US3296114A

US3296114A - Anodizing apparatus

Info

Publication number: US3296114A
Application number: US295771A
Authority: US
Inventors: James B C Lloyd
Original assignee: LLOYD METAL Manufacturing Co Ltd
Current assignee: LLOYD METAL Manufacturing Co Ltd
Priority date: 1963-07-17
Filing date: 1963-07-17
Publication date: 1967-01-03
Anticipated expiration: 1984-01-03
Also published as: GB1067423A; DE1298823B

Description

Jan. 3, 1967 J. B. c. LLOYD 3,296,114

ANODIZING APPARATUS Filed July 17, 1963 5 Sheets-Sheet l 1967 J. B. c. LLOYD 3,296,114

ANODI Z ING APPARATUS Filed July 17, 1963 5 Sheets-Sheet 2 M57 91 Vfcaun RGUEF vlt 0v Fecwr 600 or Tam:

I J2 y INVENTOR.

United States PatentO 3,296,114 ANODIZING APPARATUS James B. C. Lloyd, Orillia, Ontario, Canada, assignor to Lloyd Metal Manufacturing Company Limited, Orillia, Ontario, Canada Filed July 17, 1963, Ser. No; 295,771 16'Claims. (Cl. 204-206) This invention relates to apparatus. for surfacing metallic membranes with a protective coating and more particularly to an apparatus for continuous anodizing of one surface side of a sheet of anodizable metal, such as aluminum.

This is an improvement of the apparatus disclosed in U.S. Patent No. 2,989,445 issued to Alfred J. Lloyd et al.

on June 20, 1961. In that patent, there is disclosed an anodizing apparatus and method in which the electrolyte is caused to flow over the'surface of the sheet to be anodized, to permit higher anodizing current densities while cooling the surface being anodized. While this process has proven entirely satisfactory,certain difliculties have been encountered which are due primarily to the necessity for recirculating the electrolyte under pressure. As the electrolyte commonly used in anodizing apparatus is sulphuric acid, the corrosion of the various parts ofthe anodizing apparatus which come in contact with the acid causes maintenance and replacement problems which reduces'the efliciency of the apparatus. In the present invention some of these disadvantages have been overcome by reducing the number of parts of the apparatus in contact with the acid, and providing novel means for causing the electrolyte to flow over the surface of the sheet being anodized.

During the anodizing process, electric current is caused to flow between the electrolyte and the aluminum sheet to be surfaced through the area of interface contactby establishing a potential difference therebetween, the metallic surface comprising in effect the anode and the electrolyte the cathode. This current creates heat at the aluminumelectorlyte interface which is deleterious to the anodic surface if allowed to build up to high temperatures. It is, therefore, necessary to provide some mechanism for cooling the electrolyte and particularly the surface of the sheet during-the anodizing process.

In Patent No. 2,989,445,'the surface of the aluminum sheet is cooled by the flowing of the electrolyte over such surface within the anodizing zone. The electrolyte is collected, cooled at a point remote from the aluminum sheet, and recirculated to the anodizing zone. In the present apparatus, there is provided novel means for creating a flow of electrolyte over the surface of the sheet within the anodizing zone, to dissipate the heat created by the anodization process. The apparatus by which this result accomplished is both economical and simple in construction.

Accordingly, it is an object of the present invention to provide anodizing apparatus having a novel means for flowing the electorlyte over an anodizing interface.

It is another object of the present invention to provide an endless belt within the electrolyte, disposed adjacent to the surface of the metallic membrane to be surfaced, said endless belt having a plurality of surface discontinuities such as to cause the flowing of electrolyte over the surface of the metallic membrane in response to motion of such belt.

It is a further object of the present invention to provide a plurality of conduits or cooling means disposed within the electrolyte and adapted to cool the electrolyte during the anodizing process.

It is another object of the present invention to utilize the cooling conduits within the electrolyte as a cathode for the performance of the anodizing process.

Patented Jan. .3, 19.67

It is a further object of the present invention to provide a novel anodizing apparatus comprising an electrode in contact with the sheet to be surfaced, means for connecting said electrode to a relatively positive potential, and pressure differential means for maintaining said sheet in close contact with said conductors.

It is another object of the present invention to provide novel vacuum means for maintaining the sheet in close contact with such electrode.

Other and further objects and advantages of the present invention will become clear upon examination of the accompanying specification, claims, and drawings.

In one embodiment of the present invention there is provided an anodizing apparatus comprising a tank for holding a quantity of electrolyte, the tank having a plurality of sides and an open bottom, the bottom being closed by an anodizable metallic sheet in sliding contact with the tank, thereby to form an interface between the sheetand the electorlyte. Electrode means is disposed underneath the tank in electrical contact with the lower surface of the sheet, which electrode means connects the sheet-tonne terminal of a source of electerical potential. Connecting means are-provided for connecting the electrolyte within the tank to the other terminal of the source of electrical potential, whereby current flows between the electrolyte and the sheet. Pressure differential means is provided for holding the metallic sheet in close association with .the electrode means, and cooling means comprising a conduit is disposed within the tank in contact with the electrolyte and is adapted to channel a quantity of coolant through the electrolyte thereby to cool the electrolyte. Agitating means comprising an endless belt having. support. means is disposed within the tank, and is adapted to support a portion of said belt in parallel relation to the metallic membrane, the belt having a plurality of, discontinuities in the surface thereof, thereby flowing the electrolyte over the surface of the sheet as the endless belt is circulated.

For a more complete understanding of the invention, reference will now be made to the accompanying drawings in which:

FIG. 1 is a vertical longitudinal schematic section of apparatus embodying the present invention;

FIG. 2 is an enlarged vertical longitudinal section of a portion of the apparatus of FIG. 1;

FIG. 3 is a perspective view of a portion of the apparatus of FIG. 1, with certain parts of the apparatus cut away;

FIG. 4 is a perspective view of the agitator belt associated with the apparatus of FIG. 1;

FIG. 5 is a perspective view of an alternative embodiment of the belt of FIG. 4;

FIG. 6 is a horizontal section of the apparatus illustrated in FIG. 1;

FIG. 7 is a vertical transverse section taken along the section 77 in FIG. 6;

FIG. 8 is a longitudinal sectional view of an exhauster associated with the apparatus of FIG. 1; and

FIG. 9 is a schematic diagram of the pumping arrangement incorporating the valve of FIG. 8.

Referring now to the drawings and more particularly to FIG. 1, there is shown an apparatus 8 for the continuous anodizing of one surface of an anodizable metal (such as aluminum) sheet 12 supported on a supply roll roll 10, which sheet is horizontally drawn through the anodizing apparatus 8 and accumulated on a collection drum 14. Asource of power may be provided at the drum 14 to draw the sheet 12 from the supply roller 10. For closer control of the sheet 12, powered rollers 16 contacting the sheet 12 may be used to draw the sheet through the apparatus. Tensioning or idler rollers 18 maintain the sheet in proper tension and control the sheet being removed from the supply roll 10. A plurality of weir boxes 20, 22, 24, 26, and 28 and an anodizing chamber or tank 19 are adapted to contain solutions suitable for use in the anodizing of the sheet 12. The sheet 12 is slidably supported by a supporting surface 23 in each of the weir boxes 20, 22, 24, 26, and 28, which surface holds the sheet 12 in substantially a single plane while it is being drawn through the apparatus. The weir boxes are of simple construction, being rectangular in shape, having sides 34, and equipped with perforated bottoms such as disclosed in the above identified patent. The bottom of the electrolyte tank 19 is more fully disclosed hereinafter.

The weir boxes 20, 22, 24, 26, and 28 are situated in sequence above the sheet 12 and are adapted to discharge fiuid contents onto the top surface or side of the moving sheet 12. The fluid flows over the surface of the sheet 12 and is collected in troughs 40 associated with collecting tanks 42, all as described in the above identified patent. Wiping means 48, disposed intermediate the weir boxes contact the surface of the moving metal sheet 12 and divert the surface liquids into the troughs 40 and essentially segregate the fluid from each dispensing weir box 20, 22, 24, 26, and 28 to its associated and respective collecting troughs 40 and tanks 42.

A pump 35 and a pipe 37 is provided for each weir box tank associated with the weir boxes 20, 22, 24, 26, and 28 each pump 35 circulating the fluid in its tank 42 through its pipe 37 to its corresponding weir box.

The anodizing chamber or tank 19 is provided with a pair of side walls 62 and 64, a pair of

end walls

66 and 68 which are joined to the side walls 62 and 64 in fluidtight relationship, and a removable top wall 63 having a hood 65 connected to a duct 67. Each of the side walls 62 and 64 is provided, near the bottom thereof, with a ledge 70 and 72, respectively, each of which traverse the entire length of its respective side wall. A support base 74 is secured to the bottom surfaces of the ledges 70 and 72, and is adapted to support a plurality of graphite blocks 60, which form a portion of one of the anodizing electrodes. Each of the graphite blocks 60 is supported on the support base 74 by three conductive pins 76 which pass through the support base 74 and contact one of three longitudinal bus bars 75. A washer 78, mounted on each of the pins 76, maintains its respective graphite electrode 60 in spaced relationship from the support base 74. Each of the bus bars 75 is provided with a terminal projection 77 at one of its ends,.and the terminals 77 are interconnected by a transverse bus bar 79 to which the source of potential may be connected.

The upper surface of the graphite electrodes 60 is in the same plane as the upper surface of the ledges 70 and 72 so that the sheet 12 is evenly supported throughout substantially its entire width by the ledges 70 and 72 and the electrode 60. A small gap, however, exists between the ends of each of the blocks 60 and the ledges 70 and 72, and between each pair of adjacent blocks 60, for a purpose which will hereinafter be described. The support base 74 is provided with upturned ends 75 (FIG. 2), adapted to contact the bottom surface of the sheet 12, thereby to form a closed chamber 93 bounded on the top by the sheet 12, on the bottom by the support base 74, at the ends by the upturned portions 75, and at the sides by the interior sides of the ledges 70 and 72.

A tray consisting of a bowed bottom portion 82 (FIG. 7) and side portions 84 and 86 is disposed beneath the anodizing tank 19 by suitable supports 88 and 90, for the purpose of catching any electrolyte which drips down through the tank 19, so that such electrolyte is not wasted.

The support base 74 of the tank 19 is supported by a plurality of transverse walls 91 (FIG. 3) resting in the tray 82. Each of the walls 91 is provided with an aperture 97 near the bottom of the tray 82 to permit the electrolyte to be drained from the tray 82 through a port 95.

the tank 19 and are connected to serve as the cathode.

The elements 63 are preferably hollow aluminum tubes, which are connected to conduct a supply of cooled fluid flowing therethr-ough to maintain the electrolyte within the tank 19 at a suitable temperature.

An endless belt 54 is supported on a pair of

rollers

56 and 58, in parallel relation to the sheet 12 and with its lower portion in proximity to the upper surface of the sheet 12. Each of the

rollers

56 and 58, upon which the belt 54 is mounted, is fixed to an axial shaft, 124 and 126 respectively, each of which are journaled in the side walls 62 and 64 of the tank 19 through an appropriate fluid seal 59, which may be of any known construction, preferably using a material which is not attacked by the electrolyte 50, such as rubber when the electrolyte 50 is sulphuric acid. Each of the

shafts

124 and 126 is connected to a pulley 128, between which pulleys is mounted a belt 130,

so that the two

rollers

56 and 58 may be rotated together. The shaft 124 is provided with an additional pulley 131, which is driven by a motor, such that the belt 54 is continuously moved about the two

rollers

56 and 58.

In one embodiment of the invention, the belt 54 is provided with a plurality of circular apertures 132 (FIGS. 3, 4 and 6), which are disposed in rows aligned along paths forming an angle to the direction of movement of the belt. Thus, as the belt 54 is circulated by the rotation of the

rollers

56 and 58, each portion of the upper surface of the sheet 12 comes into proximity with one of the apertures 132 sometime during the period it is inthe tank 19. The movement of the belt 54 is such that the portion nearest the sheet 12 moves in a direction opposite to the direction of movement of the sheet 12. This achieves a very rapid flowing of electrolyte relative to the surface of the sheet 12.

The belt 54 is preferably constructed of rubber or other resilient material, but does not interfere with the conduction of electric current between the electrolyte 50 and the sheet 12, since the apertures in the belt 54 make up a substantial proportion of the surface area of the belt 54. t This proportion is preferably of the magnitude of about 50%. Although other forms of discontinuities in the surface of the belt 54 operate to provide a flowing of electrolyte over the surface of the sheet 12, apertures are preferred as they permit current to freely pass between the sheet 12 and the cathode tubes 63.

In FIG. 5, there is shown an alternative form of belt, 54', mounted on the roller 56, which belt has a plurality of discontinuities such as slots 134 of random length and position, aligned transverse to the direction of movement of the belt. In this embodiment of the ,belt, the total area of the discontinuities such as slots 134 is approximately 50% of the area of the belt 54, and so conduction between electrodes is not impaired. The belt 54' creates a relatively high degree of turbulence within the electrolyte 50, which :agitates it sufficiently to maintain the surface of the sheet 12 at a relatively cool temperature, and which causes the electrolyte to flow over the surface of the sheet 12.

Referring again to FIG. 2, a conduit 92 communicates with the chamber 93 bounded above by the sheetx12 and below by the bottom wall 74. The conduit 92 is connected to a vacuum pump 104 (FIG. 9) which serves the dual purpose of evacuating from the chamber 93 any electrolyte which may leak in between the bottom surface of the sheet 12 and the upper surfaces of the ledges and 72, and holding the sheet 12 in close contact with the top surfaces of the graphite blocks 60.

FIG. 9 is a schematic diagram of the vacuum arrangement connected with the conduit 92. The tank 19 is illustrated schematically as having three vacuum conduits 92 94, and 96 connected through a vacuum line 98 to an exhauster 100. The exhauster is in circuit with a storage tank 102 in which is stored electrolyte,and a pump 104 which circulates the electrolyte within'the tank 102. The exhauster itself is shown in FIG. '8 in cross section. The exhauster is composed of an inlet portion 104, a nozzle portion 106, and an exhaust portion 108. Each of the three portions has a circular cross section, and are all aligned with a common axis. The inlet portion 104 is provided with threads cooperating with corresponding threads on both the nozzle portion 106 and exhaust portion 108. The interior diameter of the nozzle portion 106 narrows from a port 110 to its interior termination 111 to increase the velocity of the electrolyte flowing from left to right therethrough, and to direct such electrolyte into the exhaust portion 103. The exhaust portion 108 is provided with a funnel shaped inlet port 112 and a flared outlet port 114. The inlet portion has an inlet port 115 which communicates via a passageway 117 with a chamber 119 surrounding the termination 111 of the nozzle portion 106. Thus fluid flowing through the nozzle portion 106 entrains fluid in the chamber 119 into its stream, thereby creating a vacuum at the inlet port 115.

In operation, the inlet port 115 is connected to the three ports 92, 94, 96 illustrated schematically in FIG. 9, one of which is shown in cross section in FIG. 2. The pump of FIG. 9 is connected to the port 110 of the nozzle portion 106, and is caused to circulate electrolyte through the exhauster 100 to the tank 102, which is connected to the outlet port 114 of the exhaust portion 108. The flow of the electrolyte through the port 112 causes air and/ or liquid, which is present within the inlet portion 104, to be entrained into the stream, thus evacuating the chamber 93 of both air and liquid. The evacuation of the chamber 93 causes the sheet 12 to be pressed down by atmospheric pressure relatively firmly on the graphite blocks 60 and the ledges 70 and 72, thereby increasing the degree of sealing between the sheet 12 and the ledges and also effecting the the tighter contact of the bottom of the sheet 12 with the upper surface of the graphite electrodes 60, to reduce the resistance between sheet 12 and the graphite block 60 which would otherwise operate to elevate the temperature of the sheet 12. The reduction of such resistance is therefore very desirable.

It will be recalled that gaps are provided at the top of the chamber 93 between each pair of adjacent blocks 60, and between the ends of the blocks 60 and the ledges 70 and 72. These gaps permit the vacuum within the chamber 93 to operate on the bottom of the sheet 12 to allow atmospheric pressure to hold the sheet 12 against the blocks 60 and ledges 70 and 72, as described above.

FIG. 6 is a horizontal sectional view of the apparatus embodying the present invention and shows the arrangecent of the tubes 63, which simultaneously act as cooling coils and as the cathode in the electrical system. Each of the tubes 63 is provided with a flange at each of its ends 116, which holds the tube in fixed relationship to the side walls 62 and 64, and in substantial fluidtight relationship therewith. Each of the ends of the tubes is provided with a rubber hose 118 which interconnects a plurality of such tubes in a circuit through which cooling fluid, such as water, may be passed. The cooling fluid is preferably refrigerated by conventional apparatus and recirculated through the tubes 63 or, alternatively, cool tap water or other relatively cool fluid may be passed through the tubes 63 once and then discharged. The cooling tubes 63 are all electrically connected together by an individual bus bar 119 mounted on each of the cooling tubes 63, and spaced from the wall 64 by an insulating spacer member 121 secured to the side wall 64. A longitudinal bus bar 123 interconnects each of the individual bus bars 121, and is in turn connected to the negative terminal of the source of electrical potential.

The cooling tubes 63 are preferably arranged in a plane parallel to the sheet 12, in a plurality of groups of fourtubes each, the flow of coolant through each of said groups being connected in parallel, as indicated by the directions of the arrows indicating the direction of coolant flow in FIG. .6. Thus, the temperature of the cooling tubes 63 is substantially uniform throughout the tank 19, without any substantial gradient from one end of the tank 19 to the other. Some of the tubes 63 are connected together by hoses 118 to form closed fluid paths terminating in a hose 120, which is connected to a source of coolant and a tube 122, which is connected to the reservoir for such coolant.

For the purpose of replacing any electrolyte which may'drip down into the tray 82, illustrated in FIG. 7, there is provided an inlet conduit 136, by which more electrolyte may be added to the tank 19, and an over- 'flow' conduit 137 to regulate the level of electroylte in the tank 19. In addition, adnain or outlet conduit 138 (FIG. 6) is provided adjacent the bottom of the weir box 23 for draining the electrolyte 50 in order to permit access to clean the interior of the weir box 23, and to inspect the graphite blocks 60. The inlet and outlet conduits are provided with valves (not shown) to regulate the entry and exit of electrolyte from the weir box 23.

When the apparatus of the present invention is used to anodize aluminum, hydrogen is given off which'rises to the surface of the tank. This hydrogen, and other gases which may collect at the top of the tank are preferably drawn off by an exhaust fan (not shown) connected to the duct 67. Without further elaboration, the foregoing will so fully explain the character of the present invention that others may, by applying current knowledge, readily adapt the same for use under varying conditions of service while retaining certain features which may properly be said to constitute the essential items of novelty involved, which items are intended to be defined and secured by the following claims.

What is claimed is:

1. Anodizing apparatus comprising a tank for containing a quantity of electrolyte, said tank having side walls and end walls, said walls being provided adjacent the bottom thereof with means for sealingly engaging a metallic sheet to be anodized, whereby the bottom of said tank is closed, means for connecting an electrical potential between said electrolyte and said sheet, whereby anodizing current flows between said electrolyte and said sheet, and means for flowing said electrolyte over the surface of said sheet, said last named means comprising an endless belt mounted on a pair of rollers disposed within said tank, said belt being positioned parallel and closely adjacent to the surface of the sheet to be anodized at the bottom of said tank and having a plurality of discontinuities in the surface thereof adapted to cause said electrolyte to flow over the surface of said sheet when said rollers are rotated.

2. Apparatus according to claim 1, wherein each of said rollers is mounted on a shaft, means for connecting said shafts to rotate in synchronism, and means for rotating said rollers.

3. Apparatus according to claim 1, wherein said plurality of discontinuities in said belt comprise a plurality of apertures.

4. Apparatus according to claim 3, wherein said apertures are disposed in a plurality of rows oriented transverse to the direction of movement of said belt, holes in adjacent rows being disposed so as to trace a path along the surface of said sheet overlapping with the path traced by the corresponding hole in the next adjacent row.

5. Apparatus according to claim 1, wherein said discontinuities comprise a plurality of slots disposed in said belt and oriented in a direction perpendicular to the direction of movement of the slots relative to the surface of said sheet.

6. Apparatus according to claim 1 including a cooling conduit disposed within said electrolyte, and a source of coolant adapted to fiow through said conduit to cool said electrolyte.

7. Apparatus according to claim 6, wherein there is provided a plurality of conduits for supporting a plurality of independent flows of coolant, each of said conduits being disposed within said tank substantially along a plane including the axes of said pair of said belt rollers.

8. Apparatus according to claim 6, wherein said conduit comprises a hollow tube of electrically conductive material, and means connecting said conduit to said electrical potential, whereby said cooling conduit comprises the anodizing cathode.

9. Anodizing apparatus comprising a tank adapted to contain a quantity of electrolyte, said tank having side walls and end walls, said walls being provided adjacent the bottom thereof with means for sealingly engaging a metallic sheet to be anodized and whereby the tank is closed, means for establishing a potential difference between said electrolyte and said sheet, whereby a current flows therethrough, said last named means including electrode contact means in sliding contact with a surface of said sheet, and pressure differential means operative to force said sheet tightly into contact with said electrode means.

10. Apparatus according to claim 9, wherein said pressure differential means comprises a chamber disposed beneath said tank, said chamber having side walls, each of said side walls having a ledge extending normally therefrom, the top of said chamber being closed by said sheet resting on said ledges, and vacuum means connected to said chamber for evacuating fluid from said chamber to cause said sheet to be forced downwardly into engagement with said ledges, thereby sealing saidchamber from the electrolyte Within said tank.

11. Apparatus according to claim 10, wherein said electrode means comprises a plurality of conductive blocks disposed within said chamber in coplanar arrangement between said ledges adjacent a surface of said sheet, each pair of adjacent ones of said blocks being spaced apart to expose said surface to the pressure in said chamber.

12. Apparatus according to claim 10, wherein said vacuum means comprises an exhauster having a hollow nozzle portion, a hollow inlet portion, and a hollow outlet portion; means for connecting a source of pressurized fluid to said nozzle portion, means for connecting a low pressure reservoir to said outlet portion, and means for connecting said chamber to said inlet portion, said nozzle portion having a taperedrinterior bore which nar-. rows inwardly, the interior of said inlet portion being connected to said nozzle portion at the narrow end of said bore, whereby fluid within said chamber is entrained into the stream of fluid flowing from said nozzle portion into said outlet portion.

13. Anodizing apparatus according to claim 1 including a plurality of hollow cooling tubes disposed within said electrolyte, means for establishing an electrical potential difference between said electrolyte and said tubes, and means for causing a coolant to flow through said tubes to remove the heat from said electrolyte, which is created during anodizing.

14. Apparatus according to claim 13, wherein said cooling tubes are of conductive material and are disposed in substantially a plane parallel to the surface of said sheet to be anodized.

15. Apparatus according to claim 14, wherein said tank has a pair of opposed side walls and said tubes are supported at each end by said side walls, said tubes being connected together to form a plurality of conduit paths each including a plurality of tubes.

16. Apparatus according to claim 15, wherein said tubes are connected together by insulating hoses to form said conduit paths, conductor means electrically connected to each of said tubes at one end thereof, bus bar means interconnecting each of said conductor means, and means connecting said bus bar means to one terminal of a source of electrical potential.

References Cited by the Examiner UNITED STATES PATENTS 568,099 9/1896 Pelatan et al. 204206 1,191,386 7/1919 Battle 204206 X 2,307,928 1/1943 Hogaboom 204141 2,515,614 7/1950 Schumacher 204274 2,989,445 6/1961 Lloyd et al 204-28 3,038,850 6/1962 Wagner 204206 3,079,308 2/ 1963 Ramirez et al 20428 3,082,164 3/1963 Palmer 204255 3,223,610 12/1965 Inoue 204224 JOHN H. MACK, Primary Examiner.

W. VANSISE, Assistant Examiner.

Claims

1. ANODIZING APPARATUS COMPRISING A TANK FOR CONTAINING A QUANTITY OF ELECTROLYTE, SAID TANK HAVING SIDE WALLS AND END WALLS, SAID WALLS BEING PROVIDE ADJACENT THE BOTTOM THEREOF WITH MEANS FOR SEALINGLY ENGAGING A METALLIC SHEET TO BE ANODIZED, WHEREBY THE BOTTOM OF SAID TANK IS CLOSED, MEANS FOR CONNECTING AN ELECTRICAL POTENTIAL BETWEEN SAID ELECTROLYTE AND SAID SHEET, WHEREBY ANODIZING CURRENT FLOWS BETWEEN SAID ELECTROLYTE AND SAID SHEET, AND MEANS FOR FLOWING SAID ELECTROLYTE OVER THE SURFACE OF SAID SHEET, SAID LAST NAMED MEANS COMPRISING AN ENDLESS ELT MOUNTED ON A PAIR OF ROLLERS DISPOSED WITHIN SAID TANK, SAID BELT BEING POSITIONED PARALLETL AND CLOSELY ADJACENT TO THE SURFACE OF THE SHEET TO BE ANODIZED AT THE BOTTOM OF SAID TANK AND HAVING A PLURALITY OF DISCONTINUITIES IN THE SURFACE THEREOF ADAPTED TO CAUSE SAID ELECTROLYTE TO FLOW OVER THE SURFACE OF SAID SHEET WHEN SAID ROLLERS ARE ROTATED.