METHOD FOR IMPROVING A MATERIAL FOR WATCH MOVEMENTS

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method for improving the mechanical characteristics, such as wear resistance and / or tribological characteristics, of a timepiece. TECHNICAL BACKGROUND OF THE INVENTION

[0002] The daily proximity of magnets and equipment generating magnetic fields can significantly disrupt the operation of a timepiece such as a watch. It is therefore interesting to find solutions to limit the magnetic sensitivity of watch movements, and in particular by using materials with low magnetic susceptibility.

[0003] However, the low magnetic susceptibility of a material is generally antagonistic to good mechanical and tribological characteristics. It has already been proposed, in documents EP 2 757 423 and EP 3 273 303, to surface harden materials with low magnetic susceptibility using carburizing, nitriding or boriding. The aim of these documents is to integrate carbon, nitrogen or boron atoms into interstitial or substitutional sites of a material with low magnetic susceptibility.

[0004] Although the hardness of the external surface is indeed increased using the methods of these documents, it has however been noted during tests that such interstitial integration gives satisfaction for a rather short time and that the coefficient of friction and, incidentally, the resistance to wear plummets in the short term leading, in the long term, to a more rapid deterioration than with the material without interstitial integration. SUMMARY OF THE INVENTION

[0005] The aim of the invention is to propose a new method for sustainably improving the tribological properties, such as, in particular, the wear resistance and / or the mechanical properties of a watch part made from a material without degrading its resistance to corrosion.

[0006] To this end, the invention relates to a method for manufacturing a timepiece comprising a step a intended to form a timepiece based on a non-magnetic metallic material and a step b intended to carry out at least one ion implantation of atoms of at least two different types of chemical elements, a first chemical element being chosen from carbon, nitrogen, oxygen and boron and a second chemical element, different from the first chemical element, being chosen from silicon and boron, to form chemical compounds of these two different chemical elements in the crystal lattice of the material of the timepiece in order to improve the tribological properties such as, in particular, the wear resistance and / or the mechanical characteristics of the timepiece without degrading the corrosion resistance of the material of the timepiece.

[0007] Advantageously according to the invention, the method does not integrate single chemical elements in an interstitial or substitutional manner as in documents EP 2 757 423 and EP 3 273 303 but chemical compounds which are much more stable in the crystal lattice of the material of the timepiece, that is to say which in particular are more difficult to combine with chemical elements already present in the material of the timepiece such as chromium and which have a very limited possibility of migration in or between each mesh of the crystal lattice.

[0008] Typically, borides and / or carbides and / or nitrides or, more generally, metal-ceramic composites associated with elements such as boron, nitrogen and carbon can be advantageously obtained, forming a modification of the crystal lattice of the material of the timepiece, i.e. an interruption of the periodicity of the crystal for a crystalline material of the timepiece or a surface and / or volume change for an amorphous material of the timepiece. Of course, in the case of a semi-crystalline material, i.e. comprising mixed crystalline and amorphous parts, these effects can be combined.

[0009] In fact, a lasting improvement in the wear resistance and friction coefficient of the watch part, i.e. both in the short term and in the long term, was observed compared to a part formed solely from step a. In addition, the corrosion resistance of the material of the watch part is not degraded, or even, depending on the material of the watch part used, such as copper-based, is improved. Finally, step b can advantageously be used in addition to modify the color of the watch part.

[0010] The part thus manufactured can therefore advantageously form all or part of a watch casing or a watch movement. The invention has proven useful for the manufacture of watch arbors such as a pivot, a barrel bung or a winding stem, gears such as a toothed wheel or a pinion and various parts used in friction such as a jumper, a pawl, a barrel drum or a barrel spring blade.

[0011] The invention may also include one or more of the following optional features, taken alone or in combination.

[0012] In order to prepare the watch part for step b, step a may, according to a first variant, comprise additive manufacturing. According to a second variant, step a may comprise a first sub-step of manufacturing the material in the form of a blank and a second sub-step of shaping the blank.

[0013] The non-magnetic metallic material may be a material based on copper (pure or alloy), nickel (pure or alloy), gold (pure or alloy), silver-palladium alloy (binary alloy, pure or comprising more alloying element(s)), cobalt (pure or alloy), chromium (pure or alloy), tungsten (pure or alloy), non-magnetic iron (pure or alloy), titanium (pure or alloy) or stainless steel of the austenitic type such as 316L. Of course, other types of materials and in particular other non-magnetic metallic materials may be envisaged without departing from the scope of the invention.

[0014] According to an alternative, step b may comprise an ion implantation sub-step for several different types of chemical elements at the same time or several ion implantation sub-steps, each ion implantation being implemented for a single type of chemical element at the same time. For example, the first part of the alternative makes it possible to limit the number of sub-steps while the second part of the alternative makes it possible to use different ion implantation techniques such as, for example, beamline ion implantation (in English "beamline ion implantation") and plasma immersion implantation (in English "plasma immersion ion implantation" or "PIII") making it possible in particular to obtain a greater number of chemical compounds.

[0015] According to another alternative, step b can be carried out hot or, after step b, a heat treatment step c is carried out in order to facilitate the formation of the chemical compounds. Typically, step b is preferably carried out at a temperature between 300°C and 500°C or step c is preferably carried out at a temperature between 300°C and 500°C for a duration between 1 hour and 24 hours. The heat input is preferred to improve the combination between the chemical elements integrated by ion implantation and to implant the latter more deeply in the timepiece. The method according to the invention may comprise, before step b and / or after step b, a finishing step d intended to modify the surface condition of the timepiece. Typically, step d may comprise a polishing sub-step and / or a rolling sub-step and / or a decoration sub-step.For example, a polishing sub-step after step b may be necessary if the outer surface of the timepiece before the ion implantation of the chemical elements is very rough, a rolling step may improve the hardness and geometric precision of the timepiece, and a decoration step may improve the aesthetics of the timepiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other features and advantages of the invention will emerge clearly from the description given below, for information purposes only and in no way limiting, with reference to the appended drawings, in which: There figure 1 is a schematic view of a timepiece according to the invention; The figure 2 is a perspective view of a clock tree; The figure 3 is a partial perspective view of an escapement mechanism of a watch movement. DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

[0017] In the various figures, identical or similar elements bear the same references, possibly with the addition of an index. The description of their structure and function is therefore not systematically repeated.

[0018] In all that follows, the orientations are the orientations of the figures. In particular, the terms "upper", "lower", "left", "right", "above", "below", "forward" and "backward" are generally understood in relation to the direction in which the figures are represented.

[0019] A "non-magnetic material" means a material that is not or only slightly influenced by magnetism. Such a material is a material whose magnetic susceptibility is low or very low (χm is negative or slightly positive, for example, less than 1 10 -3 or 1 10 -4). Such a material can therefore be a paramagnetic or diamagnetic material.

[0020] “Based on” means a material or alloy constituting at least 50% by total mass or weight of a given part.

[0021] By "timepiece" we mean all types of instruments for measuring or counting time such as clocks, small clocks, watches, etc.

[0022] By "watch movement" we mean all types of mechanism capable of counting time and powered by mechanical energy (for example a barrel) or electrical energy (for example a battery).

[0023] By "dressing" we mean all types of devices capable of containing, displaying, decorating and / or controlling a watch movement such as, for example, all or part of a case, a bracelet or a display.

[0024] In the following, unless otherwise indicated, all percentages (%) indicated are percentages by total mass or weight.

[0025] The timepiece was developed to apply to the watchmaking field. Thus, the timepiece may form all or part of a watch casing 2 such as all or part of a dial, a display such as a hand or a disc, a case, a bracelet or a control member such as a crown, a winding stem or a push button. The timepiece may also form all or part of a movement 3 such as all or part of an escapement device such as a Swiss lever mechanism 15, 16, 17, a resonator such as a balance-spring mechanism, an energy source such as a barrel, an automatic winding system, a gear train such as a mobile or a toothed wheel, a spring, a screw, a bridge or a plate.

[0026] The invention has proven useful for the manufacture of watch arbors A, B, C such as a pivot 21, 22, 23, 24, a barrel bung or a winding stem, gears such as a toothed wheel 18 or a pinion 19 and various parts used in friction such as a jumper, a pawl, a barrel drum or a barrel spring blade.

[0027] To this end, the invention relates to a method for manufacturing a timepiece comprising a first step a intended to form a timepiece. The material of the timepiece may or may not comprise a crystalline lattice, that is to say may be at least partially amorphous such as, for example, an amorphous metal alloy, also called "bulk metallic glass" (BMG). The timepiece is based on at least one non-magnetic metallic material. In order to prepare the timepiece for step b, step a may, according to a first variant, comprise additive manufacturing.Such manufacturing could, but is not limited to, a lithography process, such as photolithography, to form a mold in which a deposition, such as galvanic growth, gas phase growth, chemical growth, injection or casting, is then carried out to form the timepiece. It is also possible to form the timepiece by three-dimensional printing.

[0028] According to a second variant, step a may comprise a first sub-step of manufacturing the material in the form of a blank, such as for example a bar, a plate or a billet, from casting in a mold, followed by a second sub-step of shaping the blank, such as for example bar turning such as turning, milling, mechanical or laser machining, and / or shaping by matting such as rolling or stamping.

[0029] Regardless of the steps implemented during step a, the timepiece is preferably finished, i.e. it has substantially its final dimensions and geometries before the start of step b (it may be envisaged, depending on the timepiece to be manufactured, the addition of an optional step d as explained below). In addition, the preferred non-magnetic metallic material may be a material based on copper (pure or alloy), nickel (pure or alloy), gold (pure or alloy), silver-palladium alloy (binary alloy pure or comprising more alloying element(s)), cobalt (pure or alloy), chromium (pure or alloy), tungsten (pure or alloy), non-magnetic iron (pure or alloy), titanium (pure or alloy) or stainless steel of the austenitic type such as the 316L type.Of course, other types of materials and in particular other non-magnetic metallic materials can be envisaged without departing from the scope of the invention.

[0030] The method then comprises a step b intended to carry out at least one ionic implantation of atoms of at least two different types of chemical elements to form chemical compounds of these two different chemical elements in the crystal lattice of the material of the timepiece in order to improve the tribological properties such as, in particular, the wear resistance and / or the mechanical characteristics of the timepiece without degrading the corrosion resistance of the material of the timepiece. Finally, step b can advantageously be used in addition to modify the color of the timepiece.

[0031] It is thus desired to integrate a first chemical element, such as carbon, nitrogen, oxygen or boron, and at least one second chemical element, such as silicon or boron, in order to form chemical compounds, such as silicon carbide, boron carbide, silicon boride, carbon nitride, silicon nitride or boron nitride. Therefore, in the example explained above, if the first chemical element selected is boron, the second chemical element different from the first can therefore only be silicon to form a silicon boride.

[0032] Advantageously according to the invention, it is thus possible to obtain, for example, borides and / or carbides and / or nitrides or, more generally, metal-ceramic composites associated with elements such as boron, nitrogen and carbon, forming a modification of the crystal lattice of the material of the timepiece, i.e. an interruption of the periodicity of the crystal for a crystalline material of the timepiece or a surface and / or volume change for an amorphous material of the timepiece. Of course, in the case of a semi-crystalline material, i.e. comprising mixed crystalline and amorphous parts, these effects can be combined.

[0033] Thus, step b can include an ion implantation sub-step for several different types of chemical elements at the same time, which makes it possible to limit the number of sub-steps.

[0034] Alternatively, step b may comprise several ion implantation sub-steps, each ion implantation being implemented for a single type of chemical element at the same time, which makes it possible to use different ion implantation techniques such as, for example, ion beam implantation (in English "beamline ion implantation") and plasma immersion implantation (in English "plasma immersion ion implantation" or "PIII"), making it possible in particular to obtain a greater number of chemical compounds.

[0035] Alternatively, step b may be carried out hot or, after step b, a heat treatment step c is carried out to facilitate the formation of the chemical compounds. Typically, step b is preferably carried out at a temperature between 300°C and 500°C or step c is preferably carried out at a temperature between 300°C and 500°C for a period between 1 hour and 24 hours. The heat input is preferred to improve the combination of the chemical elements integrated by ion implantation and to implant them more deeply in the timepiece.

[0036] The temperature is preferably between 400°C and 480°C and, even more preferably, between 400°C and 450°C, that is to say for example is equal to 400°C, 405°C, 410°C, 415°C, 420°C, 425°C, 430°C, 435°C, 440°C, 445°C, 450°C or can vary between two of these temperatures. The duration of step c is preferably between 2 hours and 12 hours and, even more preferably, between 3 hours and 7 hours, that is to say for example is equal to 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours or an intermediate duration between two of these values. The temperature and, possibly, the duration of step c depend on the type of material of the watch part and / or the chemical elements integrated.

[0037] Finally, the method according to the invention may comprise, before step b and / or after step b, a finishing step d intended to modify the surface condition of the timepiece. Typically, step d may comprise a polishing sub-step and / or a rolling sub-step and / or a decoration sub-step. For example, a polishing sub-step after step b may be necessary if the outer surface of the timepiece, before the ion implantation of the chemical elements, is very rough, a rolling step may improve the hardness and geometric precision of the timepiece and a decoration step may improve the aesthetics of the timepiece.

[0038] A comparative study reproducing the friction conditions of a watch pivot was conducted to measure the variations in friction coefficient and wear resistance for three types of samples. A first type of sample comprises parts formed from 316L type austenitic steel which have undergone polishing. A second type of sample comprises parts formed from 316L type austenitic steel which have undergone polishing, ion implantation of atoms of a single chemical element and then heat treatment at 425°C for at least 3 hours. Finally, a third type of sample comprises, advantageously according to the invention, parts formed from 316L type austenitic steel (step a) which have undergone polishing (step d), at least one ion implantation of chemical compounds formed by several combined chemical elements (step b) and then heat treatment at 425°C for at least 3 hours (step c).

[0039] Although the hardness of the external surface is indeed increased on the second type of samples, it was noted that an interstitial integration of nitrogen atoms gave satisfaction for a fairly limited duration and that a degradation of the contact surface occurred in the short term.

[0040] In the case of the third type of samples according to the invention, a lasting improvement in wear resistance and coefficient of friction of the watch part, i.e. both in the short term and in the long term, was observed, in particular for chemical compounds of the silicon carbide type compared to those of the first type of samples. In addition, the corrosion resistance of the austenitic steel of the 316L type is not degraded.

[0041] Advantageously according to the invention, the method does not integrate single chemical elements in an interstitial or substitutional manner as in documents EP 2 757 423 and EP 3 273 303 but chemical compounds which are much more stable in the crystal lattice of the material of the timepiece, that is to say which in particular are more difficult to combine with chemical elements already present in the material of the timepiece such as chromium and which have a very limited possibility of migration in or between each mesh of the crystal lattice.

[0042] The invention is not limited to the embodiments and variants presented and other embodiments and variants will become clear to those skilled in the art. Thus, the embodiments and variants can be combined with each other without departing from the scope of the invention.

Claims

1. Method for manufacturing a timepiece comprising the following steps: a. Forming a timepiece (A, B, C) based on a non-magnetic metallic material; b. Making at least one ion implantation of atoms of at least two different types of chemical elements, a first chemical element being selected from carbon, nitrogen, oxygen and boron and a second chemical element, different from the first chemical element, being selected from silicon and boron, to form chemical compounds of these two different chemical elements in the crystalline network of the material of the timepiece to improve the tribological properties such as, in particular, the wear resistance and / or the mechanical characteristics of the timepiece (A, B, C) without impairing the corrosion resistance of the material of the timepiece.

2. Method according to the preceding claim, wherein the non-magnetic metallic material is a material based on copper, based on nickel, based on gold, based on a silver-palladium alloy, based on cobalt, based on chromium, based on tungsten, based on non-magnetic iron, based on titanium or based on austenitic type stainless steel.

3. Method according to one of the preceding claims, wherein step b comprises a sub-step of ion implantation for several different types of chemical element at the same time.

4. Method according to claim 1 or 2, wherein step b comprises several sub-steps of ion implantation, each ion implantation being implemented for a single type of chemical element at the same time.

5. Method according to one of the preceding claims, wherein step b is carried out hot to facilitate the formation of the chemical compounds.

6. Method according to the preceding claim, wherein step B is carried out at a temperature of between 300 °C and 500 °C.

7. Method according to one of claims 1 to 4, comprising, after step b, a step c of heat treatment to facilitate the formation of the chemical compounds in the timepiece.

8. Method according to the preceding claim, wherein step c is carried out at a temperature of between 300 °C and 500 °C for a duration of between 1 hour and 24 hours.

9. Method according to one of the preceding claims, comprising, before step b and / or after step b, a finishing step intended to modify the surface condition of the timepiece (A, B, C).