CH718549A2 - Watch component and method of manufacturing such a watch component. - Google Patents

Abstract

The present invention relates to a timepiece component (1) comprising at least one part (2) made of silicon carbide, the outer surface of said part (2) being covered with at least one layer of graphene (4). The present invention also relates to a method for manufacturing such a timepiece component (1), said method comprising: a) a step of manufacturing a raw part of the timepiece component comprising at least one part made of silicon carbide; b) a step of producing a blank of the timepiece component comprising at least one part made of silicon carbide at least by machining the raw part obtained in step a); c) a step of finishing by precision machining without force at least of the part consisting of silicon carbide in order to obtain at least one part consisting of finished silicon carbide (2); and d) a step of forming at least one layer of graphene (4) on the outer surface of at least the portion consisting of finished silicon carbide (2) obtained in step c) in order to obtain said component watchmaker (1).

Description

Technical area

The present invention relates to a watch component comprising at least one part made of silicon carbide.

The present invention also relates to a timepiece movement and a timepiece comprising such a timepiece component.

The present invention also relates to a method of manufacturing such a watch component.

State of the art

[0004] Such timepiece components comprising a part made of silicon carbide have been developed in recent years. In particular, silicon carbide has been proposed for making watch pivot pins, and more particularly balance pins, because of its non-magnetic properties, to replace traditional pivot pins, made of steel.

[0005] The manufacture of a traditional watchmaking pivot pin in steel consists, from a hardenable steel bar, in carrying out precision bar turning operations to define different active surfaces (bearing, shoulder, pivots, etc.) then subjecting the turned shaft to heat treatment operations comprising at least one quench to improve the hardness of the shaft and one or more tempers to improve its toughness. The heat treatment operations are followed by a rolling operation of the axle pivots, an operation which consists in polishing the pivots to bring them to the required dimensions. During this rolling operation, the hardness as well as the roughness of the pivots are further improved via surface hardening. One thus obtains, at the end of the process, an axis having pivots with the required dimensions, hardness and roughness. It should be noted that rolling can hardly be implemented with materials whose hardness is greater than 600 HV.

[0006] Watchmakers' pivot axes, and in particular precision axes such as balance axes, conventionally used in mechanical watch movements, are made in grades of free-cutting steels which are generally martensitic carbon steels including lead and manganese sulphides to improve their machinability. A steel of this known type, designated 20 AP, is typically used for these applications. Lead-free alternatives such as Finemac are also used.

[0007] This type of material has the advantage of being easily machinable, in particular of being suitable for bar turning and has, after adequate quenching and tempering treatments, high mechanical properties which are very advantageous for the production of axles. pivoting watchmakers. These steels have in particular a high wear resistance and hardness after heat treatment. Typically the hardness of the pivots of an axle made of 20 AP steel can reach a surface hardness exceeding 700 HV after heat treatment and rolling.

[0008] Although providing satisfactory mechanical properties for the watchmaking applications described above, this type of material has the disadvantage of being magnetic and of being able to disturb the rate of a watch after being subjected to a magnetic field, and this in particular when this material is used for the production of a balance shaft cooperating with a spiral balance made of ferromagnetic material. It will also be noted that these martensitic steels are also sensitive to corrosion.

In an attempt to remedy these drawbacks, a solution has been proposed, consisting in using austenitic stainless steels which have the particularity of being non-magnetic, that is to say of the paramagnetic, diamagnetic or antiferromagnetic type, whose relative magnetic permeability is less than or equal to 1.01.

[0010] However, these austenitic steels have a crystallographic structure that does not allow them to be quenched and to achieve hardnesses and therefore wear resistances compatible with the requirements for the production of watchmaking pivot axes. One way to increase the hardness of these steels is hardening, however this hardening operation does not make it possible to obtain hardnesses greater than 500 HV for this type of material. Consequently, in the context of parts requiring high resistance to wear by friction and having to have pivots presenting little or no risk of breakage or deformation, the use of this type of steel remains limited.

Another solution proposed consisted in depositing on the pivot axes hard layers of materials such as amorphous carbon known under the English name “diamond like carbon (DLC). However, significant risks of delamination of the hard layer and therefore the formation of debris which can circulate inside the watch movement and come to disturb the operation of the latter, which is not satisfactory, have been observed.

Another approach has been considered to overcome the disadvantages of austenitic stainless steels, namely the surface hardening of these pivot pins by nitriding, carburizing or nitrocarburizing. However, these treatments are known to lead to a significant loss of corrosion resistance due to the reaction of nitrogen and/or carbon with the chromium of the steel and the formation of chromium nitride and/or carbide. chromium causing a localized depletion of the chromium matrix, which is detrimental for the desired watchmaking application.

[0013] An additional chemical Ni deposition operation seems necessary in order to overcome these corrosion problems, which complicates and greatly increases the cost of the manufacturing process.

[0014] Other approaches still exist, such as achievements in titanium alloys, hard metal, certain oxides, or ceramics such as silicon carbide as described above. However, the use of these materials does not make it possible to obtain satisfactory performances specific to horological components, other than non-magnetism.

The present invention aims to remedy these drawbacks by proposing a watch component, and more particularly a non-magnetic pivot pin, having mechanical properties compatible with the wear and shock resistance requirements required in the watchmaking field, but also limiting sensitivity to magnetic fields.

Another object of the invention is to provide a method of manufacturing such a watch component, in particular a non-magnetic pivot axis, and more particularly a precision axis, allowing extremely simple and economical production.

Disclosure of Invention

To this end, the invention relates to a timepiece component comprising at least one part consisting of silicon carbide.

According to the invention, the outer surface of said part consisting of silicon carbide is covered with at least one layer of graphene.

[0019] In a particularly advantageous manner, the timepiece component consists entirely of silicon carbide, the outer surface of said timepiece component being covered with at least one layer of graphene.

[0020] Advantageously, said timepiece component is arranged to form a pivot axis, preferably a balance shaft, the part consisting of silicon carbide covered with at least one layer of graphene of the pivot axis being arranged to form a pivot provided at at least one end of said pivot axis.

[0021] Thus, the surface hardness of said part of the timepiece component according to the invention, and in particular the hardness of the pivots, is that of silicon carbide, reaching and even exceeding values of 2000 HV.

[0022] In addition, the use of at least one layer of graphene on the surface of said part makes it possible to greatly improve the properties of rigidity and the elastic limit of the watch component according to the invention, compared to a known watch component. .

[0023] In addition, the coefficient of friction of graphene being very low, said part, and in particular the pivot, can have a coefficient of friction less than or equal to 0.2 without lubrication.

[0024] In addition, silicon carbide is non-magnetic and graphene has a high resistance to corrosion.

[0025] Therefore, in the case of a pivot pin, all the performance of a current non-magnetic pivot pin is improved.

The present invention also relates to a timepiece movement and a timepiece comprising a timepiece component as defined above.

The present invention also relates to a method for manufacturing a watch component as defined above, said method comprising: a) a step of manufacturing a raw part of the watch component comprising at least one part consisting of carbide silicon; b) a step of producing a blank of the timepiece component comprising at least one part consisting of silicon carbide at least by machining the raw part obtained in step a); c) a step of finishing by precision machining without force at least of the part consisting of silicon carbide in order to obtain at least one part consisting of finished silicon carbide; and d) a step of forming at least one layer of graphene on the outer surface of at least the part consisting of finished silicon carbide obtained in step c).

The method according to the invention makes it possible to significantly reduce the production time and to reduce the number of operations necessary for the manufacture of a watch component, and in particular a pivot axis, made of a non-magnetic material while presenting the mechanical properties compatible with the wear and shock resistance requirements required in the watchmaking field, in comparison with watchmaking components traditionally made from different metal alloys. Remarkably, the method according to the invention makes it possible to avoid rolling operations.

Brief description of the drawings

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 : Figure 1 is a schematic view of a pivot of a pivot axis according to the invention; and FIG. 2 is a schematic representation of the steps of a method according to the invention.

Embodiments of the Invention

Referring to Figure 1, the present invention relates to a watch component 1 comprising at least a part 2 made of silicon carbide, that is to say entirely of silicon carbide.

According to the invention, the outer surface of said part 2 is covered with at least one layer of graphene 4. Thus, part 2 comprises a core of silicon carbide and at least one outer layer of graphene 4, preferably directly in contact with the silicon carbide core.

[0032] Advantageously, the timepiece component consists entirely of silicon carbide, its entire outer surface then being entirely covered with at least one layer of graphene. Since silicon carbide is non-magnetic, the timepiece component according to the invention then has the advantage of being non-magnetic in order to limit its sensitivity to magnetic fields.

[0033] Such a watch component is for example a pivot pin, a mobile, a spring, in particular a spiral spring.

Advantageously, part 2 has a surface of revolution, such as a cylindrical or conical surface.

[0035] Advantageously, said timepiece component 1 is arranged to form a timepiece pivot axis. In this case, said part 2 of the pivot pin, made of silicon carbide covered with at least one layer of graphene, is arranged to form a pivot provided at at least one end of said pivot pin. These pivots are each intended to pivot in a bearing, typically in an orifice of a stone or ruby.

Said part 2, in particular when it is in the form of a pivot, has an outer diameter less than or equal to 200 μm, preferably less than or equal to 100 μm, preferably less than or equal to 90 μm, and more preferably less than or equal to 70 μm.

[0037] Preferably, the horological pivot pin is a balance pin, comprising a plurality of sections of different diameters, conventionally defining bearing surfaces and shoulders arranged along a shank between two end portions defining the two pivots, only one end being represented here in FIG. 1. Of course, other types of horological pivot axes can be envisaged, such as, for example, axes of horological mobiles, typically escapement pinions, or even stems of anchor. Parts of this type have, at the level of the body, diameters that are preferably less than 2 mm, and pivots with a diameter that is preferably less than 0.2 mm as described above, with an accuracy of a few microns.

[0038] Preferably, the entire pivot pin is made entirely of silicon carbide covered with graphene. However, the graphene-coated silicon carbide Part 2 can be limited to the pivot and shank.

The invention is described here in the context of an application to a pivot axis in which at least the pivot constitutes part 2, but it is specified that the rest of the description applies to any watch component according to the invention.

[0040] Silicon carbide is polycrystalline or monocrystalline. Preferably, the silicon carbide used in the invention is monocrystalline.

[0041] According to the variants, it is possible to have one or more layers of graphene 4.

[0042] Preferably, the graphene layer 4 is a native graphene layer which has been obtained by growth.

The graphene layer 4 can also be a deposited graphene layer which has been obtained by an “external” deposition of graphene, preferably directly on the silicon carbide or on another layer of graphene already present.

The two variants can be combined so that it is possible to provide at least one native graphene layer on the surface of at least part 1, and at least one graphene layer deposited on said native graphene layer .

Preferably, the graphene layer 4 has a thickness comprised between 0.5 nm and 20 nm, preferably between 1 nm and 10 nm, and preferentially between 1 nm and 5 nm, limits included.

In a particularly advantageous manner, part 2, and preferably the entire watch component 1, 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 test methods are defined in the following standards ASTM C1327 and ISO 6507.

In a particularly advantageous manner, part 2, and preferably the entire watch component 1, 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 or equal to 50 nm, preferably less than or equal to 25 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 including terminals. The roughness Ra is defined according to the ISO 4287 standard.

The graphene layer or layers 4 make it possible to increase the tribological properties of the timepiece component, in particular by very drastically reducing the coefficient of friction. The watch component according to the invention is therefore a part lubricated for life.

The graphene layer or layers 4 also make it possible to increase the mechanical properties of the timepiece component, in particular because graphene is at least 100 times more rigid than steel and tolerates extremely high elastic deformations.

[0050] Therefore, in a particularly advantageous manner, part 2, and preferably the entire watch component 1, according to the invention has a very low coefficient of friction, less than or equal to 0.2, preferably less than or equal at 0.1.

In addition, in a particularly advantageous manner, part 2, and preferably the entire watch component 1, according to the invention has a toughness greater than or equal to 6 MPa.m<1/2> and a resistance to tensile Rm greater than or equal to 600 MPA.

In a particularly advantageous manner, part 2, and preferably the entire watch component 1, according to the invention has a Young's modulus greater than or equal to 300 GPa.

The Young's modulus, the tenacity and the tensile strength are measured and calculated by tensile-compression tests known to those skilled in the art.

[0054] In addition to being non-magnetic, silicon carbide is corrosion resistant.

Thus, in addition to being non-magnetic, at least part 2, and preferably the watch component 1, according to the invention has all the satisfactory performances specific to watch components for which one seeks, on the surface, a hardness greater than 750 HV in order to resist wear, a low friction coefficient to limit lubrication, a smooth state (Ra < 0.5 µm) for friction and isochronism, corrosion resistance, and for which a core having high rigidity, toughness and breaking strength Rm (high elastic limit).

The invention also relates to the method of manufacturing a watch component as described above. The method according to the invention advantageously comprises the following steps, described in relation to FIG. 2: a) a step of manufacturing a raw part of the timepiece component comprising at least one part consisting of silicon carbide; b) a step of producing a blank of the timepiece component comprising at least one part consisting of silicon carbide at least by machining the raw part obtained in step a); c) a step of finishing by precision machining without force at least of the part consisting of silicon carbide in order to obtain at least one part consisting of finished silicon carbide, that is to say which has its final configuration in terms of dimensions, roughness and geometry; and d) a step of forming at least one layer of graphene 4 on the outer surface of at least the part consisting of finished silicon carbide obtained in step c) in order to obtain the timepiece component 1 according to invention.

It is considered that the graphene layer, in view of its thickness, does not modify the dimensions and the geometry of the component obtained in step c), nor its roughness.

When the watch component is arranged to form a pivot axis, said part 2 consisting of silicon carbide covered with at least one layer of graphene 4 is arranged to form at least one pivot provided at at least one end of said axis of pivoting.

Advantageously, said part 2 consisting of silicon carbide covered with at least one layer of graphene 4 constitutes the watch component as a whole, so that the watch component obtained is made of silicon carbide entirely covered with at least one graphene layer 4.

[0060] Advantageously, step a) is carried out by laser machining methods, water jet machining or any other appropriate material removal method. Preferably, the raw part of the timepiece component 1 consists entirely of silicon carbide.

Advantageously, the machining performed during step b) to produce the blanks is machining by material removal, using methods similar to those of step a). These blanks are produced if necessary with the dimensions necessary to obtain a watch component that ultimately presents the desired geometric characteristics, taking into account all the stages of the process.

[0062] Next comes step c) of reworking and finishing the watch component by precision machining without force at least of the part made of silicon carbide.

In the present description, machining without force is called unconventional machining according to 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 large cutting forces are involved. A machining without force is therefore a machining without direct contact between the part to be machined and a machining tool which would be capable of exerting a force or a constraint on said part.

Advantageously, the forceless precision machining carried out during step c) is femto laser turning, ECM electrochemical turning, or electroerosion turning (for example wire EDM).

The machining operations of this step are advantageously carried out by femtosecond pulsed laser micromachining with a laser of wavelengths comprised for example between 200 nm and 2000 nm, preferably between 400 nm and 1000 nm, terminals included. The parameters of the laser 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.

[0066] Thanks to precision machining without force by femto laser, this finishing operation makes it possible to achieve surface states with a roughness Ra preferably less than or equal to 100 nm. Preferably, at least the part consisting of finished silicon carbide obtained in step c) 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 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 rolling operations.

Thus, in a particularly advantageous manner, the method according to the invention does not include any rolling step, in particular after step c) or step d) since the part consisting of finished silicon carbide obtained in step c) already has the required dimensions, hardness and roughness, which are traditionally obtained only after a rolling operation.

Preferably, step d) of forming at least one layer of graphene is carried out by growing native thermal graphene on the surface of the component, according to a method chosen from the group comprising heating under vacuum, heating (for example with a light source) under an inert atmosphere (for example argon), or by any other suitable method. The generation of multiple layers of native graphene can also be done for example by processes using hydrogen.

The process according to the invention makes it possible to obtain a non-magnetic timepiece component having improved mechanical properties, in particular rigidity, capable of ensuring lifetime lubrication, in a simple and economical manner. Indeed, the method according to the invention makes it possible to eliminate the rolling operation traditionally used, so that the number of operations necessary for the manufacture of the timepiece component is reduced, the production time being considerably reduced.

Claims (25)

1. Watch component (1) comprising at least one part (2) made of silicon carbide, characterized in that the outer surface of said part (2) is covered with at least one layer of graphene (4). 2. Watch component (1) according to claim 1, characterized in that it consists entirely of silicon carbide, and in that its outer surface is covered with at least one layer of graphene (4). 3. Watch component (1) according to one of the preceding claims, characterized in that the silicon carbide is monocrystalline. 4. Watch component (1) according to one of the preceding claims, characterized in that the graphene layer (4) is a layer of native graphene which has been obtained by growth. 5. Watch component (1) according to one of the preceding claims, characterized in that the graphene layer (4) is a deposited graphene layer which has been obtained by depositing graphene. 6. Watch component (1) according to one of the preceding claims, characterized in that the graphene layer (4) 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. 7. Watch component (1) according to one of the preceding claims, characterized in that said part (2) 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 at 50 nm, preferably less than or equal to 25 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. 8. Timepiece component (1) according to one of the preceding claims, characterized in that said part (2) has a surface hardness greater than or equal to 2000 HV, and preferably greater than or equal to 2500 HV. 9. Timepiece component (1) according to one of the preceding claims, characterized in that said part (2) has a coefficient of friction less than or equal to 0.2, preferably less than or equal to 0.1. 10. Timepiece component (1) according to one of the preceding claims, characterized in that said part (2) has a toughness greater than or equal to 6 MPa.m<1/2> and a tensile strength Rm greater than or equal to at 600 MPa. 11. Timepiece component (1) according to one of the preceding claims, characterized in that said part (2) has a Young's modulus greater than or equal to 300 GPa. 12. Watch component (1) according to one of the preceding claims, characterized in that said part (2) has an outer diameter of less than 200 μm, preferably less than 100 μm, preferably less than 90 μm, and more preferably less at 70 µm. 13. Watch component (1) according to one of the preceding claims, characterized in that it is arranged to form a pivot axis, preferably a balance axis. 14. Watch component (1) according to claim 13, characterized in that said part (2) consisting of silicon carbide covered with at least one layer of graphene (4) of the pivot axis is arranged to form a pivot provided at at least one end of said pivot axis. 15. Watch movement comprising a watch component (1) according to one of claims 1 to 14. 16. Timepiece comprising a timepiece movement according to claim 15 or a timepiece component (1) according to one of claims 1 to 14. 17. A method of manufacturing a timepiece component (1) according to one of claims 1 to 14, comprising: a) a step of manufacturing a raw part of the timepiece component comprising at least one part consisting of silicon carbide; b) a step of producing a blank of the timepiece component comprising at least one part consisting of silicon carbide at least by machining the raw part obtained in step a); c) a step of finishing by precision machining without force at least of the part consisting of silicon carbide in order to obtain at least one part consisting of finished silicon carbide (2); and d) a step of forming at least one layer of graphene on the outer surface of at least the portion consisting of finished silicon carbide (2) obtained in step c). 18. Method according to claim 17, characterized in that step a) is carried out by machining by removing material. 19. Method according to one of claims 17 to 18, characterized in that the machining performed during step b) is machining by removal of material. 20. Method according to one of claims 17 to 19, characterized in that the precision machining without force carried out during step c) is a turning by femto laser, an electrochemical turning, or a turning by electroerosion. 21. Method according to one of claims 17 to 20, characterized in that at least the portion consisting of finished silicon carbide (2) obtained in step c) 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 15 nm, and preferably less than or equal to 12 nm, more preferably less than or equal at 10 nm, and more preferably between 5 nm and 9 nm, limits included. 22. Method according to one of claims 17 to 21, characterized in that it does not include any rolling step after step c) or step d). 23. Method according to one of claims 17 to 22, characterized in that step d) of forming at least one layer of graphene (4) is carried out by growing native graphene, according to a method chosen from the group including vacuum heating and inert atmosphere heating. 24. Method according to one of claims 17 to 23, characterized in that the graphene layer (4) 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. 25. Method according to one of claims 17 to 24, characterized in that the timepiece component is arranged to form a pivot axis, said part (2) consisting of silicon carbide covered with at least one layer of graphene (4 ) of the pivot pin being arranged to form at least one pivot provided at at least one end of said pivot pin.