CH719428A2 - Clockwork stone and process for manufacturing such a stone. - Google Patents

Abstract

The present invention relates to a timepiece constituting a bearing (4) or a counter-pivot comprising at least one part (14) made of silicon carbide, said part (14) comprising at least one layer of native epitaxial graphene (16). ) generated on its external surface. The present invention also relates to a method of manufacturing such a stone (4), said method comprising: a) a step of manufacturing a stone intended to constitute a cushion or a counter-pivot comprising at least one 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 part (14) consisting of silicon carbide of the stone intended to constitute a cushion or a counter- pivot obtained in step a) to obtain said timepiece constituting a bearing (4) or a counter-pivot.

Description

Technical area

[0001] The present invention relates to a timepiece constituting a bearing or a counter-pivot comprising at least one part made of silicon carbide.

[0002] The present invention also relates to a watch movement and a timepiece comprising such a stone.

[0003] The present invention also relates to a process for manufacturing such a stone.

State of the art

[0004] A watchmaking stone constituting a pivot bearing or bearing is a part comprising a recess forming an oil cup receiving a lubricant, said stone being pierced with a hole in which a pivot of a pivot axis moves.

[0005] A watchmaking stone constituting a counter-pivot is an undrilled stone, flat on one side and convex on the other. The counter-pivot is placed on the bushing, the end of the axle pivot passing through the bushing pressing against the flat face of the counter-pivot.

[0006] 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. Ruby being very expensive, it was proposed for example in patent FR 2322113 to replace it with sintered silicon carbide enriched with 3 to 4% by weight of boron carbide.

[0007] The quality of the pivots and stones is of primary importance for the stability of operation, the autonomy of operation and for the longevity of a mechanical watch.

[0008] A bearing is required to work with a minimum of friction and to maintain this quality as long as possible. To achieve this dual requirement, the pivot, the stone and the lubricant must meet certain conditions, namely: • the surface condition of the pivots and stones must be as careful as possible • the diameter of the pivots must be small, especially for the balance-escapement regulating body • 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 on the stems or on the stones outside of a certain limit.

[0009] To retain a maximum quantity of oil for a pivot of given dimensions, it is necessary to create a capillary angle of approximately 20° between the pivot and the oiler, which allows the oiler to maintain the oil. stably. There must also be sufficient “play” between the pivot and the hole in the stone. If this clearance is insufficient, the oil cannot form a lubricant buffer between the walls of the hole and the pivot.

[0010] There are two main types of pivots: the span pivot and the cone pivot. Reach pivots are used in the gears up to the escape wheel except in very high quality movements where they go up to the seconds wheel. Cone pivots are used for the balance axis and escape wheel in high quality watches.

[0011] In watchmaking, fluid lubrication is an excellent solution in terms of a good coefficient of friction and low wear rates. However, oil is not free from defects: it spreads, leaks, becomes contaminated, turns red, gums and blocks the mechanism if it is too old.

[0012] Studies have focused on dry lubricants or even self-lubricating mechanical surfaces or devices. Research also revolves around the qualities of diamond or silicon. Some offer even different solutions for certain very specific applications, such as watchmaking ball bearings without lubrication, in which the balls are made of a special alloy.

Friction is defined by a dimensionless coefficient, denoted µ. In the present application, a friction coefficient is a dynamic friction coefficient. It is characterized by the following relationship: µ = Ft/Fn, where Ftest the friction force and Fnthe normal load on the surface.

[0014] The dynamic friction coefficient µ can vary greatly depending, among other things, on the state of the surfaces and environmental parameters. Thus, for metal-metal contact in air, µ 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.

[0015] Tribology is the science which studies friction. We then speak of tribological contact when two surfaces are put into relative movement with respect 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 deformations and chemical changes at different scales, as well as the transfer of materials.

[0016] Five main parameters influence the 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 weariness of partners. All these phenomena influence friction and result in energy losses in contact. Friction generates mechanical energy in the form of heat.

[0017] This rise in temperature promotes the phenomena of welding, diffusion of elements or even reaction with the ambient environment (oxidation, salt formation). Furthermore, 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.

[0018] Lubrication in watchmaking has three main objectives: • allow the conservation of isochronism • reduce wear • reduce energy loss through friction.

[0019] In addition, the lubricant must be chemically stable, that is to say, retain its properties over time. The lubricant must hold well in place, not be subject to the phenomenon of 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.

[0020] Lubrication is obtained by application of foreign bodies placed between the partners, preventing direct contact of the materials and resulting in a reduction in friction, therefore energy losses, a reduction in wear, and an increase mechanical performance. It can be in three forms: solid, liquid or gas.

[0021] PVD (abbreviation for Physical Vapor Deposition) is a technique for producing thin layers of lubricating coatings.

[0022] This process has been used for several years in industries, particularly in the watchmaking industry for surface finishes. It makes it possible to deposit metals for which a deposit is difficult to achieve using the traditional galvanic method, or to deposit ceramics from metals with interesting properties from a mechanical, chemical or even aesthetic point of view.

For example, deposition can be carried out by cathode sputtering. It is a plasma vacuum deposition technique. It is done at room temperature in an enclosure maintained at low pressure (around 10<-1> to 10<-2>Pa). It allows all types of materials to be deposited, whether simple or compound, conductive or dielectric, on all types of substrates, conductive or not, which can be placed under vacuum and withstand slight heating.

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

The growth of the layer depends on the surface state on which it grows. The layer reproduces the same surface condition, so that the roughness or surface defects will be found in the layer. It is by this method that, for example, lubricating coatings such as silico titanium carbide (TiSiC) and amorphous carbon are deposited.

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 in tension.

[0027] The tribological properties of this deposit are influenced by the transfer of elements between the partners in contact, the reduction in roughness during contact break-in, the tribochemical reactions between TiC and H2O in the atmosphere leading to the formation a protective layer of titanium oxide (TiOx) on the surface, and the release of amorphous carbon atoms.

[0028] The hardness of the deposit obtained is approximately 1000 to 1200HV. Its color is metallic gray, similar to steel.

[0029] The amorphous carbon coating, known under the English name “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, named sp<2>, corresponds to the graphitic form of carbon. This hybridization forms a soft material, thermal and electrical conductor, black in color. It has a sheet structure, the atoms of which are arranged in hexagons. Covalent bonds, therefore strong, link the atoms of the same sheet together while Van der Waals bonds, weak bonds, link the sheets together, which is at the origin of the lubricating properties of graphite.

The second hybridization, called sp<3>, is the diamond form of carbon. This hybridization of carbon is hard, transparent, insulating and has a face-centered cubic structure, with covalent bonds.

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

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

[0034] However, the deposition of a hard coating has the disadvantage of leading to 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 beyond. disrupt the functioning of the latter, which is not satisfactory.

The present invention aims to remedy these drawbacks by proposing a process for manufacturing a timepiece stone constituting a bearing or a counter-pivot going beyond the current state of the art.

[0036] Another aim of the invention is to propose a manufacturing process making it possible to manufacture extremely quickly and reliably watchmaking stones constituting a bearing or a counter-pivot, components intended for watch movements whose demands in terms of performance and isochronism are extremely high.

Another aim of the invention is to propose a timepiece stone constituting a bearing or a counter-pivot having a surface whose properties are very significantly increased or improved compared to existing components.

Disclosure of the invention

[0038] For this purpose, the invention relates to a method of manufacturing a watchmaking stone constituting a bearing or a counter-pivot comprising at least one part made of silicon carbide, said method comprising: a) a step of manufacture of a stone intended to constitute a bearing or a counter-pivot comprising at least one 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 bearing or a counter-pivot obtained in the step a) to obtain said timepiece stone constituting a bearing or a counter-pivot.

[0039] According to another variant, the invention relates to a process for manufacturing a timepiece stone constituting a bearing or a counter-pivot comprising at least one part made of silicon carbide, said process comprising: c) a step manufacturing a raw piece of stone 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 stone intended to constitute a bearing or a counter-pivot comprising at least one part made of silicon carbide at least by machining the raw 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 at least one 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 at least said part intended to be in contact with a pivot of a pivot axis made of carbide of silicon on which the graphene layer obtained in step f) was generated, to obtain said timepiece constituting a bearing or a counter-pivot.

[0040] 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 graphene by sublimation of silicon carbide according to a process chosen from the group comprising heating in an oven and heating by a light source, under vacuum or under gas assistance.

Concretely, we proceed to the generation of native graphene on the silicon carbide surface of the stone intended to constitute a bearing 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 making it possible to obtain a better coefficient of friction, and to increase the rigidity properties as well as the maximum admissible elastic stress.

[0042] The present invention also relates to a timepiece stone constituting a bearing or a counter-pivot obtained by the manufacturing process defined above.

[0043] The present invention also relates to a timepiece 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.

[0044] In a particularly advantageous manner, the timepiece 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 over its entire external surface.

[0045] The present invention also relates to a watch movement and a timepiece comprising a timepiece constituting a bearing or a counter-pivot as defined above.

Brief description of the drawings

[0046] 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 drawings appended in which: – 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; – Figures 2a to 2d schematically represent the steps of a first variant of the manufacturing process according to the invention; and – Figures 3a to 3e schematically represent the steps of a second variant of the manufacturing process according to the invention.

Modes of carrying out the invention

[0047] Referring to Figure 1, there is shown for example a cone pivot 1 of a watch pivot axis 2, such as a balance axis, mounted in a bearing. Said bearing conventionally comprises a cushion-type stone 4 and a counter-pivot type stone 6 supported by a bezel 8. The operation and configuration of such a bearing are known to those skilled in the art and do not require more detail here. details.

[0048] With reference to Figures 2c and 2d, the bearing 4 is pierced with a hole 10 in which the pivot 1 moves. It also includes a recess 12 forming an oil cup arranged to receive a lubricant.

[0049] The dimensions, for example, of a bearing are very small. With reference to Figure 2c, the exterior diameter DE is typically between 0.5 mm and 3 mm, the thickness E is between 0.05 mm and 1 mm, and the interior diameter of the hole 10 is between 0.05 mm and 2 mm.

[0050] In another example not shown, the pivot can also be a reach pivot.

The bearing 4 can be curved in the case of a cone pivot or flat in the case of a reach pivot.

The hole 10 of the bearing 4 can be cylindrical or olive-shaped.

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

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, part 14 consists solely of silicon carbide, with no other added element, with the exception of the inevitable impurities. Indeed, such added elements are likely to hinder correct generation of native epitaxial graphene, or even to prevent the generation of native epitaxial graphene.

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

[0056] 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, part 14 comprises a core of silicon carbide and at least one layer of graphene native 16 exterior, directly in contact with the silicon carbide core.

[0057] Advantageously, said part 14 is intended at least to be in contact with a pivot of the pivot axis

[0058] Advantageously, the stone constituting the bearing 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 over the entire external surface of the stone, or at least on the part intended to be in contact with a pivot of the pivot axis, such as for example the surfaces of the hole 10 for the bearing.

[0059] Native epitaxial graphene, generated by sublimation of silicon carbide, can be distinguished from graphene obtained by other processes, such as by deposition of a coating, by a lower mobility of charge carriers.

[0060] More particularly, the native epitaxial graphene layer 16 has a charge carrier mobility of less than 5000 cm<2>V-1 s-1, which makes it possible to distinguish it from a graphene coating obtained by deposition.

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

[0062] The native epitaxial graphene layer also differs from a graphene layer obtained by CVD deposition, for example by better adhesion.

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

[0064] Preferably, the layer of native epitaxial graphene 16 was obtained by growth by sublimation of the silicon carbide of the part 14 consisting of silicon carbide. Details of the process will be given below. The adhesion of such a layer of native epitaxial graphene to silicon carbide is therefore excellent, without any risk of delamination.

Preferably, the layer of native epitaxial graphene 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, limits included.

[0066] In a particularly advantageous manner, 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 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. Vickers hardness testing methods are defined in the following standards ASTM C1327 and ISO 6507.

[0067] In a particularly advantageous manner, the external surface of 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 roughness Ra less than or equal to 0.5 µm, preferably less than or equal to 0.1 µm, 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.

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.

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 more rigid than steel and tolerates extremely high elastic deformations.

[0070] As a result, in a particularly advantageous manner, 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 coefficient very low dynamic friction, 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.

[0071] Furthermore, 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 greater toughness. or equal to 6 MPa.m<1/2> and a tensile strength Rm greater than or equal to 600 MPA.

[0072] 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 Young's modulus greater than or equal to 300 GPa.

[0073] Young's modulus, toughness and tensile strength are measured and calculated by traction-compression tests known to those skilled in the art.

[0074] Thus, the combination of silicon carbide and native epitaxial graphene makes it possible to obtain a cushion or counter-pivot type stone having all the performances required for this type of watch component, namely resistance to wear, coefficient of low friction, smooth state (Ra < 0.5 µm) 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.

[0075] The invention also relates to a process for manufacturing a timepiece stone constituting a bearing 4 or a counter-pivot 6 as described above, said process comprising the following steps, described in relation to the Figures 2a to 2d: a) a step of manufacturing a stone 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; 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 consisting of silicon carbide of the stone intended to constitute a bearing or a counter-pivot obtained at step a) to obtain said timepiece constituting a bearing 4 or a counter-pivot 6, as shown in Figure 2d.

[0076] 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 raw piece of stone intended to constitute a bearing or 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 raw 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 substep a2), as shown in Figure 2c.

[0077] According to another variant, the method of manufacturing a timepiece stone constituting a bearing 4 or a counter-pivot 6 comprising at least one part 16 made of silicon carbide according to the invention may comprise, with reference to the Figures 3a to 3e: c) a step of manufacturing a raw piece of stone 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 substep 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 a 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 consisting 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 Figure 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 at least said part intended to be in contact with a pivot of a pivot axis made of carbide of silicon on which the graphene layer 16 obtained in step f) was generated, to obtain said timepiece constituting a bearing 4 or a counter-pivot 6, as shown in Figure 3e.

[0078] Advantageously, the stone intended to constitute a bearing or a counter-pivot is formed entirely 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 over its entire external surface, so that said timepiece constituting a bearing 4 or a counter-pivot 16 obtained is entirely made of silicon carbide completely 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 has at least one layer of native epitaxial graphene 16, the layer of native epitaxial graphene generated on the parts which are not intended to be in contact with a pivot of the pivot axis may have been eliminated by subsequent machining according to step g).

[0079] Advantageously, with reference to Figure 2a or 3a, sub-step a1) or step c) is carried out by machining methods by laser, by water jet or any other method material removal or by appropriate cutting. Preferably, the raw piece of stone intended to constitute a bearing or a counter-pivot is made entirely of silicon carbide, with the exception of the inevitable impurities. Such a raw part is obtained for example from monocrystalline, polycrystalline silicon carbide wafers or in any other crystalline configuration.

[0080] Advantageously, the machining carried out during sub-step a2) or step d) to produce the blanks is machining by removal of material, using methods similar to those of sub-step -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 necessary dimensions to obtain a bearing or a counter-pivot ultimately presenting the desired geometric characteristics, taking into account all the stages of the process.

[0081] 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 bearing. 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 recess 12 and the convex if necessary, and the oliveing of the hole 10, all or part of these operations being carried out depending on the destination of the stone.

[0082] 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 the drilling of the hole 10, the machining of the internal diameter DI of the hole 10, the machining of the recess 12 and the olive of hole 10 in the case of a bearing for example.

[0083] With reference to Figure 3e, the machining carried out in step g) consists of carrying out different 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 recess 12 if it was not formed in step e), the machining of the convex if necessary, all or part of these operations being carried out according to the destination of the stone.

[0084] All or part of these operations can be carried out by traditional machining methods.

[0085] Advantageously, all or part of the machining operations carried out during sub-step a3), step e) or step g) is carried out by precision machining without force at the less of the part 14 consisting 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), and at least of the part 14 consisting of silicon carbide on which the layer of native epitaxial graphene 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).

[0086] For example, drilling and olive drilling 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 recess 12 and the convex if necessary, being carried out in the traditional way.

[0087] In the present description, non-conventional machining is called force-free machining in which there is no mechanical action transmitted by direct contact and force between a tool and the part, unlike conventional machining where there is direct contact between the tool and the workpiece and in which significant cutting forces are involved. Force-free machining is therefore machining without direct contact between the part to be machined and a machining tool which would be likely to exert a force or stress on said part.

[0088] Advantageously, the force-free precision machining carried out during sub-step a3), during step e) or during step g) is femto laser turning, turning electrochemical ECM, or electrical discharge turning (e.g. wire EDM).

[0089] The machining operations of one or the other of this step a3) or e) or g) are advantageously carried out by femto-second pulsed laser micromachining with a laser of wavelengths included for example between 200 nm and 2000 nm, preferably between 400 nm and 1000 nm, limits included. The laser parameters can be for example: average power between 1 W and 100 W, energy per pulse between 20 µJ and 4000 µJ, frequency between 100 kHz and 1000 kHz, pulse duration between 100 fs and 2 ps. Femto laser turning attacks the part rotating radially and not normally, and without heat transfer.

[0090] In a particularly advantageous manner, in the case of the first variant of the process, substep a3) of precision machining without force is the last substep of step a) of manufacturing 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).

[0091] Thanks to force-free precision machining by femto laser, this last operation of the process of preparing the stone intended to constitute a bearing or a counter-pivot makes it possible to achieve surface conditions with a roughness Ra preferably less than or equal to 100 nm. Preferably, at least the part 14 consisting of finished silicon carbide obtained in substep a3) has a roughness Ra less than or equal to 0.5 µm, and preferably less than or equal to 0.1 µm, 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, terminals included, which avoids traditional finishing operations, such as polishing, requiring moving the stones to a finishing machine different from the machining machine.

[0092] 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 substep a3), nor its roughness.

[0093] In the context of the second variant of the process, in a particularly advantageous manner, step g) of precision machining without force is the last step of the process of manufacturing the watch stone constituting a bearing 4 or a counter-pivot 6.

[0094] Thanks to force-free precision machining 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 conditions with a roughness Ra preferably less than or equal to 100nm. 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) is 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 µm, and preferably less than or equal to 0.1 µm, 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 at 10 nm, and more preferably between 5 nm and 9 nm, terminals included, which makes it possible to avoid traditional finishing operations, such as polishing, requiring moving the stones to another finishing machine.

[0095] 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 growth of native thermal graphene on the surface of at least one layer of native epitaxial graphene 16. minus the part 14 consisting of silicon carbide of the stone intended to constitute a bearing or a counter-pivot, by sublimation of the silicon carbide, preferably according to a process chosen from the group comprising heating in a vacuum or assisted oven gas, heating by a light source (infrared lamp or infrared laser) in vacuum or gas-assisted chambers, or by any other appropriate method. The generation of multiple layers of native graphene can also be done, for example, by processes using hydrogen.

Preferably, the layer of native epitaxial graphene 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.

[0097] The method according to the invention makes it possible to obtain a timepiece stone constituting a bearing or a counter-pivot having improved mechanical properties, in particular better rigidity and a very low coefficient of friction. Furthermore, when the machining of the stone is carried out by precision machining without force, we obtain a particularly rapid and simple process to implement. Indeed, the process 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.

[0098] For example, machining a complete bearing by femto laser takes, considering only operations by femto laser, between 12 and 18 seconds, this according to the current state of the art. This time includes the machining operations of the external diameter, the internal diameter, the olive of the latter, the machining of the hollow and the convex. Thus, depending on the machining required for the bearing or the counter-pivot, this time can be further reduced and optimized.

[0099] Furthermore, the use of silicon carbide advantageously makes it possible to easily form at least one layer of native epitaxial graphene.

[0100] Furthermore, the graphene layer is hydrophobic, which makes it possible to improve the resistance of the stone to corrosion. The graphene layer having a very low coefficient of dynamic friction also makes it possible to eliminate lubrication.

Claims (26)

1. Method for manufacturing a timepiece stone constituting a bearing (4) or a counter-pivot (6) comprising at least one part (14) made of silicon carbide, comprising: a) a step of manufacturing a stone intended to constitute a bearing or a counter-pivot comprising at least one 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 part (14) made of silicon carbide of the stone intended to constitute a bearing or a counter-pivot obtained in step a) to obtain said timepiece constituting a bearing (4) or a counter-pivot (6). 2. Method according to claim 1, characterized in that step a) comprises the following substeps: a1) a step of manufacturing a raw piece of stone intended to constitute a bearing or a counter-pivot comprising at least one part (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 part (14) made of silicon carbide at least by machining the raw part obtained in the sub-step a1); And a3) a step of machining at least the part (14) made of silicon carbide of the blank obtained in sub-step a2). 3. Method for manufacturing a timepiece stone constituting a bearing (4) or a counter-pivot (6) comprising at least one part (14) made of silicon carbide, comprising: c) a step of manufacturing a raw piece of stone 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 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 ) ; e) at least one step of machining the part (14) made of silicon carbide of the blank obtained in step d) to form at least one part intended to be in contact with a pivot of an axis of pivoting; f) a step of generating at least one layer of native epitaxial graphene (16) on the external surface of at least the part (14) consisting 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 at least said part intended to be in contact with a pivot of a pivot axis made of silicon carbide on which was generated the layer of native epitaxial graphene (16) during step f), to obtain said timepiece constituting a bearing (4) or a counter-pivot (6). 4. Method according to one of claims 1 to 3, characterized in that step b) or f) of generating at least one layer of native epitaxial graphene (16) is carried out by growth of the graphene by sublimation of the carbide of silicon according to a method chosen from the group comprising heating in an oven and heating by a light source. 5. Method according to one of the preceding claims, characterized in that the layer of native epitaxial graphene (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 5nm. 6. Method according to one of claims 2 to 5, characterized in that substep a1) and/or a2), respectively step c) and/or d), is carried out by machining by removing material or by cutting. 7. Method according to claim 6, characterized in that the machining carried out during sub-step a2) or step d) is machining by material removal. 8. Method according to one of claims 2 to 7, characterized in that the machining of sub-step a3), respectively of step e) and/or step g), is precision machining without force. 9. Method according to claim 8, characterized in that 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 cushion or a counter -pivot making it possible to obtain at least one part (14) consisting of finished silicon carbide on the external surface of which at least one layer of native epitaxial graphene (16) is generated according to step b). 10. Method according to claim 9, characterized in that at least the part (14) consisting of finished silicon carbide obtained in substep a3) has a roughness Ra less than or equal to 0.5 µm, and preferably less than or equal to 0.1 µm, 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. 11. Method according to claim 8, characterized in that step g) of precision machining without force is the last step of the process of manufacturing the timepiece stone constituting a bearing (4) or a counter-pivot ( 6). 12. Method according to claim 11, 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 has been generated (16) obtained in step f) 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 µm, and preferably less than or equal to 0.1 µm, 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 equal to 12 nm, more preferably less than or equal to 10 nm, and more preferably between 5 nm and 9 nm, limits included. 13. Method according to one of claims 8 to 12, characterized in that the precision machining without force carried out during sub-step a3), respectively during step e) or during step g ), is femto laser turning, electrochemical turning, or spark erosion turning. 14. Method according to one of the preceding claims, characterized in that the stone intended to constitute a bearing (4) or a counter-pivot (6) consists entirely of silicon carbide, and in that the at least one layer native epitaxial graphene (16) is generated over its entire external surface. 15. Clockwork stone constituting a bearing (4) or a counter-pivot (6) obtained by the method according to one of claims 1 to 14. 16. Timepiece constituting a bearing (4) or a counter-pivot (6) comprising at least one part (14) made of silicon carbide, characterized in that said part (14) comprises at least one layer of graphene native epitaxial (16) generated on its external surface. 17. Timepiece constituting a bearing (4) or a counter-pivot (6) according to claim 16, characterized in that the layer of native epitaxial graphene has a charge carrier mobility of less than 5000 cm<2>V -1 s-1. 18. Timepiece constituting a bearing (4) or a counter-pivot (6) according to one of claims 16 to 17, characterized in that the layer of native epitaxial graphene (16) was obtained by growth by sublimation silicon carbide from the part (14) consisting of silicon carbide. 19. Timepiece constituting a bearing (4) or a counter-pivot (6) according to one of claims 16 to 18, characterized in that the layer of native epitaxial graphene (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. 20. Timepiece constituting a bearing (4) or a counter-pivot (6) according to one of claims 16 to 19, 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 µm, and preferably less than or equal to 0.1 µm, 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 . 21. Timepiece stone constituting a bearing (4) or a counter-pivot (6) according to one of claims 16 to 20, characterized in that it is made entirely of silicon carbide, and in that it comprises at least one native epitaxial graphene layer (16) generated present on at least a portion intended to be in contact with a pivot of a pivot axis, and preferably on its entire external surface. 22. Timepiece stone constituting a bearing (4) or a counter-pivot (6) according to one of claims 16 to 21, characterized in that the silicon carbide is monocrystalline. 23. Timepiece stone constituting a cushion (4) according to one of claims 16 to 22, characterized in that the stone is a flat or convex cushion. 24. Timepiece stone constituting a cushion (4) according to one of claims 16 to 23, characterized in that the stone is a cushion comprising a cylindrical or olive hole (10). 25. Watch movement comprising a timepiece stone constituting a bearing (4) or a counter-pivot (6) according to one of claims 15 to 24. 26. Timepiece comprising a watch movement according to claim 14 or a timepiece constituting a bearing (4) or a counter-pivot (6) according to one of claims 15 to 24.