CH716925A2 - Pierre, in particular for a clockwork movement, and its manufacturing process. - Google Patents

Abstract

The invention relates to a method of manufacturing a stone of poly-crystalline type, in particular for a timepiece, the stone comprising for example poly-ruby of Al 2 O 3 Cr type or Zirconia of ZrO 2 type. , the method comprising a first step of producing a precursor (21), characterized in that it comprises a second step of pressing the precursor (21) in order to form a body, the pressing 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 being provided with 'a wire (17) at least partially passing through the lower die (16) to open into the pressing space (25), the lower die (16) being able to slide around the wire (17), the pressing being carried out by the bringing together the lower die (16) and the upper die (22) to form a body comprising a lower face e provided with a hole. The invention further relates to a stone and a pressing device.

Description

Field of the invention

The invention relates to a method of manufacturing a stone, in particular for a timepiece movement.

[0002] The invention also relates to a stone, in particular of a timepiece movement, for example an industrial stone or a technical ceramic.

[0003] The invention also relates to a timepiece movement comprising such a stone.

The invention also relates to a pressing device for implementing the method.

Background of the invention

[0005] In the state of the art of watchmaking, stones of the ruby, ZrO2 or sapphire type are used in particular to form counter-pivots or guide elements, called bearings, in timepieces. These counter-pivots and guide elements are intended to come into contact with the pivots in order to make the latter movable in rotation with minimal friction. Thus, they form, for example, all or part of a bearing of an axis mounted in rotation. The guide elements generally include a through hole for inserting the axis of the pivot.

Figure 1 is a representation of a bearing 1 for a pivot 2 of a rotating mobile 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.

In principle, synthetic industrial stones are used in watch movements. In particular, the Verneuil-type process is known for manufacturing stones of the monocrystalline type. There are also stones of the poly-crystalline type, which are manufactured by pressing a precursor with a view to obtaining a green body of the future stone from a pressing tool. The stones are then sintered, machined to obtain a finished shape with the desired dimensions. In particular, concerning the guide elements made of poly-crystalline stone, the pressing tool is for example provided with a wire participating in the construction of a hole blank.

[0008] However, these techniques for machining these poly-crystalline stones do not make it possible to obtain holes of small dimensions. In particular, it is possible to go up to diameters of 0.11 mm, thanks to the usual techniques known today. But it is not possible to go below this value. In order to be able to descend below, it is necessary to have recourse to laser technologies, which are difficult to implement industrially, and which do not make it possible to directly obtain a quality surface condition of the hole.

Summary of the invention

The object of the present invention is to overcome all or part of the drawbacks mentioned above, by proposing a method for manufacturing a large-scale stone allowing the production of a very small diameter hole.

To this end, the invention relates to a method of manufacturing a poly-crystalline type stone, in particular for a timepiece, the stone comprising for example poly-ruby of the al2O3Cr type or ceramic Zirconia of ZrO2 type, the process comprising a first step of producing a precursor.

The method is remarkable in that it comprises a second step of pressing the precursor in order to form a body, the pressing being carried out using a pressing device provided with an upper die and a lower die defining a pressing space in which the precursor is placed, the device being provided 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 operated by the bringing together of the lower die and the upper die to form a body comprising a lower face provided with a hole.

[0012] Thus, this process makes it possible to form green bodies which, after sintering and machining, will give stones with a hole of very small diameter, in particular less than or equal to 0.1mm. This method is further implemented by an easy-to-use pressing device, the pressing device used being an improvement of a device used for the manufacture of a green body. The invention therefore makes it possible to manufacture these stones industrially on a large scale, without having recourse to expensive and complicated systems to implement.

According to a particular embodiment of the invention, the pressing step is performed by moving the lower die towards the upper die around the fixed wire.

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

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

According to a particular embodiment of the invention, a flaring is formed around the hole on its underside during the pressing step, the lower die further being provided with a convex part.

[0017] According to a particular embodiment of the invention, the flaring has a conical, rounded or plateau shape, the convex part of the lower die having a corresponding convex part around the wire.

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

According to a particular embodiment of the invention, the method comprises a third step of sintering said body in order to form the inorganic body.

According to a particular embodiment of the invention, the method comprises a fourth machining step to cut the stone to predefined dimensions, in particular to form a through hole.

According to a particular embodiment of the invention, the method comprises a fifth finishing step, for example lapping and / or brushing and / or polishing of the inorganic body.

The invention also relates to a stone, in particular for a timepiece movement, formed from a body of the poly-crystalline type and comprising, for example, poly-ruby of the al2O3Cr type or of the Zirconia of the ZrO2 type. , the body being capable of being obtained by the process according to the invention. The stone is remarkable in that the body includes an underside provided with a hole whose diameter is less than 0.11mm.

According to a particular embodiment of the invention, the diameter of the hole is within an interval ranging from 0.2 to 0.8mm, or even from 0.4 to 0.6mm.

According to a particular embodiment of the invention, the stone comprises a flare around the hole on its underside.

According to a particular embodiment of the invention, the flaring has a conical, rounded or plateau shape.

The invention also relates to a timepiece comprising such a stone, in particular for a balance bearing.

The invention also relates to a pressing device for the manufacture of a stone, in particular for a timepiece, the device comprising a housing defining a housing, an upper die and a lower die configured to be able to move. in the housing, 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 with respect to at the lower die and centered on the collar of the upper die, the lower die comprising an orifice for receiving the yarn, the lower die being able to slide around the yarn.

According to a particular embodiment of the invention, the lower die comprises a convex part to form a flare around the hole on the underside of the body.

According to a particular embodiment of the invention, the flaring has a conical, rounded or plateau shape.

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: FIG. 1 is a schematic representation of a bearing for a pivot according to an embodiment known from the state of the art; FIG. 2 is a block diagram of a method for producing a stone according to the invention; FIG. 3 is a schematic representation of part of a pressing device according to the invention; Figure 4 is a schematic representation of the part of Figure 4 with the precursor; FIG. 5 is a schematic representation of the pressing device according to the invention; FIG. 6 is a schematic representation of the pressing device according to the invention during pressing; FIG. 7 is a schematic representation of a first embodiment of a green body obtained after the pressing step of the method according to the invention; FIG. 8 is a schematic representation of a second embodiment of a green body obtained after the pressing step of the method according to the invention; FIG. 9 is a schematic representation of a third embodiment of a green body obtained after the pressing step of the method according to the invention; FIG. 10 is a schematic representation of a stone obtained by the method according to the invention; FIG. 11 is a schematic representation of a system for manufacturing a stone comprising a pressing device according to the invention.

Detailed description of the preferred embodiments

As explained above, the invention relates to a method of manufacturing a stone capable of forming a guide element of a timepiece. The stone is for example intended to come into contact with a pivot, also called a journal, for example of a balance axis, in order to make the latter movable in rotation with minimal friction. It is therefore understood that the present invention makes it possible in particular to produce a stone which can form all or part of a bearing of an axis mounted in rotation, such as that shown in FIG. 1.

The stone is formed from a precursor, modeled as a green body, which becomes a mineral body of the poly-crystalline type for sapphire, the body comprising for example poly-ruby of the al2O3Cr type or Zirconia ceramic ZrO2 type. The mineral body is cut to become the final stone.

In embodiment 5 of the method, shown in Figure 2, such a method comprises a first step 7 of producing a precursor from a mixture of at least one powder material with a binder. This material can be, in a non-limiting and non-exhaustive manner, ceramic. This step 7 is intended to form a precursor from a ceramic-based powder taken up in the binder.

In this context, the ceramic-based powder may comprise at least one metal oxide, one metal nitride or one 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, or more zirconium oxide. In addition, the binder can be of various natures such as, for example, of polymeric types or of organic types.

The embodiment then comprises 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 Figures 4 to 7, which are described later in the description. The pressing step 8 makes it possible to obtain a green body provided with a hole. It is therefore understood that the shape of the hole is provided by the shape of the wire 17 of the lower die 16 of the pressing device 20.

The method comprises a third sintering step 9 of said green body in order to form the mineral body of the future stone in said at least one material. The material can be, as we mentioned previously, ceramic. In other words, this step 9 is intended to sinter the green body in order to form a ceramic body of the future pierced stone. Preferably according to the invention, the sintering step 9 can comprise pyrolysis, for example by thermal debinding.

The method 10 comprises a fourth machining step 11, in particular to cut the mineral body to predefined dimensions, in particular in order to obtain a hole through the stone. Machining consists, for example, in planing the upper face of the body. Thus, by removing an upper part of the body, the hole is opened in the upper face of the body to obtain a through hole from the lower face. The machining step 11 also comprises a sub-step of shaping the lower face to obtain a predefined stone thickness.

The method comprises a fifth finishing step 12, for example lapping and / or brushing and / or polishing of the inorganic body. This finish makes it possible to give the stone a surface state compatible with its use. Such a finishing step also allows the adjustment of the final dimensions and / or the removal of edges and / or the local modification of the roughness.

Figures 3 to 6, the pressing device 20 comprises a housing 15 provided with a chamber closed by an upper die 22, and inside which a lower die 16 can slide. Each die 16, 22 is fixed on a double-acting press. The upper die 22 and the lower die 16 define a pressing space 25 in which the precursor 21 is disposed.

In Figures 3 and 4, only the lower die 16 is shown. The device 10 is also provided with a wire 17 at least partially passing through the lower die 16 to open 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 comprises an orifice 19 for passage of 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.

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

A second embodiment of the lower die comprises a rounded portion of rounded shape. In a third embodiment, the convex part has the shape of a plate with a rounded edge. The second and the third embodiment of the lower die are not shown in the figures, but the shape of the convex part corresponds to the shape of the flare 34, 38, 48 of the bodies 30, 33, 43 corresponding to the figures. 7 to 9.

The precursor 21 is positioned in the pressing space 25, as shown in Figure 4. Then, the upper die 22 is positioned above the housing to close it.

The upper die 22 comprises a substantially planar surface. Thus, during pressing, the upper face of the green body is substantially flat.

The pressing 8 is carried out by bringing the upper die 22 and the lower die 16 together, so as to compress the precursor 21 in the pressing space 25. Preferably, the pressing 8 is performed by the displacement of the lower die 16 towards the upper die 22 around the fixed wire 17. Thus, the precursor 21 is packed against the upper die 22 to give the green body a shape corresponding to the pressing space 25 once the two dies 16, 22 close together. The green body therefore takes the form of the upper 22 and lower 16 dies for the upper 36 and lower 37 faces of the body.

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

Figure 7 shows the green body 30 thus obtained. The green body 30 comprises a planar upper face 36. The green body 30 comprises a lower face 37 provided with a hole 32. The hole 32 was formed by the wire during the pressing. The hole 32 has a cylindrical shape. The hole 32 has a chosen depth. At this stage, the hole 32 is not through, but has a bottom. Thanks to the method, a hole 32 of very small diameter is obtained, which may in particular be less than 0.1 mm, or even less than 0.05 mm.

In this embodiment, the lower face 37 of the body 30 is provided with a flared portion 34, the flared portion 34 bordering the hole 32. The flared portion 34 has a conical shape. This flaring then forms a cone of engagement of the pierced 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 top. The first opening 39 is larger than the second 41, and is formed in the lower face 37 of the body 30. The connection of the cone 34 and the hole 32 is effected through the second opening 41 to form a ridge. Thus, the flaring 34 makes it possible to easily insert the pivot of an axis of a moving part in rotation, in particular 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 the hole 8 from protruding too much. For example, an angle of between 60 ° and 140 °, preferably between 90 ° and 120 °, is chosen.

In Figure 8, a second embodiment of a green body comprises a flared portion of rounded shape, which has a radius of curvature. The rounded shape borders the body hole, being centered around it. The hole is arranged in the bottom of the flare.

A third embodiment of the green body, shown in Figure 9, comprises a flare in the form of a plate with a rounded edge.

Once formed, the green body 30 is subjected to the sintering step to obtain an inorganic body, which retains an identical shape.

FIG. 10 shows an example of a stone 40 obtained after all the steps of the method 10. Such a stone 40 can be used as a guide element mounted in a bearing, such as that of FIG. 1. However, such a stone cannot be limited to the watchmaking field and can be applied to any element mounted mobile with respect to a bearing, or to an industrial stone (water jet nozzle, etc.), or a technical ceramic (insulator, etc.). Stone 40 includes the characteristics described in the process above. The stone 40 is crossed by a hole 42 intended to receive a pivot. The stone 40 has an upper face 46 and a lower face 47, one of which comprises a functional element, here a cone 44, communicating with the through hole 42. The upper face 36 is substantially planar and comprises 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 comprises 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 0.18mm and a diameter of 0.8mm, and a hole of diameter less than 0.1mm. Such dimensions allow the use of very small diameter pivots. Preferably, the entire upper face 36 has the same height. Thus, the upper face 36 of the body is flat, outside the hole 32. Material can also be removed from the upper face 36 during the machining step, to obtain a desired stone thickness.

The machining step 11 can also include a sub-step of planing the peripheral face 52 of the mineral body 30, in order to give it a determined diameter. The machining step 11 can also include a sub-step of planing the lower face 37, or even of widening or cutting the hole 32.

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

Referring to Figure 11, the invention also relates to a manufacturing system 60 of the stone. This system 60 comprises the following different devices: a device 51 for producing a precursor from a mixture of at least one powdered material with a binder; a device 20 for pressing the precursor material as defined above; a sintering device 53 of said green body, and a device 54 for machining the body 30 of the future stone resulting from the sintering of the green body.

It will be noted that at least two of these devices 20, 51, 53 and 54 can together form a single entity of the system 60. Such a system 60 is suitable for implementing the method for manufacturing the stone 40 shown on Figure 10, going through the steps of Figure 2.

Claims (17)

1. Method (10) for manufacturing a stone (40) of the poly-crystalline type, in particular for a timepiece, the stone (40) comprising, for example, poly-ruby of the al2O3Cr type or of the Zirconia of the type. ZrO2, the method comprising a first production step (7) of a precursor (21), characterized in that it comprises a second pressing step (8) of 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 placed, the device (20) being provided with a wire (17) passing at least in part through the lower die (16) to open into the pressing space (25), the lower die (16 ) being able to slide around the wire (17), the pressing (8) being operated by the bringing together of the lower die (16) and the upper die (22) to form a body (30) comprising a lower face (37) provided with a hole (32). 2. Method according to claim 1, characterized in that the pressing (8) is carried out by moving the lower die (16) towards the upper die (22). 3. Method according to claim 1 or 2, characterized in that during pressing (8), a substantially planar upper 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, characterized in that the upper die (22) is fixed during pressing (8). 5. Method according to any one of the preceding claims, characterized in that a flaring (34) is formed around the hole (32) on its underside (37), during the pressing step (8). , the lower die (16) being further provided with a domed portion (18). 6. Method according to claim 5, characterized in that the flaring (34) has a conical, rounded or plateau shape, the convex part (18) of the lower die (16) having a corresponding convex part around the wire. (17). 7. Method according to any one of the preceding claims, characterized in that the method (10) comprises a third step of sintering (9) of said body (30) in order to form an inorganic body. 8. Method according to claim 5, characterized in that the method (10) comprises a fourth machining step (11) to cut the stone to predefined dimensions, in particular to form a through hole (32). 9. Method according to claim 6, characterized in that the method (10) comprises a fifth finishing step (12), for example lapping and / or brushing and / or polishing of the inorganic body. 10. Stone (40), in particular for a timepiece movement, formed from a body of poly-crystalline type and comprising, for example, poly-ruby of the al2O3Cr type or of Zirconia of the ZrO2 type, the body (30 ) being obtainable by the method (10) according to any one of the preceding claims, characterized in that the body (30) comprises a lower face (37) provided with a hole whose diameter is less than 0.11 mm. 11. Stone according to claim 10, characterized in that the diameter of the hole (32) is within an interval ranging from 0.2 to 0.8mm, or even from 0.4 to 0.6mm. 12. Stone of claim 10 or 11, characterized in that it comprises a flare (34, 38, 48) around the hole (32) on its underside (37). 13. Stone according to claim 12, characterized in that the flaring (34, 38, 48) has a conical, rounded or plateau shape. 14. Timepiece, comprising a stone according to any one of claims 10 to 13, in particular for a bearing. 15. Pressing device (20) for the manufacture of a stone (30), in particular for a timepiece, the device (60) comprising an upper die (22) and a lower die (16) configured to be able to fit. moving relative to each other in a housing, the dies (16, 22) defining a pressing space (25) in which a precursor (21) can be disposed, characterized in that the device (20) is provided with a wire (17) passing at least partially through the lower die (16) to open into the pressing space, the lower die (16) being able to slide around the wire (17). 16. A pressing device (20) according to claim 15, characterized in that the lower die (16) comprises a domed portion (18) to form a flare (34, 38, 48) around the hole (32) on the face. lower (37) of the body (30, 33, 43). 17. A pressing device (20) according to claim 15, characterized in that the flaring (34, 38, 48) has a conical, rounded or plateau shape.