WO2015189278A2

WO2015189278A2 - Oscillator for a timepiece balance spring assembly

Info

Publication number: WO2015189278A2
Application number: PCT/EP2015/062954
Authority: WO
Inventors: Frédéric DIOLOGENT; Gaël GUERLESQUIN; Romain MOYSE
Original assignee: Cartier Création Studio Sa
Priority date: 2014-06-11
Filing date: 2015-06-10
Publication date: 2015-12-17
Also published as: WO2015189278A3

Abstract

The present invention relates to a hairspring (3) to be provided on a balance wheel (2) of a balance spring assembly (1) of a mechanical timepiece, characterized in that said hairspring is manufactured using a titanium alloy containing: a titanium base; 10 at.% to 40 at.% of at least one element among Nb, Ta, or V; 0 at.% to 3 at.% oxygen; 0 at.% to 6 at.% zirconium; and 0 at.% to 5 at.% hafnium. The hairspring of the invention is less temperature-sensitive and has lower density than a conventional hairspring.

Description

Oscillator for a sprung balance assembly of a part

watch

Technical area

The present invention relates to an oscillator such as a spiral spring for equipping a balance of a sprung-balance assembly of a mechanical timepiece. The invention also relates to a regulating member comprising the spiral spring.

State of the art

[0002] Mechanical watches generally comprise a regulator member composed of a flywheel called a balance wheel on the axis of which is fixed a spiral spring called spiral or spiral spring. The balance-balance spiral around its equilibrium position at a frequency that depends in particular on the rigidity of the balance spring and the moment of inertia of the balance.

It is well known that the diurnal gait of a mechanical movement depends essentially on the sprung balance whose oscillation frequency can be influenced by changes in external factors, such as a change in temperature or temperature. presence of a magnetic field. The temperature variations are likely to cause thermal expansion of the balance and spiral which essentially cause a variation in the moment of inertia of the balance and a variation of the return torque of the balance spring. Magnetic fields act essentially on the hairspring and are likely to disturb or cancel its action on the balance. The amplitude variations of the oscillations of the balance are related to the weight and the inertia of the balance and are likely to cause a lack of isochronism of the sprung balance. Thus, all these parameters are capable of modifying the natural frequency of the sprung balance. As far as the spirals are concerned, we have already for a long time, in a manner still considered satisfactory, minimized the variations in the way due to temperature variations by manufacturing them in alloys whose elasticity remains practically constant in the usual temperature range of use. These include iron-nickel alloys known under the names such as invar or élinvar and allowing, in the best quality, to obtain a deviation of +/- 0.6 seconds per degree in 24h, but can still be sensitive to the effect of a magnetic field. More recently, spirals made of non-magnetic materials such as silicon, quartz, glass or diamond have been proposed. However, the use of these materials as spiral always has certain disadvantages, especially because of their sensitivity to magnetism and / or temperature change.

Brief summary of the invention

The present invention relates to an oscillator of a mechanical timepiece such as a tuning fork or especially a spiral spring for equipping a balance of a set of sprung balance. According to the invention, the oscillator is made of a titanium alloy of

comprising a titanium base, between 10 at.% and 40% of at least one of Nb, Ta or V; between 0% and 3% oxygen, between 0% and 6% zirconium; and between 0% and 5% of hafnium.

[0006] In one embodiment, the alloy comprises between 55 at% and 80 at% titanium, at 20% at least 30% of at least one of Nb, Ta or V; between 0.1 at.% and 3 at.% oxygen, between 0 at.% and 6 at.% zirconium; and between 0% and 5% of hafnium. The alloy may also comprise 0.3 to 3 at% oxygen.

[0007] In another embodiment, the alloy further comprises between 0% and 5% aluminum. [0008] In yet another embodiment, the alloy comprises between 0.3 and 3 at% oxygen.

[0009] In yet another embodiment, the alloy comprises between 23 and 27 at% of at least one of Nb, Ta or V, and preferably between 23 and 27 at. Nb.

In still other embodiments, the alloy comprises one of the following compositions: 23% of niobium, 2% of zirconium, 0.7% of tantalum, 12% of oxygen and, preferably, the rest of titanium; or 24% of niobium, 0.5% of oxygen and, preferably, the balance of titanium; or 26.32% niobium, 2% zirconium, 0.68% tantalum, 1.5% oxygen, and most preferably the titanium residue; or 25.1% niobium, 4.32% aluminum and, preferably, the rest of titanium.

In one embodiment, the alloy comprises less than 0.1 at.% Of one of the following impurities: silicon, iron, carbon, and nitrogen. Preferably, the oscillator is a spiral spring, and the present invention also relates to a sprung-balance assembly comprising said spiral, and a watch movement comprising the sprung-balance assembly.

An advantage of the oscillator of the invention is its low thermoelastic coefficient (CTE) reducing the need for thermocompensation of the spiral spring. The natural oscillation frequency of the sprung balance assembly is therefore more stable as a function of the

temperature. In addition, the spiral spring of the invention is practically insensitive to magnetic fields and the operation of the balance-spiral assembly will not be disturbed by such magnetic fields. Other advantages of the invention will appear on reading the description which follows. Brief description of the figures

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

Figure 1 shows a top view of a sprung-balance assembly for a watch movement, according to one embodiment;

Figure 2 shows an axial sectional view of the sprung balance assembly, according to one embodiment; and

FIGS. 3, 4 and 5 show the evolution of the Young's modulus according to the temperature, as well as the CTE, on various samples of the titanium alloys concerned by the invention.

Example (s) of Embodiment of the Invention [0015] FIGS. 1 and 2 illustrate, by way of example, a sprung balance assembly 1 intended for a watch movement. FIG. 1 shows a view from above of the sprung balance assembly 1 comprising a rocker 2 and a spiral (or spiral) spring 3. The rocker 2 comprises a serge 4 and two radial arms 5 made in one piece with the serge 4. The rocker 2 is mounted on a shaft 6 which can be manufactured conventionally steel or any other material. Referring to Figure 2 which is an axial sectional view of the sprung balance assembly 1, is also shown a double exhaust plate 7 and an impulse pin 8, intended to cooperate with an anchor (not shown) . The inner end of the hairspring 31 can be fixed to the shaft 6, for example, by means of a collar 9. The outside of the hairspring 32 can be fixed on the balance 2, for example via a piton (not shown). The other elements of the regulating organ are conventional and are not

However, it is admitted that the rocker is set in motion, for example, thanks to the energy provided by an escape wheel and an exhaust anchor. In one embodiment, the hairspring 3 is made of a titanium alloy, in particular of the β type, which has a very low Young's modulus (or modulus of elasticity) and a very high elastic deformation limit σ. compared to those of a conventional metal. More particularly, the alloy comprises titanium, at least one of tantalum, niobium and vanadium, and oxygen. The alloy may also comprise zirconium and / or hafnium.

In one embodiment, the titanium alloy has a

composition comprising (in atomic percentages) between 55 at.% and 80 at.% of titanium, between 20 at.% and 30% of at least one of Nb, Ta or V; between 0.1 at.% and 3 at.% oxygen, between 0 at.% and 6 at.% zirconium; and between 0% and 5% of hafnium.

In one advantageous embodiment, the titanium alloy has a composition comprising (in atomic percentages):

a titanium base;

between 10% and 40% of at least one of niobium, vanadium or tantalum;

between 0% and 3% oxygen;

between 0% and 6% zirconium;

between 0% and 5% hafnium;

between 0% and 5% aluminum.

The composition of the titanium alloy may also comprise impurities typically comprising less than 0.5% of silicon, less than 0.5% of iron, less than 0.5% of carbon, and less than 0.5% of nitrogen. In particular, the titanium alloy comprises between 10% and 40% of at least one of niobium, vanadium or tantalum; between 0% and 3% oxygen; between 0% and 6% zirconium; between 0% and 5% hafnium; between 0% and 5% aluminum; less than 2% impurities; and the rest of titanium. [0021] Preferably, the composition of the titanium alloy

comprises between 23 at.% and 27 at.% of at least one of Nb, Ta or V, and more preferably the alloy comprises between 23 and 27 at.% Nb. In a variant, the alloy comprises between 0.6 and 0.7 at.% Of Ta. In another variant, the alloy comprises between 1.1 and 1.2 at.

oxygen. In yet another embodiment, the alloy comprises 2 at.% Zr.

Still preferably, the composition of the titanium alloy comprises one of the following compositions (in atomic percentages):

Composition 1: 23% niobium, 2% zirconium, 0.7% tantalum, 12% oxygen and, preferably, the rest of titanium.

Composition 2: 24% niobium, 0.5% oxygen and, preferably, the rest of titanium.

Composition 3: 26.32% niobium, 2% zirconium, 0.68% tantalum, 1.5% oxygen, and most preferably the titanium residue.

Composition 4: 25.1% niobium, 4.32% aluminum and, preferably, the rest of titanium.

In the ranges of temperature and the specific tolerances required by the watch industry, the titanium alloy has advantageous properties compared to other materials including other types of titanium-based alloys. Table 1 compares certain physical properties of the titanium alloy which is the subject of this invention with a grade 2 titanium alloy, a grade 5 titanium alloy and an elinvar type alloy. The data in Table 1 refer to composition 1: Ti-23% Nb-0.7% Ta-2% Zr-1 .2% 0 (% at). Other compositions may also comprise Ti-9% Nb-12% Ta-3% V-6% Zr-1 .5% 0 (% at.) Ref. [Saito et al. Science 300 (2003) 464-467], Ti-20% Nb-0.7% Ta-2% Zr-2% 0 (% at.) Ref. [T. Furuta et al. Mater. Trans. (2007) 1 124-1 130] or Ti-25.1% Nb-4.32% Al (% at.) Ref. [Matlakhova et al. Revista Metéria 1 1 -1 (2007) 41 -47]. These results show that, in comparison with the other titanium and elinvar alloys, the titanium alloy considered has a lower density, a lower Young's modulus and a lower thermoelastic coefficient (CTE) β. Like the other titanium alloys, and unlike Elinvar, the titanium alloy considered is non-ferromagnetic. The titanium alloy considered may also have a degree of hardening greater than 90%. (ref [Saito et al., Science 300 (2003) 464-467], [Kuramoto, S. et al.

Mater. Se. Eng A442 (2006) 454-457], [M. Tane et al. Acta Mater. 61 (2013) 139-1 50]).

Table 1

The spiral 3 titanium alloy according to the present invention will likely be insensitive to temperature. Its frequency is very stable and varies very little depending on the temperature. In addition, this material is likely to be consistent with the margins established by the chronometric criteria of the Swiss watch industry.

By its lower density, the spiral 3 of the invention has the advantage of a lower displacement of its center of mass due to its gravity. The spiral 3 sags therefore less under its own weight. The effect of

movement of the center of mass on the watch is also weaker. Indeed, the torque disrupting the movement of the watch because of the displacement of the center of mass is directly proportional to the mass of the hairspring. In the case where the hairspring has a large diameter, the impact of the inertia of the hairspring relative to the inertia of the pendulum will be even lower. The lighter titanium alloy hairspring also makes it possible to have an oscillation frequency and therefore a resolution greater than a conventional hairspring. In other words it is possible to make a spiral spring which has the same high oscillation frequency as a known smaller spiral. The low Young's modulus of the spiral 3 made in the titanium alloy concerned makes it possible to increase the thickness of the spiral 3, for example with respect to a spiral in élinvar, for the same stiffness. The inaccuracies in the manufacture of the hairspring 3 resulting in a change in thickness of the hairspring will thus have less influence on the stiffness of the hairspring 3. In other words, at equal thickness, the spiral spring made of titanium alloy may have a greater height. that a spring élinvar conventional and therefore a lower collapse of the spiral spring 3 when the latter is arranged in the plane of a watch movement.

The hairspring 3 regulates the oscillation period of the pendulum 2. The accuracy of a movement of a mechanical watch depends on the stability of the natural frequency of the oscillator formed by the hairspring 1. When the temperature varies, the thermal expansions of the spiral 3 and the balance 2, as well as the variation of the Young's modulus of the spiral 3, modify the natural frequency of this oscillating assembly, disturbing the accuracy of the watch.

The spiral 3 made of titanium alloy which is the subject of this invention is diamagnetic and is not disturbed by a magnetic field.

Furthermore, the titanium alloy has a coefficient of thermal expansion whose amplitude is about ten times lower than that of grade 2 and 5 titanium alloys and élinvar (see Table 1). The The sensitivity of the spiral 3 to temperature variations is therefore very low and the natural frequency of the sprung balance 1 comprising the spiral 3 will therefore be very little influenced by these temperature variations. The method of manufacturing the spiral 3 can therefore be simplified compared to that of a thermocompensated spiral, for example by the application of an additional coating on the surface of the spiral. It is however possible to compensate thermally 3 spiral. For example, the coefficient

thermoelastic β of the titanium alloy can be modified by a

heat treatment of the alloy or by cold deformation. FIGS. 3 and 4 show experimental measurements of Young's modulus (E) and CTE as a function of temperature for the titanium alloy according to composition 1 (FIG. 3) and composition 3 (FIG. 4). FIG. 5 shows values of the evolution of the Young's modulus (E) and of the CTE according to the temperature in the for the titanium alloy according to the composition 4 measured by Matlakhova et al. in Revista Metéria 1 1 -1 (2007) 41 -47.

In one embodiment, the rocker 2 is also made of the same titanium alloy as that used to manufacture the spiral 3. The embodiment of the balance 2 and the spiral 3 from the same alloy avoids the compensating effect of the balance spring 3 with respect to the balance 2, which thus has an almost constant inertia. As a result, self-compensation between the balance and the balance spring becomes negligible.

Alternatively, the rocker 2 can also be made of other materials and having characteristics favorable to the manufacture of a rocker for use in a pendulum-balance assembly of a timepiece. Examples of these materials for the balance 2 include, among others, silicon, quartz, glass, silicon carbide, or ceramic. These materials are appreciated for their lightness, their elasticity, their non-magnetic character, favoring their use in the aforementioned field. In another embodiment, the hairspring 3 (and the pendulum 2) can be produced using a laser cutting, wire cutting, machining, rolling, drawing or wire cutting process. an equivalent process. The hairspring 3 can also be made using a rolling and deformation process, or any other suitable method. A surface treatment can also be applied to the spiral spring thus produced.

Instead of a hairspring 3, the oscillator of the present invention may have other shapes, such as in particular a tuning fork.

Reference numbers used in the figures

1 spiral balance assembly

2 pendulum

3 spiral spring

4 serge

5 radial arms

6 tree

7 double exhaust tray

8 impulse ankle

9 ferrule

31 inner end of the hairspring

32 outer spiral spiral

Claims

claims

1. Oscillator (3) for equipping a balance (2) with a balance spring assembly (1) of a mechanical timepiece, characterized in that the oscillator is made of a titanium alloy comprising a base of titanium and between 10 and 40 at% of at least one of Nb, Ta or V; between 0% and 3% oxygen, between 0% and 6% zirconium; and between 0% and 5% of hafnium.

Oscillator according to claim 1,

wherein the alloy comprises from 55 to 80% to 80% by weight of titanium, from 20 to 30% by weight of at least one of Nb, Ta or V; and between 0.1 at.% and 3 at.% oxygen; between 0% and 6% zirconium; and between 0% and 5% of hafnium.

Oscillator according to Claim 1 or 2,

wherein the alloy comprises between 0% and 5% aluminum.

Oscillator according to one of Claims 1 to 3,

wherein the alloy comprises between 0.3 and 3 at% oxygen.

Oscillator according to one of Claims 1 to 4,

wherein the alloy comprises between 23 and 27 at% of at least one of Nb, Ta or V.

Oscillator according to Claim 5,

wherein the alloy comprises from 23 to 27 at% Nb.

7. Oscillator according to claim 5 or 6,

wherein the alloy comprises between 0.6 and 0.7 at.% Ta.

Oscillator according to one of Claims 5 to 7,

wherein the alloy comprises between 1.1 and 1.2 at% oxygen.

Oscillator according to one of Claims 5 to 8,

wherein the alloy comprises 2 at.% Zr.

10. Oscillator according to claim 9,

wherein the alloy comprises 23% niobium, 2% zirconium, 0.7% tantalum, and 12% oxygen.

1 1. Oscillator according to claim 10,

wherein the remainder of the alloy comprises titanium.

Oscillator according to Claim 9,

wherein the alloy comprises 26.32% niobium, 2% zirconium, 0.68% tantalum, and 1.5% oxygen.

Oscillator according to Claim 12,

wherein the remainder of the alloy comprises titanium.

Oscillator according to claim 5 or 6,

wherein the alloy comprises 24% niobium and 0.5% oxygen.

5. The oscillator according to claim 14,

wherein the remainder of the alloy comprises titanium.

Oscillator according to claim 5 or 6,

wherein the alloy comprises 25.1% niobium and 4.32% aluminum.

17. Oscillator according to claim 16,

wherein the remainder of the alloy comprises titanium.

18. Oscillator according to one of claims 1 to 17,

wherein the alloy further comprises less than 0.1 at.% of one of the following impurities: silicon, iron, carbon, and nitrogen.

19. Oscillator (3) according to one of claims 1 to 18, wherein the oscillator is a tuning fork.

20. Oscillator (3) according to one of claims 1 to 18, wherein the oscillator is a spiral spring.

21. Spiral spring according to Claim 20,

performed using a laser cutting, wire cutting, machining, rolling or drawing process.

22. Sprung balance assembly (1) comprising the hairspring (3) according to claim 20 or 21.

23. sprung balance assembly (1) according to claim 22, wherein the rocker (2) is made of the same titanium alloy that used to manufacture the spiral (3).

24. Watch movement comprising the sprung balance assembly (1) according to claim 23.