DE9411523U1 - Device for anodizing workpieces - Google Patents

Description

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Dipl.Phys. Ulrich Twelmeier Dipl. Ing. D.Jendryssek-Neumann Dr. phiI. naf. Rudolf Bauer - 7990 Dip/. Ing. Helmut Hubbuch-7997

06.07.1994 TW/Be

Stohrer-Doduco GmbH & Co., D-71277 Rutesheim

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Device for anodic oxidation of workpieces

Description :

The invention is based on a device for the anodic oxidation of workpieces with the features specified in the preamble of claim 1. Anodic oxidation is understood to mean processes in which firmly adhering oxide layers are produced on metallic workpieces by anodic treatment in aqueous electrolyte, in particular on workpieces made of aluminum or aluminum alloys. Aluminum has a relatively good corrosion resistance by nature, because it quickly becomes coated in air with a thin, approximately 0.01 to 0.04 μm thick, hard and extremely firmly adhering oxide film, which, due to its high hardness, is also well suited as

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would be suitable as a wear layer if it were not so thin. Through anodic oxidation, thicker oxide layers suitable as wear layers can be produced, which are harder the lower the temperature at which the anodic oxidation takes place.

It is known to hang the workpieces (') to be anodized on a frame, to laboriously connect them individually to an anode which is sharpened so that it can penetrate an oxide film on the workpiece, and to immerse the workpieces together with the support in an electrolytic liquid which is located as a bath in a container in which a stationary cathode is also suspended.

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This is also the procedure used to date for the anodic oxidation of brake calipers made of aluminum material for disc brakes in vehicles. The brake calipers have a roughly U-shaped form when viewed from the side with mounting holes on one L-leg of the U and a cylindrical blind hole on the opposite leg of the U. The blind hole is intended to accommodate a piston to form a pressure cylinder. The cylindrical surface of the blind hole is therefore subjected to friction and is therefore intended to receive a hard, anodically applied oxide layer. For this purpose, the

Brake calipers are hung with one of their mounting holes on a hook on the dipping frame and then hang more or less randomly at an angle on the dipping frame, with which they are dipped into the electrolyte liquid for anodizing. Hanging on the same frame, they are also subjected to pre- and post-treatment (e.g. cleaning, degreasing, pre-rinsing, post-rinsing). &zgr; The disadvantage of this is that the complicated shape of the workpieces results in oxide layers of uneven thickness, that the oxide layers have to be partially removed again by reworking in places where particularly small dimensional tolerances are required, e.g. on fitting holes, and that electrolyte liquid is carried over.

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The present invention is based on the object of counteracting these disadvantages by means of an easier-to-use device for anodic oxidation of workpieces, which produces more uniform oxide layers on the workpieces and at the same time requires less processing effort on the workpieces and thus enables more cost-effective work.

This object is achieved by a device having the features specified in claim 1. Advantageous further developments of the invention are the subject of the dependent claims.

According to the invention, the carrier for the workpieces has receiving devices, which are arranged and designed in such a way that the received workpieces are necessarily arranged with a predetermined alignment in a predetermined position, preferably regularly aligned in the same way. This is also a first step towards making the operation of the device more efficient, which is further achieved according to the invention by the fact that, in combination with the forced alignment of the workpieces on their carrier, the anodes are also arranged in a correspondingly predetermined manner and are arranged so that they can be raised and lowered independently of the carrier, so that they can be brought into contact with the workpieces that have already been introduced into the container with the carrier by preferably lowering them together, so that a prior individual connection of the workpieces on the carrier to their respective anode is not necessary. Several or all of the anodes can be assigned a common cathode that is immersed in the electrolyte liquid. However, it is also possible that several cathodes are provided according to the number of workpieces or the wear surfaces to be treated and - coordinated with the arrangement of the support devices of the carrier - are arranged so that they can be raised and lowered so that they can be brought closer to the workpieces and their holders by preferably simultaneous lowering. Preferably, the cathodes and/or anodes and/or electrolyte supply lines, if available also suction lines, which are preferably

rait the electrolyte supply lines, attached to the underside of a common holder, preferably on the underside of a lid, which closes the container during anodizing. In this way, anodes, cathodes, electrolyte supply lines and also the suction lines can be guided together to the workpieces to be oxidized and also removed again, with the lid being easily guided into the desired position by the edge of the container on which it rests. In order for the anodes, cathodes and electrolyte supply lines to meet the workpieces exactly, the workpiece carrier must of course also assume a predetermined position in the container, for which purpose guides and/or positioning elements, e.g. supports with index pins that engage in matching recesses in the carrier, are preferably provided in the container.

To ensure that the anodes make reliable contact with the workpieces, they are preferably spring-mounted so that they can retreat against the spring force when they hit the workpieces.

Because the workpieces are not randomly but are arranged in a predetermined position on a carrier and in this position are contacted by the anodes attached to another carrier, in particular to a cover of the device

are reproducible conditions under which the anodically produced oxide layers grow. The workpieces are therefore oxidized more evenly and reproducibly and require less rework, especially if, as is preferred, each workpiece is assigned its own cathode that can be delivered together with the anodes, thus creating essentially the same oxidation conditions for all workpieces.

Preferably, the cathodes are then also designed as electrolyte supply lines, i.e. the cathodes are tubes through which the electrolyte flows. This makes the arrangement of cathode and electrolyte supply line compact and at the same time the cathode is optimally cooled by the electrolyte. If a suction line is provided, this preferably runs with its front end section coaxially in the electrolyte supply line, especially if the electrolyte supply line is also the cathode. In this case, the arrangement is particularly compact.

If the workpieces have wear surfaces that are to receive a particularly thick oxide layer, then the cathodes are best arranged in the vicinity of the wear surfaces. If the wear surface is in a recess in the workpiece, as is the case with a brake caliper, then the workpieces are best arranged on the carrier in such a way that the recesses with their

Openings face upwards so that the cathodes assigned to the workpieces can be inserted into the recesses from above by lowering them. If the cathodes are also electrolyte feed lines, as is preferred, the workpieces do not need to be immersed in an electrolyte bath, but the recess to be oxidized, in which the wear surface is located, can be flooded and thus selectively oxidized.

The cathode is always located in the immediate vicinity of the wear surface to be oxidized and, unlike in the prior art, the wear surface is not shielded from the electric field emanating from the cathode. The desired oxide layer therefore grows very evenly on the wear surface. This means that other surface areas of the workpiece are less or not at all anodically oxidized. However, this is not a disadvantage because the wear surface is anodically oxidized in any case and for the other surfaces that are not wear surfaces, natural atmospheric oxidation is already completely sufficient as corrosion protection. The concentration of the anodic oxidation on the wear surfaces located in the recesses is even extremely advantageous because it means a considerable energy saving during anodic oxidation.

The preferred feature also contributes to the uniformity of the layer thickness during anodic oxidation,

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that the electrolyte is fed directly to the workpiece through an electrolyte feed line assigned to the respective cathode. This not only prevents the formation of diffusion barriers, but the constant supply of fresh electrolyte cools the cathode and the workpiece, thereby promoting the formation of a particularly hard oxide layer. A further advantage of this measure is that the anodic oxidation no longer has to be carried out by immersing the workpiece in the electrolyte; since the electrolyte is introduced directly into the recess that is open at the top and in which the wear surface is located, the workpiece can be flooded selectively in the area of the recess. If the recess is a blind hole, such as in a brake caliper, then the blind hole automatically fills with the electrolyte and the excess electrolyte overflows over the edge of the blind hole and is collected in the container below the workpiece carrier. This also works without any problems if there is a small hole at the bottom of the blind hole, as is the case with brake calipers, through which electrolyte can drain, because then you only have to add more electrolyte than can drain at the same time. This even has the advantage that the recess drains easily at the end of the anodizing process. Workpieces that have a recess that is open at the bottom can also be selectively treated easily in the device according to the invention.

anodically coated by designing the carrier in such a way that it closes the recess of the workpieces positioned on it. In addition, it is possible to suck the electrolyte out of the recess if you do not want it to overflow and/or if it does not easily drain through a drain opening.

The selective anodizing described is particularly economical. Using brake calipers as an example, it was estimated that when the blind hole is selectively anodized, only about 1/8 of the surface of a brake caliper is anodized, compared to the current state of the art, in which the brake calipers are anodized as a whole. This means that only about 1/8 of the electrical power is required for anodizing. In addition, the heat generated by the current is only about 1/8, and the cooling power required to keep the electrolyte at a low temperature (0° to 2 ^° C) to create a hard oxide layer is correspondingly low. In a device in which 1 million brake calipers can be anodized per year, an annual energy saving of around DM 200,000 can be achieved in this way. In addition, the equipment required is also reduced because a smaller cooling unit and smaller rectifiers are needed for the power supply.

Another advantage is that, especially when the workpieces are not immersed but held above the bath surface during anodizing, no oxide layers grow outside the recesses flooded with the electrolyte and therefore no rework, such as thread cutting, is required on surfaces that have been machined to a precise dimension before anodizing. Another advantage is that, unlike when the workpieces are immersed according to the state of the art, the anodes do not have to be regularly deoxidized in order to be able to transfer the anodizing current to the respective workpiece, and they do not have to be made of a metal that is difficult to oxidize, such as titanium, but can instead be made of aluminum or copper, which conduct electrical current much better.

Embodiments of the invention are shown schematically in the accompanying drawings.

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Figure 1 shows a vertical longitudinal section through

a top-loading system for the anodic oxidation of brake calipers,

Figure 2 shows the cross section II-II through the

The system shown in Figure 1,

Figure 3 shows a detail of a brake calliper in section with the

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inserted anode, introduced cathode and electrolyte supply line,

Figure 4 shows a second horizontally loaded plant for the anodic oxidation of work

pieces in top view,

Figure 5 shows a cross-section through the anodizing station of the system shown in Figure 4 with the electrodes lowered,

Figure 6 shows a section like in Figure 5, but with raised electrodes.

Figure 7 shows a vertical longitudinal section through a system to be fed from above, which is modified compared to the example in Figure 1,

Figure 8 shows the cross section VIII-VIII through the system shown in Figure 7,

Figure 9 shows on an enlarged scale a detail from Figure 8 of a workpiece in section with an anode attached,
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Figure 10 shows a cross-section through a horizontally loaded system for the anodic oxidation of workpieces, modified from Figure 5, with the anodes in their

lowered position, and

Figure 11 shows a section like in Figure 10, but

with raised anodes. 5

The system shown in Figure 1 has four containers 1, 2, 3 and 4 arranged one behind the other in a row, which can be fed by a carriage 5 that can be moved over them and on which a lifting device 6 is located. In the first container 1, the workpieces - in this case, these are brake calipers 7 made of an aluminum material - are cleaned, in the second container 2 they are rinsed, in the third container 3 they are anodically oxidized and in the fourth container 4 they are rinsed again.

Of particular interest according to the invention is the container 3, a container covered by a lid 8 for holding an aqueous electrolyte 9, e.g. 20% sulfuric acid. The container 3 has an edge 11 from which several positioning pins 12 protrude upwards at predetermined locations. The edge 11 serves to hold a workpiece carrier 13, e.g. a pallet 13a with suspension, which has centering holes for holding the pins 12. The workpiece carrier 13 is designed so that its pallet 13a hangs above the electrolyte level 10. On the workpiece carrier 13 there are two rows of brake callipers 7 arranged in a regular arrangement. For this purpose, the carrier 13 has supports 14 which stand upwards at predetermined locations to accommodate the brake callipers 7, and the supports 14 have a cylindrical head 15 with a reduced diameter which fits into a bore 16 of the brake calliper, with the edge of the bore

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rests on the collar surface which is formed at the transition from the support 14 to its head. Two such supports 14 each accommodate a brake calliper 7 in the position defined thereby.
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The brake calliper 7 is an approximately U-shaped structure in side view, with a cylindrical recess 17 formed on one leg and the opposite leg having the shape of a fork 18, in each of whose two prongs there is a threaded hole 19.

On the underside of the cover 8, two anodes 20 and a cathode 21 are attached for each brake calliper 7, which is hollow; the passage 22 through the cathode 21 serves as an electrolyte supply line. The cathodes protrude vertically downwards and, when the cover 8 is placed on the edge of the container 3, are introduced coaxially through the space between the two prongs of the fork 18 into the cylindrical recess 17 of each brake calliper 7, so that the downward-facing outlet opening of the electrolyte line 22 is located just in front of the bottom of the cylindrical recess 17. The anodes 20 make contact

with the upper leg of the brake calliper 20. To ensure good electrical contact between the anode 20 and the brake calliper 7, the anodes 20 are spring-mounted so that they can move back slightly when they hit the brake calliper, so that the contact pressure is determined by the spring pressure. The anodes 20, the cathodes 21 and the electrolyte supply lines 22 are attached to a suspension 23, which in turn is attached to the underside of the cover 8.

The electrolyte is supplied via a common line 24 which branches off to the hollow cathodes 21 and which runs partially in the cover 8 and is connected thereto to a hose 25 which leads to a circulation pump 27 which conveys the electrolyte liquid. The anodes 20 and the cathodes 21 are connected to stationary electrical connection contacts on the edge of the container 3 via an electrical supply line running in the cover 8. When the lid 8 is placed on top, the hose 25 forms a loop 26 which makes it possible to lift off the lid 8 without loosening the hose connection (as shown in Figure 1 using the example of the adjacent container) and to move it to the side next to the opening of the container thus exposed in order to be able to insert the carrier 13 with the workpieces 7 located thereon into the container 3 and hang it on the container edge 11, or to be able to lift it out of the container in order to transfer it to the adjacent container 4.

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The cylindrical inner surface 31 of the recess 17 is a wear surface that is to be anodically oxidized. For this purpose, when the brake callipers 7 are in the position shown in Figure 1, the pump 27 pumps electrolyte fluid through the hollow cathode 21 into the upwardly open recess 17, in which it rises up to its edge and then overflows into the electrolyte reservoir 9 of the container.

In this way, practically only the wear surface 31 is anodically oxidized, but not other dimensionally machined surfaces such as the bores 16 or 19, which therefore do not require any rework.
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The heat released by the flow of current between anode 20 and cathode 21 is carried away by the overflowing electrolyte and removed from the electrolyte by a cooling device 32 provided in the lower region of the container so that it remains cold and particularly hard oxide layers can be achieved.

Instead of letting the electrolyte overflow, it can also be sucked out of the recesses 17 if a plastic pipe is also provided in the hollow cathode 21 to form a double line, which leads to the suction side of a pump. The system shown in Figures 4 to 6 differs from the system shown in Figures 1 to 3 essentially in that it is a continuous system with horizontal loading. Parts that correspond to parts in the first system are designated in Figures 4 to 6 with the same reference numbers as in Figures 1 to 3.

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The workpieces 7 to be machined are arranged in a predetermined position and orientation on a carrier 13, which looks similar to that in Figure 2. On the carrier 13,

they run the system. The system has a loading and unloading station 50 in which the carriers 13 are loaded with the workpieces 7. This is followed by a rotary table 51 which turns the carriers 13 by 90° into the correct orientation for transfer to a buffer section 52, through which they move step by step until they are transferred at the end by a cross conveyor 53 to the loading device 54 of the actual treatment section 55. This treatment section has a number of different treatment containers, including a container 3 for the anodic oxidation of the workpieces 7.

At the outlet of the treatment section 55, as on the inlet side, there is a removal device 54a, a cross conveyor 53a, a buffer section 52a and between this and the loading and unloading station 50, a turntable 51.

In order to be able to transport the carrier 13 with the workpieces 7 into and out of the container 3, the container has two weirs 56 and 57 above the electrolyte level 9. The carrier 7 runs well guided on rollers 58 in rails 59 arranged to the side of the container 3 through the weir 56 into the container 3. In the container 3 it is positioned by positioning elements, e.g. by a stop. At a position on both sides next to the

A lifting crossbeam 61 which crosses the container 3 and is displaceable up and down is mounted on the support structure 60 provided for the container 3. The cathodes 21, anodes 20 and electrolyte supply lines 22, 24 are located on the lifting crossbeam 61. The lifting crossbeam 61 is raised during the retraction and extension of the carrier 13 (Figure 6) and is moved downwards when a carrier 7 is retracted and positioned, whereby the cathodes 21, anodes 20 and electrolyte supply lines 22, 24 assume their predetermined position in relation to the workpieces 7, as shown in Figure 2. The support structure 60 carries a hood 62 which spans the container 3 and which can be suctioned through a channel 63.

The embodiment shown in Figures 7 to 9 is similar to the embodiment shown in Figures 1 to 3. Matching or corresponding parts are therefore designated with matching reference numbers. The device shown in Figures 7 to 9 differs from the device shown in Figures 1 to 3 in that

There is not a separate cathode suspended on the lid 8 for each workpiece 7; rather, there is a stationary cathode 21 in the container 3 that is not connected to the lid 8 and is permanently immersed in the electrolytic bath 9. The anodes 20 are, as in the first embodiment, attached under the lid 8 to a suspension 23 connected to it. They are

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in this embodiment, these are reversible springs which, when the cover 8 is placed on, easily make central contact with the top of the workpieces 7, the spring force ensuring reliable contact. The workpieces shown are again brake calipers. However, the invention is not restricted to the treatment of brake calipers; rather, they are only shown as examples. Unlike in the first embodiment, the workpieces in the device according to Figures 7 to 9 are not arranged above the electrolyte level and washed around by electrolyte liquid emerging from a cathode; rather, the workpieces are completely immersed in the electrolyte liquid 9 and can therefore be anodically oxidized all around in cooperation with the immersed anodes 20 and the one immersed cathode 21, provided that this is not hindered by self-shielding by the workpieces. It would of course also be possible, however, to use a device after immersion; 20 method, each workpiece 7 is assigned its own cathode, which could be permanently installed in the container 3, but could also be suspended from the lid 9.

A cable 28 is provided to supply power to the anodes, which leads from a power source (not shown) into the cover 8, and when the cover is in place (Figure 7), a cable 28 is provided on the outside of the cover.

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holder and thereby allows the cover 8 to be lifted using the lifting gear 6 on the carriage 5 without disconnecting the electrical connection.

The device shown in Figures 10 and 11

is similar to the device shown in Figures 5 and 6; therefore, identical or corresponding parts are designated with corresponding reference numbers. The device can be part of a system as shown in Figure 4. In contrast to the device shown in Figures 5 and 6, the device shown in Figures 10 and 11 does not have a separate cathode for each of the workpieces 7, but rather a stationary cathode 21 that is separate from the lifting crossbeam 61. The anodes 20 are, as in the example according to Figures 7 to 9, coil springs that are placed under pressure on the top of the workpieces 7 by lowering the lifting crossbeam 61 and are supplied with power by a cable that moves with the lifting crossbeam 61. As in the example in Figures 7 ( 20 to 9), the device according to Figures 10 and 11 is used for the anodic treatment of workpieces by completely immersing them in the electrolyte.

Claims (10)

Expectations: 1. Device for anodic oxidation of workpieces (7) in particular of disc brake callipers, with a container (3) for holding an aqueous electrolyte (9) with a carrier (13) with receiving devices (14) for receiving several workpieces (7), with means (5, 6, 58) for inserting and removing the carrier (13) into or from the container (3), with at least one anode (20) to be connected to the workpieces (7) and with a cathode (21) immersed in the electrolyte, characterized, that the carrier (13) for the workpieces (7) has receiving devices (14) which are arranged in a predetermined manner and are designed such that they receive the workpieces (7) in a predetermined position, - 21 - and that the anodes (20) can be raised and lowered independently of the carrier (13) and are arranged in mutual relation according to the arrangement of the receiving devices (14) so that they can be placed on the workpieces (7) by lowering them. 2. Device according to claim 1, characterized in that the container (3) has guides (59) or Positioning elements (12) for the carrier (13). 10 3. Device according to claim 1 or 2, characterized in that the receiving devices (14) at least one cathode (21) is assigned to each workpiece (7) and the cathodes (21) can be raised and lowered independently of the carrier (13) and are arranged in mutual association with the arrangement of the receiving devices (14) in such a way that they are brought closer to the receiving devices (14) by lowering. 4. Device according to one of the preceding claims, characterized in that the cathodes (21) are designed as electrolyte supply lines. 5. Device according to one of the preceding claims, characterized in that each electrolyte supply line (2 2) is assigned a suction line. 6. Device according to claim 5, characterized in that the end section of the suction line facing the workpiece (7) runs in the electrolyte supply line (22), preferably coaxially. 7. Device according to one of the preceding claims, characterized in that the container (3) has a liftable lid (8), on the underside of which the cathodes (21) and/or the anodes (20) and/or the electrolyte supply lines (22, 24) and, if applicable, the suction lines are suspended. 8. Device according to one of claims 1 to 6, characterized in that the container (3) is spanned by a crossbeam (61) on which the cathodes (21), anodes (20), electrolyte supply lines (22, 24) and, if applicable, the suction lines are arranged in a suspended manner. 9. Device according to claim 7 or 8, characterized in that the electrolyte supply lines (22, 24) and optionally the suction lines are connected to a flexible supply line (25) which follows movements of the lid (8) when opening and closing the container (3). 10. Device according to one of the preceding claims, characterized in that the anodes (2 0) are spring-mounted.