Electrode for an eloxal process

Abstract

The present disclosure relates to an electrode for eloxing a component, in particular a component of a vehicle brake system, comprising an electrolyte inlet for feeding an electrolyte into the electrode, an inlet channel, which connects the electrolyte inlet to an electrolyte outlet opening formed in the region of an outer surface of the electrode, an electrolyte inlet opening formed in the region of the outer surface of the electrode at a distance from the electrolyte outlet opening, an electrolyte flow path, which runs between the electrolyte outlet opening and the electrolyte inlet opening along the outer surface of the electrode and is designed to bring a surface portion of the component, which surface portion is to be eloxed, into fluid contact with the electrolyte flowing through the electrolyte flow path, an outlet channel, and an electrolyte outlet.

Claims

1. An electrode for anodizing a component, comprising: an electrolyte inlet for feeding an electrolyte into the electrode, an inlet channel which connects the electrolyte inlet to a plurality of electrolyte exit openings in an outer surface of the electrode, a plurality of electrolyte entry openings in the outer surface of the electrode and each of the electrolyte entry openings being spaced longitudinally apart from each of the electrolyte exit openings, an electrolyte flow path that runs longitudinally between the electrolyte exit opening and the electrolyte entry opening along the outer surface of the electrode and is adapted to bring a surface section of the component to be anodized into fluid contact with the electrolyte flowing through the electrolyte flow path, an outlet channel connected to the plurality of electrolyte entry openings and an electrolyte outlet connected to the outlet channel for discharging the electrolyte from the electrode.

2. The electrode as claimed in claim 1, wherein the electrolyte inlet, the inlet channel, the plurality of electrolyte exit openings, the electrolyte flow path, the plurality of electrolyte entry openings, the outlet channel and/or the electrolyte outlet is/are shaped and/or dimensioned such that a laminar electrolyte flow is established at least in the electrolyte flow path.

3. The electrode as claimed in claim 2, wherein the inlet channel comprises: a plurality of inlet channel branches each connected to an associated electrolyte exit opening, or a plurality of inlet channel branches each connected to an associated electrolyte exit opening, an inlet channel section being arranged upstream of the inlet channel branches, wherein the inlet channel branches and/or the electrolyte exit openings are arranged equidistantly in a circumferential direction of the electrode, wherein the outlet channel comprises: a plurality of outlet channel branches each connected to an associated electrolyte entry opening, or a plurality of outlet channel branches each connected to an associated electrolyte entry opening, an outlet channel section being arranged downstream of the outlet channel branches, wherein the electrolyte entry openings and/or the outlet channel branches are arranged equidistantly in the circumferential direction of the electrode.

4. The electrode as claimed in claim 3, wherein: a number of inlet channel branches is equal to a number of outlet channel branches, and/or a number of electrolyte exit openings is equal to a number of electrolyte entry openings.

5. The electrode as claimed in claim 4, wherein: the inlet channel section and the outlet channel section have the same identical flow cross sections, and/or the inlet channel branches, the electrolyte exit openings, the electrolyte entry openings and/or the outlet channel branches have identical flow cross sections.

6. The electrode as claimed in claim 5, wherein: the flow cross section of the inlet channel section is equal to a sum of the flow cross sections of the inlet channel branches, and the flow cross section of the outlet channel section is equal to a sum of the flow cross sections of the outlet channel branches.

7. The electrode as claimed in claim 6, comprising a first electrode part having: a cylindrical first section adapted for introduction into a recess formed in the component to be anodized, in whose outer surface the plurality of electrolyte exit openings and the plurality of electrolyte entry openings are formed spaced apart from one another along a longitudinal axis of the electrode and/or along whose outer surface the electrolyte flow path runs, and/or a flange section extending radially from the outer surface of the first section, wherein the flange section has a first end face facing the component to be anodized during operation of the electrode, the first end face of the flange section carrying a seal which is adapted to seal an electrolysis gap defined by the outer surface of the first section and an inner surface of the recess formed in the component to be anodized during operation of the electrode, and/or a further cylindrical section extending along the longitudinal axis of the electrode from a second end face of the flange section which faces away from the component to be anodized during operation of the electrode.

8. The electrode as claimed in claim 7, wherein: the first electrode part is penetrated by a through-bore extending along the longitudinal axis of the electrode, wherein a section of the through-bore forms the outlet channel section and/or wherein the through-bore is fluid-tightly sealed by means of a further seal adjacent an end facing the component to be anodized during operation of the electrode, and/or inlet channel branches formed in the first electrode part extend from the second end face of the flange section in a flow direction of the electrolyte flowing through the inlet channel branches initially inclined radially inwardly to the electrolyte exit openings relative to the longitudinal axis of the electrode and subsequently inclined radially outwardly to the electrolyte exit openings relative to the longitudinal axis of the electrode, and/or outlet channel branches formed in the first electrode part extend radially inwardly from the electrolyte entry openings, parallel to sections of the inlet channel branches inclined radially outwardly relative to the longitudinal axis of the electrode, and open into the through-bore penetrating the first electrode part.

9. The electrode as claimed in claim 8, comprising a second electrode part adjacent to the first electrode part, wherein the second electrode part is penetrated by a through-bore extending along the longitudinal axis of the electrode which is adapted to accommodate the further cylindrical section of the first electrode part, and an inlet channel section formed in the second electrode part which has a ring-shaped flow cross section extends parallel to the longitudinal axis of the electrode from a first end face of the second electrode part facing the component to be anodized during operation of the electrode in a direction of a second end face of the second electrode part facing away from the component to be anodized during operation of the electrode, and in the second electrode part a first connecting channel connected to the electrolyte inlet informed which extends perpendicularly to the longitudinal axis of the electrode and/or forms a fluid-conducting connection between the electrolyte inlet formed in an outer surface of the second electrode part and the inlet channel section formed in the second electrode part.

10. The electrode as claimed in claim 9, comprising a third electrode part adjacent to the second electrode part having: a main body and a cylindrical protruding section which extends along the longitudinal axis of the electrode and during operation of the electrode projects in a direction of the component to be anodized and adjacent to the further cylindrical section of the first electrode part is accommodated in the through-bore penetrating the second electrode part, wherein in the third electrode part a second connection channel connected to the electrolyte outlet is formed which comprises a first section which penetrates the protruding section along the longitudinal axis of the electrode and a second section running perpendicularly to the longitudinal axis of the electrode in the main body and/or forms a fluid-conducting connection between the electrolyte outlet formed in an outer surface of the third electrode part and the outlet channel section formed in the first electrode part.

11. An apparatus for anodizing a component, comprising: an electrode as claimed in claim 1; an electrolyte circuit for feeding electrolyte to the electrode and for discharging electrolyte from the electrode, wherein arranged in the electrolyte circuit are an electrolyte source and/or a conveying means for conveying the electrolyte through the electrolyte circuit, and a voltage source which is connectable to the component to be anodized and the electrode and is adapted for applying opposite voltages to the component and the electrode.

12. The apparatus as claimed in claim 11, further comprising a cooling apparatus for cooling the electrode, the component and/or the electrolyte, wherein the cooling apparatus is arranged in the electrolyte circuit and is adapted for cooling the electrolyte flowing through the electrolyte circuit.

13. A process for anodizing a component, comprising: supplying an electrolyte to an electrode as claimed in claim 1 through the electrolyte inlet, passing the electrolyte through the inlet channel, passing the electrolyte through the plurality of electrolyte entry openings, passing the electrolyte through the electrolyte flow path, passing the electrolyte through the outlet channel, discharging the electrolyte from the electrode through the electrolyte outlet and applying a voltage to the component to be anodized and the electrode.

14. The process as claimed in claim 13, wherein: a temperature of the electrolyte is set to −10° C. to +20° C., the voltage is increased from 0 V to a maximum voltage of 30 V over a defined period, so that in this period a current increases from 0 A to a current which is higher than 0 A but not more than 2 A and/or the electrolyte, the electrode and/or the component are cooled to remove heat formed during the anodization.

15. The process as claimed in claim 14, wherein a cylindrical first section of a first electrode part, in whose outer surface the plurality of electrolyte exit openings and the plurality of electrolyte entry openings are formed is introduced into a recess formed in the component to be anodized.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the present disclosure are hereinbelow more particularly elucidated with reference to the accompanying schematic diagrams, where

(2) FIG. 1 shows a longitudinal section view of an electrode for an anodizing process;

(3) FIG. 2 shows a rear view of the electrode of FIG. 1;

(4) FIG. 3 shows a side view of the electrode of FIG. 1 rotated by 180° compared to FIG. 1 which illustrates a plurality of exit openings and a plurality of entry openings;

(5) FIG. 4 shows a three-dimensional view of the electrode of FIG. 1;

(6) FIG. 5 shows a front view of a first part of the electrode of FIG. 1;

(7) FIG. 6 shows a side view of the first electrode part of FIG. 5;

(8) FIG. 7 shows a front view of the first electrode part of FIG. 5;

(9) FIG. 8 shows a longitudinal section view of the first electrode part of FIG. 5;

(10) FIG. 9 shows a detailed view of an entry region of an inlet channel branch formed in the first electrode part of FIG. 8;

(11) FIG. 10 shows a three-dimensional view of the first electrode part of FIG. 5;

(12) FIG. 11 shows a three-dimensional view of the first electrode part of FIG. 5 rotated by 180° compared to FIG. 10;

(13) FIG. 12 shows a front view of a second part of the electrode of FIG. 1;

(14) FIG. 13 shows a longitudinal section view of the second electrode part of FIG. 12;

(15) FIG. 14 shows a three-dimensional view of the second electrode part of FIG. 12;

(16) FIG. 15 shows a three-dimensional view of the second electrode part of FIG. 14 rotated by 180°;

(17) FIG. 16 shows a side view of the second electrode part of FIG. 12;

(18) FIG. 17 shows a front view of a third part of the cathode of FIG. 1;

(19) FIG. 18 shows a longitudinal section view of the third electrode part of FIG. 17;

(20) FIG. 19 shows a side view of the third electrode part of FIG. 17;

(21) FIG. 20 shows a three-dimensional view of the third electrode part of FIG. 17;

(22) FIG. 21 shows a longitudinal section view of a first seal for sealing the first electrode part with respect to a bore formed in a component to be anodized;

(23) FIG. 22 shows a front view of the seal of FIG. 21;

(24) FIG. 23 shows a longitudinal section view of a second seal for sealing a front end of a main channel section formed in the first electrode part;

(25) FIG. 24 shows a rear view of the seal of FIG. 23;

(26) FIG. 25 shows the electrode of FIG. 1 during use for anodizing an inner surface of a bore formed in a component of a vehicle braking system; and

(27) FIG. 26 shows scanning electron microscope (SEM) images of an anodized component surface; and

(28) FIG. 27 shows scanning electron microscope (SEM) images of an anodized component surface.

DETAILED DESCRIPTION

(29) FIGS. 1 to 24 show an electrode 10 for use in an apparatus 100 for anodizing a component 50 illustrated in FIG. 25. In the working example shown here the component 50 is a component of a vehicle braking system, in particular a hydraulic block of a traction control system. The electrode 10 comprises a first electrode part 10a illustrated in more detail in FIGS. 5 to 11, a second electrode part 10b illustrated in more detail in FIGS. 12 to 16 and a third electrode part 10c illustrated in more detail in FIGS. 17 to 20.

(30) An electrolyte inlet 14 for feeding an electrolyte into the electrode 10 is arranged in the region of an outer surface of the second electrode part 10c and connected via a first connecting channel 15 formed in the second electrode part 10c to an inlet channel 16. The inlet channel 16 ensures formation of a fluid-conducting connection between the electrolyte inlet 14 and at least one electrolyte exit opening 18 formed in the region of an outer surface of the electrode 10.

(31) As is most apparent from FIGS. 13 and 14 the first connection channel 15 extends substantially perpendicularly to a longitudinal axis L of the electrode 10 and constitutes a fluid-conducting connection between the electrolyte inlet 14 and an inlet channel section 16a formed in the second electrode part. The inlet channel section 16a has a circular ring-shaped flow cross section and extends substantially parallel to the longitudinal axis L of the electrode 10 from a first end face of the second electrode part 10b facing the component 50 to be anodized during operation of the electrode 10 in the direction of a second end face of the second electrode part 10b facing away from the component 50 to be anodized during operation of the electrode. The inlet channel section 16a especially extends concentrically around the longitudinal axis L of the electrode 10 (see especially FIGS. 13 and 14). The inlet channel section 16a opens into a plurality of inlet channel branches 16b formed in the first electrode part 10a and each connected to an electrolyte exit opening 18.

(32) The first electrode part 10a has a cylindrical first section 19a which is shaped and dimensioned such that it may be introduced into a recess 52 formed in the component 50 to be anodized, see FIG. 25. In the working example shown here the recess 52 is in the form of a bore such as is provided for example in a hydraulic block of a traction control system of a vehicle braking system. The first electrode part 10a moreover has a flange section 19b which extends radially outward from the outer surface of the first section 19a. A first end face of the flange section 19b faces the component 50 to be anodized during operation of the electrode 10 while a second end face of the flange section 19b, opposite to the first end face, faces away from the component 50 to be anodized during operation of the electrode 10. Finally, the first electrode part 10a comprises a further cylindrical section 19c which extends from the second end face of the flange section 19b along the longitudinal axis L of the electrode 10.

(33) The inlet channel branches 16b formed in the first electrode part 10a extend from the second end face of the flange section 19b in the flow direction of the electrolyte flowing through the inlet channel branches 16b in the direction of the electrolyte exit openings 18 initially inclined radially inwardly relative to the longitudinal axis L of the electrode 10 and subsequently inclined radially outwardly relative to the longitudinal axis L of the electrode 10, see in particular FIGS. 1, 8 and 25. The electrolyte exit openings 18 are formed in an outer surface of the cylindrical first section 19a of the first electrode part 10a. The inlet channel branches 16b and the electrolyte outlet opening in 18 are in particular arranged equidistantly, i.e. at the same distances from one another, in the circumferential direction of the electrode 10, see in particular FIG. 11.

(34) Formed in the region of the outer surface of the electrode 10 spaced apart from the at least one electrolyte exit opening 18 is at least one electrolyte entry opening 20. Running along the outer surface of the electrode 10 between the at least one electrolyte exit opening 18 and the at least one electrolyte entry opening 20 is an electrolyte flow path 21 adapted to bring a surface section 54 of the component 50 to be anodized into fluid contact with the electrolyte flowing through the electrolyte flow path 21. The electrolyte entry opening 20 is connected to an outlet channel 22 which is itself connected to an electrolyte outlet 24 for discharging the electrolyte from the electrode 10.

(35) In the exemplary embodiment shown here the electrode 10 comprises a plurality of electrolyte entry openings 20 formed in the first electrode part 10a, i.e. in the cylindrical first section 19a of the first electrode part 10a, each of which open into an outlet channel branch 22a formed in the first electrode part 10a, i.e. in the cylindrical first section 19a of the first electrode part 10a, see in particular FIGS. 1, 8 and 25. The outlet channel branches 22a run substantially parallel to the sections of the inlet channel branches 16b inclined radially outwardly relative to the longitudinal axis L of the electrode 10 and open into a through-bore 25 penetrating the first electrode part 10a. The through-bore 25 extends along the longitudinal axis L of the electrode 10 and comprises a section forming an outlet channel section 22b arranged downstream of the outlet channel branches 22a.

(36) Similarly to the inlet channel branches 16b and the electrolyte exit openings 18, the electrolyte entry openings 20 and the outlet channel branches 22a are also arranged equidistantly, i.e. at the same distances from one another, in the circumferential direction of the electrode 10, see in particular FIG. 11. The electrolyte entry openings 20 are arranged along the longitudinal axis L of the electrode 10 at a distance from the electrolyte exit openings 18 which is adapted to the geometry of the recess 52 formed in the component 50 to be anodized. For example the distance between the electrolyte exit openings 18 and the electrolyte entry openings 20 may be about 1-100 mm, about 2-50 mm or about 5-20 mm.

(37) In the working example of an electrode 10 illustrated in the figures the electrolyte flow path 21 runs along the outer surface of the first cylindrical section 19a of the first electrode part 10a which is accommodated in the recess 52 formed in the component 50 to be anodized. Accordingly, the outer surface of the first cylindrical section 19a of the first electrode part 10a and an inner surface of the recess 52 define an electrolysis gap E which has a circular ring-shaped flow cross section having a radial dimension of about 1-100 mm, about 2-50 mm, about 5-20 mm or about 10 mm.

(38) In order to prevent escape of electrolyte from the electrolysis gap E during operation of the electrode 10, the electrode 10 comprises a seal 26 illustrated in detail in FIGS. 21 and 22. The seal 26 is carried by the first end face of the flange section 19b of the first electrode part 10a, see especially FIGS. 1 and 25. A further seal 27, which is illustrated in detail in FIGS. 23 and 24, seals an end of the through-bore 25 penetrating the first electrode part 10a that faces the component 50 to be anodized during operation of the electrode 10. The further seal 27 thus prevents uncontrolled escape of electrolyte from the outlet channel section 22b.

(39) The third electrode part 10c has a main body 28a and a cylindrical protruding section 28b which extends along the longitudinal axis L of the electrode 10. During operation of the electrode 10, the protruding section 28b projects in the direction of the component 50 to be anodized and is accommodated in a through-bore 29 penetrating the second electrode part 10b. The through-bore 29 formed in the second electrode part 10b also accommodates the further cylindrical section 19c of the first electrode part 10a, so that the protruding section 28b adjacent to the further cylindrical section 19c of the first electrode part 10a is arranged in the through-bore 29 formed in the second electrode part 10b.

(40) A second connecting channel 30 is formed in the third electrode part 10c. The second connecting channel 30 comprises a first section 30a penetrating the protruding section 28b along the longitudinal axis L of the electrode 10 and a second section 30b running substantially perpendicularly to the longitudinal axis L of the electrode 10 in the region of the main body 28a. The connecting channel 30 forms a fluid-conducting connection between the electrolyte outlet 24 formed in the region of an outer surface of the third electrode part 10c and the outlet channel section 22b formed in the first electrode part 10a.

(41) The electrolyte inlet 14, the inlet channel 16, i.e. the inlet channel section 16a and the inlet channel branches 16b, the electrolyte outlet openings 18, the electrolyte flow path 21, the electrolyte entry openings 20, the outlet channel 22, i.e. the inlet channel branches 22a and the outlet channel section 22b, and the electrolyte outlet 24 of the electrode 10 are shaped and dimensioned such that a laminar electrolyte flow is established at least in the electrolyte flow path 21 but especially in the entire electrode 10. At the same time the flow cross sections of the electrolyte inlet 14, the inlet channel 16, i.e. the inlet channel section 16a and the inlet channel branches 16b, the electrolyte outlet openings 18, the electrolyte flow path 21, the electrolyte entry openings 20, the outlet channel 22, i.e. the outlet channel branches 22a and the outlet channel section 22b, and the electrolyte outlet 24 are shaped and dimensioned such that the highest possible electrolyte volume flow through the electrode 10 may be realized without the formation of turbulences that impair the desired laminar flow. This is achieved by an electrode design which ensures a flow resistance for the electrolyte flow through the electrode that is substantially constant in all traversable sections of the electrode 10.

(42) In the working example of an electrode 10 shown in the figures the number of inlet channel branches 16b and associated electrolyte inlet openings 18 corresponds to the number of electrolyte outlet openings 20 and associated outlet channel branches 22a. In particular, for the electrode 10 the number of inlet channel branches 16b, electrolyte exit openings 18, electrolyte entry openings 20 and outlet channel branches 22b is in each case 10—the electrode 10 is accordingly in the form of a capillary electrode.

(43) The inlet channel section 16a and the outlet channel section 22b each have identical flow cross sections. In addition, the inlet channel branches 16b and the outlet channel branches 22a and also the electrolyte outlet openings 18 and the electrolyte inlet openings 20 each have identical flow cross sections. The flow cross section of the inlet channel section 16a especially corresponds to the sum of the flow cross sections of the inlet channel branches 16b. In addition, the flow cross section of the outlet channel section 22b corresponds to the sum of the flow cross sections of the outlet channel branches 22a. This makes it possible to establish a constant flow resistance for the electrolyte flow flowing through the electrode 10 from entry of the flow into the inlet channel 16 until exit of the flow from the outlet channel 22.

(44) For example, the inlet channel branches 16b and the outlet channel branches 22a and also the electrolyte outlet openings 18 and the electrolyte inlet openings 20 may have a circular flow cross section having a diameter of 0.1 to 10 mm, 0.2 and 5 mm or 0.5 and 2 mm. The inlet channel section 16a and the outlet channel section 22b may have a circular flow cross section having a diameter of 1 to 100 mm, 2 to 50 mm or 5 to 20 mm. When in the electrode 10 shown here having 10 inlet channel branches 16b, electrolyte outlet openings 18, electrolyte inlet openings 20 and outlet channel branches 22a respectively the diameter of the inlet channel branches 16b, the electrolyte outlet openings 18, the electrolyte inlet openings 20 and the outlet channel branches 22a is 1 mm in each case, the diameter of the inlet channel section 16a and of the outlet channel section 22b is preferably 10 mm.

(45) The apparatus 100 for anodizing a component 50 illustrated in FIG. 25 comprises not only the electrode 10 but also an electrolyte circuit 102 for feeding electrolyte to the electrode 10 and for discharging electrolyte from the electrode 10. Arranged in the electrolyte circuit 102 is an electrolyte source 104 and a conveying means 106 in the form of a pump for conveying the electrolyte through the electrolyte circuit 102. A voltage source 108 which is connectable to the component 50 to be anodized and the electrode 10 is used to apply opposite voltages to the component 50 and the electrode. In particular, the voltage source 108 is used to apply a positive voltage to the component 50 while a negative voltage is applied to the electrode 10, i.e. the electrode 10 is used as a cathode. Finally arranged in the electrolyte circuit 102 is a cooling apparatus 110 which serves to cool the electrolyte flowing through the electrolyte circuit 102 and thus remove heat generated by the anodizing process from the electrolyte circuit 102.

(46) In a process for anodizing the component 50 using the electrode 10 and the apparatus 100 an electrolyte is supplied to the electrode 10 through the electrolyte inlet 14. Employable electrolytes include for example a sulfuric acid solution (for example 220 g/L of a 90% sulfuric acid solution), a Ti K oxalate, an oxalic acid solution, a tartaric acid solution, a phosphoric acid-based solution or a solution based on citric acid and a wetting agent (surfactant). The electrolyte preferably comprises no chromium ions. The temperature of the electrolyte is set to a temperature of −10° C. to +20° C., in particular +10° C.

(47) Anodizing is an exothermic process. Heat can lead to lattice defects in the hexagonal structure during layer formation. This results in a reduced wear resistance of the layer. In some cases the component could even become the true anode again and be oxidized so as to dissolve. The abovementioned temperatures of the electrolyte ensure orderly commencement of the anodizing process.

(48) The electrolyte is passed through the inlet channel 16, i.e. the inlet channel section 16a and the inlet channel branches 16b, and the electrolyte exit openings 18 in the electrolyte flow path 21. After flowing through the electrolyte flow path 21 the electrolyte is supplied via the electrolyte entry openings 20 and the outlet channel 22, i.e. the outlet channel branches 22a and the outlet channel section 22b, to the electrolyte outlet 24 and finally discharged from the electrode 10. While the electrolyte flows through the electrolyte flow path 21 and consequently through the electrolysis gap E defined by the outer surface of the cylindrical first section 19a of the first electrode part 10a and the surface section 54 to be anodized, i.e. the inner surface of the recess 52 formed in the component 50, the voltage source 108 is used to apply opposite voltages to the electrode 10 and the component to be anodized 50.

(49) In the working example shown in the figures the component 50 is made of aluminum or is at least provided with a surface section 54 to be anodized which is made of aluminum. Accordingly, anodic oxidation produces an oxidic protective layer (anodized layer) on the surface section 54 made of aluminum. During the oxidation process the electrolyte constantly evolves oxygen and is thus at least partially consumed. After being conveyed back to the electrolyte source 104 the electrolyte may therefore be mixed with new, unconsumed electrolyte before once again being fed to the electrode 10. The aging of the electrolyte circulating in the electrolyte circuit 102 may be monitored. The electrolyte may be replaced upon exceeding predetermined threshold values.

(50) In operation of the apparatus 100 the voltage source 104 is controlled according to a predefined voltage curve which may appear as shown in the following table for example.

(51) TABLE-US-00001 Voltage (V) Current (A) Time (s) Process 22.00 0.20 12.00 Basic roughness 23.00 0.50 14.00 Basic roughness 23.00 0.60 30.00 Basic roughness 25.30 0.70 30.00 Layer thickness 25.30 1.20 30.00 Layer thickness 25.30 2.00 30.00 Layer thickness

(52) As is apparent from the table the voltage applied to the electrode 10/the component 50 may be controlled such that in a period of 12-30 seconds the voltage is increased from 22 V to 25.30 V while the current density is increased from 0.20 to 2.00 A.

(53) Without wishing to be bound to a particular theory the following describes a possible interpretation of the procedure during application of the voltage. In the first milliseconds the electrical current forms a blocking layer consisting of crystals having a high dielectric strength. After dielectric breakdown of the blocking layer the anodized layer begins to grow, thus increasing layer thickness. The voltage may be increased from 0 V to a maximum voltage of 30 V over a defined period (of 10 or 20 seconds for example), so that in this period the current increases from 0 A to a current which is higher than 0 A but not more than 2 A. The voltages and currents may be varied and chosen according to the component.

(54) Using the electrode 10, the apparatus 100 and the above-described process, the surface section 54 of the component 50 which is here formed by an inner surface of the recess 52 formed in the component 50 may be provided with an anodized layer. An aluminum oxide layer having a high degree of wear resistance may in particular be produced on the surface section 54 made of aluminum. The anodized layer built up on the surface section 54 has a hexagonal, tubular pore structure as is discernible in the scanning electron microscope images of FIGS. 26 and 27. O.sup.2−/OH.sup.− ions can drift through these pore structures and be converted into aluminum oxide [Al.sub.2O.sub.3] directly at the interface of oxide and metal. The hexagonal, tubular pore structures discernible in FIGS. 26 and 27 exhibit a particularly high wear resistance in the case of wear processes applied, especially via transverse forces, by pistons to a cylindrical surface.

Example

(55) A component having an aluminum surface was anodized using the electrode described herein. The electrolyte employed was a sulfuric acid solution (220 g/l of a 90% sulfuric acid solution). The temperature was adjusted to +10° C. The anodizing process generated heat which can influence the efficiency of the process and was therefore continuously removed.

(56) The following voltage curve was applied:

(57) TABLE-US-00002 Voltage (V) Current (A) Time (s) Process 22.00 0.20 12.00 Basic roughness 23.00 0.50 14.00 Basic roughness 23.00 0.60 30.00 Basic roughness 25.30 0.70 30.00 Layer thickness 25.30 1.20 30.00 Layer thickness 25.30 2.00 30.00 Layer thickness

(58) The FIGS. 26-27 show aluminum oxide anodized layers having the specific structures produced according to the described process. Before acquisition of the images the treated component was shock-frozen with nitrogen and mechanically fractured at the height of the treated surface. The surface structures thus revealed are specific to the described process and are distinguishable from surfaces produced with conventional anodizing processes.