EP2906740A1

EP2906740A1 - Anodizing device and anodizing method for tubular bodies

Info

Publication number: EP2906740A1
Application number: EP13777031.9A
Authority: EP
Inventors: Peter Hans Brede; Frank Fischer; Ralf Horst Noatzke
Original assignee: Noatzke Verwaltungs GmbH
Current assignee: Noatzke Verwaltungs GmbH
Priority date: 2012-10-15
Filing date: 2013-10-14
Publication date: 2015-08-19
Also published as: DE102012109812A1; WO2014060333A1

Abstract

The invention relates to an anodizing device for anodizing at least one internal surface element (22) of a metal tubular body (18) having an extension direction (24), comprising: an anodizing tank (10) for accommodating an electrolyte (16), which is in contact with the at least one surface element (22) of the tubular body (18) in at least one operating state, and an internal electrode (26; 28; 30; 32), which is at least partially surrounded by the tubular body (18) in a radial direction substantially perpendicular to the extension direction (24) in the operating state and is provided for connecting to an electric current source (12). According to the invention the anodizing device has a covering unit (38; 40; 42; 44; 46) provided for controlling a spatial distribution of an anodizing current, which covering unit is arranged continuously at least in some sections in the extension direction (24) and between the internal electrode (26; 28; 30; 32) and the at least one internal surface element (22) in the radial direction in the operating state.

Description

Description title

ANODIZING APPARATUS AND METHOD OF ELOXIDING PIPE BODY

The present invention relates to an anodizing device for anodizing at least one inner surface element of a metallic one

Pipe body with an extension direction according to the preamble of

Claim 1.

State of the art

The corrosion resistance of many, according to the electrochemical

Stress series as "base" classified metals, based on the

Protective effect of a naturally formed oxide layer. The best known is the anodic oxidation of aluminum. The anodic oxidation of aluminum is usually carried out to produce decorative surfaces, increase corrosion resistance or wear resistance, or create an adherent interface for subsequent coatings.

As is known, aluminum has a dull, silver-gray appearance due to a thin oxide film forming very rapidly in the air. This passivating oxide layer renders pure aluminum highly corrosion resistant at pH's in the range of about 4 to 9. Usually, this oxide layer reaches a thickness of about 50 nm. Much thicker, usually also wear-resistant oxide layers can be wet-chemically by anodic

Electrooxidation can be generated. The best known example of this is the formation of so-called anodized aluminum coatings. In the anodizing process, in contrast to the galvanic coating method, the protective layer is not deposited on the workpiece, but by converting the uppermost metal layer, an oxide or an oxide hydrate formed. In order to ensure high corrosion protection by these layers, but are usually additional process steps to the actual anodization perform. Because of the process-related anodizing always pore-rich

Oxide layers are formed, these are in most cases by means of

aftertreated with different compaction methods. This will then close the porous structure of the freshly anodized layer so as to achieve improved corrosion resistance. In most cases, additional densification treatment is carried out by means of different sealing or impregnating methods which seal the porous structure of the freshly anodized layer so as to provide improved corrosion resistance, pigmentation and / or lubricity in order to improve the

Wear resistance to provide.

The film formation processes are influenced by the choice of the

Electrolytes, its concentration and temperature, current type (DC, AC), current density, voltage and duration of treatment. Strong influence also exercise temperature changes. The duration of the treatment is directly related to the layer thickness to be achieved. In the electrolyte sometimes additives are mixed, which act on the composition of the oxide layers. The basic material of the layer, however, always remains

Alumina. By additions to the electrolyte, the properties of the layer can be changed.

Anodization can be carried out in solutions of various compositions, with the aid of direct or alternating current. The most common are the DC sulfuric acid (GS) and DC sulfuric acid-oxalic acid (GSX) processes. Typical bath temperatures are between 18 ° C and 30 ° C. It is known, especially wear-resistant

Aluminum surfaces can also be anodized in cooled acid baths at bath temperatures of -10 ° C to + 10 ° C.

The anodization is an exothermic reaction; i.e. it releases heat. It is important that the resulting heat from the to

Anodizing metal, such as aluminum, is dissipated sufficiently quickly so that the metallic workpiece does not heat. For example, the layer hardness of the anodized metal, often aluminum, depending on the bath temperature, wherein the layer hardness increases with decreasing bath temperature. At temperatures in the range of less than 10 ° C are significantly increased

Determine layer hardness. It is therefore a particular object of the invention to provide an anodizing device which, with a suitable design, allows a uniform anodizing of metallic tubular bodies.

Disclosure of the invention

The present invention is an anodizing device for

Anodizing at least one inner surface element of a metallic tubular body with an extension direction. The anodizing device comprises: an anodizing container for receiving an electrolyte, which in at least one operating state is in contact with the at least one surface element of the tubular body, and

an inner electrode, which in the operating state in a for

Extending direction is substantially vertical, radial direction at least partially surrounded by the tubular body and is provided for connection to an electrical power source.

An "inner surface" of a metallic tubular body should be understood in this context, in particular a surface whose extended surface normal meets the metallic tubular body.

In this context, a "tubular body" is to be understood as meaning, in particular, an elongate hollow body having a continuous wall which bounds at least one opening of the tubular body.

In this context, a "direction of extension" of a metallic tubular body is to be understood as meaning, in particular, a virtual line of points in the hollow space of the tubular body, with each point of the line leading to the continuous wall of the tubular body in at least one direction pair

In particular, directions of extension may also be formed by curved lines first point of the virtual line in the cavity and one along the virtual line furthest from that first point distant point in the cavity forms an extension length of the metallic tubular body.

It is proposed that the anodizing device has a covering unit provided for regulating a spatial distribution of an anodizing current, which in the operating state is at least partially continuous in the direction of extent and at least in the radial direction at least between the two

Inner electrode and the at least one inner surface element is arranged.

In this case, the covering unit should not comprise any lacquer layer comprising pores arranged on the inner electrode. In this context, a "lacquer layer" is to be understood as meaning, in particular, a layer which contains an electrically insulating coating material, is arranged in liquid or powdery form on the inner electrode and obtains its final shape through a drying process.

In this context, a "cover unit" is to be understood as meaning, in particular, a component which provides access to the electrolyte

Inner electrode at least partially prevented by covering.

With a suitable design, a particularly uniform anodization layer can thereby be achieved on the at least one inner surface of the metallic tubular body.

In a preferred embodiment, the cover unit has a dimension of at least 0.2 millimeters in the radial direction. In particular, the dimension in the radial direction may advantageously be at least 0.25 millimeters and, particularly advantageously, at least 0.3 millimeters.

Furthermore, it is proposed that the cover unit consists at least partially of a dielectric. Under a "dielectric" in this

In particular an electrically non-conductive material,

especially with an electrical conductivity of less than 10.sup.- ⁶ S / m. In a suitable embodiment, the spatial distribution of the anodizing current can be regulated in such a way that a uniform flow is achieved Anodization of the at least one inner surface element of the

metallic tubular body is achieved.

In addition, it is proposed that the dielectric be at least partially porous. In this context, a "porous dielectric" is to be understood as meaning in particular a dielectric which has interconnected cavities. By means of such a cover unit, the spatial distribution of the anodizing current can be effectively and cost-effectively regulated to obtain an anodization layer of uniform thickness.

In an advantageous embodiment, the cover unit is designed as a net-shaped

Tissue or knitted fabric. Under a "tissue" is intended in

In this context, in particular a surface fabric are understood, the at least two substantially perpendicular to each other

Thread systems includes. Under a "knitted fabric" should in this

Connection understood in particular a knitted fabric or knitwear

in which a sheet of one or more threads

Threads is made by stitching.

By forming a net-like fabric or a knitted fabric, the spatial distribution of the anodizing stream can be defined particularly precisely by a suitable configuration of the parameters, which include thread strength, mesh size and other variables.

Preferably, a gap size, the two by the operating state of

Inner electrode juxtaposed threads of a fabric or formed by adjacently arranged, a stitch-forming threads of a knitted fabric or through openings of the mesh tube, at least five microns and not more than ten millimeters, advantageously at least ten microns and

at most ten millimeters, and, most advantageously, at least

50 microns and at most ten millimeters. If the cover unit as

extruded net tube is formed, the spatial distribution of

Anodizing stream very precisely defined and executed in a cost-saving manner. With particular advantage, the cover unit and the inner electrode are materially interconnected. By "cohesive" should be understood in this context, in particular a compound by welding, soldering, gluing, vulcanization, molding or by a

equivalent, familiar to those skilled method is produced. Thereby, an anodizing device can be provided, in which the spatial

Distribution of the anodizing permanently furnished and temporally immutable regulated. Alternatively, a spatial distribution of the anodizing current can be set up permanently and regulated in a fixed manner over time if the covering unit and the inner electrode are connected to one another by a frictional connection, in particular a frictional connection resulting from elastic material properties. Advantageously, the frictional connection, for example by

Shrinking the cover unit to be made on the inner electrode.

Furthermore, it is proposed that the cover unit is arranged in the operating state substantially concentric with the inner electrode. As a result, in a suitable embodiment, a spatially symmetrical distribution of

Anodizing be permanently established.

In a further advantageous embodiment, the cover unit has a plurality of Durchgangsoffnungen that allow passage of ions. In this context, a "passage opening" is to be understood as meaning, in particular, an opening in the cover unit, which has a

Access of the electrolyte to the inner electrode allows. Durchgangsoffnungen can be designed straight or branched; in particular should

Include pore openings to the Durchgangsoffnungen. The Durchgangsoffnungen can also be partially or completely filled with a proton conductive material. By means of a suitable embodiment of the passage openings, a desired spatial distribution of the anodizing current for producing a uniform anodization layer on the inner surface element of the metallic tubular body can be achieved.

In addition, it is proposed that a mean surface density of

Durchgangsoffnungen the arranged in the operating state cover unit in the extension direction varies. Under a "middle surface density" should in In this context, in particular averaged over a contiguous area of at least 5 mm ² number of through holes are understood. By varying the areal density of the passage openings in the direction of extent, a uniform distribution of the anodizing stream for producing a uniform anodization layer can be achieved with a suitable design.

If the mean surface density of the through holes of the

Operating state arranged cover unit in edge regions of

Extension length is less than in a central region of the

Extension length, occurring due to a finite electrical conductivity voltage loss, which could lead to an unfavorable, non-uniform anodizing current distribution, at least partially compensated. In this case, under an "edge region" in this context, in particular a region of a calculated from an opening of the tubular body to first

Third of the extension length to be understood. In this context, a "middle region" is to be understood as meaning, in particular, a region of a second third of the extension length calculated from the opening of the tubular body.

In a further advantageous embodiment, a mean opening width of the passage openings of the cover unit arranged in the operating state is lower in edge regions of the extension length than in a middle region of the extension length. With such an arrangement can also occur due to a finite electrical conductivity voltage losses with the

As a result of an unfavorable, non-uniform anodizing current distribution be at least partially compensated.

Advantageously, the cover unit consists essentially of a plastic or a combination of plastics selected from the group consisting of polyamides, polyethylene, polypropylene, polyvinyl chloride, and the group of plastics Polyurethanes and polyvinylidene fluoride is formed. By "essentially" is to be understood in this context in particular as at least 60%, preferably more than 70% and, more preferably, more than 80%. In particular, the cover unit also completely, ie 100%, from one of these plastics or a combination of these Be formed plastics. This allows a cost-effective cover unit with high durability and resistance in an environment with

be provided electrochemical processes. Furthermore, it is proposed that the inner electrode be metallic

Round rod, is designed as a metallic wire or a metallic band. Under a "metallic rod" in this context

In particular, a metallic object can be understood whose dimension in a first direction is at least five times as large as a dimension in a second direction perpendicular to the first direction, wherein the

Dimension in the second direction is greater than or equal to two millimeters, and having a cross-section in the form of an oval in a sectional plane perpendicular to the first direction, wherein circles and ellipses are to be regarded as special cases of an oval.

In this context, a "metallic wire" is to be understood as meaning, in particular, a metallic round rod whose dimension in a first direction is at least five times greater than in a second direction perpendicular to the first, with one dimension in the second direction being less than two Millimeters.

A "metallic band" is to be understood in this context in particular as a metallic object having a substantially trapezoidal cross-section which is constant in a direction perpendicular to the cross-sectional plane at least in continuous sections, a rectangle being considered a special case of a trapezoid. Under "im

Substantially trapezoidal "is to be understood in this context that a deviation of the cross-sectional area of the band from the cross-sectional area of a trapezoid inscribed in the cross-sectional area of the band is less than 20%, more preferably less than 10% of the cross-sectional area of the band in the cross-sectional plane.

In particular, a "band" should also have a plurality of metallic ones

Individual wires, which may form a braid or are fixed in their relative arrangement by a dielectric coating, which may also be formed as a cover unit include.

By a suitable configuration of the inner electrode, a desired spatial distribution of the anodizing current for producing a uniform Anodizing layer on the inner surface element of the metallic

Tube body can be achieved.

When the inner electrode is substantially made of a metal selected from a group consisting of steel, titanium or a titanium alloy, and aluminum or an aluminum alloy

Internal electrodes are provided with high durability and resistance in an environment with electrochemical processes.

In a further advantageous refinement, the inner electrode has cross sections in planes which are arranged perpendicular to the extension direction and which, in the operating state, have a smaller extent in edge regions of the extension length

Have cross-sectional area than in a central region of

Extension length. As a result, due to a finite electrical conductivity occurring voltage losses, which could lead to an unfavorable, non-uniform Eloxierstromverteilung, at least partially compensated. In a suitable design can be achieved that an electric field strength along the extension direction of

Inner electrode is substantially constant despite line losses occurring, whereby a uniform anodizing can be made possible.

A particularly simple realization of such internal electrodes can be achieved if the cross-sections are substantially oval-shaped. Another object of the present invention is an anodizing process for anodizing at least one inner surface element of a metallic tubular body using an anodizing in the previously described manner or anodized, with which a particularly uniform anodization along the extension length of the metallic tubular body can be produced.

With particular advantage, the metallic tubular body consists essentially of aluminum, whereby a tubular body can be produced with a particularly durable and resistant anodization.

drawing

Further advantages emerge from the following description of the drawing. In the Drawing is an embodiment of the invention shown. The drawings, the description and the claims contain numerous features

Combination. The person skilled in the art will expediently also consider the features individually and combine them into meaningful further combinations.

Show it:

Fig. 1 is a schematic overall view of an inventive

Eloxiervorrichtung,

2 shows a detailed view of the anodizing device according to FIG. 1,

4 shows a detailed view of a further embodiment of an anodizing device, FIG. 5 shows a detailed view of a further embodiment of an anodizing device, FIG. 6 shows a detailed view of a further embodiment of an anodising device, and FIG

7 shows a detailed view of a further embodiment of an anodizing device.

Description of the embodiments

This description contains several embodiments of the invention. The individual embodiments have features whose function is identical or fundamentally identical in each embodiment. These features are identified by reference numerals, which consist of a number of the variant and the number of the feature common to all embodiments and thus form a single number. A description of the function of a feature of an embodiment may therefore also be included in a description of one of the preceding embodiments.

Fig. 1 shows a schematic overall view of an inventive

Eloxiervorrichtung. The anodizing device is provided for anodizing at least one inner surface element 122 of a metallic tubular body 1 18 with an extension direction 124 and comprises an anodizing container 110 for receiving an electrolyte 16. The electrolyte 1 16 comprises a 5% aqueous sulfuric acid solution, wherein the sulfuric acid in a known manner to increase the electrical

Conductivity of the water is used. The electrolyte 1 16 is filled so high in an operating state in the anodizing container 1 10 that the tubular body 1 18 is completely surrounded by the electrolyte 1 16.

The anodizing device further has an inner electrode 26, which in the

Operating state in a direction of extension 124 substantially perpendicular, radial direction at least partially surrounded by the tubular body 1 18 and is provided for connection to an electrical power source 1 12.

The current source 1 12 is designed as a DC voltage source. The

Inner electrode 26 is galvanically connected to the negative pole U. of the current source 1 12 and thus connected as a cathode. Electrically parallel to

Internal electrode 26 are connected to both sides of the tubular body 1 18 to lower the current density plate-shaped graphite electrode 1 14 arranged. At the cathode, hydrogen gas separates during operation of the anodizing device.

The metallic tubular body 1 18 consists of an alloy of aluminum, magnesium and silicon, wherein the proportion of aluminum is more than 99%, so that the tubular body 1 18 consists essentially of aluminum. The tubular body 1 18 is formed as a straight, hollow circular cylinder whose an inner cavity 120 facing surface of the cylinder jacket surface forms an inner surface element 122 of the tubular body 1 18 (FIG. 2). The electrolyte 1 16 is connected to the at least one surface element 122 of the

Tube body 1 18 thus in direct contact.

The metallic tubular body 1 18 is connected to the positive pole U +

DC voltage source galvanically connected and connected as an anode. Oxidation of the aluminum takes place at the anode during operation of the anodizing device.

Furthermore, the anodizing device has a covering unit 38 provided for regulating a spatial distribution of an anodizing current, which in the operating state in the direction of extent 124 is in a full Extension length is arranged continuously and in the radial direction between the inner electrode 26 and the at least one inner surface element 122.

The arrangement of the tubular body 1 18, the cover unit 38 and the

Inner electrode 26 is shown in FIG. 2 in a sectional detail view of the anodizing device according to FIG. 1.

The along a central axis 134 of the hollow cylindrical tubular body 1 18 and on both sides projecting beyond this inner electrode 26 is formed as a cylindrical rod made of a titanium alloy, which is durable with respect to the described electrochemical load.

The cover unit 38 consists entirely of a porous dielectric, which is formed by a polyurethane (PU) foam and is adhesively bonded to the inner electrode 26 by an adhesive process during the curing of the PU foam. The cover unit 38 is arranged coaxially to the inner electrode 26 in the operating state illustrated in FIGS. 1 and 2.

The interconnected open pores of the PU foam constitute a plurality of through openings 48 which allow passage of ions. As indicated in the detail view of FIG. 2, an average surface density of the through openings 48 of the cover unit 38 arranged in the operating state varies in the extension direction 124, namely, the mean surface density of the through openings 48 increases from a highest value in a central region 152 of the extension length of the cover unit 38 on both sides in the direction of edge regions 154 of the extension length of the cover 38 from. The passage openings 48 allow access of the electrolyte 1 16 to the inner electrode 26, while the cover unit 38 prevents the access of the electrolyte 1 16 to the inner electrode 26 at locations without through opening 48.

The electrical resistance of the inner electrode 26 leads during the anodization to a voltage drop along the extension length, so that an electric field strength in the central region 152 of the extension length decreases, which would result in uniform surface density of the through holes 48, that there move the ions slower and a local ^- I ^-

Anodizing current density decreases. Due to the increase in the mean surface density of the through openings 48, this effect is compensated so that over the extension length a substantially uniform anodizing current density can be achieved.

The same effect can be achieved with the cover unit 40 shown in FIG. In this cover unit 40 is a mean opening width of

Through openings 50 of the cover unit 40 arranged in the operating state are smaller in edge regions 254 of the extension length than in a central region 252 of the extension length. The illustrated in Fig. 3 inner electrode 28 is formed as a rod and has a on the

Extension length uniform, oval cross section.

FIG. 4 shows a further alternative embodiment of a cover unit 42. The cover unit 42 is designed as a helix winding 56 around an inner electrode 28 according to FIG. 3. The helix winding 56 is partially made of a dielectric and is of a PVC-covered metal wire 58 with a circular

Cross section formed in the operating state in engagement with a surface 336 of the inner electrode 28 is wound such that a distance between two successive in the direction of extension 324 turns in the central region 352 of the extension length is greater than in one of the edge regions 354 of the extension length. In the middle region 352 of the extension length, a larger anodizing current is thereby enabled than in the edge regions 354 of FIG

Extension length, which as described above on the

Extension length substantially uniform anodizing current density can be achieved. At contact points of the helix winding 56 with the inner electrode 28 of the PVC sheath of the metal wire 58 is firmly bonded by gluing with the

Internal electrode 28 connected.

In the embodiment of FIG. 5, a cover unit 44 is attached to the surface 436 of an alternatively designed inner electrode 30, which consists of polyamide and is formed as a knitted stocking. The cover unit 44 is pulled in an operating state over the inner electrode 30, which is formed by a flat band of titanium with a rectangular cross-section and rounded edges. The cover unit 44 is dimensioned relative to the inner electrode 30 such that it is held on the inner electrode 30 by the elastic material properties of the polyamide by adhesion. to Further stabilization, a primer may be applied to the inner electrode 30 before coating.

Another embodiment of a cover unit 46, which is extruded

Net hose made of polypropylene and connected to an inner electrode 26 according to FIG. 2 by adhesive bonding is shown in FIG. 6.

FIG. 7 shows a further embodiment of an inner electrode 32. The inner electrode 32 has in the direction perpendicular to the extension direction 624th

arranged levels circular cross sections, which in the operating state in the

Edge regions 654 of the extension length have a smaller cross-sectional area than in the central region 652 of the extension length. The cover unit 40 corresponds to the exemplary embodiment according to FIG. 3.

, _c

- 15 -

LIST OF REFERENCE NUMBERS

10 anodizing tanks

12 power source

14 graphite electrode

16 electrolyte

18 tubular body

20 cavity

22 area element

24 extension direction

26 inner electrode

28 inner electrode

30 inner electrode

32 internal electrode

34 central axis

36 surface

38 Cover unit

40 cover unit

42 Cover unit

44 Cover unit

46 Cover unit

48 passage opening

50 passage opening

52 middle range

54 border area

56 Helix winding

58 metal wire

U minus pole

U ₊ positive pole

Claims

claims

1 . Anodizing device for anodizing at least one internal

Planar element (22) of a metallic tubular body (18) having an extension (24), comprising:

an anodization container (10) for receiving an electrolyte (16), which in at least one operating state with the at least one

Surface element (22) of the tubular body (18) is in contact, and an inner electrode (26; 28; 30; 32), which in the operating state in a direction to the Erstreckungsnchtung (24) substantially perpendicular radial direction at least partially from the tubular body (18) surrounded and for connection to an electrical power source (12) is provided, characterized by

a covering unit (38; 40; 42; 44; 46) provided for regulating a spatial distribution of an anodizing current, which in the operating state in the extension means (24) is continuous at least in sections and in the radial direction between the inner electrode (26; 28; 30; 32 ) and the at least one inner surface element (22) is arranged.

2. Anodizing device according to claim 1, characterized in that the

Cover unit in the radial direction has a dimension of at least 0.2 millimeters.

3. Anodizing device according to claim 1 or 2, characterized in that the cover unit (38; 40; 42; 44; 46) at least partially consists of a dielectric.

4. Anodizing device according to claim 3, characterized in that the

Dielectric is at least partially porous.

5. Anodising device according to one of the preceding claims, characterized in that the covering unit (38; 40; 42; 44; 46) is designed as a net-shaped fabric or as a knitted fabric.

6. Anodising device according to one of the preceding claims, characterized in that the covering unit (38; 40; 42; 44; 46) is designed as an extruded net tube.

7. Anodizing device according to claim 5 or 6, characterized in that a gap size, which is formed by two in the operating state of the inner electrode juxtaposed threads of a fabric or by adjacently arranged, a stitch-forming threads of a knitted fabric or through openings of the mesh tube, at least five microns and not more than ten millimeters.

8. Anodizing device according to one of the preceding claims, characterized in that the cover unit (38; 40; 42; 44; 46) and the inner electrode (26; 28; 30; 32) are connected to one another in a material-locking manner.

9. Anodizing device according to one of the preceding claims, characterized in that the cover unit (38; 40; 42; 44; 46) in

Operating state substantially concentric with the inner electrode (26; 28; 30; 32) is arranged.

10. An anodizing device according to one of the preceding claims, characterized in that the cover unit (38; 40; 42; 44; 46) has a plurality of passage openings (48; 50) which allow passage of ions.

1 1. Anodizing device according to one of the preceding claims, characterized in that an average surface density of

Through-openings (48; 50) of the cover unit (38; 40; 42; 44; 46) arranged in the operating state vary in the extension direction (24) in such a way that the mean surface density of the through-openings (48; 50) decreases in edge regions (54) of an extension length is as in a middle region (52) of the extension length.

12. Anodizing device according to one of the preceding claims, characterized in that an average opening width of the passage openings (48; 50) arranged in the operating state Covering unit (38; 40; 42; 44; 46) is smaller in edge regions (54) of the extension length than in a central (52) region of the extension length.

13. An anodizing device according to one of the preceding claims, characterized in that the cover unit (38; 40; 42; 44; 46) essentially consists of a plastic which is selected from a group selected from the plastics of the group of the polyamides, of polyethylene, of polypropylene, of polyvinyl chloride, of the group of polyurethanes and of polyvinylidene fluoride.

14. Anodizing device according to one of the preceding claims, characterized in that the inner electrode (26; 28; 30; 32) is designed as a metallic round rod, as a metallic wire or as a metallic band.

An anodizing apparatus according to any one of the preceding claims, characterized in that the inner electrode (26; 28; 30; 32) consists essentially of a metal selected from a group consisting of steel, titanium or a titanium alloy, and of Aluminum or an aluminum alloy is formed.

16. Anodising device according to one of the preceding claims, characterized in that the inner electrode (26; 28; 30; 32) has cross-sections in planes arranged perpendicular to the extension direction, which in the operating state have a smaller cross-sectional area in edge regions (54) of the extension length than in one middle region (52) of the extension length.

17. Anodizing device at least according to claim 16, characterized in that the cross-sections are substantially oval-shaped.

18. Anodization methods for m atl at least one of a surface element (22) of a metallic tubular body (18), characterized in that an anodising device according to one of the preceding claims is used ,

19. Anodizing method according to claim 18, characterized in that the metallic tubular body (18) consists essentially of aluminum.