CH707740B1 - A bearing comprising first and second functional elements on two distinct faces and its method of manufacture. - Google Patents

Abstract

The invention relates to a bearing (1) comprising a body (2) of sintered ceramic through which a hole (3) passes. According to the invention, the body (3) comprises an upper (4) and lower (6) surface each of which comprises a functional element (8, 10) communicating with said hole. The invention relates to the field of watch stones. The invention also relates to the method of manufacturing such a pad.

Description

Field of the invention

The invention relates to a pad for a timepiece and in particular such a pad comprising first and second functional elements on two separate faces.

Background of the invention

It is known to manufacture bearings from monocrystalline alumina by reducing by machining the volume of a rough blank. However, once a first face is machined to form a first functional element, it becomes very difficult to produce a second functional element on another face because of the fragility generated by the machining of the first face.

[0003] Therefore, even with a second functional element on another face which is not geometrically extensive, the scrap rate is too high.

Summary of the invention

The object of the present invention is to overcome all or part of the drawbacks mentioned above by providing a bearing comprising first and second functional elements on two distinct faces which are geometrically extended and a manufacturing process making it possible to drastically reduce the rate of scum.

To this end, the invention relates to a method of manufacturing a pad comprising the following steps: a) forming a ceramic precursor from a ceramic-based powder taken in a binder; b) compressing, using an upper die and a lower die, the ceramic precursor in order to form a green body of the future pad with upper and lower surfaces respectively comprising first and second functional elements; c) sintering the green body to form a ceramic body; d) forming a through hole in the body in order to connect said first and second functional elements.

[0006] Advantageously according to the invention, each face of the pad can thus be directly formed with at least one functional element on each face even in a very extensive manner without inducing prohibitive reject rates.

[0007] In accordance with other advantageous characteristics of the invention: the ceramic-based powder comprises at least one metal oxide, one metal nitride or one metal carbide; the ceramic-based powder comprises aluminum oxide and, optionally, chromium oxide; each die comprises at least one punch intended to form a distinct functional element; said at least one punch has a spherical and / or conical and / or parallelepipedal surface; step b) is carried out by bringing the upper and lower dies together in a housing; step c) comprises pyrolysis; the method includes a final pad finishing step which may include lapping and / or brushing and / or polishing.

[0008] In addition, the invention relates to a bearing obtained from such a method and comprising a sintered ceramic body traversed by a hole characterized in that the body has an upper and lower surface each of which comprises an element. functional communicating with said hole.

[0009] Such a pad can in particular be mounted or form all or part of a plate or a bridge of a watch movement.

Brief description of the drawings

Other features and advantages will emerge clearly from the description which is given below, by way of indication and in no way limiting, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a double-acting press; Figures 2 to 5 are variants of matrices; FIGS. 6 and 7 are representations at different stages in the manufacture of a pad according to the invention; FIGS. 8 and 9 are representations of two examples of bearings according to the invention.

Detailed description of the preferred embodiments

As explained above, the invention relates to a pad intended to come into contact with a pivot in order to make the latter movable in rotation with minimal friction. It is therefore understood that the present invention makes it possible to form all or part of a bearing of an element mounted to rotate.

According to the invention, such a pad is intended to be mounted in a bridge or a plate or to form all or part of a plate or a bridge of a watch movement. However, the invention cannot be limited to the horological field and can be applied to any element mounted to move relative to a bearing.

Advantageously according to the invention, the bearing comprises a sintered ceramic body which passes through a hole intended to receive the pivot, also called a journal. The body comprises, advantageously according to the invention, an upper surface and a lower surface each of which comprises at least one functional element communicating with the hole.

Figures 8 and 9 show two examples of bearings 1, 11 according to the invention. The bearing 1 of FIG. 8 comprises a generally annular body 2 comprising a hole 3, preferably centered, opening out between an upper surface 4 and a lower surface 6. Advantageously according to the invention, the hole 3 communicates with a substantially spherical recess 5 on the upper face 4 forming a first functional element 8. In addition, the hole 3 also communicates with a substantially conical recess 7 on the lower face 6, forming a second functional element 10. It is also noted that the wall of the body 2 at the level of hole 3 has an olivage intended to minimize contact with a pivot but also to facilitate possible lubrication.

The pad 11 of Figure 9 comprises a generally annular body 12 having a hole 13, preferably centered, opening between an upper surface 14 and a lower surface 16. Advantageously according to the invention, the hole 13 communicates with a recess 15 substantially spherical on the upper face 14 forming a first functional element 18. In addition, the hole 13 also communicates with a substantially spherical recess 17 on the lower face 16, forming a second functional element 20. It is also noted that the wall of the body 12 at the level of the hole 13 has chamfers intended to prevent contact with a pivot from breaking said wall.

Using these two examples, it can be seen, advantageously according to the invention, that each functional element 8, 10, 18, 20 is independent and can also be extended geometrically on each of the faces 4, 6, 14, 16. Of course, as explained below, several functional elements 8, 10, 18, 20, which may or may not be identical, can also be formed on the same face 4, 6, 14, 16. Likewise, as explained below- below, each functional element 8, 10, 18, 20 cannot be limited to a recess 5, 7, 15, 17 which is substantially spherical or substantially conical, but has a different shape or forms several combined shapes.

The variety of production of bearings will be better understood from Figures 1 to 7 showing a method of manufacturing a bearing according to the invention. The method comprises a first step a) intended to form a ceramic precursor from a ceramic-based powder taken up in a binder.

According to a special embodiment of the invention, the ceramic-based powder may comprise at least one metal oxide, a metal nitride or a metal carbide. For example, the ceramic-based powder may include aluminum oxide in order to form synthetic sapphire or a mixture of aluminum oxide and chromium oxide in order to form synthetic ruby. In addition, the binder can be of various natures such as, for example, of the polymer type or of the organic type.

The method comprises a second step b) intended to compress, using an upper die 23 and a lower die 25, the ceramic precursor 22 in order to form a green body 27 of the future pad 1 with upper 24 and lower 26 surfaces respectively comprising first and second functional elements 28, 30.

As visible in Figure 1, each die 23, 25 is fixed to an arm of a double-acting press 21. According to the invention, one of the dies 23, 25 (or both) is brought closer to the other in the directions A in a casing 29 in order to form not only the upper 24 and lower 26 faces but also the outer walls.

It is obviously possible that several green body 27, identical or not, can be formed at the same time during step b). Such a variant can thus use two plates on which the respective dies 23, 25 are movably mounted, one of the plates being able to be used in its thickness to form the casing 29 described above for each future green body 27.

It is therefore understood that each green body 27 formed during step b) already comprises the blanks 28, 30 of the future first and second functional elements 8, 10. To obtain these blanks 28, 30, each die 23, 25 substantially planar comprises at least one punch 31, 32 intended to form a distinct functional element. In Figure 1, it can be seen that the upper die 23 comprises a punch 31 with a substantially spherical surface allowing, for example, to form an cruet and that the lower die 25 comprises a punch 32 with a substantially conical surface allowing, for example , to form a release cone to mount the pivot more easily, in particular when it has to be mounted blind in the bearing.

It is therefore understood that the wide variety of functional elements 8, 10, 18, 20 on each pad 1, 11 is directly provided by the shape of the dies without the future pad being weakened. By way of example, other shapes of punch can be envisaged, several punches can be present on the same die, the die can itself form curved surfaces or even a punch can itself support a second punch. Non-limiting variants of matrices are presented in FIGS. 2 to 5 in order to better show the variety of bearings obtained according to the invention.

Thus, as visible in Figure 3, the substantially planar die 37 may include a punch 36 with a substantially parallelepipedal surface. In the example illustrated in FIG. 2, the substantially planar die 35 may include a punch 31 with a substantially spherical surface and a punch 33 extending annularly in a conical manner to form a chamfer on the outer wall of the green body. In Figure 4, it can be seen, the die 38 comprising a curvature 34, that is to say not planar, widening around a punch 31 with a substantially spherical surface. Finally in a last alternative proposal, as visible in FIG. 5, the die 39 comprising a curvature 34, that is to say not planar, can also include a first punch 36 with a substantially parallelepipedal surface and a second punch 32 as an extension of the first with a substantially conical surface.

Preferably a gap i is left between each blank of the first and second functional elements 28, 30 in order to avoid their deterioration during step c) generating a shrinkage. The overall thickness of the green body 27 being between 250 μm and 1 mm, the gap i is preferably between 10 and 100 μm. It is therefore understood that the proportions of the shrinkage are more homogeneous than if the hole between the first and second functional elements 28, 30 were already present before the sintering.

The method comprises a third step c) intended to sinter the green body 27 to form a ceramic body 41. Preferably according to the invention, step c) comprises pyrolysis. Step c) generates a shrinkage comprised between 15% and 30% of the volume of the green body 27. Finally, the method comprises a fourth step d) intended to form a through hole 43 in the body 41 in order to connect the first and second functional elements 28, 30. Step d) is preferably carried out using destructive radiation of the laser type in order to obtain very precise engraving. However, step d) can be achieved using other types of process such as, for example, mechanical removal such as mechanical drilling or high pressure water etching.

The method can also include a final step of finishing the pad. Such a final finishing step can thus comprise a lapping and / or a brushing and / or a polishing allowing the adjustment of the final dimensions and / or the removal of edges and / or the local modification of the roughness.

Of course, the present invention is not limited to the example illustrated but is susceptible to various variants and modifications which will appear to those skilled in the art. In particular, other types of functional elements formed by other geometries of punches and / or dies can advantageously be envisaged according to the invention.

Claims (15)

1. A method of manufacturing a bearing (1, 11) comprising the following steps: a) forming a ceramic precursor from a ceramic-based powder (22) taken in a binder; b) compress, using an upper die (23, 25, 35, 37, 38, 39) and a lower die (23, 25, 35, 37, 38, 39), the ceramic precursor ( 22) in order to form a green body (27) of the future pad (1, 11) with upper (24) and lower (26) surfaces respectively comprising first and second functional elements (28, 30); c) sintering the green body (27) to form a ceramic body (41); d) forming a through hole (43) in the body (41) to connect said first and second functional elements. 2. Method according to the preceding claim, characterized in that the ceramic-based powder comprises at least one metal oxide, a metal nitride or a metal carbide. 3. Method according to the preceding claim, characterized in that the ceramic-based powder comprises aluminum oxide. 4. Method according to the preceding claim, characterized in that the ceramic-based powder further comprises chromium oxide. 5. Method according to one of claims, characterized in that each die (23, 25, 35, 37, 38, 39) comprises at least one punch (31, 32, 33, 34, 36) intended to form a said separate functional element. 6. Method according to the preceding claim, characterized in that at least one said punch (31, 32, 33, 34, 36) has a spherical surface. 7. Method according to claim 5 or 6, characterized in that at least one said punch (31, 32, 33, 34, 36) has a conical surface. 8. Method according to one of claims 5 to 7, characterized in that at least one said punch (31, 32, 33, 34, 36) comprises a parallelepipedal surface. 9. Method according to one of the preceding claims, characterized in that step b) is carried out by bringing the upper dies (23, 25, 35, 37, 38, 39) and lower (23, 25, 35, 37) together. , 38, 39) in a housing (29). 10. Method according to one of the preceding claims, characterized in that step c) comprises pyrolysis. 11. Method according to one of the preceding claims, characterized in that it comprises a final step of finishing the pad (1, 12). 12. Method according to the preceding claim, characterized in that the final finishing step comprises lapping and / or brushing and / or polishing. 13. Bearing (1, 11) obtained from the method according to one of claims 1 to 12 and comprising a body (2, 12) of sintered ceramic traversed by a hole (3, 13) characterized in that the body ( 3, 13) has an upper (4, 14) and lower (6, 16) surface each of which has a functional element (8, 18, 10, 20) communicating with said hole. 14. Clockwork movement plate characterized in that it comprises a bearing (1, 11) according to claim 13. 15. Watch movement bridge characterized in that it comprises a bearing (1, 11) according to claim 13.