desired, both sides) of the completely metallic housing of which the electrode plates form a part.

The operating procedure, for example with the apparatus shown in FIG. 2, will now be self-evident. The aluminum strip 10 is continuously drawn through the system, entering at the region of the liquid discharge header 55 (through the seal 12S-126, seen in FIG. 3), traversing the sections 50, 52 and 51 and leaving through the seal 106- 107. The entire interior of the apparatus is kept filled with electrolyte, flowing rapidly in a longitudinal direction along the strip, from the inlet header 54 to the outlet assembly 55, return of the electrolyte being effected via the reservoir 58 and pump 60, all arranged to maintain a desired temperature in the electrolyte as it travels along the faces of the strip, with minimum temperature rise between the ends of `the treating assembly 50-51.

Current flows from the source to the electrodes 72, 76 (see FIGS. 2, 3 and 6), thence across the electrolyte to the upper and lower strip surfaces for the desired cathodic cleaning action in the chamber 50, .the further path of the current being through the strip itself, and then from the strip, as anode, into and through the electrolyte in the zone 51, to the cathode or return electrodes 83, 84, and lthence back to the source 130. The anodizing operation 1s thus performed in the section 51, achieving the desired oxide coating on the strip. While some leakage current flows between the electrodes 72, 76 and the electrodes 83, `84, the arrangement is such that this is an economically minor part of the total current, thus affording an operation which is particularly advantageous from the standpoint not only of efliciency, but also of reliability and of safe temperature control at high speed, these and other features of the process representing special advantages of value beyond the relatively minor losses of the leakage current through the section 52.

By way of specific example, one effective embodiment 0f equipment constructed substantially as shown in FIGS. 2 to 7 inclusive comprised a first treatment section 50 having an overall length between flanges 69 and 70 of about 60 inches, and a following anodizing section 51 having a similarly measured length of 5 6 inches, the dimensions of the interior channel throughout being about 2 inches high and about 27 to 28 inches wide (having some very minor variation along the path), i.e. so that the cross-sectional area of the liquidfilled path was approximately 55 square inches. The total length of the intermediate insulating section 52, i.e. between the last of the electrodes 72, 76 and the nearer end of the electrodes 83, 84 was about 15 inches. This arrangement accommodated strip aluminum of widths ranging from a few inches, or even less, to 25 or 26 inches, with abundant cooling effect by the turbulently flowing electrolyte throughout the length of the strip in the enclosed channel.

As a specific instance of operation with a system as just described, aluminum strip 10.6 inches wide and 0.0235 inch thick was continuously moved through the apparatus at a rate of about 5 feet per minute. Electrolyte consisting of 15% (by weight) sulfuric acid solution was continuously flowed through the system, countercurrent to the strip, with a Velocity of approximately 5 linear feet per second, such being achieved with a total volume flow of approximately 850 gallons per minute. Direct current was supplied to achieve a density of approximately 600 amperes per square foot in the anodizing region, i.e. as measured at each surface of the sheet, considered as regions equal in length to the electrodes 83, 84. This required a current flow through the strip (exclusive of leakage) of 4,950 amperes and was achieved with an impressed D.C.

1 1 voltage of 44 volts, i.e. between the electrodes 72, 76 and the electrodes 83, 84.

Under these circumstances, a highly desirable poroustype anodic coating was produced on both surfaces of the strip having a thickness of about 0.9 mil. The leakage current between the sections 50 and 51, i.e. passing through the electrolyte, was found to be approximately 200 amperes and thus represented not more than 3.9% of the total current of 5,150 amperes. This value of leakage current agreed substantially with that calculated for the body of electrolyte inches long and having a crosssection of 55 square inches, taking the specific resistivity of the stated sulfuric acid solution as 2 ohm-centimeters. The described ow of electrolyte was effectively turbulent throughout the length of the strip in all sections of the apparatus, and the temperature of the electrolyte was readily controlled at a value of about 26 C., Le. as flowing along the strip surfaces, with no more than about 2 C. rise between the inlet 54 and the outlet 55.

An example of very high speed operation for anodizing aluminum strip in the above described and dimensioned apparatus, with a similarly small proportion of by-pass current, is as follows: In 15% sulfuric acid at 60 C., strip 0.010 inch thick and 12 inches wide was treated at 420 feet per minute with a total current (D.C.) of 5000 amperes. The voltage requirement was 33 volts and the resultant anodic film thickness was 0.01 mil.

As will now be appreciated, the cross-section of the electrolyte-filled region of the treating system, particularly the cross-section of the intermediate zone between the first liquid contact region and the anodizing region, is selected to achieve ample liquid flow while limiting the by-pass or leakge current to a very minor proportion, conveniently not more than about 10% and very preferably less than 5%, of the total current ow required. lf the applied voltage on the cell is E, the relations of the cross-sectional area A and the length L of the liquidfilled intermediate or connecting zone are readily determinable from the following expression for the leakage current:

This equation is simply derived from Ohms Law, expressing the leakage current I in terms of the voltage E, the dimensional values noted above ant the specific resistivity p of the electrolyte, in ohm-centimeters, the values A and L being appropriately converted to square centimeters and rentimeters respectively. The cross-sectional area A can usually be taken as that of the connecting region, i.e. disregarding the cross-section of the strip or other article unless, of course, it is exceptionally thick.

The cross-sectional value A is basically determined by the requirements of electrolyte flow, it being generally found that for high speed anodizing of strip at current densities of 100 amperes per square foot and above, a flowing layer of electrolyte of at least about 1/2 inch, and preferably about 1 inch, in thickness, is desirable, while in the case of wire a cylindrical sheath, in effect, of electrolyte should be provided having a radial thickness of lat least 1A inch and more conveniently 1/2 inch or more. Determination of a minimum cross-sectional area may ordinarily be modified to agree with practical considerations of the apparatus, e.g. as where the system is designed to accommodate various widths of strip (as shown) or various thicknesses of wire or rod.

The applied voltage E, of course, is determined by the requirements of anodizing, not only to achieve the desired current density and provide ow of such operating current through the strip or wire in the region between the operating zones, but also to account for supplemental voltage drops as due to the various well-known anodic and cathodic polarization phenomena in electrochemical systems of the sort contemplated. That is to say, determination of voltage, in addition to the basic resistance of the metal of the strip or wire through which the current passes, and the resistivity of the electrolyte, involves these further resistive effects, which must be calculated or determined, as will be readily understood, in order to arrive at the required overall voltage E. With determined values of E and A, the length L of the intermediate section between sets of electrodes is then readily calculated for the maximum by-pass current to be tolerated, and as indicated above, L is generally found to be a completely feasible and indeed relatively short length.

As another example of the process, a situation of wire treatment may ybe considered, wherein the sections 15, 16 and 17 (considered as an embodiment of the diagram of FIG. l) are of cylindrical tubular shape, being essentially pipe, as with a conductive section 15 of lead pipe for the cleaning region and of stainless steel pipe 16 for the anodizing region with an insulating section 17 of pipe between, the metal pipe sections serving also as the respective electrodes. As an example, aluminum wire of 0.036 inch diameter was anodized with a total current of 300 amperes. The wire speed was 200 feet per minute and the resulting anodic film thickness was 4 to 5 microns. When the cross-sectional area of the insulating section 17 was in the range 15 to 36 square inches and the length of the insulating section 15 to 30 feet, the leakage currents were in the range 25 to 45 amperes, i.e. depending on the length and cross-sectional area of the intermediate liquid body. By reducing the channel crosssection to that of a 1/2 inch inside diameter pipe and with intermediate section 17 of the order of only 10 inches in length, leakage currents can be reduced to about 1% of the total of 300 amperes.

In general the voltage required for anodizing operations on aluminum sheet or strip, in a system of the character shown in the drawings is of the order of about 25 volts to about 60 volts, i.e. for high speed continuous treatment at current densities upwards of amperes per square foot of surface to be anodized, and preferably higher, even up to 2000 amperes per square foot or more. -Under some circumstances, e.g. as in wire treatment as explained above, the applied voltage may be considerably higher, even up to values of about 200 volts or more, so that the entire range of voltage with which the preferred aspects of the invention are concerned extends upwards of 15 volts to relatively high values. These voltage values or ranges are given as including the supplemental voltage drops mentioned hereinabove, due to accompanying electrolytic effects, eg. polarization phenomena at the various surfaces where current enters or leaves the liquid.

A particularly suitable electrolyte for the process iS an aqueous solution of sulfuric acid, having a concentration, say, in the range from about 2% to about 50%, and most advantageously in the range from 5% to 40%. An effective example of such electrolyte is a 15% sulfuric acid solution. All concentrations here stated are given by weight. The specic resistivity of such electrolytes is in the range of 1 to 5 ohm-centimeters, particular values for a given concentration, or for other electrolytes, being known or readily determinable. As will be apparent, these aqueous electrolytes have a resistivity which is of the order of a million times that of common metals, such as aluminum and its alloys.

In some cases, other electrolytes may be used as appropriate for a desired anodizing operation, e.g. acid electrolytes of generally equivalent function. Thus in addition to sulfuric acid, examples of suitable electrolytes for anodic treatment as here described are chromic acid, diand tri-basic organic acids, or their equivalents, all of these and like electrolytes being usable either separately or in suitable combinations as will be readily understood by those skilled in the art.

Although the first electrode means, such as in the region S0, may simply serve for effecting liquid electrical contact to the passing work, the function of cathode clean- 13 ing is found to be very effective, it is understood to have -both electrochemical and chemical aspects, in that hydrogen is usually evolved from the surface of the passing aluminum, and such evolution, together with the chemical action of the acid, very rapidly cleans the surfaces of foreign material such as dirt and grease.

As will be appreciated, for effective anodizing (anodic coating) operations the speed of travel of the strip, wire or like article and the current density are mutually selected to achieve desired results of film thickness and speed of operation, Within limits of efficiency and economy. Thus strip or wire speeds may range from 1 to 500 linear feet per minute and current densities, say, from 100 amperes per square foot and upward, usually 250 amperes per square foot or more and very preferably, for true high speed operation, in a range of 500 amperes per square foot and above. As current densities are carried up to or especially beyond the range of 2000 to 4000 amperes per square foot, heat removal may become difficult with ordinary mechanical arrangements for circulating electrolyte.

It is particularly contemplated, in preferred operation, that the flowing electrolyte be kept in a turbulent condition, e.g. as achieved by selection of suitably high velocity, or by the employment of baffles (not shown) or the like. With the flow arranged longitudinally of the path of the strip or other article and with turbulence uniform across the strip, unusually effective heat exchange is achieved. As will be appreciated, selection of a suitable flow rate for substantial turbulence can be calculated under known principles, for a given cross-sectional shape and size of path, i.e. to yield a Reynolds number in the range of turbulent flow. Conventionally such numbers larger than about 2500 signify a condition of turbulence, although for best results in present procedures, ow conditions may be those corresponding to substantially higher Reynolds numbers, for example a value of 20,000, which is fully appropriate for anodizing at 600 amperes per square foot. Even greater turbulence can be used, e.g. with Reynolds numbers up to 100,000, for extremely high current densities.

The temperature to be maintained in the flowing electrolyte adjacent the strip, as by suitable thermostatic control (not shown) in the tank 58, may conveniently range from room temperature, say. 20 C., even up to 100 C., particularly useful values being from 40 C. to 70 C.

As also indicated above, other types of anodizing operation may be performed by the described process and in systems such as here illustrated. For instance, alternating current treatment may vbe utilized, with one terminal of the source connected to the electrodes of section 15 or 50 and the other to those of section 16 or 51. In such case the electrodes are preferably made of graphite.

The invention will be seen to afford a highly simpliied, reliable and easily controlled method of continuous anodizing, permitting high speed travel of the passing strip, wire or the like, with effective heat exchange between the electrolyte and the work throughout, while applying a satisfactory anodic coating of essentially any desired thickness.

It will be appreciated that although certain special advantages of the invention are realized with horizontal arrangements, e.g. of strip travel, such as shown in the drawings, other constructions and modes of procedure may be employed. Thus for example in some cases, the elongated tank (including tanks which are constituted by pipes or pipe-like vessels, may be disposed in inclined or even vertical positions, e.g. for a corresponding direc tion of travel of the strip, wire or the like under treatment. In all such cases, the arrangement includes means for providing the desired How of liquid through the tank from end to end, and likewise means at the ends for restraining escape of electrolyte while admitting passage of the article directly through each end.

The apparatus particularly disclosed above may also be useful for other purposes than in the anodizing op erations (the term anodizing being employed herein to mean the production of anodic coatings on aluminum) to which the invention is primarily directed and with which the new methods or procedures are concerned.

It is further to be understood that to the extent embraced by the appended claims, the invention is not limited to the specific operations and structures herein shown and described but may be carried out in other ways with out departure from its spirit.

We claim:

1. A method of continuously anodizing a surface of an elongated aluminum article, comprising advancing said article lengthwise through an elongated, electrolytecontaining zone having two electrodes at areas respectively arranged in spaced succession lengthwise thereof, while exposing said surface to the electrolyte throughout the length of said zone, passing electric current from a source to the electrode at one of said areas, then from said last-mentioned electrode through the electrolyte to said surface of the article, conducting said current through the article, and passing said current from said surface of the article into and through the electrolyte to the other electrode at the other of said areas and thence back to the source, for producing an anodic coat ing on said surface, while advancing said electrolyte along said surface in a continuing stream of large cross-section free of localized restriction from one end to the other end of the zone, and maintaining a body of said electrolyte of sufficient length between said electrode areas to inhibit by-pass of current through the electrolyte from one area to the other, said body of electrolyte having the aforesaid cross-section, and said body having a length such that by reason of said inhibiting effect, said =bypass of current, deterbined as the value I=EA/pL where E is the voltage of the electric current applied by said source, A is the area of said cross-section, L is said length and p is the specific resistivity of the electrolyte, is not more than about 10% of the total current applied by said source.

2. A method of continuously anodizing a surface of an elongated aluminum article, comprising advancing said article lengthwise through a liquid electrolyte-containing zone having two electrodes of respectively different electrical polarity spaced along the path of the article in said zone, while exposing said surface to said electrolyte and maintaining said electrolyte in motion over said surface, throughout said path, said motion being turbulent relative to and throughout said surface, passing current through the electrolyte between each electrode and the surface of the article, the current which is related t0 at least one of said electrodes being effective in passing from the article to said one electrode to provide anodic coating action on said surface, maintaining adjacent said surface at all regions thereof throughout the zone and without local restriction, a body of electrolyte which is sufficient in quantity and extent of motion to provide effective liquid heat exchange with all of said surface between said spaced electrodes in the zone, and maintaining a sufficient length of said body of electrolyte between the spaced electrodes in the direction of said path, to prevent by-pass of current, through the electrolyte between the electrodes, which is more than a minor fraction of the total current carried by said electrodes.

3. A method as defined in claim 2, wherein said current for providing anodic coating action is passed at a value to maintain a current density of at least about amperes per square foot of said surface, with a voltage between the electrodes greater than 10 volts, and said electrolyte is advanced continuously in turbulent flow over said surface from one end to the other of said zone in a direction aligned with the path of travel of the article.

4. A method as defined in claim 3, wherein said length of electrolyte body between said electrodes is maintained of sufficient length to prevent by-pass of current which is more than 10% of the total current carried by said electrodes.

5. A method of continuously anodizing a surface of an elongated aluminum article to produce a porous anodic coating thereon, comprising advancing said article lengthwise through an electrolyte-containing zone having two electrodes at areas respectively arranged in spaced succession along the path of the article, said zone containing said electrolyte suitable for the aforesaid anodizing operation, while exposing said surface to the electrolyte throughout the length of said zone along said path, supplying electric current from a source thereof to and from said electrodes, passing current from the electrode at the first said area in said path through the electrolyte to said surface of the article, conducting said current in the article, and then passing said current from said surface into and through the electrolyte to the electrode at the second area for producing said porous anodic coating on Said surface, while advancing said electrolyte throughout Said zone, from and to a single source of circulation, in a continuing stream of large cross-section adjacent said surface at all locatities of said path and free of localized restriction, for effective heat exchange with said surface at every locality of the path, and maintaining said advancing electrolyte in a body of sufcient length between said electrode areas to prevent by-pass current, through said electrolyte therebetween, which is more than a minor fraction of the total first-mentioned supplied current from the source.

6. A method as defined in claim 5, which comprises advancing said electrolyte in turbulent flow over said surface in a direction aligned with the path of travel of the article while maintaining said current at a value, for producing said anodic coating, sufiicient to provide a current density of at least about 250 amperes per square foot of said surface.

7. A method as defined in claim 6, in which the article is aluminum strip advanced continuously lengthwise through the zone so that at least one of its two sides constitutes the above-mentioned surface, said electrolyte flow being maintained in turbulence substantially uniformly across said first-mentioned surface.

8. A method as defined in claim 7, wherein said length of electrolyte body between said electrode areas is maintained of sufficient length to prevent bypass of current which is more than about of said total first-mentioned current.

9. A method as defined in claim 7, in which said current is passed into and from both sides of said strip for producing said anodic coating on both sides; and which includes advancing said electrolyte along both sides in turbulent flow, all from and to said `single circulation source, and maintaining said electrolyte in said condition of turbulence substantially uniformly across both said sides.

10. A method as defined in claim 9, in which the source provides direct current to said electrodes at a voltage between them of at least about l5 volts, While maintaining said current at a value of at least about 500 amperes per square foot of the total surface of 4both sides of the strip in the aforesaid second area, said electrolyte being a sulfuric acid solution having a concentration in the range of about 2% to about 50%, and the passage of current to the strip at the first area in the path of the strip effecting cathodic cleaning on both sides thereof, and the passage of current from the strip at the second area effecting said anodic coating on both sides thereof.

11. Apparatus for continuous anodic treatment of an aluminum strip, comprising in combination, a closed tank arranged to be filled with liquid electrolyte and having provision for continuous advance of said strip lengthwise from one end to the other of the tank, including liquiddow-restraining means at the ends of the tank for respectively admitting and discharging the strip directly through said ends, first and second electrode means in the tank, arranged for exposure to the electrolyte and spaced along the path of the strip to provide resistance of electrolyte to by-pass current through the electrolyte between the electrode means, said electrode means being disposed for passage of current between the first electrode means and a surface of the strip and for passage of current between said surface and the second electrode means, for effecting anodizing action on said surface at least with respect to said last-mentioned passage of current, liquid inlet means and outlet means at respective ends of the tank, and means associated with said inlet and outlet means for continuously delivering and discharging electrolyte to and from the tank, to provide continuous flow of electrolyte from one end to the other of the tank along both surfaces of the strip, said tank being shaped to provide unrestricted electrolyte flow in heat-exchange Contact with both said surfaces at all localities through said tank, said first electrode means comprising a pair of electrode structures respectively adjacent opposite faces of the passing strip at a first treating region of the tank, and the second electrode means comprising a pair of electrode structures respectively adjacent opposite faces of the passing strip at a second treating region of the tank, said tank having a hollow section of electrical insulating material disposed between said treating regions and thereby spacing the electrode means as aforesaid, said apparaatus including a source of direct current, and said four electrodes structures constituting said two pairs having associated means for selectively and collectively connecting them with said source of current to provide cathodic cleaning action at the first treating region selectively on one and both surfaces of the strip, and anodic film-forming action at the second treating region selectively, on only one surface of the strip, on both surfaces of the strip to the same extent, and on both surfaces of the strip differentially.

12. Apparatus for continuous anodic treatment of an elongated aluminum article, comprising in combination, an elongated closed tank having provision for continuous advance of said article lengthwise from one end to the other of the tank, including article-admitting sealing means in the respective ends of the tank, said tank having substantially uniform internal cross-section throughout its length between said ends, first and second electrode means in the tank, arranged for exposure to liquid electrolyte therein and spaced along the path of the article, said electrode means being disposed for passage of current between the first electrode means and a surface of the article and for passage of current between said surface and the second electrode means, for effecting anodizing action on said surface at least with respect to said last-mentioned passage of current, liquid inlet means and outlet means at respective ends of the tank, said tank being arranged to be completely filled with liquid electrolyte supplied therein, and means associated with said inlet and outlet means for continuously delivering and discharging electrolyte to and from the tank, to provide continuous turbulent flow of electrolyte from one end to the other of the tank, filling the same and in heat-exchange contact with said surface, said tank being free of localized restriction to electrolyte flow at all localities between said electrode means, said tank comprising wall means throughout its length surounding the path of the article, and each of said electrode means comprising electrically conductive structure embodied in said wall means on at least two opposite sides of said path, each conductive structure being exposed to the electrolyte over an extended area lengthwise of the tank, said wall means including a region between said areas which constitutes the aforesaid spacing of said electrode means along the path of the article, and said last-mentioned region of wall means consisting of electrical insulating material and being elongated in the direction of article travel relative to one crosswise dimension of the tank, to provide resistance in the contained electrolyte to by-pass current through said electrolyte between the first and second electrode means.

13. Apparatus as defined in claim 12, wherein the article is strip material of aluminum, said tank being oblong in cross-section to accommodate said strip in horizontal position, and having a long horizontal crosswise `dimensin and a short vertical crosswise dimension, each of said first and second electrode means comprising the aforesaid electrode structures being embodied in the wall means of the tank that extend over said horizontal crosswise dimension both above and below the strip.

14. Apparatus as dened in claim 12, wherein the article is strip material of aluminum, said tank being shaped to accommodate said strip, having a long crosswise dimension corresponding to the width of the strip and having a short crosswise dimension in a direction perpendicular to the faces of the advancing strip, each of said first and second electrode means comprising electrode structure constituting at least part of one wall of the tank, arranged along the path of the strip and extending crosswise of the tank over said long transverse dimension thereof, the portion of the tank between said electrode means having a length in the direction of strip travel which is equal to at least several times said short crosswise dimension of the tank.

15. Apparatus as defined in claim 14, wherein each of said first and second electrode means comprises electrode structure in both of the walls of the tank which lie in the long crosswise dimension thereof, whereby -said electrode structures of each electrode means face opposite surfaces of the strip and anodizing treatment is effected on both said surfaces.

16. Apparatus as defined in claim 15, wherein said short crosswise dimension of the tank is about two inches, said tank including provision for advance of the strip through the tank at a central locality so that each surface of the strip is spaced from the electrode means by a distance of about one inch.

17. In apparatus for continuous anodic treatment of an elongated aluminum article, in combination, a tank adapted to be filled with liquid electrolyte and having provision for continuous advance of said article lengthwise through the tank from one end to the other thereof, first and second electrode means in the tank, arranged for exposure to the electrolyte and spaced along the path of the article, a source of current having its terminals respectively connected to said electrode means for flow of current through the electrolyte to and from the advancing article, to provide anodizing treatment on a surface of the article by passage of current from said surface through the electrolyte to at least one of said electrode means, and means associated with the aforesaid ends of the tank, for passing liquid electrolyte in continuous flow through the tank from one end to the other, said tank being dimensioned in cross-section to provide space for said continuous flow of electrolyte in heat-exchange contact with said surface of the article at all localities throughout the tank `between its ends, and said tank being further dimensioned and arranged to constitute the electrolyte-containing space separating the first and second electrode means as a region elongated relative to one dimension of said cross-section, for inhibiting by-pass of current through the electrolyte between the electrode means, the article being strip material of aluminum, said tank being shaped to accommodate said strip, having a long crosswise dimension corresponding to the width of the strip and having a short crosswise dimension in a direction perpendicular to the faces of the advancing strip, each of said first and second electrode means 1comprising electrode structure constituting at least part of one wall of the tank, arranged along the path of the strip and extending crosswise of the tank over said long transverse dimension thereof, the portion of the tank between said electrode means having a length in the direction of strip travel which is equal to at least several times said short crosswise dimension of the tank, the tank at the region of one electrode means comprising wall structure of insulating material having transverse pockets therein partly open along localities at the interior of the tank, the electrode structure for said region comprising a plurality of conductive electrode elements removably received in said pockets and exposed to the interior of the tank through said open localities, said wall structure including shoulder means along the pockets retaining said electrode elements in place.

18. In apparatus for continuous anodic treatment of an elongated aluminum article, in combination, a tank adapted to be filled with liquid electrolyte and having provision for continuous advance of said article lengthwise through the tank from one end to the other thereof, first and second electrode means in the tank for exposure to the electrolyte and arranged in spaced relation along the path of the article, a source of current having its terminals respectively connected to said electrode means for predetermined flow of current through the electrolyte to and from the advancing article, to provide anodizing treatment on a surface of the article by passage of current from said surface through the electrolyte to at least one of said electrode means, and means associated with the aforesaid ends of the tank, for passing liquid electrolyte in continuous ow through the tank from one end to the other in heat-exchange contact with the article, said tank being dimensioned in the space between the electrode means to provide said flow of electrolyte over a large cross-section and without restriction, in said contact with said surface of the article throughout said space, and said tank and electrode means being mutually constructed and arranged to provide a sufficient distance between the electrode means for preventing by-pass current, through the electrolyte between the electrode means, which is more than a minor fraction of the predetermined current delivered from the source to said electrode means, said tank comprising electrical insulating structure in the region thereof along the space between the electrode means.

19. In apparatus for continuous electrolytic treatment of an elongated metal article, in combination, an elongated closed tank adapted to be completely lled with liquid electrolyte and having provision for continuous advance of said article lengthwise through the tank from end to end thereof, including article-admitting sealing means in the respective ends of the tank for passage of the article directly through said ends, said tank having substantially uniform internal cross-section throughout its length, first and second electrode means in the tank, mutually spaced along the path of the article, a source of direct current having its terminals respectively connected to said electrode means for -ow of current from one electrode means through the electrolyte to the article, through the article and from the article through the electrolyte to the other electrode means, and means associated with the aforesaid ends of the tank, for passing liquid electrolyte in continuous ow through the tank from end to end in heat-exchange contact with the article, said tank comprising electrical insulating structure in the region thereof along the space between the electrode means, and said region of the tank and said electrode means being muturally constructed and arranged to provide a sufiicient length of said space between the electrode means for preventing iby-pass current in the electrolyte which is more than a minor fraction of the current delivered from the source to the electrode means.

20. In apparatus for continuous electrolytic treatment of an elongated aluminum article, in combination, a tank adapted to be filled with liquid electrolyte and having provision for continuous advance of said article length- Wise through the tank from one end to the other thereof,

first and second electrode means in the tank for exposure to the electrolyte and arranged in spaced relation along the path of the article, a source of current having its terminals respectively connected to said electrode means for predetermined ow of current through the electrolyte to and from the advancing article, to provide electrolytic treatment on a surface of the article by passage of current through the electrolyte between said surface and at least one of said electrode means, and means associated with the aforesaid ends of the tank, for passing liquid electrolyte in continuous ow through the tank from one end to the other in heat-exchange contact with the article, said tank being dimensioned in the space between the electrode means to provide said flow of electrolyte over a large cross-section and without restriction, in said contact with said surface of the article throughout said space, and said tank and electrode means being mutually constructed and arranged to provide a sufficient distance between the electrode means for preventing by-pass current, which is more han a minor fraction of the predetermined current delivered from the source to said electrode means, said tank comprising electrical insulating structure in the region thereof along the space between the electrode means.

21. In apparatus for continuous electrolytic treatment of an elongated metal article, in combination, an enlongated closed tank adapted to be completely filled with liquid electrolyte and having provision for continuous advance of said article lengthwise through the tank from end to end thereof, including article-admitting sealing means in the respective ends of the tank for passage of the article directly through said ends, said tank having substantially uniform internal cross-section throughout its length, first and second electrode means in the tank, mutually spaced along the path of the article, a source of current having its terminals respectively connected to said electrode means for flow of current through the electrolyte between one electrode means and the article, through the article and through the electrolyte between the article and the other electrode means, and means associated with the aforesaid ends of the tank, for passing liquid electrolyte in continuous low through the tank from end to end in heat-exchange contact with the article, said tank comprising electrical insulating structure in the region thereof along the space between the electrode means, and said region of the tank and said electrode means being mutually constructed and arranged to provide a sucient length of said space between the electrode means for preventing by-pass current in the electrolyte which is more than a minor fraction of the current delivered from the source to the electrode means.

References Cited UNITED STATES PATENTS 2,930,739 3/1960 Burnham 204-28 2,974,097 3/1961 Ramirez et al. 204-206 1,483,722 2/1924 Eustis 20413 1,768,358 6/1930 Harrison 204-13 XR 2,165,326 7/1939 Yerger et al. 204-211 2,267,146 1'2/ 1941 Wilson 204-206 2,307,928 1/1943 Hogaboom 204-141 2,541,275 2/1951 Odier 204-211 2,989,445 6/ 1961 Lloyd et al. 204-28 3,038,850 6/1962 Wagner 204-'206 3,079,308 2/ 1963 Ramirez et al 204-28 JOHN H. MACK, Primary Examiner W. B. VANSISE, Assistant Examiner U.S. Cl. X.R.

ggo UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent No, 3,471,375 Dated october 7, 1969 l i )l i Inventods) IwllllarnErnes/z Cooke I 1u1 5ml ts and Jaques It is certified that error appears in the above-identified patent and that said Letters Patent are 'hereby corrected as shown below:

Column 2 line 30 for "economic" read eco1omca1- column 6 line 16 for '.39"V read -29- column 1l `1 ine 33 for "lcakge" read -1eakage line 44 for "ant" read -and- 'line 47 for "rentmeters" read ,--centmeters- Column 14, line 36 for "deterbned" read -determined-- column 16 line 31 for "apparaatus" read -apparatuscolumn 17, line l0, for "dmensin" r'ead --d menson= g column 19 line 19 ftcr "current insert -through the electrolyte between the electrode means line 21 For "han" read -than- I slaasnmu' SEL'. 06231970 wSEAL) Attest:

Eawaumewhw. Ik A mwa r, saeunm, m. l Officer omissioner or Patents

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