Horological jewel and method for manufacturing such a jewel

Abstract

The present invention relates to a horological jewel constituting a bearing (4) or an endstone comprising at least one part (14) which is made of silicon carbide and which comprises at least one part intended to be in contact with a pin of a pivot axis, said part (14) comprising at least one layer of native epitaxial graphene (16) generated on its outer surface. The present invention further relates to a method for manufacturing such a jewel (4), said method comprising: a) a step of manufacturing a jewel intended to constitute a bearing or an endstone comprising at least one part (14) made of silicon carbide, said manufacturing step comprising at least one step of machining at least said part intended to be in contact with a pin of a pivot axis by forceless precision machining; and b) a step of generating at least one layer of native epitaxial graphene (16) on the outer surface of at least the silicon carbide part (14) of the jewel intended to constitute a bearing or an endstone obtained in step a) in order to obtain said horological jewel constituting a bearing (4) or an endstone.

Description

[0001] WATCHMAKING STONE AND METHOD FOR MANUFACTURING SUCH A STONE

[0002] Technical field

[0003] The present invention relates to a watch jewel constituting a bearing or a counter-pivot comprising at least one part made of silicon carbide.

[0004] The present invention also relates to a watch movement and a timepiece comprising such a stone.

[0005] The present invention also relates to a method of manufacturing such a stone.

[0006] State of the art

[0007] A watch jewel constituting a pivot bearing or pad is a part comprising a hollow forming an oiler receiving a lubricant, said jewel being pierced with a hole in which a pivot of a pivot axis moves.

[0008] A watch jewel constituting a counter-pivot is an undrilled jewel, flat on one side and domed on the other. The counter-pivot is placed on the bearing, with the end of the axis pivot passing through the bearing pressing against the flat face of the counter-pivot.

[0009] These stones are used to reduce friction at the pivot. They are traditionally made from corundum, in the form of sapphire or ruby, or more often now from synthetic ruby. Since ruby ​​is very expensive, it has been proposed, for example, in patent FR 2322113, to replace it with sintered silicon carbide enriched with 3 to 4% by weight of boron carbide.

[0010] The quality of the pivots and jewels is of prime importance for the stability of operation, the autonomy of operation and the longevity of a mechanical watch. A bearing is required to work with a minimum of friction and to maintain this quality for as long as possible. To achieve this dual requirement, the pivot, jewel and lubricant must meet certain conditions, namely:

[0011] • the surface condition of the pivots and stones must be as neat as possible

[0012] • the diameter of the pivots must be small, especially for the balance-escapement regulating organ

[0013] • the dimensions and profile of the stones must allow them to receive a certain quantity of oil which they must keep around the pivot, preventing it from spreading onto the stems or onto the stones outside a certain limit.

[0014] To retain the maximum amount of oil for a pivot of given dimensions, a capillary angle of approximately 20° must be created between the pivot and the oiler, which allows the oiler to hold the oil stably. There must also be sufficient "clearance" between the pivot and the stone hole. If this clearance is insufficient, the oil cannot form a lubricant buffer between the walls of the hole and the pivot.

[0015] There are two main types of pivots: the bearing pivot and the cone pivot. Bearing pivots are used in the gear trains up to the escape wheel, except in very high-quality movements where they extend to the seconds wheel. Cone pivots are used for the balance staff and escape wheel in high-quality watches.

[0016] In watchmaking, fluid lubrication is an excellent solution in terms of its good friction coefficient and low wear rates. However, oil is not without its drawbacks: it spreads, leaks, becomes contaminated, turns red, gums up, and blocks the mechanism if it is too old.

[0017] Studies have focused on dry lubricants and even self-lubricating mechanical surfaces or devices. Research is also focusing on the qualities of diamond or silicon. Some propose even different solutions for certain very specific applications, such as lubrication-free watch ball bearings, in which the balls are made of a special alloy. Friction is defined by a dimensionless coefficient, denoted p. In the present application, a coefficient of friction is a dynamic coefficient of friction. It is characterized by the following relationship: = Ft / Fn, where Ft is the friction force and Fn the charge normal to the surface.

[0018] The dynamic friction coefficient p can vary greatly depending on, among other things, the condition of the surfaces and environmental parameters. Thus, for metal-metal contact in air, p can vary between 0.2 and 1.5. In the presence of a solid lubricant, it generally reaches between 0.05 and 1 and between 0.1 and 0.2 in the presence of a lubricating oil.

[0019] Tribology is the science that studies friction. Tribological contact occurs when two surfaces are placed in relative motion relative to each other. The complete tribological process of contact between two surfaces, called partners, is complex to understand because it simultaneously involves friction, wear, mechanical deformation, and chemical changes at different scales, as well as the transfer of materials.

[0020] Five main parameters influence contact: the nature, the difference in hardness and the surface condition of the two materials in contact, as well as the size and hardness of the debris present, which comes either from an external source or from the wear of the partners. All these phenomena influence friction and result in energy losses in the contact. Friction generates mechanical energy in the form of heat.

[0021] This rise in temperature promotes welding phenomena, diffusion of elements or even reaction with the surrounding environment (oxidation, salt formation). In addition, other elements exert an influence, such as environmental parameters (temperature, humidity, presence of pollutants, etc.), the forces involved and the speed of movement during contact.

[0022] Lubrication in watchmaking has three main objectives: to enable the preservation of isochronism, to reduce wear, and to reduce energy loss through friction.

[0023] In addition, the lubricant must be chemically stable, i.e., it must retain its properties over time. The lubricant must have good stability, not be subject to evaporation, have good shear resistance to limit wear, and have good resistance to cold. Finally, it must not have a corrosive effect on the lubricated surface.

[0024] Lubrication is achieved by applying foreign bodies placed between the partners, preventing direct contact between the materials and resulting in a reduction in friction, therefore energy losses, a reduction in wear, and an increase in mechanical efficiency. It can be of three forms: solid, liquid or gaseous.

[0025] PVD (short for Physical Vapor Deposition) is a technique for producing thin layers of lubricating coatings.

[0026] This process has been used for several years in industry, particularly in the watchmaking industry for surface finishing. It allows the deposit of metals for which a deposit is difficult to achieve by traditional galvanic means, or even the deposit of ceramics from metals with interesting properties from a mechanical, chemical or even aesthetic point of view.

[0027] For example, sputtering can be used to deposit the material. This is a plasma vacuum deposition technique. It is carried out at room temperature in an enclosure maintained at low pressure (around 10 1 at 10 2Pa). It allows the deposit of all types of materials, whether simple or composite, conductive or dielectric, on all types of substrates, conductive or not, which can be placed under vacuum and withstand slight heating.

[0028] The sputtering phenomenon is a physical mechanism. It can be compared to the collision of billiard balls. The incident ion bombarding the target material will set an atom of this material in motion, this movement will be transmitted to the other atoms in contact until a surface atom is ejected. These atoms will then be deposited on the substrate.

[0029] The growth of the layer depends on the surface condition on which it grows. The layer reproduces the same surface condition, so that roughness or surface defects will be found in the layer. This method is used, for example, to deposit lubricating coatings such as titanium silicon carbide (TiSiC) and amorphous carbon.

[0030] TiSiC is a ternary ceramic. The layer formed on the substrate is composed of nano-crystallized titanium carbide (TiC), amorphous silicon carbide (SiC), and amorphous carbon (C). The SiC molecules are repelled and group together into nodules. There are then too many carbon atoms to bond with the titanium atoms. The carbon gives lubricating properties to the layer and the silicon provides hardness due to the nodules present, which put the layer under tension.

[0031] The tribological properties of this deposit are influenced by the transfer of elements between the contact partners, the reduction of roughness during the lapping of the contact, the tribochemical reactions between the TiC and H2O from the atmosphere resulting in the formation of a protective layer of titanium oxide (TiO x ) on the surface, and the release of amorphous carbon atoms.

[0032] The hardness of the resulting deposit is approximately 1000 to 1200HV. Its color is metallic gray, similar to steel.

[0033] The amorphous carbon coating, known as "diamond-like carbon" (DLC), is widely used in various sectors of industry and in watchmaking, as a functional or decorative surface treatment. Carbon has two crystallized forms, called hybridizations, with very different properties. They are distinguished by the spatial arrangement of their atoms and the nature of the bonds. The first hybridization, called sp2 , corresponds to the graphitic form of carbon. This hybridization forms a soft, thermally and electrically conductive material, black in color. It has a sheet structure, whose atoms are arranged in hexagons. Covalent bonds, therefore strong, bind the atoms of the same sheet together while Van der Waals bonds, weak bonds, bind the sheets together, which is the origin of the lubricating properties of graphite.

[0034] The second hybridization, named sp 3 , is the diamond form of carbon. This hybridization of carbon is hard, transparent, insulating, and face-centered cubic in structure, with covalent bonds.

[0035] An amorphous carbon coating consists of a variable amount of sp hybridization 3 (diamond) in an sp hybridization matrix 2(graphite). The amorphous carbon coating, obtained by PVD, contains on average less than 5% hydrogen and between 40% and 80% sp hybridization 3 .

[0036] The layers obtained are dark gray to black in color, and have interesting properties of hardness and resistance to friction.

[0037] However, the deposition of a hard coating has the disadvantage of causing significant risks of delamination of the hard layer and therefore the formation of debris which can circulate around the pivot and more generally inside the watch movement and disrupt its operation, which is not satisfactory.

[0038] The present invention aims to remedy these drawbacks by proposing a method of manufacturing a watch jewel constituting a bearing or a counter-pivot going beyond the current state of the art.

[0039] Another object of the invention is to provide a manufacturing method for manufacturing extremely quickly and reliably watch jewels constituting a bearing or a counter-pivot, components intended for watch movements whose demands in terms of performance and isochronism are extremely high. Another object of the invention is to provide a watch jewel constituting a bearing or a counter-pivot having a surface whose properties are very significantly increased or improved compared to existing components.

[0040] Disclosure of the invention

[0041] To this end, the invention relates to a method for manufacturing a watch jewel constituting a bearing or a counter-pivot comprising at least one part made of silicon carbide which comprises at least one part intended to be in contact with a pivot of a pivot axis, said method comprising: a) a step of manufacturing a jewel intended to constitute a bearing or a counter-pivot comprising at least one part made of silicon carbide, said manufacturing step comprising at least one step of machining at least said part intended to be in contact with a pivot of a pivot axis of the part made of silicon carbide;and b) a step of generating at least one layer of native epitaxial graphene on the external surface of at least the part made of silicon carbide of the stone intended to constitute a cushion or a counter-pivot obtained in step a) to obtain said watch stone constituting a cushion or a counter-pivot.;

[0042] According to the invention, the machining of at least said part intended to be in contact with a pivot of a pivot axis of the part made of silicon carbide of step a) comprises precision machining without force.

[0043] According to another variant, the invention relates to a method for manufacturing a watch jewel constituting a bearing or a counter-pivot comprising at least one part made of silicon carbide which comprises at least one part intended to be in contact with a pivot of a pivot axis, said method comprising: c) a step of manufacturing a rough part of the jewel intended to constitute a bearing or a counter-pivot comprising at least one part made of silicon carbide; d) a step of producing a blank of the jewel intended to constitute a bearing or a counter-pivot comprising at least one part made of silicon carbide at least by machining the rough part obtained in step c); e) at least one step of machining the part made of silicon carbide of the blank obtained in step d) to form the part intended to be in contact with a pivot of a pivot axis;f) a step of generating at least one layer of native epitaxial graphene on the external surface of at least the part made of silicon carbide of the blank obtained in step e); and g) at least one step of machining the blank obtained in step f), with the exception of said part intended to be in contact with a pivot of a pivot axis made of silicon carbide on which the layer of graphene obtained in step f) has been generated, to obtain said watch jewel constituting a bearing or a counter-pivot.;

[0044] According to the invention, the machining of step e) and / or step g) comprises precision machining without force.

[0045] In a particularly preferred manner, step b) or f) of generating at least one layer of native epitaxial graphene is carried out by growth of the graphene by sublimation of the silicon carbide according to a method chosen from the group comprising heating in an oven and heating by a light source, under vacuum or under gas assistance.

[0046] Concretely, we generate native graphene on the silicon carbide surface of the stone intended to constitute a cushion or a counter-pivot. This native graphene will constitute a skin or layer which will cover the entire surface of the stone intended to constitute a cushion or a counter-pivot. This graphene will contribute to improving the properties of silicon carbide, with extremely high mechanical properties, for example by allowing a better coefficient of friction to be obtained, and increasing the rigidity properties as well as the maximum admissible elastic stress.

[0047] The present invention also relates to a watch jewel constituting a bearing or a counter-pivot obtained by the manufacturing method defined above.

[0048] The present invention also relates to a watch jewel constituting a bearing or a counter-pivot comprising at least one part made of silicon carbide, said part comprising at least one layer of native epitaxial graphene generated on its external surface. Advantageously, said part is intended at least to be in contact with a pivot of the pivot axis.

[0049] In a particularly advantageous manner, the watch jewel constituting a bearing or a counter-pivot is made entirely of silicon carbide, and comprises at least one layer of native epitaxial graphene generated present on at least one part intended to be in contact with a pivot of the pivot axis, and preferably on its entire external surface.

[0050] In a particularly advantageous manner, said watch jewel constitutes a bearing, the part intended to be in contact with a pivot of a pivot axis being a hole, and at least one layer of native epitaxial graphene being generated on the surface of said hole.

[0051] The present invention also relates to a watch movement and a timepiece comprising a watch jewel constituting a bearing or a counter-pivot as defined above.

[0052] Brief description of the drawings

[0053] Other characteristics and advantages of the present invention will appear on reading the following detailed description of an embodiment of the invention, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0054] - Figure 1 is a schematic view of a pivot of a pivot axis positioned in a bearing comprising a bearing and a counter-pivot according to the invention;

[0055] - figures 2a to 2d schematically represent the steps of a first variant of the manufacturing method according to the invention; and

[0056] - figures 3a to 3e schematically represent the steps of a second variant of the manufacturing method according to the invention.

[0057] Embodiments of the invention

[0058] With reference to Figure 1, there is shown for example a cone pivot 1 of a watch pivot axis 2, such as a balance staff, mounted in a bearing. Said bearing conventionally comprises a cushion-type jewel 4 and a counter-pivot-type jewel 6 supported by a setting 8. The operation and configuration of such a bearing are known to those skilled in the art and do not require further details here.

[0059] With reference to figures 2c and 2d, the bearing 4 is pierced with a hole 10 in which the pivot 1 moves. It also comprises a hollow 12 forming an oiler arranged to receive a lubricant.

[0060] The dimensions of, for example, a bearing are very small. Referring to Figure 2c, the outer diameter DE is typically between 0.5 mm and 3 mm, the thickness E is between 0.05 mm and 1 mm, and the inner diameter of the hole 10 is between 0.05 mm and 2 mm.

[0061] In another example not shown, the pivot may also be a range pivot.

[0062] The bearing 4 may be curved in the case of a cone pivot or flat in the case of a bearing pivot. The hole 10 of the bearing 4 may be cylindrical or olive-shaped.

[0063] The counter-pivot 6 is an undrilled stone, flat on the side of the pad 4 and domed on the other side. The counter-pivot 6 is placed on the pad 4, the end of the pivot 1 of the axis 2 passing through the pad 4 pressing against the flat face of the counter-pivot 6.

[0064] The stone constituting a bearing 4 or a counter-pivot 6 comprises at least one part 14 made of silicon carbide, that is to say entirely of silicon carbide. Advantageously, the part 14 is made solely of silicon carbide, without any other added element, with the exception of the inevitable impurities. Indeed, such added elements are likely to harm correct generation of native epitaxial graphene, or even prevent the generation of native epitaxial graphene.

[0065] Preferably, the silicon carbide is polycrystalline or monocrystalline. Preferably, the silicon carbide used in the invention is monocrystalline.

[0066] According to the invention, said part 14 comprises at least one layer of native epitaxial graphene 16 generated on the external surface of said part 14. Thus, the part 14 comprises a silicon carbide core and at least one external layer of native graphene 16, directly in contact with the silicon carbide core.

[0067] Advantageously, said part 14 is intended at least to be in contact with a pivot of the pivot axis.

[0068] Advantageously, the stone constituting the pad 4 or the counter-pivot 6 is made entirely of silicon carbide (with the exception of the inevitable impurities), said at least one layer of native epitaxial graphene 16 generated being present on the entire external surface of the stone, or at least on the part or the zone intended to be in contact with a pivot of the pivot axis, such as for example the surfaces of the walls of the hole 10 for the pad. The native epitaxial graphene, generated by sublimation of the silicon carbide, can be distinguished from the graphene obtained by other methods, such as by deposition of a coating, by a lower mobility of charge carriers.

[0069] More specifically, the native epitaxial graphene layer 16 has a charge carrier mobility of less than 5000 cm 2 V-1 s-1 , which allows it to be distinguished from a graphene coating obtained by deposition.

[0070] The native epitaxial graphene layer can also be distinguished from a graphene layer obtained by Raman spectroscopy deposition.

[0071] The native epitaxial graphene layer also differs from a graphene layer obtained by CVD deposition, for example, by better adhesion.

[0072] Depending on the variants, it is possible to have one or more layers of native epitaxial graphene 16.

[0073] Preferably, the native epitaxial graphene layer 16 was obtained by sublimation growth of the silicon carbide of the part 14 made of silicon carbide. Details of the process will be given below. The adhesion of such a native epitaxial graphene layer to the silicon carbide is therefore excellent, without any risk of delamination.

[0074] Preferably, the native epitaxial graphene layer 16 has a thickness of between 0.5 nm and 20 nm, preferably between 1 nm and 10 nm, and preferably between 1 nm and 5 nm, inclusive.

[0075] In a particularly advantageous manner, the part 14, with its native epitaxial graphene layer 16, and preferably the entire stone constituting the bearing 4 or the counter-pivot 6, according to the invention, has a surface hardness greater than or equal to 2000 HV, and preferably greater than or equal to 2500 HV, due to the use of silicon carbide. The Vickers hardness test methods are defined in the following standards ASTM C1327 and ISO 6507.

[0076] In a particularly advantageous manner, the external surface of the part 14 with its native epitaxial graphene layer 16, and preferably the entire stone constituting the pad 4 or the counter-pivot 6, according to the invention has a roughness Ra less than or equal to 0.5 pm, preferably less than or equal to 0.1 pm, preferably less than or equal to 50 nm, preferably less than or equal to 25 nm, preferably less than or equal to 20 nm, preferably less than or equal to 15 nm, and preferably less than or equal to 12 nm, more preferably less than or equal to 10 nm, and more preferably between 5 nm and 9 nm, limits included. The roughness Ra is defined according to the ISO 4287 standard.

[0077] The layer or layers of graphene 16 make it possible to increase the tribological properties of the stone, in particular by very drastically reducing the coefficient of friction. The stone according to the invention is therefore a part lubricated for life.

[0078] The layer or layers of graphene 16 also make it possible to increase the mechanical properties of the stone, in particular because graphene is at least 100 times stiffer than steel and tolerates extremely high elastic deformations.

[0079] Therefore, in a particularly advantageous manner, the part 14 with its layer of native epitaxial graphene 16, and preferably the entire stone constituting the bearing 4 or the counter-pivot 6, according to the invention has a very low dynamic friction coefficient, less than or equal to 0.2, preferably less than or equal to 0.1, and more preferably less than or equal to 0.05.

[0080] Furthermore, in a particularly advantageous manner, the part 14 with its layer of native epitaxial graphene 16, and preferably the entire stone constituting the pad 4 or the counter-pivot 6, according to the invention has a toughness greater than or equal to 6 MPa.m 1 / 2and a tensile strength Rm greater than or equal to 600 MPA.

[0081] In a particularly advantageous manner, the part 14 with its native epitaxial graphene layer 16, and preferably the entire stone constituting the pad 4 or the counter-pivot 6, according to the invention has a Young's modulus greater than or equal to 300 GPa. The Young's modulus, the toughness and the tensile strength are measured and calculated by tensile-compression tests known to those skilled in the art.

[0082] Thus, the combination of silicon carbide and native epitaxial graphene makes it possible to obtain a bearing or counter-pivot type stone with all the performances required for this type of watch component, namely wear resistance, low friction coefficient, smooth state (Ra < 0.5 pm) for friction and isochronism, high maximum admissible elastic stress, while eliminating the adhesion problems of thin layers traditionally deposited to improve the properties of the base material.

[0083] The invention also relates to a method of manufacturing a watch jewel constituting a bearing 4 or a counter-pivot 6 as described above, said method comprising the following steps, described in relation to Figures 2a to 2d: a) a step of manufacturing a jewel intended to constitute a bearing or a counter-pivot comprising at least one part 14 made of silicon carbide, as shown in Figures 2a to 2c, said manufacturing step comprising at least one step of machining at least said part intended to be in contact with a pivot of a pivot axis of the part 14 made of silicon carbide by precision machining without force;and b) a step of generating at least one layer of native epitaxial graphene 16 on the external surface of at least said part 14 made of silicon carbide of the stone intended to constitute a cushion or a counter-pivot obtained in step a), in particular at least on the external surface of the part intended to be in contact with a pivot of a pivot axis, to obtain said watchmaking stone constituting a cushion 4 or a counter-pivot 6, as shown in FIG. 2d.;

[0084] Step a) of the method according to the invention advantageously comprises the following sub-steps, described in relation to Figures 2a to 2d: a1) a step of manufacturing a rough part of the stone intended to constitute a bearing or a counter-pivot comprising at least one part 14 made of silicon carbide, as shown in Figure 2a; a2) a step of producing a blank of the stone intended to constitute a bearing or a counter-pivot comprising at least one part made of silicon carbide 14 at least by machining the rough part obtained in sub-step a1), as shown in Figure 2b; and a3) a step of machining at least the part made of silicon carbide 14 of the blank obtained in sub-step a2), as shown in Figure 2c, said machining step a3) comprising at least the precision machining without force of the part intended to be in contact with a pivot of a pivot axis.

[0085] According to another variant, the method of manufacturing a watch jewel constituting a bearing 4 or a counter-pivot 6 comprising at least one part 14 made of silicon carbide which comprises at least one part intended to be in contact with a pivot of a pivot axis according to the invention may comprise, with reference to Figures 3a to 3e: c) a step of manufacturing a rough part of the jewel intended to constitute a bearing or a counter-pivot comprising at least one part 14 made of silicon carbide, as shown in Figure 3a, this step corresponding to sub-step a1) of the first variant of the method;d) a step of producing a blank of the stone intended to constitute a bearing or a counter-pivot comprising at least one part 14 made of silicon carbide at least by machining the raw part obtained in step c), as shown in Figure 3b, this step corresponding to sub-step a2) of the first variant of the method; e) at least one step of machining the part made of silicon carbide 14 of the blank obtained in step d) to form the part intended to be in contact with a pivot of a pivot axis, such as the hole 10, as shown in Figure 3c, said hole 10 being able to be olived during this step e);f) a step of generating at least one layer of native epitaxial graphene 16 on the external surface of at least the part 14 made of silicon carbide of the blank obtained in step e), and in particular on said part intended to be in contact with a pivot of a pivot axis, such as the surfaces of the hole 10 for example, as shown in FIG. 3d, this step being similar to step b) of the first variant of the method; and g) at least one step of machining the blank obtained in step f), with the exception of said part intended to be in contact with a pivot of a pivot axis made of silicon carbide on which the graphene layer 16 obtained in step f) has been generated, to obtain said watch jewel constituting a bearing 4 or a counter-pivot 6, as shown in FIG. 3e.;

[0086] The machining of step e) and / or step g) includes precision machining without force.

[0087] According to another embodiment applied specifically to a watchmaking stone constituting a bearing 4 comprising at least one part 14 made of silicon carbide, said part 14 comprising a hole 10 intended to be in contact with a pivot of a pivot axis, a method of manufacturing said bearing may comprise: a') a step of manufacturing a stone intended to constitute a bearing comprising at least the part 14 made of silicon carbide comprising said one hole 10, or a blank of such a stone; and b') a step of generating at least one layer of native epitaxial graphene 16 at least on the external surface of the hole 10 of the part 14 made of silicon carbide of the stone intended to constitute a bearing or its blank obtained in step a) to obtain said bearing 4 or a blank.

[0088] According to a variant, step a') makes it possible to obtain a practically finished pad, in which only the graphene layers generated according to step b') are missing, in a similar manner to the method comprising steps a) and b). Step a') may comprise the same sub-steps a1) to a3) as step a) according to the invention, with force-free precision machining preferably being used in step a3).

[0089] According to another variant, step a') makes it possible to obtain a bearing blank in which at least the hole 10 is machined, preferably by precision machining without force, the graphene layers being generated at least on the surface of the hole 10 according to step b'), and the method then comprises at least one additional machining step (preferably precision machining without force) of the blank obtained in step b'), with the exception of the hole 10, to obtain the finished bearing 4, in a similar manner to the method according to steps c) to g).

[0090] All information in the description above and below relating to the methods according to steps a) to b) or c) to g) according to the invention also applies to the method according to steps a') to b').

[0091] Advantageously, the stone intended to constitute a bearing or a counter-pivot is formed in its entirety by said part 14 consisting entirely of silicon carbide, with the exception of the inevitable impurities, the at least one layer of native epitaxial graphene 16 being generated on its entire external surface, or at least on the external surface of the part intended to be in contact with a pivot of a pivot axis, so that said watchmaking stone constituting a bearing 4 or a counter-pivot 16 obtained is entirely made of silicon carbide totally covered with at least one layer of native epitaxial graphene 16 or at least the part intended to be in contact with a pivot of the pivot axis, such as the walls of the hole 10, has at least one layer of native epitaxial graphene 16,the native epitaxial graphene layer generated on the parts which are not intended to be in contact with a pivot of the pivot axis may have been removed by subsequent machining according to step g). Advantageously, with reference to Figure 2a or 3a, sub-step a1) or step c) is carried out by laser, water jet or any other material removal method or by suitable cutting. Preferably, the rough part of the stone intended to constitute a bearing or a counter-pivot is made entirely of silicon carbide, with the exception of unavoidable impurities. Such a rough part is obtained for example from wafers of monocrystalline, polycrystalline silicon carbide or in any other crystalline configuration.,

[0092] Advantageously, the machining carried out in sub-step a2) or step d) to produce the blanks is machining by material removal, using methods similar to those of sub-step a1) or step c). The blank obtained is in the form of a flat, undrilled stone, as shown in Figure 2b or 3b. This blank is produced if necessary with the dimensions necessary to obtain a bearing or counter-pivot ultimately having the desired geometric characteristics, taking into account all the steps of the process.

[0093] In the case of the first variant of the method, with reference to figure 2c, the machining carried out during sub-step a3) consists of carrying out different operations necessary to obtain a bearing or a counter-pivot, such as drilling the hole 10, machining the internal diameter DI of the hole 10, machining the external diameter DE of the stone, machining the hollow 12 and the convexity if necessary, and the olive-shaping of the hole 10, all or part of these operations being carried out according to the destination of the stone.

[0094] In the case of the second variant of the method, with reference to figure 3c, the machining carried out during step e) consists of carrying out different operations necessary to obtain the part intended to be in contact with a pivot of a pivot axis of a bearing or a counter-pivot, such as drilling the hole 10, machining the internal diameter DI of the hole 10, machining the hollow 12 and olive-cutting the hole 10 in the case of a bearing for example.

[0095] With reference to Figure 3e, the machining carried out during step g) consists of carrying out various operations necessary to obtain a bearing or a counter-pivot, not carried out in step e), such as the machining of the external diameter DE of the stone, the machining of the hollow 12 if it has not been formed in step e), the machining of the camber if necessary, all or part of these operations being carried out depending on the destination of the stone.

[0096] All or part of these operations can be carried out using traditional machining methods.

[0097] According to the invention, all or part of the machining operations carried out during step a), and more particularly during sub-step a3), step e) or step g) is carried out by precision machining without force of at least the part intended to be in contact with a pivot of a pivot axis of the part 14 made of silicon carbide of the blank in the case of sub-step a3), at least of the part intended to be in contact with a pivot of a pivot axis made of silicon carbide in the case of step e), or at least of the part 14 made of silicon carbide on which the native epitaxial graphene layer 16 was generated during step f) and which is not intended to be in contact with a pivot of the pivot axis in the case of step g).

[0098] For example, drilling and olive cutting can be carried out by precision machining without force, the other machining operations of the internal diameter DI of the hole 10, the external diameter DE of the stone, the hollowing 12 and the doming if necessary, being carried out in the traditional manner.

[0099] In this description, forceless machining is defined as unconventional machining in which there is no mechanical action transmitted by direct contact and force between a tool and the workpiece, unlike conventional machining where there is direct contact between the tool and the workpiece and in which significant cutting forces are involved. Forceless machining is therefore machining without direct contact between the workpiece and a machining tool that would be likely to exert a force or stress on said workpiece.

[0100] Advantageously, the force-free precision machining carried out during step a), and more particularly during sub-step a3), during step e) or during step g) is femto laser turning, ECM electrochemical turning, or electroerosion turning (for example wire EDM). The machining operations of either of this step a3) or e) or g) are advantageously carried out by femtosecond pulsed laser micromachining with a laser of wavelengths of, for example, between 200 nm and 2000 nm, preferably between 400 nm and 1000 nm, inclusive. The laser parameters can be for example: average power between 1 W and 100 W, energy per pulse between 20 J and 4000 pJ, frequency between 100 kHz and 1000 kHz, pulse duration between 100 fs and 2 ps. Femto laser turning attacks the rotating part radially and not normally, and without heat transfer.

[0101] In a particularly advantageous manner, in the case of the first variant of the method, the sub-step a3) of precision machining without force is the last sub-step of the manufacturing step a) of the stone intended to constitute a bearing or a counter-pivot making it possible to obtain at least one part 14 made of finished silicon carbide on the external surface of which at least one layer of native epitaxial graphene 16 will be generated according to step b).

[0102] Thanks to the precision machining without force by femto laser, this last operation of the process for preparing the stone intended to constitute a bearing or a counter-pivot makes it possible to achieve surface states with a roughness Ra preferably less than or equal to 100 nm. Preferably, at least the part 14 made of finished silicon carbide obtained in sub-step a3) has a roughness Ra less than or equal to 0.5 pm, and preferably less than or equal to 0.1 pm, preferably less than or equal to 50 nm, preferably less than or equal to 25 nm, preferably less than or equal to 20 nm, preferably less than or equal to 15 nm, and preferably less than or equal to 12 nm, more preferably less than or equal to 10 nm, and more preferably between 5 nm and 9 nm, limits included, which makes it possible to avoid traditional finishing operations, such as polishing, requiring moving the stones to a finishing machine different from the machining machine.

[0103] It is considered that the native epitaxial graphene layer 16, given its thickness, does not modify the dimensions and geometry of the component obtained in sub-step a3), nor its roughness. In the context of the second variant of the method, in a particularly advantageous manner, the force-free precision machining step g) is the last step of the method for manufacturing the watch jewel constituting a bearing 4 or a counter-pivot 6.

[0104] Thanks to the precision machining without force by femto laser, this last operation of the manufacturing process of the bearing 4 or the counter-pivot 6 makes it possible to achieve surface states with a roughness Ra preferably less than or equal to 100 nm. Preferably, the external surface of the part intended to be in contact with a pivot of a pivot axis made of silicon carbide on which at least one layer of native epitaxial graphene 16 obtained in step f) has been generated and the external surface of the part not intended to be in contact with a pivot of a pivot axis obtained in step g) have a roughness Ra less than or equal to 0.5 pm, and preferably less than or equal to 0.1 pm, preferably less than or equal to 50 nm, preferably less than or equal to 25 nm, preferably less than or equal to 20 nm, preferably less than or equal to 15 nm, and preferably less than or equal to 12 nm, more preferably less than or equal to 10 nm, and more preferably between 5 nm and 9 nm, inclusive, which makes it possible to avoid traditional finishing operations, such as polishing, requiring the stones to be moved to another finishing machine.

[0105] With reference to Figure 2d or 3d, step b) or step f) of generating at least one layer of native epitaxial graphene 16 is carried out by growing native thermal graphene on the surface of at least the part 14 made of silicon carbide of the stone intended to constitute a pad or a counter-pivot or at least on the external surface of the part intended to be in contact with a pivot of a pivot axis, by sublimation of the silicon carbide, preferably according to a method chosen from the group comprising heating in a vacuum or gas-assisted furnace, heating by a light source (infrared lamp or infrared laser) in vacuum or gas-assisted enclosures, or by any other suitable method. The generation of multiple layers of native graphene can also be done for example by methods using hydrogen.

[0106] Preferably, the native epitaxial graphene layer 16 has a thickness of between 0.5 nm and 20 nm, preferably between 1 nm and 10 nm, and preferably between 1 nm and 5 nm.

[0107] The method according to the invention makes it possible to obtain a watchmaking stone constituting a bearing or a counter-pivot having improved mechanical properties, in particular better rigidity and a very low coefficient of friction. In addition, when the machining of the stone is carried out by precision machining without force, a particularly rapid and simple process is obtained. Indeed, the method according to the invention makes it possible to eliminate all the finishing operations requiring movement of the stones between the machining machine and the finishing machines traditionally used, so that the number of operations necessary for the manufacture of the stone is reduced, the production time being considerably reduced.

[0108] For example, machining a complete bearing by femto laser takes, considering only femto laser operations, between 12 and 18 seconds, according to the current state of the art. This time includes the machining operations of the outer diameter, the inner diameter, the oliveing ​​of the latter, the machining of the hollow and the crown. Thus, depending on the machining required for the bearing or the counter-pivot, this time can be further reduced and optimized.

[0109] In addition, the use of silicon carbide advantageously makes it possible to easily form at least one layer of native epitaxial graphene.

[0110] Furthermore, the graphene layer is hydrophobic, which improves the stone's resistance to corrosion. The graphene layer, which has a very low dynamic friction coefficient, also eliminates lubrication.

Claims

Demands 1. A method for manufacturing a watch jewel constituting a bearing (4) or a counter-pivot (6) comprising at least one part (14) made of silicon carbide which includes at least one part intended to be in contact with a pivot of a pivot axis, comprising: a) a manufacturing step of a jewel intended to constitute a bearing or a counter-pivot comprising at least one part (14) made of silicon carbide, said manufacturing step comprising at least one machining step of at least said part intended to be in contact with a pivot of a pivot axis of the part (14) made of silicon carbide;and b) a step of generating at least one layer of native epitaxial graphene (16) on the external surface of at least the portion (14) made of silicon carbide of the stone intended to constitute a bearing or a counter-pivot obtained in step a) to obtain said watch stone constituting a bearing (4) or a counter-pivot (6); characterized in that the machining of at least said portion intended to be in contact with a pivot of a pivot axis of the portion (14) made of silicon carbide of step a) comprises precision machining without force.; 2. A method according to claim 1, characterized in that step a) comprises the following substeps: a1) a step of manufacturing a rough piece of the stone intended to constitute a bearing or a counter-pivot comprising at least one portion (14) made of silicon carbide; a2) a step of producing a blank of the stone intended to constitute a bearing or a counter-pivot comprising at least one portion (14) made of silicon carbide by machining the rough piece obtained in substep a1); and a3) a step of machining at least the portion (14) made of silicon carbide of the blank obtained in substep a2). said machining step a3) comprising at least the precision machining without force of the part intended to be in contact with a pivot of a pivot axis. Method for manufacturing a watch jewel constituting a bearing (4) or a counter-pivot (6) comprising at least one part (14) made of silicon carbide which includes at least one part intended to be in contact with a pivot of a pivot axis, comprising: c) a step of manufacturing a rough piece of the jewel intended to constitute a bearing or a counter-pivot comprising at least one part (14) made of silicon carbide; d) a step of producing a blank of the jewel intended to constitute a bearing or a counter-pivot comprising at least one part (14) made of silicon carbide by machining the rough piece obtained in step c);(e) at least one machining step of the portion (14) made of silicon carbide of the blank obtained in step (d) to form the portion intended to be in contact with a pivot of a pivot axis; (f) a step of generating at least one layer of native epitaxial graphene (16) on the external surface of at least the portion (14) made of silicon carbide of the blank obtained in step (e); and (g) at least one machining step of the blank obtained in step (f), with the exception of said portion intended to be in contact with a pivot of a pivot axis made of silicon carbide on which the layer of native epitaxial graphene (16) was generated in step (f), to obtain said watch jewel constituting a bearing (4) or a counter-pivot (6);characterized in that the machining of step e) and / or step g) comprises precision machining without force. Method according to claim 2, characterized in that substep a3) of precision machining without force is the last substep of the manufacturing step a) of the stone intended to constitute a bearing or a counter pivot for obtaining at least a part (14) made of carbide; finished silicon on the external surface of which at least one layer of native epitaxial graphene is generated (16) according to step b).

5. A method according to claim 4, characterized in that at least the portion (14) made of finished silicon carbide obtained in substep a3) has a roughness Ra less than or equal to 0.5 pm, and preferably less than or equal to 0.1 pm, preferably less than or equal to 50 nm, preferably less than or equal to 25 nm, preferably less than or equal to 20 nm, preferably less than or equal to 15 nm, and preferably less than or equal to 12 nm, more preferably less than or equal to 10 nm, and more preferably between 5 nm and 9 nm, inclusive.

6. Method according to claim 3, characterized in that the step g) of precision machining without force is the last step of the method of manufacturing the watchmaking stone constituting a bearing (4) or a counter pivot (6).

7. A method according to claim 6, characterized in that the external surface of said part intended to be in contact with a pivot of a pivot axis made of silicon carbide on which at least one layer of native epitaxial graphene (16) obtained in step f) has been generated and the external surface of the part not intended to be in contact with a pivot of a pivot axis obtained in step g) have a roughness Ra less than or equal to 0.5 pm, and preferably less than or equal to 0.1 pm, preferably less than or equal to 50 nm, preferably less than or equal to 25 nm, preferably less than or equal to 20 nm, preferably less than or equal to 15 nm, and preferably less than or equal to 12 nm, more preferably less than or equal to 10 nm, and more preferably between 5 nm and 9 nm, inclusive.

8. A method according to any one of the preceding claims, characterized in that the forceless precision machining carried out in step a), respectively in step e) or in step g), is a femto laser turning, an electrochemical turning, or an electro-erosion turning.

9. A method according to any one of the preceding claims, characterized in that step b) or f) of generating at least one epitaxial graphene layer native (16) is produced by growing graphene by sublimation of silicon carbide according to a process selected from the group comprising heating in a furnace and heating by a light source. A process according to any one of the preceding claims, characterized in that the native epitaxial graphene layer (16) has a thickness of between 0.5 nm and 20 nm, preferably between 1 nm and 10 nm, and preferably between 1 nm and 5 nm. A process according to any one of claims 2 to 10, characterized in that substep a1) and / or a2), respectively step c) and / or d), is carried out by machining by material removal or by cutting. A process according to claim 11, characterized in that the machining carried out during substep a2) or step d) is machining by material removal.A method according to any one of the preceding claims, characterized in that the stone intended to constitute a bearing (4) or a counter-pivot (6) is made entirely of silicon carbide, and in that at least one layer of native epitaxial graphene (16) is generated over its entire external surface. A watch stone constituting a bearing (4) or a counter-pivot (6) obtained by the method according to any one of claims 1 to 13. A watch stone constituting a bearing (4) or a counter-pivot (6) comprising at least one portion (14) made of silicon carbide which includes at least one portion intended to be in contact with a pivot of a pivot axis, characterized in that said portion (14) comprises at least one layer of native epitaxial graphene (16) generated on its external surface.watchmaking stone constituting a bearing (4) or a counter-pivot (6) according to claim 15, characterized in that the native epitaxial graphene layer has a charge carrier mobility of less than 5000 cm. 2 V-1 s-1.

17. Watchmaking stone constituting a bearing (4) or a counter-pivot (6) according to any one of claims 15 to 16, characterized in that the native epitaxial graphene layer (16) was obtained by sublimation growth of silicon carbide from the part (14) made of silicon carbide.

18. Watchmaking stone constituting a bearing (4) or a counter-pivot (6) according to any one of claims 15 to 17, characterized in that the native epitaxial graphene layer (16) has a thickness between 0.5 nm and 20 nm, preferably between 1 nm and 10 nm, and preferably between 1 nm and 5 nm.

19. Watchmaking stone constituting a bearing (4) or a counter-pivot (6) according to any one of claims 15 to 18, characterized in that the external surface of the part (14) made of silicon carbide covered with at least one layer of native epitaxial graphene (16) has a roughness Ra less than or equal to 0.5 pm, and preferably less than or equal to 0.1 pm, preferably less than or equal to 50 nm, preferably less than or equal to 25 nm, preferably less than or equal to 20 nm, preferably less than or equal to 15 nm, and preferably less than or equal to 12 nm, more preferably less than or equal to 10 nm, and more preferably between 5 nm and 9 nm, inclusive.

20. Watchmaking stone constituting a bearing (4) or a counter-pivot (6) according to any one of claims 15 to 19, characterized in that it is made entirely of silicon carbide, and in that it comprises at least one layer of native epitaxial graphene (16) generated present on at least one part intended to be in contact with a pivot of a pivot axis, and preferably on its entire external surface.

21. Watchmaking stone constituting a bearing (4) or a counter-pivot (6) according to any one of claims 15 to 20, characterized in that the silicon carbide is monocrystalline.

22. Watchmaking stone constituting a bearing (4) according to one of the claims 15 to 21, the part intended to be in contact with a pivot of an axis of pivoting being a hole (10), characterized in that at least one layer of native epitaxial graphene (16) is generated on the surface of said hole (10).

23. A watch jewel constituting a bearing (4) according to claim 22, characterized in that the jewel is a flat or domed bearing.

24. A watch jewel constituting a bearing (4) according to any one of the claims 22 to 23, characterized in that the hole (10) is cylindrical or olive-shaped.

25. Watch movement comprising a watch jewel constituting a bearing (4) or a counter-pivot (6) according to any one of claims 15 to 24.

26. A timepiece comprising a timepiece movement according to claim 25 or a timepiece jewel constituting a bearing (4) or a counter-pivot (6) according to any one of claims 15 to 24.

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