EP2510405A1

EP2510405A1 - Method for making a spring for a timepiece

Info

Publication number: EP2510405A1
Application number: EP10801554A
Authority: EP
Inventors: Thomas Gyger; Vincent von Niederhäusern
Original assignee: Rolex SA
Current assignee: Rolex SA
Priority date: 2009-12-09
Filing date: 2010-12-09
Publication date: 2012-10-17
Anticipated expiration: 2030-12-09
Also published as: JP5744050B2; JP2013513781A; US9104178B2; EP2510405B1; CH704391B1; WO2011069273A1; US20120281510A1; CN102713770B; CN102713770A

Abstract

The invention relates to a method for making a spring for a timepiece that comprises at least one monobloc ribbon of metal glass including at least one curvature. The method is characterized in that said method comprises the step of shaping by means of plastic-deformation said monobloc ribbon in order to obtain at least a portion of said curvature.

Description

METHOD FOR MANUFACTURING A SPRING FOR A WATCHPIECE PART

The present invention relates to a method of manufacturing a spring for a timepiece which comprises at least one monolithic ribbon of metal glass comprising at least one curvature.

It has already been proposed in EP 0 942 337 a watch comprising a motor spring amorphous metal. In fact, only one blade formed of an amorphous metal laminate assembled with epoxy resin is described herein. Alternatively, a blade assembly by spot welding of both ends and the point of inflection of the free spring shape has been proposed.

The major problem of such a blade is the high risk of delamination of the laminate during its shaping and following repeated arming and disarming to which such a spring is subjected. This risk is all the more accentuated as the resin ages poorly and loses its properties.

This solution does not guarantee the functionality and the fatigue behavior of the spring. In addition, the modeling of the theoretical form of the proposed spring does not take into account the behavior of a laminate material.

The use of several thin blades assembled is due to the difficulty of obtaining thick metal glass blades, the known methods developed in the 1970s for amorphous ribbons used for their magnetic properties, making it impossible to manufacture than ribbons up to thirty microns by rapid quenching.

The international application published under the number WO 2007/038882 describes a composite material composed of a substantially continuous amorphous matrix comprising graphite particles. This composite material is supposed it can be used to manufacture particularly springs, however, no indication is given as to the process of. manufacture of such springs. In addition, the size of the particles dispersed in the matrix of the composite is of the same order of magnitude as the typical thickness of watch springs, which raises doubts about the use of such a composite for this application.

US Patent No. 5,772,803 relates to an object comprising a torsion spring obtainable by cooling at a speed less than 500 ° C / s of a liquid metal alloy to obtain a massive amorphous metal alloy, then put in the shape of this alloy. The only formatting mentioned in this document is casting in a mold. It turns out that the casting of an alloy with high mechanical performance, in particular with a high elastic limit, produces ribbons that are flexibly brittle in the dimensions necessary to make a mainspring.

French patent No. FR 1 553 876 relates to a device and a method for the manufacture of watch spirals. The nature of the strips used for the manufacture of these spirals is not indicated in this document. Given the age of the document, it can be assumed that it is a polycrystalline metal alloy for Invar®-type self-compensating coil springs, such as the Nivarox® alloy (FeNi base alloy).

U.S. Patent No. 3,624,883 relates to a method of manufacturing a spring wound spirally and attached to a ferrule comprising attaching a ribbon to a ferrule and then rotating the latter and submitting of the assembly to a heat treatment to freeze the ribbon in its wound position. The nature of the ribbon is not indicated in this document. This patent claiming a priority dated 1968, and given the description, it is likely that the ribbon was polycrystalline metal alloy for spiral springs (hair spring) of the same type as that described in the French patent No. FR 1 553 876 cited above. It is known to those skilled in the art that the role and therefore the properties of the spiral spring are very different from that of the mainspring or mainspring.

The application of the. The aforementioned technique to metal glasses is therefore not obvious because of the large differences between a crystalline metal alloy and an amorphous metal alloy called "metal glass".

As indicated in the "Backgroud of the invention" part of the aforementioned international application No. WO 2007/038882, solid metal glasses are fragile and therefore their plastic deformation at ambient temperature is strongly discouraged.

Similarly, in their article "Deformation behavior of the Zr ₄ i.2 ii3. Cui2.5NiioBe ₈ ₂ 5 2. bulk metallic glass over a wide-range of strain-rates and temperatures Materialia Acta 51, 3429-3443 (2003) , authors J. Lu et al., state "In spite of their metallic bonding, the following is the case:" (see page 3430, 2 ^nd paragraph).

The plastic deformation of an amorphous metal alloy is only possible by the creation of sliding strips. This deformation mechanism is totally different from that of crystalline metal alloys. Plastic deformation of an amorphous metal alloy is generally undesirable because it results in a rapid breakage of the stressed part.

It is therefore clear to those skilled in the art that the elastic limit is a limit not to be crossed under pain to damage the material. Therefore, for those skilled in the art, any plastic deformation of a solid metal glass is to be avoided.

Another fundamental difference between a multi-phase polycrystalline alloy such as Nivaflex® (CoNiCr base high performance alloy) and an amorphous metal alloy is that, in order to achieve its maximum mechanical properties, the Nivaflex® alloy must be hardened by hardening and by precipitation of phases during a heat treatment. In the case of an amorphous metal alloy, its mechanical characteristics are obtained during solidification and its mechanical properties can not be improved by plastic deformation and / or a subsequent heat treatment. Thus, it is necessary to apply heat treatment Nivaflex® barrel springs to obtain the desired mechanical properties, which is not the case for a metal glass spring.

Summary of the invention

The inventors discovered with surprise that it was possible to plastically deform a ribbon of metal glass, and to use it industrially with its plastic deformation, in particular in the form of a spring mechanically stressed repeatedly in the barrel of a watch movement.

They then used this discovery in a method of manufacturing a spring for a timepiece according to claim 1.

This method therefore makes it possible to manufacture functional clock springs made of metal glass, in particular cylinder springs, on an industrial scale. The characteristics and advantages of the method which is the subject of the invention will become apparent during the description which follows, illustrated by various diagrams.

Figure 1 is a ductility / brittleness diagram depending on the annealing conditions;

Figure 2a is a fixing diagram at different temperatures;

Figure 2b is a break strain chart versus annealing time at different temperatures;

Figures 3a, 3b are diagrams corresponding to those of Figures 2a and 2b for another alloy; Figures 4a, 4b are diagrams corresponding to those of Figures 2a and 2b respectively for another alloy; Figure 5a is a plan view of the free form of a spring;

Figure 5b is a plan view of the free form of the same spring whose curvatures correspond to 60% of the theoretical free form; and

FIGS. 6a and 6b show the winding / disarming curves of a barrel spring, part of which has been shaped hot, and the inner part has been shaped by plastic deformation, respectively of a mainspring of which the shaping was done entirely by plastic deformation (cold forming), with the torque in [mNm] as a function of the number of revolutions of development.

Detailed exposition of the invention

For the implementation of the method according to the invention, it is advantageous to use a metal alloy capable of forming, by cooling an amorphous or essentially amorphous metal alloy, called "metallic glass", in because of the excellent mechanical properties resulting from their particular structure.

It is particularly advantageous to use metal glasses whose mechanical properties are superior to those of conventional polycrystalline alloys used in the prior art, such as the Nivaflex® alloy. As a result, the invention presented below relates more particularly to metal glasses whose elastic limit is greater than 2400 MPa.

Examples of such amorphous metal alloys include alloys based on Ni, Co and / or Fe.

During their research, the inventors have also found that to achieve a functional spring, that is to say guaranteeing a certain restoring torque and good reliability when used in a timepiece, the ribbon must preferably be made of an amorphous or essentially amorphous alloy with the thickness required to achieve the functional properties and to be initially ductile in flexion. Indeed, beyond a certain thickness, the ribbon can show a fragile behavior in bending, which would degrade the reliability of the spring.

To obtain a high-performance clock spring, such as a mainspring, the thickness of the ribbon will advantageously be at least 50 μm, since smaller thicknesses do not make it possible to obtain a sufficient return torque. Likewise, the thickness will advantageously be from

According to an advantageous embodiment of the invention, one obtains both a small thickness and an amorphous character by hypertrempe, or by projecting the liquid metal alloy capable of forming the metallic glass on a cold and moving substrate, such as a rotating cylinder, possibly a rotating cylinder cooled with water.

Such a projection can be achieved for example by implementing a method such as "Planar flow casting", "Melt-spinning" and "Twin roll casting".

Preferably, the parameters of the projection and the cooling are chosen so as to obtain a cooling rate of the liquid metal alloy greater than 10000 ° C./s. Such a cooling rate, obtained by hyper-quenching, indeed favors the ductility by the formation of "free volume" in the structure of the metallic glass.

The cooling rates obtained using a molding technique, such as for example the injection of the liquid metal alloy into a copper mold, are significantly lower and do not allow, for high-strength metal glasses of which we have knowledge, to obtain both a sufficient thickness and ductility to the good function of a high performance watch spring.

In addition, it is desirable that the projection is performed so as to obtain a monolithic ribbon having a thickness between 50 and 150 μπι, preferably between 50 and 120μιτι, and more preferably between 50 and 100 μπι. The metal glass obtained under these conditions is then clearly different from solid metallic glass ("Bulk metallic glass (BMG)") whose thickness is greater than 1 mm.

In the case of the mainspring, the spring can not be used directly after the casting in the form of straight ribbon, but must be shaped in order to develop the desired torque, as described in WO 2010/000081A1. We must therefore be able to format the ribbon so that it takes a given free form, before the stages of strapping and winding in a barrel.

As regards the shaping of the monolithic ribbon of metal glass, the plastic deformation is advantageously carried out at ambient temperature and under ambient atmosphere. This plastic deformation must not degrade the mechanical properties of the tape, so as to allow its repeated mechanical stress, for example in a barrel.

According to an advantageous embodiment of the invention, in addition to the curvature formed by plastic deformation, an additional curvature is achieved by deforming the tape elastically, for example in a setting, and fixing the new shape obtained with a heat treatment to a temperature and for a duration not leading to weakening of the spring. This additional curvature can in particular be carried out on the portions of the ribbon which are not curved by plastic deformation. The heat treatment may be ^"carried out before or after the plastic deformation, preferably before plastic deformation, in particular if the heat treatment affects the plastically deformed zone.

The appropriate temperature and treatment time (annealing) are chosen in a temperature and duration window in which the alloy of said metal glass retains its ductile flexural behavior. This window thus corresponds in practice to a deformation at break greater than 2%. These conditions make it possible to achieve the following objectives:

i) lengthen the duration of treatment limit before fra ^¬ gilisation, ii) fix the shape, iii) maintain the mechanical properties obtained after manufacture of the tape (hardness and ductility) and iv) avoid crystallization. Example 1

Tapes of Ni ₅ 3Nb2oZr ₈ TiioCo ₆ Cu ₃ (yield strength: 2600MPa) were made by "planar flow casting", which consists in forming a flow of liquid metal on a cooled wheel. From 10 to 20 g of alloy are placed in a dispensing nozzle heated between 1050 and 1150 ° C. The slit width of the nozzle is between 0.2 and 0.8mm. The distance between the nozzle and the wheel is between 0.1 and 0.3mm. The wheel on which the molten alloy is deposited is a copper alloy wheel and driven at a speed of 5 to 20m / s. The pressure exerted to bring the molten alloy out through the nozzle is between 10 and 50kPa. Table 1 below gives the characteristics of three ribbons obtained.

Table 1 - Characteristics of three ribbons used in alloy i ₅ 3Nb2oZr ₈ iioCo6Cu3

Thermal properties were measured by DSC

(Differential Scanning Calorimetry) on Setaram Setsys

Evolution 1700 at 10 ° C / min under Ar 20ml / min:

· Tg = 558 ° C ± 2 ° C

• ^■ Tx = 606 ° C ± 1 ° C

Tg and Tx are little influenced by the conditions of elaboration of the ribbons.

To determine the fixing coefficient of the shape of the spring, a ribbon is wound in a ring of internal diameter C 0 and the diameter taken by the ribbon after the heat treatment is measured in its free state, or diameter "fixed" D _f . The fixing coefficient is calculated by the ratio between the fully relaxed diameter, assumed to be equal to the inside diameter of the ring C, and the diameter of curvature of the fixed tape D _f .

Form fixing relaxation annealing was performed on 30mm long tapes wound inside aluminum rings with an internal diameter of 7.8mm, which is close to typical spring bending diameters. barrel. A Logotherm® resistance furnace in ambient atmosphere was used. The rings are placed on thermostatic alumina studs in the center of the oven to ensure temperature homogeneity and rapid heat transfer. The treatment time is counted from the moment of closure of the oven door. One second before the end of the countdown, we take the ring with a pair of pliers and soak it very quickly in about 2 liters of water at room temperature.

Once the tape has cooled down, the bending diameter of the relaxed tape is measured with a vernier caliper with an accuracy of 0.2mm.

To evaluate the ductile or brittle nature of the bending tape, the tape attached between the two parallel surfaces of the caliper is placed as in a 2-point bend test. The gap at break is noted by slowly bringing the two parallel surfaces of the caliper closer together.

To determine the deformation at break of the ribbon or blade, it must be taken into account that the curvature of a blade bent at 180 ° between two parallel surfaces at a distance B from each other is not constant radius. It goes through a maximum located at the apex. The radius of curvature at the apex is related to the spacing by the following relation, and does not depend on the properties of the material nor the dimensions of the ribbon: Equation 1 with α = 0.835

Apex deformity is expressed approximately as e

Equation 2 ε =

2R aB

For a ribbon with an initial curvature K ₀ = 1 / non-zero Ro, the deformatio to the external fiber becomes:

Equation 3

We obtain the maximum deformation before rupture ε _Γ with the breaking gap B _r and the initial curvature (0.5 Do) -1

When B _r becomes 2 * e, the deformation is limited to 1.

The sample is considered fragile if the deformation at rup ^¬ ture is less than 2% (without any prior plastic deformation).

FIG. 1 represents the mechanical behavior of the Ni ₅ 3Nb ₂ _O Zr ₈ Tii ₀ Co ₆ Cu ₃ alloy strips at a thickness of 81 microns at the different temperatures and annealing times to which they have been subjected. It can be seen that there is a window of annealing parameters that does not weaken the ribbons. This window is large enough to allow formatting reproducibly. The time limit increases by decreasing the temperature. For annealing in an oven, it is necessary to place in the case of this alloy at more than 50 °, advantageously 100 ° C., below Tg to have a suitable time from the technological point of view, ie a duration of several minutes at least. With hot air heating followed by quenching, the technologically suitable treatment time is shorter (less than one minute) and the temperature may be accordingly higher. As stress relaxation following the fixing of the form is not _complete. the form after fixing treatment is dilated with respect to the shape imposed during the annealing. It was noted that the fixing coefficients Do / D _f for a given temperature were aligned on a sigmoidal curve and that the curve could be modeled by equation (4), which is a model that was used to describe some aspects of the relaxation of metallic glasses, in particular by Fan et al (Acta Materialia 52 (2004) 667-674):

Equation 4

where β and t ₀ are constants.

The relaxation of the curvature is faster for a thin ribbon than for a thick ribbon. It was found that the Evolu ^¬ curvature does not depend on forced diameter, which allows to have a single fixing coefficient D ₀ / D _f for the shaping of a deflection adjusting spring. The COMPOR ^¬ apparel depicted in Figure 2 (a) show that the higher the temperature, the higher the relaxation is fast.

The essentially amorphous nature of the raw and annealed ribbons was confirmed by X-ray diffraction. Two anneals were analyzed: the first in the ductile domain (430 ° C / 30min) and the second in the brittle domain (530 ° C / 10min ). Thus, no crystalline phase is detected in any of the samples. It should be noted, however, that this characterization technique would not allow to detect with certainty the presence of nanocrystals, which is not excluded. On the other hand, these nanocrystals can sometimes play a favorable role for the mechanical properties of metallic glasses. It is apparent from Figures 1 and 2a that the higher the temperature, the more ductile-brittle transition occurs at high fixing coefficients. Thus, for the Ni ₅₃ b ₂ ozr ₈ iioCo ₆ Cu _3, only near the glass transition temperatures allow to fix the shape of more than 95% without embrittlement.

Example 2

FIGS. 3a, 3b respectively show fixing and breaking deformation curves for a 68 μτα thick ribbon made of an amorphous Nx ₆ oa ₄ o (at.%, Elastic limit: 2900 MPa) alloy, whose Tg = 740 ° C and Tx = 768 ° C. These curves resulting from tests at 520 ° and 570 ° C show that the fixing behavior is similar to that of the alloy Ni ₅₃ Nb ₂ oZr ₈ TiCo ₆ Cu ₃ and that at 520 ° C, embrittlement does not occur. reached for the durations tested (up to 30 minutes).

Example 3

FIGS. 4a and 4b respectively show fixing and breaking deformation curves for a 73 μηα thick strip made of an organic N ₂ O ₃ alloy (elastic limit: 2700 MPa), whose Tg = 721 ° C. C and Tx = 747 ° C. These curves also show that the behavior is comparable to that of the two previous alloys.

The results reported on these diagrams make two observations: i) it is possible to give a curvature to a metal glass ribbon by fixing below its glass transition temperature and ii) there is a temperature range and of treatment time in which the alloy remains ductile.

The sigmoidal behavior of the expansion and deformation at break as a function of time or annealing time, observed on the strips of Ni ₅₃ Nb ₂ OZr ₈ TiCo ₆ Cu ₃ , is similar to that of the other alloys tested. This behavior has also been observed on Fe- and / or Co-based alloys, some of which do not show Tg or have Tg> Tx. It can therefore be assumed that this behavior is generalizable to other metal-glass alloys, and is therefore not limited to Ni-based alloys and / or those that exhibit a Tg <Tx.

As a general rule, an alloy must satisfy a necessary condition so that the shaping below Tg, respectively below Tx for an alloy does not show Tg or with Tg> Tx, can be used for a spring: the superimposition of "fixing" and "ductility" windows. In the cases presented, the time required to fix the shape is significantly less than the time limit which corresponds to the transition to a fragile state.

It has already been mentioned that the fixing coefficient depends on the thickness of the ribbon but not on the imposed curvature. The inventors have verified that it is possible to obtain the theoretical free form of a mainspring using a single fixing coefficient by performing a copper setting. A 0.3 mm thick slit was electroeroded in a 1.5 mm thick copper plate, with a profile corresponding to the desired free shape of the spring but with curvature radii contracted to 60% to account for expansion Do / D _f , while maintaining the length of the different segments of the free form at 100%.

A metal glass ribbon was placed in the slit of the installation by making it undergo an elastic deformation and the fixing process was carried out in an oven under ambient atmosphere between two ceramic studs thermostated at 430 ° C., for 3 min, followed by the tempering of the pose. This treatment corresponds to a fixing at C / D _f = 60% according to the abaques obtained by ring fixing. The ribbon, once out of his pose, shows a free form corresponding almost perfectly to the desired free form. Figures 5a, 5b respectively represent the desired free shape and the free form with the curvatures contracted at 60% of the setting.

According to another embodiment of the method, the spring is shaped not in an oven but by hot gas jet. A device of type "Sylvania Heater SureHeat Jet 074719" with a power of 8kW is used to heat compressed air and project it against the setting containing the tape. The apparatus makes it possible to heat a gas (air, or a neutral gas such as argon, nitrogen or helium) up to 700 ° C., the ribbon being inserted into the slot of the copper setting by elastic deformation as previously.

The copper installation is placed perpendicular to the hot gas distribution tube. It could also be maintained with a certain inclination, for example 45 °. The fixture is mounted on a three-position linear guiding system for i) placing the copper fixture in a raised position, out of range of the gas jet ii) positioning it in the hot gas jet and iii) immersing it immediately in a cooling liquid, such as water for example, at the end of hot treatment.

According to still other embodiments of the method, the setting containing the tape is placed in a vacuum oven, or between two ceramic hot plates, these modes being given by way of non-limiting examples. The shaping can also be carried out in two or more stages of heat treatment.

So far, we have considered only the fact of fixing a desired shape to a ribbon initially substantially straight, that is to say without any other curvature than that resulting the manufacture of the ribbon. The shape given corresponds precisely to the shape of the negative or positive curvatures of a mainspring around a point of inflection. However, the parts at both ends are wound inside circular recesses in the pose made necessary by the limitations due to the thickness of the slit become greater than the inter-turn space of the desired free shape; they can not follow the desired shape along the length of the spring.

With a crystalline alloy ribbon for springs commonly used, such as for example Nivaflex®, obtaining the desired shape could be done by cold plastic deformation. This is particularly the case for the inner end of the spring ("shells", "shelling" stage). It is indeed necessary to secure the spring to the barrel shaft: as the theoretical curve of the spring gives larger radii of curvature than that of the shaft, it becomes necessary to bind the curvature formed by the spring around the shaft, at the theoretical curvature, by a cold deformation of the spring.

However, this step can not be transposed directly to the metal glass ribbons: as indicated above, the plastic deformation of the metal glasses is strongly discouraged.

Surprisingly, it was found that plastic deformation of the ribbon was possible for the various alloys tested, without fragile breaking of the ribbon and without affecting the mechanical properties of the shaped ribbon. Such a ribbon can then be used as a spring, in particular as a high performance spring, more particularly as a mainspring. This unexpected finding thus makes it possible to give the desired final shapes by cold plastic deformation before or after a possible heat treatment for fixing. This shaping by plastic deformation can be limited to the shell (internal end, see below), but can also be performed on a larger part of the spring, or even on the whole of the shape given to the spring.

Note here that the squab (cut at the inner end of the spring which allows it to hang on the pin of the plug of the barrel shaft) is cut by stamping in a traditional way. Other methods of attaching the spring to the barrel shaft can of course be used, such as welding.

A sliding flange intended to be fastened to the outer end of the spring is made in a strip of thickness 110 μιη of the same alloy as that of the ribbon, obtained by the same technique of "planar flow casting" and shaped by deformation cold plastic (see below) to give it the typical curvature of a self-winding, self-locking barrel spring flange. The welding is carried out by resistance (by point) as usual. Other fixing modes are of course also conceivable, such as laser welding for example.

FIG. 6a shows the armoring and disarming characteristic of a spring of alloy Ni ₅₃ Nb ₂ oZr ₈ TiCo ₆ Cu ₃ of 81μπι of thickness shaped by cold plastic deformation for the internal end (shell), then by heating hot gas jet in a setting as described above, with conditions corresponding to a fixing coefficient of 60%. The spring gives a completely satisfactory behavior, making it possible to reach the desired torque and number of turns, and shows a good fatigue behavior. However, the spring measured in FIG. 6a comprises a shell formed by cold plastic deformation over a greater or lesser length (typically 40 mm in the case of FIG. 6a) with good reproducibility, and the resulting mainspring spring shows good performance. The inventors therefore wanted to know if the method for obtaining the curvature of the shell by plastic deformation was applicable to the entire spring.

The technique of shelling consists of deforming the blade by hammering. The adjustment of the curvature is effected by two parameters: the step of displacement of the ribbon between two hammer strokes and the amplitude of the deformation, regulated by the angle of rotation of the hammer around its axis. It is necessary to adjust the parameters according to the alloy and the thickness of the ribbon.

The shaping by cold plastic deformation takes place in two stages: first, the outer end of the ribbon is introduced in order to apply a negative curvature according to the desired theoretical curvature up to the point of inflection. Then the inner end is introduced to apply a positive curvature according to the theoretical curvature.

FIG. 6b shows the armoring and disarming characteristic of a Ni ₅₃ Nb ₂ oZr ₈ Tii ₀ Co ₆ Cu ₃ alloy spring of 81μπι thickness shaped by cold plastic deformation only. Despite the absence of fixing by heat treatment, the behavior of the spring is in all respects comparable to that of Figure 6a.

The shaping of metal glass alloy ribbons by plastic deformation is not limited to the alloy only Ni ₅₃ Nb ₂ oZr ₈ iioCo ₆ Cu ₃ . For example, the alloys of Figures 3 and 4 can also be shaped by plastic deformation. Other amorphous Ni base alloys, Fe and / or Co may also be shaped with at least one plastic deformation step, and may be heat-treated to obtain additional curvature.

As can be seen in the foregoing description, it is possible to give a curvature to a ribbon of amorphous metal alloy at temperatures well below Tg, respectively well below Tx for an alloy showing no Tg or with Tg> Tx, this for several families of amorphous alloys. The "fixing coefficient", that is to say the ratio between the imposed curvature and the curvature obtained after heat treatment, depends on the thickness of the tape but does not depend on the curvature imposed, thus making it possible to implement shape of a barrel spring with variable curvature. This coefficient also depends on the shaping means used (furnace, jet of gas, etc.) and the characteristics of the equipment, because the temperature directly under the ribbon is difficult to measure accurately.

In addition, the fixing annealing must not make the ribbon fragile and must therefore be at a temperature and for a period less than the point of weakness. In our experience, several Ni-based amorphous alloys as mentioned herein, but also based on Fe or Co, exhibit sufficient annealing embrittlement resistance to apply hot forming to them.

The above implies that for an alloy having a good formatting window, several treatments can lead to the same rate of fixing of the shape. It is thus possible to choose the treatment conditions so as to maximize the performance of the spring, or even combine the treatments or combine them with one or more plastic deformations cold or hot. Finally, it is possible to fix the form of ribbons in various alloys, including Ni5 ₃ b2oZr ₈ TiioCo ₆ Cu3, plastically deforming the spring near the inner end, or over its entire length, supplementing if necessary the implementation shaped by heat treatment in an annealing window at a temperature below Tg and / or Tx, with an industrially applicable treatment time. The ribbons remain ductile, do not lose their mechanical strength and retain their amorphous or essentially amorphous character. This process makes it possible to obtain, among other things, functional barrel springs with excellent characteristics.

The method described above can also be applied to the shaping of other springs than the mainspring, whether for components of the watch movement (jumper spring, or sliding flange for a mainspring, for example) or watchmaking clothing, case or bracelet.

Claims

1. - Method of manufacturing a spring for a timepiece comprising at least one monolithic ribbon of metal glass comprising at least one curvature, characterized in that it comprises a step of shaping by plastic deformation of said monolithic ribbon so to obtain at least a portion of said curvature.

2. - Method according to claim 1, wherein the forming step by plastic deformation of the monolithic ribbon is preceded by a step of obtaining the ribbon which comprises the projection of a liquid metal alloy capable of forming a metal glass on a cooled and moving substrate.

3. - Process according to claim 2, wherein obtaining the monolithic ribbon metal glass is carried out by hyperemperature according to one of the methods called "Planar flow casting", "Melt-spinning", and "Twin roll casting" .

4. - Method according to claim 2 or 3, wherein the projection is performed so as to obtain a cooling rate of the liquid metal alloy greater than 10000 ° C / s.

5. - Method according to one of claims 1 to 4, wherein the projection is performed so as to obtain a monolithic ribbon having a thickness between 50 and 150 μηι.

6. A process according to one of claims 1 to 5, wherein the forming step by plastic deformation is preceded or followed by a step of fixing at least a portion of the monolithic ribbon.

7. A process according to one of claims 1 to 5, wherein the forming step by plastic deformation is preceded or followed by a step of fixing said curvature portion by heat treatment of at least this portion. of curvature.

8. The method of claim 7, wherein the fixing step is performed by an elastic deformation of said tape in a setting followed by a fixing of the shape by said heat treatment.

9. A process according to one of claims 7 and 8, wherein the heat treatment is carried out at a temperature and for a duration corresponding to a deformation at break of the metal glass greater than 2%.

10. - The method of claim 9, wherein said temperature of the heat treatment is less than 50 ° C below the glass transition temperature Tg of said metal glass or the crystallization temperature Tx for an alloy showing no Tg or in which Tg> Tx.

11. The process according to claim 10, wherein said temperature of the heat treatment is less than 100 ° C below the glass transition temperature Tg of said metallic glass or at the crystallization temperature. x for an alloy showing no Tg or in which Tg> Tx.

12. A method according to claim 8 or one of claims 9 to 11, when they refer to claim 8, wherein the setting used for shaping the spring comprises the profile of the spring substantially corresponding to the free shape desired for the spring with curvature radii contracted according to the fixing coefficient depending on the thickness and alloy of said ribbon and the temperature and duration chosen for fixing, the length of the segments of said profile corresponding to the length of said free form.

13. The method of claim 6 to 12, wherein the fixing coefficient is between 60% and 90%, preferably between 85 and 90%.

14. - Method according to one of the preceding claims, wherein said plastic deformation is performed at room temperature.

15. - Method according to one of the preceding claims, wherein using a metal glass having a yield strength greater than 2400 MPa.

16. - Method according to one of the preceding claims, wherein the spring is a barrel spring and the plastic deformation is applied at least to its inner part.

17. - Method according to one of claims 1 to 16, wherein the entire spring is shaped by plastic deformation.

18. - Method according to one of the preceding claims, wherein the spring is a mainspring comprising positive curvatures, respectively negative, on either side of a point of inflection.