CH707740A2 - Pad having first and second functional elements on two distinct faces and its manufacturing process. - Google Patents

Abstract

The invention relates to a bearing (1) comprising a sintered ceramic body (2) 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 also relates to a method of manufacturing such a pad. The invention relates to the field of timepieces.

Description

Field of the invention

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

Background of the invention

It is known to manufacture bearings from monocrystalline aiumine machining by reducing 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.

Therefore, even with a second functional element on another face which is geometrically small, the scrap rate is too high.

Summary of the invention

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

For this purpose, the invention relates to a method of manufacturing a pad comprising the following steps: <tb> a) <SEP> forming a ceramic precursor from a ceramic-based powder taken in a binder; <tb> b) <SEP> compress, using an upper die and a lower die, the ceramic precursor to form a green body of the future pad with upper and lower surfaces respectively having first and second functional elements; <tb> c) <SEP> sinter the green body to form a ceramic body; <tb> d) <SEP> forming a through hole in the body to connect said first and second functional elements.

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 very extensively without inducing crippling rejection rates.

According to other advantageous features of the invention: the ceramic powder comprises at least one metal oxide, a metal nitride or a metal carbide; the ceramic-based powder comprises aluminum oxide and, optionally, chromium oxide; each die has at least one punch for forming a separate functional element; said at least one punch has a spherical and / or conical and / or parallelepipedic surface; step b) is performed by bringing the upper and lower dies into a housing; step c) comprises pyrolysis; the method comprises a final step of finishing the pad that may include lapping and / or brushing and / or polishing.

In addition, the invention relates to a pad obtained from the method according to one of the preceding claims and comprising a sintered ceramic body traversed by a hole characterized in that the body comprises an upper and lower surface of which each comprises a functional element communicating with said hole.

Such a pad may in particular be mounted or form all or part of a turntable or a watch movement bridge.

Brief description of the drawings

Other features and advantages will become apparent from the description which is given below, for information only and not limiting, with reference to the accompanying drawings, in which: <tb> fig. 1 <SEP> is a schematic representation of a double-acting press according to the invention; <tb> figs. 2 to 5 <SEP> are variants of matrices according to the invention; <tb> figs. 6 and 7 <SEP> are representations at different stages of manufacture of a pad according to the invention; <tb> figs. 8 and 9 <SEP> are representations of two examples of pads 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 mobile in rotation with minimal friction. It is thus clear that the present invention makes it possible to form all or part of a bearing of a rotatably mounted element.

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 platen or a watch movement bridge. However, the invention is not limited to the watchmaking domain and can be applied to any member mounted to move relative to a bearing.

Advantageously according to the invention, the pad comprises a sintered ceramic body which is traversed by a hole for receiving the pivot, also called pin. 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 pads 1,11 according to the invention. The pad 1 of FIG. 8 comprises a generally annular body 2 having a hole 3, preferably centered, opening 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 recess 7 substantially conical on the lower face 6 forming a second functional element 10. It is also noted that the wall of the body 2 at the hole 3 has an olivage to minimize contact with a pivot but also facilitate a 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 body wall 12 at the hole 13 comprises chamfers intended to prevent contact with a pivot breaking said wall.

With the aid of 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 geometrically extended on each of the faces 4, 6, 14, 16. Of course, as explained below, several functional elements 8, 10, 18, 20, which may be identical or different, may also be formed on the same face 4, 6, 14, 16. Similarly, as explained below, below, each functional element 8, 10, 18, 20 can not be limited to a recess 5, 7, 15, 17 substantially spherical or substantially conical, but have a different shape or form several combined shapes.

The variety of production of the pads will be better understood from Figures 1 to 7 showing a method of manufacturing a pad according to the invention. The method comprises a first step a) for forming a ceramic precursor from a ceramic-based powder taken in a binder.

According to the invention, the ceramic-based powder may comprise at least one metal oxide, a metal nitride or a metal carbide. For example, the ceramic powder may comprise aluminum oxide to form synthetic sapphire or a mixture of aluminum oxide and chromium oxide to form synthetic ruby. In addition, the binder can be of various kinds, for example of the polymer type or 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 to form a green body 27 of the future pad 1 with upper surfaces 24 and lower 26 respectively comprising first and second functional elements 28, 30.

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

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

It is therefore understood that each green body 27 formed in 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 matrix 23, 25 substantially planar comprises at least one punch 31, 32 for forming a separate functional element. In FIG. 1, it can be seen that the upper die 23 comprises a punch 31 with a substantially spherical surface making it possible, for example, to form an oiler and that the lower die 25 comprises a punch 32 with a substantially conical surface allowing, for example to form a clearance cone to mount the pivot more easily including when it is to be mounted blind in the pad.

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 is weakened. By way of example, other forms of punch may be envisaged, several punches may be present on the same matrix, the matrix may itself form curved surfaces or a punch may itself support a second punch. Non-limiting variants of matrices according to the invention are shown in Figures 2 to 5 to better show the variety of pads obtained according to the invention.

Thus, as shown in Figure 3, the substantially planar matrix 37 may comprise a punch 36 with a substantially parallelepipedic surface. In the example illustrated in Figure 2, the substantially planar matrix 35 may include a punch 31 with a substantially spherical surface and a punch 33 annularly extending conically to form a chamfer on the outer wall of the green body. In Figure 4, we can see, the matrix 38 having a curvature 34, that is to say non-planar, flaring around a punch 31 with a substantially spherical surface. Finally, in a last variation proposal, as can be seen in FIG. 5, the matrix 39 comprising a curvature 34, that is to say non-planar, may also comprise a first punch 36 with a substantially parallelepipedic surface and a second punch 32 in extension of the first with a substantially conical surface.

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

The method comprises a third step c) for sintering the green body 27 to form a body 41 of ceramic. Preferably according to the invention, step c) comprises a pyrolysis. Step c) causes a shrinkage of 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 a very precise etching. However, step d) can be obtained using other types of processes such as, for example, mechanical shrinkage such as mechanical drilling or high-pressure water etching.

The method may also include a final step of finishing the pad. Such a final finishing step may thus include a lapping and / or brushing and / or 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 shown but is susceptible to various variations and modifications that will occur to those skilled in the art. In particular, other types of functional elements formed by other punch geometries and / or matrices can be advantageously envisaged according to the invention.

Claims (15)

A method of manufacturing a pad (1, 11) comprising the steps of: a) forming a ceramic precursor from a ceramic-based powder (22) in a binder; b) compressing, with the aid of an upper matrix (23, 25, 35, 37, 38, 39) and a lower matrix (23, 25, 35, 37, 38, 39), the ceramic precursor ( 22) 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 the claims, characterized in that each matrix (23, 25, 35, 37, 38, 39) comprises at least one punch (31, 32, 33, 34, 36) for forming an element distinct functional. 6. Method according to the preceding claim, characterized in that said at least one punch (31, 32, 33, 34, 36) comprises a spherical surface. 7. The method of claim 5 or 6, characterized in that said at least one punch (31, 32, 33, 34, 36) comprises a conical surface. 8. Method according to one of claims 5 to 7, characterized in that said at least one punch (31, 32, 33, 34, 36) comprises a parallelepiped surface. 9. Method according to one of the preceding claims, characterized in that step b) is performed by bringing the upper (23, 25, 35, 37, 38, 39) and lower (23, 25, 35, 37) matrices closer together. , 38, 39) in a housing (29). 10. Method according to one of the preceding claims, characterized in that step c) comprises a 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 a lapping and / or brushing and / or polishing. 13. Pad (1, 11) obtained from the method according to one of the preceding claims 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 having a functional element (8, 18, 10, 20) communicating with said hole. 14. watch movement movement characterized in that it comprises a pad (1,11) according to the preceding claim. 15. Clockwork movement bridge characterized in that it comprises a bearing (1,11) according to claim 13.