HK1202169B - Bearing including first and second fuctional elements on two distinct faces - Google Patents

Description

Carrier comprising a first and a second functional element on two distinct faces

Technical Field

The present invention relates to a support (bearing) for a timepiece, in particular a support comprising a first and a second functional element on two distinct faces.

Background

It is known to manufacture bearings from single crystal alumina by reducing the volume of the blank. However, once a first face is (machined) to form a first functional element, it becomes very difficult to form a second functional element on another face because of the fragility caused by machining the first face.

Therefore, even if the second functional element with a limited geometry is formed on the other side, the rejection rate is very high.

Disclosure of Invention

It is an object of the present invention to overcome all or part of the aforementioned drawbacks by proposing a carrier comprising first and second functional elements with a wide range of geometries on two distinct faces and a manufacturing method that greatly reduces the scrap rate.

Accordingly, the present invention relates to a method of manufacturing a carrier, the method comprising the steps of;

a) forming a ceramic precursor (precursor) from a ceramic-based powder in a binder;

b) pressing a ceramic precursor with an upper die and a lower die to form a green body of a carrier to be made, the green body having a top surface and a bottom surface comprising a first and a second functional element, respectively, and leaving a material thickness between the first and second functional elements;

c) sintering the green body to form a ceramic body;

d) a through-hole is formed in the ceramic body to connect the first and second functional elements.

Advantageously according to the invention, each face of the carrier can thus be directly formed with at least one functional element on each face, even in a very extensive manner, i.e. even with substantially identical areas on each face, without leading to an excessively high rejection rate.

According to other advantageous features of the invention:

-the maximum cross section of each of said functional elements is between 1.5 and 5 times the cross section of said hole;

-the ceramic-based powder comprises at least one metal oxide, metal nitride or metal carbide;

-the ceramic based powder comprises alumina and possibly chromium oxide;

-each mould comprises at least one stamp (stamp) intended to form a different functional element;

-said at least one stamp comprises a spherical and/or conical and/or parallelepiped-shaped surface;

step b) is carried out by moving the upper and lower moulds relative to each other in the housing;

-step c) comprises pyrolysis;

the method comprises a final step of finishing the carrier, which may comprise grinding and/or buffing and/or polishing.

Furthermore, the invention relates to a support obtained by a method according to any of the preceding variants and comprising a sintered ceramic body crossed by a hole, characterized in that said ceramic body has a top face and a bottom face, each face comprising a functional element communicating with said hole. The maximum cross-section of each functional element may be 1.5 to 5 times the cross-section of the hole.

In particular, the carrier may be mounted on, or form all or part of, the bottom plate or bridge of the timepiece movement.

Drawings

Other features and advantages will appear clearly from the following description, given by way of non-limiting example with reference to the accompanying drawings, in which;

figure 1 is a schematic view of a double action press according to the present invention;

figures 2 to 5 are variants of the mould according to the invention;

figures 6 to 7 are schematic views of different manufacturing steps for a carrier according to the invention;

figures 8 and 9 are schematic views of two exemplary bearings according to the invention.

Detailed Description

As mentioned above, the present invention relates to a carrier intended to be in contact with a pivot so that the pivot can move rotationally with minimal friction. It is thus clear that the invention may form all or part of a carrier for a rotatably mounted element.

According to the invention, said carrier is intended to be mounted in, or to form all or part of, a bridge or a bottom plate of a timepiece movement. However, the invention is in no way limited to the field of horology and can be applied to any element mounted movably with respect to the carrier.

Advantageously according to the invention, the carrier comprises a sintered ceramic body crossed by a hole intended to receive a pivot, also known as a trunnion (trunnions). According to the invention, the ceramic body advantageously comprises a top face and a bottom face, each comprising at least one functional element communicating with the pores.

Fig. 8 and 9 show two exemplary carriers 1 and 11 according to the invention. The carrier 1 of fig. 8 has a generally annular body 2, which body 2 comprises a preferably central aperture 3, which aperture 3 opens between a top surface 4 and a bottom surface 6. Advantageously according to the invention, the hole 3 communicates with a substantially spherical recess 5 on the top surface 4 forming a first functional element 8. In the example visible in fig. 8, the first functional element 8 flares away from the hole 3 to a maximum cross section which is more than about 4.5 times the cross-sectional width of the hole 3. Furthermore, the hole 3 may also communicate with a substantially conical recess 7 on the bottom surface 6 forming the second functional element 10. In the example visible in fig. 8, the second functional element 10 flares away from the hole 3 to a maximum cross section which is more than about 2 times the cross-sectional width of the hole 3. It is also noted that the wall of the body 2 surrounding the hole 3 has an olive-shaped cut-out intended to minimize contact with the pivot and at the same time to also contribute to any lubrication.

The carrier 11 of fig. 9 has a generally annular body 12, which body 12 comprises a preferably central aperture 13, which aperture 13 opens between a top surface 14 and a bottom surface 16. Advantageously according to the invention, the hole 13 communicates with a substantially spherical recess 15 on the top surface 14 forming a first functional element 18. The hole 13 furthermore communicates with a substantially spherical recess 17 in the bottom surface 16, which recess forms a second functional element 20. In the example visible in fig. 9, the first and second functional elements 18, 20 are symmetrically tapered away from the hole 13 to a maximum cross-section that is more than about 3.5 times the cross-sectional width of the hole 13. It is also noted that the wall of the body 12 surrounding the hole 13 has a chamfer intended to prevent contact with the pivot from damaging said wall.

With reference to these two examples, it can be seen that advantageously according to the invention each functional element 8, 10, 18, 20 is independent and can have a maximum section of the same extension on each face 4, 6, 14, 16. Of course, several identical or different functional elements 8, 10, 18, 20 can also be formed on the same side 4, 6, 14, 16, as explained below. Likewise, as described below, each functional element 8, 10, 18, 20 is by no means limited to a substantially spherical or substantially conical recess 5, 7, 15, 17, but may have different shapes or form a variety of combinations of shapes.

The versatility of the manufacture of the carrier will be more apparent from fig. 1 to 7, which fig. 1 to 7 show a method of manufacturing a carrier according to the invention. The method comprises a first step a) intended to form a ceramic precursor from a ceramic-based powder in a binder.

According to the invention, the ceramic-based powder may comprise at least one metal oxide, at least one metal nitride or at least one metal carbide. For example, the ceramic-based powder may include alumina to form artificial sapphire, or a mixture of alumina and chromium oxide to form artificial ruby. Furthermore, the binder may be of various types, such as (high molecular) polymers or organic types.

The method comprises a second step b) of pressing the ceramic precursor 22 via the upper and lower dies 23, 25 to form a green body 27 of the carrier 1 to be manufactured, the green body 27 having a top surface 24 and a bottom surface 26 comprising the first and second functional elements 28, 30, respectively.

As can be seen in fig. 1, each die 23, 25 is fixed to one arm of the double action press 21. According to the invention, one (or both) of the moulds 23, 25 is moved inside the casing 29 close to the other in the direction a, so as to form not only the top and bottom faces 24, 26 but also the outer walls.

It is obviously possible to form several identical or different green bodies 27 simultaneously in step b). This variant can thus employ two plates on which the respective dies 23, 25 are movably mounted, and one of which has a thickness that can be used to form the shells 29 described above for each green body 27 to be made.

It is thus clear that each green body 27 formed in step b) already comprises a blank 28, 30 of the first and second functional element 8, 10 to be made. To obtain these blanks 28, 30, each substantially planar mold 23, 25 comprises at least one stamp 31, 32 intended to form a different functional element. Fig. 1 shows: the upper mould 23 comprises a stamp 31 having a substantially spherical surface to form, for example, an oil bath, and the lower mould 25 comprises a stamp 32 having a substantially conical surface to form, for example, a clearance cone (clearance cone) for easier mounting of the pivot, in particular when the pivot has to be non-penetratingly mounted in the carrier.

It follows that the various functional elements 8, 10, 18, 20 on each carrier 1, 11 can be provided directly by the shape of the mould without thereby weakening the carrier to be made. For example, other stamp shapes are envisioned, several stamps may be present on the same mold, the actual mold may form an arcuate surface, or the actual stamp may carry a second stamp. Non-limiting variants of the mold of the invention are shown in figures 2 to 5 to better illustrate the various supports obtained according to the invention.

Thus, as seen in fig. 3, a substantially planar mold 37 may include a stamp 36 having a substantially parallelepiped surface. In the example shown in fig. 2, the substantially planar mold 35 may include a stamp 31 having a substantially spherical surface, and a chamfered stamp 33 extending annularly in a conical manner to form on the outer wall of the green body. Fig. 4 shows a mold 38 comprising a curved surface 34 (i.e., non-planar) that gradually expands around the stamp 31 having a generally spherical surface 34. Finally, in the last-proposed variant, as can be seen in fig. 5, the mold 39 comprising the curved surface 34 (i.e. which is not planar) may also comprise a first stamp 36 having a substantially parallelepiped surface, and a second stamp 32 extending from the first stamp having a substantially conical surface.

Preferably according to the invention, a certain material thickness i is left between each blank of the first and second functional elements 28, 30 to prevent degradation thereof in the step c) of causing shrinkage. Since the total thickness of the green body 27 is between 250 μm and 1mm, the material thickness i is preferably between 10 and 100 μm. It follows that the proportion of any shrinkage is more uniform than if pores between the first and second functional elements 28, 30 were already present before sintering.

The method comprises a third step c) for sintering the green body 27 to form the ceramic body 41. Preferably, according to the invention, step c) comprises pyrolysis. This step c) causes a shrinkage of the green body 27 of between 15% and 30% in volume. Finally, the method comprises a fourth step d) of forming a through hole 43 in the ceramic body 41 for connecting the first and second functional elements 28, 30. Step d) is preferably carried out using destructive laser radiation to obtain a very precise etching. However, other types of processes may be used to achieve step d), for example, mechanical shrinkage such as mechanical drilling or high pressure water etching.

The method may further comprise a final step of finishing the carrier. This final finishing step may thus comprise a grinding and/or buffing and/or polishing to allow adjustment of the final dimensions and/or local correction of the shrinkage and/or roughness of the edges.

It follows that it is possible to obtain a maximum cross section of each functional element 8, 18, 10, 20 which may be substantially identical (fig. 9) or different (fig. 7, 8), constant (stamp 36) or non-constant (stamp 31, 32), and preferably 1.5 to 5 times the cross section of the hole 3, 13, without rendering the method more difficult to implement or leading to less desirable rejection rates. In fact, the beveled or olivary cut-out of the carrier hole, which provides a maximum cross-section of more than 1 times the cross-section of said hole, should not be interpreted as a functional element in the sense of the present invention.

Of course, the invention is not limited to the examples shown, but may have various modifications and substitutions that can occur to those skilled in the art. In particular, other types of functional elements formed by other stamps and/or mold geometries are advantageously contemplated according to the present invention.

Claims (13)

1. A method of manufacturing a carrier (1, 11), comprising the steps of;

a) forming a ceramic precursor from a ceramic-based powder (22) in a binder;

b) pressing the ceramic precursor (22) with an upper mold (23, 25, 35, 37, 38, 39) and a lower mold (23, 25, 35, 37, 38, 39) to form a green body (27) of the carrier (1, 11) to be made, the green body (27) having a top surface (24) and a bottom surface (26) comprising a first and a second functional element (28, 30), respectively, and leaving a material thickness i between the first and the second functional element to prevent degradation of the first and the second functional element in the step c) causing shrinkage;

c) sintering the green body (27) to form a ceramic body (41);

d) a through hole (43) is formed in the ceramic body (41) to connect the first and second functional elements.

2. Method according to claim 1, characterized in that the maximum cross section of each functional element is 1.5 to 5 times the cross section of the through hole (43).

3. The method of claim 2, wherein the ceramic-based powder comprises at least one metal oxide, at least one metal nitride, or at least one metal carbide.

4. The method of claim 3, wherein the ceramic-based powder comprises alumina.

5. The method of claim 4, wherein the ceramic-based powder further comprises chromium oxide.

6. Method according to claim 1, characterized in that each mould (23, 25, 35, 37, 38, 39) comprises at least one stamp (31, 32, 33, 34, 36) intended to form different functional elements.

7. The method according to claim 6, characterized in that the at least one stamp (31, 32, 33, 34, 36) comprises a spherical surface.

8. The method according to claim 6, characterized in that the at least one stamp (31, 32, 33, 34, 36) comprises a conical surface.

9. Method according to claim 6, characterized in that said at least one stamp (31, 32, 33, 34, 36) comprises a surface of parallelepiped shape.

10. Method according to claim 1, characterized in that step b) is carried out by moving the upper mold (23, 25, 35, 37, 38, 39) and the lower mold (23, 25, 35, 37, 38, 39) relative to each other in a housing (29).

11. The method of claim 1, wherein step c) comprises pyrolysis.

12. Method according to claim 1, characterized in that it comprises a final step of finishing the carrier (1, 11).

13. A method according to claim 12, wherein the final finishing step comprises burnishing and/or buffing and/or polishing.