STONE, ESPECIALLY FOR A CLOCK MOVEMENT, AND ITS MANUFACTURING METHOD

Description

Scope of the invention

[0001] The invention relates to a method for manufacturing a stone, particularly for a watch movement, for example an industrial stone or a technical ceramic.

[0002] The invention also relates to a pressing device for implementing the process. Background of the invention

[0003] In the current state of watchmaking technology, ruby, zinc oxide (ZrO2), or sapphire gemstones are used, among other things, to form counter-pivots or guiding elements, known as bearings, in watch components. These counter-pivots and guiding elements are designed to make contact with pivots to allow them to rotate with minimal friction. Thus, they form, for example, all or part of a bearing for a rotating shaft. The guiding elements generally include a through hole for inserting the pivot shaft.

[0004] There figure 1This is a representation of a bearing 1 for a pivot 2 of a rotating object according to the prior art. The bearing 1 comprises a bearing block 3, in which is arranged a guide element 4, which is here a stone. The stone has a through hole 5 to receive the end 6 of the pivot 2. Thus, the pivot 2 can rotate in the hole 5.

[0005] In principle, synthetic industrial jewels are used in watch movements. The Verneuil process, in particular, is known for manufacturing single-crystal jewels.

[0006] There are also polycrystalline stones, which are manufactured by pressing a precursor to obtain a green body of the future stone using a pressing tool. The stones are then sintered and machined to obtain a finished shape with the desired dimensions. In particular, for polycrystalline stone guide elements, the pressing tool is, for example, equipped with a wire that helps create a rough hole. An example of this type of manufacturing process for a polycrystalline stone with a hole is described in patent application EP 3 483 665.

[0007] However, these machining techniques for polycrystalline stones do not allow for the creation of small holes. Specifically, diameters as small as 0.11 mm can be achieved using current standard techniques. But it is not possible to go below this value. To achieve smaller diameters, laser technologies are required, which are difficult to implement industrially and do not allow for a high-quality surface finish on the hole. Summary of the invention

[0008] The aim of the present invention is to overcome all or part of the aforementioned drawbacks, by proposing a method for manufacturing a stone on a large scale allowing the creation of a very small diameter hole.

[0009] To this end, the invention relates to a method for manufacturing a polycrystalline type stone, in particular for a watch part, the stone comprising for example poly-ruby of type al2O3Cr or zirconia ceramic of type ZrO2, the method comprising a first step of producing a precursor.

[0010] The process is remarkable in that it includes a second step of pressing the precursor to form a body, the pressing being carried out using a pressing device having an upper die and a lower die defining a pressing space in which the precursor is placed, the device being equipped with a wire passing at least partially through the lower die to open into the pressing space, the lower die being able to slide around the wire, the pressing being carried out by bringing the lower die and the upper die together to form a body comprising a lower face having a hole.

[0011] This process allows the formation of green bodies, which, after sintering and machining, produce stones with a very small diameter hole, specifically 0.1 mm or less. Furthermore, this process is implemented using an easy-to-use pressing device, an improvement on a device used for manufacturing green bodies. The invention therefore makes it possible to manufacture these stones industrially on a large scale, without resorting to expensive and complicated systems.

[0012] According to a particular embodiment of the invention, the pressing step is carried out by moving the lower die towards the upper die around the fixed wire.

[0013] According to a particular embodiment of the invention, during pressing, a substantially flat upper face of the body is formed, the upper die being provided with a substantially flat surface.

[0014] According to a particular embodiment of the invention, the upper die is fixed during pressing.

[0015] According to a particular embodiment of the invention, a flare is formed around the hole on its lower face during the pressing step, the lower die also being provided with a domed part.

[0016] According to a particular embodiment of the invention, the flare has a conical, rounded, or flat shape, the convex part of the lower die having a corresponding convex part around the wire.

[0017] According to a particular embodiment of the invention, the upper die remains fixed during pressing.

[0018] According to a particular embodiment of the invention, the process includes a third sintering step of said body in order to form the mineral body.

[0019] According to a particular embodiment of the invention, the process includes a fourth machining step to cut the stone to predefined dimensions, in particular to form a through hole.

[0020] According to a particular embodiment of the invention, the process includes a fifth finishing step, for example a lapping and / or a brushing and / or a polishing of the mineral body.

[0021] The invention further relates to a pressing device for the manufacture of a stone, in particular for a watch part, the device comprising a housing defining a cavity, an upper die and a lower die configured to be able to move in the cavity, the dies defining a pressing space in which a precursor can be placed, the device being provided with a wire passing at least in part through the lower die to open into the pressing space, the wire being fixed relative to the lower die and centered on the collar of the upper die, the lower die comprising an orifice for receiving the wire, the lower die being able to slide around the wire.

[0022] According to a particular embodiment of the invention, the lower matrix includes a domed part to form a flare around the hole on the lower face of the body.

[0023] According to a particular embodiment of the invention, the flare has a conical, rounded, or flat shape. Brief description of the drawings

[0024] Other features and advantages will become clear from the description given below, which is indicative and in no way exhaustive, with reference to the attached drawings, in which: there figure 1 is a schematic representation of a pivot bearing according to a known state-of-the-art embodiment; the figure 2 is a synoptic diagram of a method for producing a stone according to the invention; the figure 3 is a schematic representation of part of a pressing device according to the invention; the figure 4 is a schematic representation of part of the figure 4 with the precursor; the figure 5 is a schematic representation of the pressing device according to the invention; the figure 6is a schematic representation of the pressing device according to the invention during pressing; the figure 7 is a schematic representation of a first embodiment of a green body obtained after the pressing step of the process according to the invention; the figure 8 is a schematic representation of a second embodiment of a green body obtained after the pressing step of the process according to the invention; the figure 9 is a schematic representation of a third embodiment of a green body obtained after the pressing step of the process according to the invention; the Figure 10 is a schematic representation of a stone obtained using the process according to the invention; the figure 11 is a schematic representation of a stone manufacturing system comprising a pressing device according to the invention. Detailed description of preferred embodiments

[0025] As explained above, the invention relates to a method for manufacturing a stone capable of forming a guiding element in a timepiece. The stone is, for example, intended to come into contact with a pivot, also called a trunnion, for example of a balance staff, in order to make the latter rotate with minimal friction. It is therefore understood that the present invention makes it possible, in particular, to produce a stone that can form all or part of a bearing for a rotating shaft, such as the one shown in the illustration. figure 1 .

[0026] The stone is formed from a precursor, shaped into a green body, which becomes a polycrystalline mineral body for sapphire, the body including, for example, poly-ruby of the al2O3Cr type or zirconia ceramic of the ZrO2 type. The mineral body is cut to become the final stone.

[0027] In embodiment 5 of the process, shown in the figure 2Such a process includes a first step 7 of producing a precursor from a mixture of at least one powdered material with a binder. This material may be, but is not limited to, ceramics. This step 7 is intended to form a precursor from a ceramic-based powder embedded in the binder.

[0028] In this context, ceramic-based powder may contain at least one metal oxide, metal nitride, or metal carbide. For example, ceramic-based powder may contain aluminum oxide to form synthetic sapphire, a mixture of aluminum oxide and chromium oxide to form synthetic ruby, or zirconium oxide. Furthermore, the binder can be of various types, such as polymers or organic compounds.

[0029] The embodiment then includes a second pressing step 8 of the precursor from an upper die and a lower die of a pressing device, in order to form a green body of the future stone. The pressing step is shown in the figures 4 to 7 which are described later in the description. The pressing step 8 produces a green body with a hole. It is therefore understood that the shape of the hole is determined by the shape of the wire 17 of the lower die 16 of the pressing device 20.

[0030] The process includes a third sintering step 9 of said green body to form the mineral body of the future stone in said at least one material. The material can be, as previously mentioned, a ceramic. In other words, this step 9 is intended to sinter the green body to form a ceramic body of the future drilled stone. Preferably, according to the invention, the sintering step 9 may include pyrolysis, for example by thermal debinding.

[0031] The process 10 includes a fourth machining step 11, specifically for shaping the mineral body to predefined dimensions, particularly to create a through hole. The machining involves, for example, planing the upper face of the body. Thus, by removing a portion of the upper surface, a hole is created in the upper face, resulting in a through hole from the lower face. The machining step 11 also includes a substep for shaping the lower face to achieve a predefined stone thickness.

[0032] The process includes a fifth finishing step 12, for example, honing and / or brushing and / or polishing of the mineral body. This finishing gives the stone a surface finish suitable for its intended use. Such a finishing step also allows for the adjustment of final dimensions and / or the removal of edges and / or the local modification of roughness.

[0033] On the figures 3 to 6The pressing device 20 comprises a housing 15 with a chamber closed by an upper die 22, and within which a lower die 16 can slide. Each die 16, 22 is fixed to a double-acting press. The upper die 22 and the lower die 16 define a pressing space 25 in which the precursor 21 is placed.

[0034] On the figures 3 And 4 Only the lower die 16 is shown. The device 10 is further equipped with a wire 17 that passes at least partially through the lower die 16 and opens into the pressing space 25. The wire 17 is fixed relative to the lower die 16 and centered on the lower die 16. The lower die 16 includes a passage 19 for the wire 17. Thus, the lower die 16 slides around the wire 17. The wire 17 is therefore stationary relative to the lower die 16.

[0035] The lower matrix 16 is further provided with a domed portion 18. According to a first embodiment, shown on the figure 4 The curved part 18 is conical in shape with a large opening angle, for example within a range from 60° to 140°, preferably between 90° and 120°. The curved part 18 is centered on the lower matrix 16, so that the passage 19 and therefore the wire 17 are arranged at the apex of the curved part 18.

[0036] A second embodiment of the lower die has a rounded, convex portion. In a third embodiment, the convex portion has a rounded, flat shape. The second and third embodiments of the lower die are not shown in the figures, but the shape of the convex portion corresponds to the shape of the flare 34, 38, 48 of the corresponding bodies 30, 33, 43. figures 7 to 9 .

[0037] The precursor 21 is positioned in the pressing space 25, as shown in the figure 4 Then, the upper matrix 22 is positioned above the housing to close it.

[0038] The upper matrix 22 comprises a substantially flat surface. Thus, during pressing, the upper face of the green body is substantially flat.

[0039] The pressing 8 is performed by bringing the upper die 22 and the lower die 16 together, so as to compress the precursor 21 within the pressing space 25. Preferably, the pressing 8 is performed by moving the lower die 16 towards the upper die 22 around the fixed wire 17. Thus, the precursor 21 is pressed against the upper die 22 to give the green body a shape corresponding to the pressing space 25 once the two dies 16 and 22 are brought together. The green body therefore takes the shape of the upper die 22 and the lower die 16 for the upper face 36 and the lower face 37 of the body.

[0040] Thus, such a pressing step 8 is intended to compress the precursor 21 in order to form the green body of the future stone drilled with a hole on the lower face 37. Preferably, the upper die 22 remains fixed and does not move under the effect of the pressure of the lower die 16 during the pressing 8.

[0041] There figure 7 The diagram shows the resulting green body 30. The green body 30 has a flat upper face 36. The green body 30 has a lower face 37 with a hole 32. The hole 32 was formed by the wire during pressing. The hole 32 has a cylindrical shape. The hole 32 has a chosen depth. At this stage, the hole 32 is not a through hole, but has a bottom. Thanks to this process, a hole 32 of very small diameter is obtained, which can be less than 0.1 mm, or even less than 0.05 mm.

[0042] In this embodiment, the lower face 37 of the body 30 has a flared portion 34, the flared portion 34 bordering the hole 32. The flared portion 34 has a conical shape. This flare then forms a cone for engaging the drilled stone 40. The cone 12 is preferably circular. The cone has a first opening 39 at its base and a second opening 41 at its apex. The first opening 39 is larger than the second 41 and is formed in the lower face 37 of the body 30. The connection between the cone 34 and the hole 32 is made via the second opening 41 to form an edge. Thus, the flared portion 34 allows for easy insertion of the pivot of a rotating part's axis, particularly in the event of an impact. The angle of the cone is chosen to prevent the edge formed by the top of the cone and hole 8 from being too sharp. For example, an angle between 60° and 140° is chosen, preferably between 90° and 120°.

[0043] On the figure 8A second embodiment of a green body includes a flared, rounded portion with a radius of curvature. The rounded shape borders the hole in the body, being centered around it. The hole is located at the bottom of the flare.

[0044] A third embodiment of the green body, represented on the figure 9 , includes a flared, tray-shaped opening with a rounded edge.

[0045] Once formed, the green body 30 is subjected to the sintering stage to obtain a mineral body, which retains an identical shape.

[0046] There Figure 10 shows an example of stone 40 obtained after all the steps of process 10. Such stone 40 can be used as a guide element mounted in a bearing, such as that of the figure 1However, such a stone is not limited to the watchmaking field and can be applied to any moving part mounted on a bearing, or to an industrial stone (water jet nozzle, etc.), or a technical ceramic (insulator, etc.). The stone 40 has the characteristics described in the previous process. The stone 40 has a hole 42 through it for receiving a pivot. The stone 40 has an upper face 46 and a lower face 47, one of which includes a functional element, here a cone 44, communicating with the through hole 42. The upper face 36 is substantially flat and includes the other side of the through hole 42. In other words, the hole 42 communicates with the upper face 46 and with the lower face 47. Such a through hole 32 includes a first opening 49 defined in the mineral body and opening into the lower face 37.The through hole 32 also includes a second opening 51 defined in the mineral body 30 and opening into the upper face 36. Such a stone has, for example, a thickness of 0.18 mm and a diameter of 0.8 mm, and a hole with a diameter of less than 0.1 mm. Such dimensions allow the use of very small diameter pivots. Preferably, the entire upper face 36 has a uniform height. Thus, the upper face 36 of the body is flat, except for the hole 32. Material can also be removed from the upper face 36 during the machining stage to obtain a desired stone thickness.

[0047] Machining step 11 may also include a substep of planing the peripheral face 52 of the mineral body 30 to give it a specific diameter. Machining step 11 may also include a substep of planing the lower face 37, or even of enlarging or cutting the hole 32.

[0048] Of course, the present invention is not limited to the illustrated example but is susceptible to various variations and modifications that will become apparent to those skilled in the art. In particular, other types of functional elements formed during the pressing stage can advantageously be considered according to the invention.

[0049] With reference to the figure 11 The invention also relates to a stone manufacturing system 60. This system 60 comprises the following various devices: a device for producing a precursor 51 from a mixture of at least one powdered material with a binder; a device for pressing the precursor material as defined above; a device for sintering said green body 53, and a device for machining the body 30 of the future stone resulting from the sintering of the green body.

[0050] It should be noted that at least two of these devices 20, 51, 53 and 54 can together form a single entity of system 60. Such a system 60 is capable of implementing the manufacturing process of the stone 40 represented on the Figure 10 , going through the stages of the figure 2 .

Claims

1. Method (10) for manufacturing a jewel (40) of the polycrystalline type, in particular for a timepiece, the jewel (40) comprising, for example, poly-ruby of the type al2O3Cr or Zirconia of the type ZrO2, the method comprising a first step (7) of producing a precursor (21), the method comprising a second step (8) of pressing the precursor (21) in order to form a body (30), the pressing (8) being carried out using a pressing device (20) provided with an upper die (22) and a lower die (16) defining a pressing space (25) in which the precursor (21) is disposed, the device (20) being provided with a wire (17) passing through at least part of the lower die (16) to open out into the pressing space (25), the lower die (16) being capable of sliding about the wire (17), the pressing (8) taking place by bringing the lower die (16) and the upper die (22) closer to one another to form a body (30) comprising a bottom face (37) provided with a hole (32).

2. Method according to claim 1, characterised in that the pressing (8) is carried out by displacing the lower die (16) towards the upper die (22).

3. Method according to claim 1 or 2, characterised in that during pressing (8), a substantially planar top face of the body is formed, the upper die (22) being provided with a substantially planar surface.

4. Method according to any one of the preceding claims, characterised in that the upper die (22) is stationary during the pressing step (8).

5. Method according to any one of the preceding claims, characterised in that a flaring (34) is formed about the hole (32) on the bottom face (37) thereof during the pressing step (8), the lower die (16) being furthermore provided with a domed part (18).

6. Method according to claim 5, characterised in that the flaring (34) has a conical, rounded or plateau shape, the domed part (18) of the lower die (16) having a corresponding domed part about the wire (17).

7. Method according to any one of the preceding claims, characterised in that the method (10) comprises a third step (9) of sintering said body (30) in order to form a mineral body.

8. Method according to claim 7, characterised in that the method (10) comprises a fourth machining step (11) to cut the jewel to predefined dimensions, in particular to form a through-hole (32).

9. Method according to claim 8, characterised in that the method (10) comprises a fifth finishing step (12), for example for lapping and / or brushing and / or polishing the mineral body.

10. Pressing device (20) for manufacturing a jewel (30), in particular for a timepiece, the device (60) comprising an upper die (22) and a lower die (16) configured such that one can move relative to the other inside a housing, the dies (16, 22) defining a pressing space (25) in which a precursor (21) can be disposed, the device (20) being provided with a wire (17) passing through at least part of the lower die (16) to open out into the pressing space, the lower die (16) being capable of sliding about the wire (17).

11. Pressing device (20) according to claim 10, characterised in that the lower die (16) comprises a domed part (18) to form a flaring (34, 38, 48) about the hole (32) on the bottom face (37) of the body (30, 33, 43).

12. Pressing device (20) according to claim 11, characterised in that the flaring (34, 38, 48) has a conical, rounded or plateau shape.