Method And Device For The Electrophoretic Production Of Sheet-Like Blanks From A Metal Slurry Or Ceramic Slip

Abstract

The invention makes it possible to produce very thin ceramic blanks as a precursor for ceramic discs, for example for use as faces in wrist watches. On the other hand, the production of metal blanks for use in CAD/CAM machines is possible with the invention. Both methods are based on depositing the material from a slurry or slip by electrophoresis. The essence of the invention is the isolation of the peripheral region of the precipitation electrodes that is produced by a non-conducting frame. This allows the precipitated mass to be easily lifted off from the precipitation electrode. The subsequent sintering with a possibly proceeding machining operation allows precision articles to be produced.

Description

The invention relates to a method and an apparatus for the production of electrophoretic flat blanks from a metal or ceramic slurry.

STATE OF THE ART

The preparation of sinterable precursors by electrophoresis of slurry is well known in the dental art. As an example, for the production of metal frames that are first prepared by electrophoretic deposition of a metal slurry followed by sintering, refer to DE 10 2005 052 113 A1. A comparable technique for the manufacture of ceramic dental components is described for example in EP 1280475 B1. Going further into this technique in detail is therefore not required.

But with the prior art the easy production of flat products made of ceramic with a diameter of more than 20 mm is not possible, in particular when the thickness is less than 1 mm. As an example dials of watches may be mentioned. But these can be prepared by the technique according to the invention without difficulty. On the other hand there does not exist in itself a need for the production of thin disk-shaped metal products because such products can be easily stamped out of sheet metal. However, the inventive method allows the production of mechanically stable blanks for a CAD/CAM method. Such blanks are produced according to WO 2011/023 490 A1 in a different, non-electrophoretic method. In that case the drying time of several hours can be considered a disadvantage, although in the electrophoretic production immediately after the end of electrophoresis, there is a stable product which can be immediately machined, and sintered.

PROBLEM TO BE SOLVED

It is therefore an object of the invention indicated in claim 1 and the apparatus based thereon, to enable a precise production of sinterable, flat blanks of metallic or ceramic slurry. Within that area in the context of the application are understood not only planar but also slightly curved objects, which may additionally be profiled (shaped) on a surface.

DESCRIPTION OF THE INVENTION

In the drawings:

FIG. 1 shows a vertical section through the machine according to the invention ;

FIG. 2 shows the section in the plane AA of FIG. 1

In FIG. 1 is shown a part section through the device for carrying out the invention. In a conductive container 1, which is connected to the negative pole of a DC power source, there is an electrophoretic suspension 2, which is kept in motion by an agitator 3 to prevent the formation of agglomerates. By means of a substrate holder 4, a precipitation electrode 5, which is polarized positive, can be immersed in and moved out of the electrophoretic suspension. This device is not different so far from the above mentioned prior art for the production of tooth parts by electrophoresis.

New compared to the above technique is that the precipitation electrode 5 is flat and its edge is covered by an insulating frame 6. In the embodiment of FIG. 2 of the description, the precipitation electrode 5 can be acted upon from both sides.

With the apparatus shown, for example, ceramic discs with a diameter of 30 mm and a thickness less than 1.5 mm of alumina can be produced. For this purpose, a precipitation electrode 5 from zinc sheet is clamped into the frame 6 and electrophoretically coated. At a deposition time of 180 seconds and a current of 35 mA, two slices of the desired size have formed on the collecting electrode 5. The well known electrophoretic suspension 2 requires, for a viscosity measurement, a necessary cycle time of 38 sec for a flow rate of 10 ml in a measuring funnel having a diameter of 2.3 mm. After coating, the alumina slice can easily be taken off from the collecting electrode. The reason for this lies in the zinc oxide layer that has been formed and which acts in the manner of a separation layer. Subsequently, the blanks obtained are, as usual, sintered.

If the products to be manufactured should not be perfectly flat on both sides, the collecting electrode can be coated on one side only. However, this opens up the possibility to produce curved products.

A further possibility of the invention exists to produce characters raised or embossed on the slice, e.g. digits of a clock. For this purpose, corresponding recesses or corresponding raised characters shall be provided only in the surface of the collecting electrode.

The isolation of the collecting electrode at the edge of the frame 6 is essential to the invention, because the edge area of the electrode must be free of slurry for avoidance of drying cracks.

However, the invention can also be used for the production of metal ingots. WO 2011/023490 A1 discloses a method for the production of tooth parts from dental metal powder in which method a slurry is poured into a mold and a stable blank is formed by drying in the mold, which blank is formed to a metallic tooth part by machining and sintering. These blanks may have a diameter of 96 mm and a thickness of 20 mm. Such discs can also be produced by electrophoresis, if the apparatus shown in FIGS. 1 and 2 is dimensioned accordingly. A change in the slip composition as compared to the prior art is not necessary.

LIST OF REFERENCE NUMERALS

• 1 container
• 2 electrophoretic suspension
• 3 stirrer
• 4 substrate holder
• 5 precipitation electrode
• 6 frame

Claims

1. A process for the manufacture of a flat blank made of a metal or ceramic slurry 2 by electrophoresis, characterized by covering an edge area of a flat collecting electrode 5 with an insulating frame 6 during the electrophoresis.

2. A method according to claim 1, characterized in that the precipitation electrode 5 is coated on one or both sides.

3. A method according to claim 2, characterized by using a collecting electrode 5 made of zinc, and an alumina slurry as an electrophoresis suspension 2.

4. A method according to claim 1, characterized by forming the surface of the collecting electrode 5 with raised or recessed symbols.

5. A device for carrying out the method according to claim 1, with a container 1 filled with conductive electrophoresis suspension 2, which container is connected to the negative pole of a DC power source, wherein the suspension can be stirred by a stirrer 3 for the prevention of agglomerates, characterized by a positive polarity and vertically movable substrate holder 4 that supports a frame 6 to cover the edge portion of the collecting electrode 5.

6. Apparatus according to claim 5, characterized by a two-part frame 6.

7. A method according to claim 2, characterized by forming the surface of the collecting electrode 5 with raised or recessed symbols.

8. A device for carrying out the method according to claim 2 with a container 1 filled with conductive electrophoresis suspension 2, which container is connected to the negative pole of a DC power source, wherein the suspension can be stirred by a stirrer 3 for the prevention of agglomerates, characterized by a positive polarity and vertically movable substrate holder 4 that supports a frame 6 to cover the edge portion of the collecting electrode 5.

9. Apparatus according to claim 8, characterized by a two-part frame 6.

10. A method according to claim 3, characterized by forming the surface of the collecting electrode 5 with raised or recessed symbols.

11. A device for carrying out the method according to claim 3 with a container 1 filled with conductive electrophoresis suspension 2, which container is connected to the negative pole of a DC power source, wherein the suspension can be stirred by a stirrer 3 for the prevention of agglomerates, characterized by a positive polarity and vertically movable substrate holder 4 that supports a frame 6 to cover the edge portion of the collecting electrode 5.

12. Apparatus according to claim 11, characterized by a two-part frame 6.