EP3839652A1 - Hairspring for balance wheel-hairspring oscillator and method for manufacturing same - Google Patents

Abstract

Spiral spring (1) for a watch balance-sprung oscillator, the material of said spring (1) comprising a binary alloy comprising: - a mass percentage of gold between 45% and 55%; - possible impurities up to 0.5% in percentage mass; - the palladium balance.

Description

Technical area

The present invention relates to the field of watchmaking. It relates more particularly to a spiral spring for a balance-spring oscillator, the thermoelastic coefficient of which is close to zero.

State of the art

The most commonly used kind of clock oscillator today is the balance-spring oscillator. This oscillator is composed of an inertial mass mounted in bearings such that it is capable of pivoting in a back-and-forth rotation under the effect of a spiral spring (typically flat) which provides a torque of reminders. The oscillations are maintained by an escapement, a large number of types of which are well known to those skilled in the art.

If the elasticity of the spiral spring, that is to say its Young's modulus E, varies as a function of the temperature, the oscillation frequency of the balance-spring is not constant and the precision of the rate of the movement. is not guaranteed.

In order to solve this problem, many alloys have been developed, such as Elinvar, whose thermoelastic coefficient is close to zero in the temperature range encountered in practice (typically 0 ° C to + 40 ° C). By “thermoelastic coefficient” is meant the variation of Young's modulus as a function of temperature, that is to say dE / dT, and, for this reason, this parameter is also called “thermal coefficient of Young's modulus”. .

Watchmakers are always on the lookout for new materials for balance springs which are not only insensitive to temperature or not at all, but are also non-magnetic, corrosion resistant and from which the making of a balance spring is relatively easy. easy.

The aim of the invention is therefore to provide a spiral spring made of a material which fulfills these requirements, as well as its manufacturing process.

Disclosure of the invention

• un pourcentage massique d'or entre 45% et 55% ;
• des éventuelles impuretés jusqu'à 0.5% en pourcentage massique ;
• la balance en palladium.

More precisely, the invention relates to a spiral spring for a watch balance-sprung oscillator, as defined by claim 1. According to the invention, the material of said spring comprises (or even consists of) a binary alloy comprising:

• a mass percentage of gold between 45% and 55%;
• any impurities up to 0.5% by mass percentage;
• the palladium scale.

These alloys are non-magnetic, corrosion resistant, easy to machine, and have a thermoelastic coefficient close to zero, that is to say between -12 Pa.K ^-1 and +2.8 Pa.K ^-1 , depending on the composition and any heat treatment carried out.

In addition, and surprisingly, this coefficient can be easily manipulated by varying the mass percentage of gold and / or the heat treatment of the alloy during the manufacture of the spring. The elasticity of the spring therefore varies little or not as a function of the temperature, which makes it possible to make the operation of the oscillator in which it is integrated as close to 0 s / d as possible. For the rest, it is even possible to thermocompensate the oscillator as a whole if the thermoelastic coefficient of the spring is chosen to compensate and therefore to cancel the effect of variations in the inertia of the balance due to changes in temperature.

The spring according to the invention is preferably monolithic, that is to say without an outer layer, but can nevertheless include one or more layers on its surface.

Advantageously, the mass percentage of gold is between 48% and 55%, preferably between 48% and 52%, more preferably between 49% and 51%, more preferably substantially 50% (i.e. say between 49.5% and 50.5%). These composition ranges provide coefficients thermoelastic even closer to zero (approximately -5 Pa.K ^-1 to +2.8 Pa.K ^-1 ). Surprisingly, a composition of substantially 50% gold by weight represents a particularly versatile alloy, with which the thermoelastic coefficient can be manipulated between wide limits of -5 Pa.K ^-1 to +2.8 Pa.K ^-1 simply by varying heat treatment.

The spiral spring according to the invention can be integrated into a sprung balance oscillator comprising a balance rotatably attached to one end of said spiral spring, this oscillator being able to be integrated into a timepiece intended to equip a timepiece such as than a wristwatch.

1. a) se munir d'un fil en alliage binaire palladium-or comprenant :
   • un pourcentage massique d'or entre 45% et 55%, de préférence entre 48% et 52%, encore de préférence substantiellement 50% ;
   • des éventuelles impuretés jusqu'à 0.5% en pourcentage massique ;
   • la balance en palladium ;
2. b) mettre ledit ressort spiral en forme par n'importe quel procédé connu.

The invention also relates to a method of manufacturing such a spiral spring. This process comprises the following steps:

1. a) use a binary palladium-gold alloy wire comprising:
   • a mass percentage of gold between 45% and 55%, preferably between 48% and 52%, more preferably substantially 50%;
   • any impurities up to 0.5% by mass percentage;
   • the palladium balance;
2. b) shaping said spiral spring by any known method.

The spiral spring of the invention can thus be manufactured.

Advantageously, step b) can be preceded by a heat treatment of said yarn, and / or can be followed by such a heat treatment. These two heat treatments can be identical or different.

Advantageously, the heat treatment can include annealing, optionally followed by quenching.

Advantageously, said heat treatment can comprise heating to a temperature between 250 ° C and 600 ° C, preferably between 300 ° C and 450 ° C, more preferably between 350 ° C and 450 ° C. This heating can follow the annealing and the aforementioned possible quenching, and makes it possible to precisely manipulate the thermoelastic coefficient of the spiral spring.

This heating temperature can be maintained for a period of time lying between 1 hour and 20 hours, preferably between 5 hours and 15 hours, more preferably between 10 hours and 15 hours.

Brief description of the drawings

• Fig. 1 est un graphique illustrant la variation du coefficient thermoélastique du module de Young en fonction de la composition d'un alliage binaire Pd-Au, selon trois traitements thermiques différents ;
• Fig. 2 est un graphique illustrant l'effet sur le coefficient thermoélastique du module de Young de certains traitements thermiques, pour certaines compositions de l'alliage binaire Pd-Au,
• Fig. 3 est un diagramme schématique d'un procédé de fabrication d'un ressort spiral selon l'invention ; et
• Fig. 4 représente en vue isométrique un ressort spiral selon l'invention.

Other details of the invention will emerge more clearly on reading the following description, given with reference to the appended drawings in which:

• Fig. 1 is a graph illustrating the variation of the thermoelastic coefficient of Young's modulus as a function of the composition of a binary Pd-Au alloy, according to three different heat treatments;
• Fig. 2 is a graph illustrating the effect on the thermoelastic coefficient of Young's modulus of certain heat treatments, for certain compositions of the binary alloy Pd-Au,
• Fig. 3 is a schematic diagram of a method of manufacturing a spiral spring according to the invention; and
• Fig. 4 shows in isometric view a spiral spring according to the invention.

Embodiment of the invention

The spiral spring 1 according to the invention is intended to form part of a conventional balance-spring oscillator, as described in the preamble. Such a spiral spring 1 of conventional shape has been illustrated on figure 4 , but such an oscillator, which is very well known, has not been illustrated here. However, it should be noted that the spiral spring 1 as well as the balance can take any known shape. Typically, the balance comprises a rim linked to an axis by a plurality of arms, the spiral spring 1 being made integral with said axis by means of a ferrule or the like, which may be integral with the spring 1 or may be a separate part to which the spring 1 is attached.

The particularity of the spiral spring 1 according to the invention lies in the material which constitutes it.

The material of the spring 1 is a binary palladium-gold alloy, which comprises a mass percentage of gold between 45% and 55%, preferably between 48% and 55%, more preferably between 48% and 52%, more preferably Between 49% and 51%, more preferably substantially 50% (i.e. between 49.5% and 50.5%).

With the exception of a possible percentage by mass of impurities which can be tolerated up to 0.5%, preferably up to 0.3% or even better up to 0.1%, the remainder of the alloy consists of palladium.

These alloys are non-magnetic, corrosion resistant and easy to work with, so they are particularly suitable for the manufacture of spiral springs.

After numerous tests, the applicant has observed that the thermoelastic coefficient of these alloys is close to zero in these ranges of compositions, and can be handled very easily between approximately -12 Pa.K ^-1 and +2.8 Pa.K ^-1 by composition as well as heat treatment, as shown in the graphs of the figures 1 and 2 .

More precisely, the figure 1 illustrates the relationship between the composition of the Pd-Au alloy in mass percentage of gold (x axis) and the thermoelastic coefficient of Young's modulus (y axis) for four different heat treatments.

Curve A illustrates this ratio for an annealed alloy, having been heated to 1000 ° C. for 1 hour, then cooled at a rate of 300 ° C./h. Other temperatures and annealing times are also possible.

Curve B represents the results obtained by carrying out a quenching in water from a temperature of 1000 ° C., the material having been maintained at this temperature for 10 minutes.

Curve C represents the results obtained by carrying out a quenching in water from a temperature of 1000 ° C, the material having been maintained at this temperature for 10 minutes, and the quenching having been followed by a heat treatment at 360 ° C for 15 hours.

From this graph it is clear how the thermoelastic coefficient can be varied at will to obtain a desired value which is close to zero. It should be noted that one does not necessarily wish to obtain a value of zero, since the variation in stiffness of the spring 1 can be chosen to compensate for the variation in the inertia of the balance during changes in temperature, and thus make the oscillator frequency as close as possible to the desired nominal value.

For example, in the classic case of a balance wheel whose inertia increases when the temperature rises, which tends to reduce the oscillation frequency, a slightly positive thermoelastic coefficient tends to increase the oscillation frequency and can compensate at less partially the effect of the expansion of the balance. In such a case, a point on the curve C which corresponds to a Pd-50% Au alloy represents the maximum positive thermoelastic coefficient (+2.8 Pa.K ^-1 ) which is achievable.

In the case of a balance whose inertia decreases when the temperature rises, a negative thermoelastic coefficient will compensate for it.

The figure 2 illustrates the variation of the thermoelastic coefficient with respect to the temperature of said heat treatment for binary Pd-Au alloys varying between 45% by mass Au and 55% by mass Au, the heat treatment being carried out for 15 hours. This graph clearly shows that compositions comprising between 49% by mass and 52% by mass of gold make it possible to obtain a thermoelastic coefficient of zero or positive, the heat treatment being carried out at a temperature between 300 ° C and 450 ° C. , depending on the alloy.

A consideration of figures 1 and 2 leads to the conclusion that the Pd-50% Au alloy represents the most versatile alloy for a hairspring 1 according to the invention, its thermoelastic coefficient being able to be varied at will between -4 Pa.K ^-1 (annealing) and + 2.8 Pa.K ^-1 (heat treatment at between 350 ° C and 400 ° C) by varying the temperature of said heat treatment.

The figure 3 schematically illustrates, in the form of a block diagram, a method of manufacturing a spiral spring 1 according to the invention. In this figure, optional steps have been represented by dotted blocks.

1. a) se doter d'un fil d'alliage Pd-Au dans un alliage tel que décrit ci-dessus, et
2. b) mettre en forme ledit fil afin de former ledit ressort 1.

This process comprises, at a minimum, the following steps:

1. a) use a Pd-Au alloy wire in an alloy as described above, and
2. b) shaping said wire in order to form said spring 1.

Said wire may be of round, oval, square, rectangular or similar section, its making by drawing or the like being well known to those skilled in the art. It can be shaped by calendering or the like.

If the thermoelastic coefficient of the alloy as delivered is already suitable for the desired purpose, no heat treatment is to be carried out.

However, if it is desired to modify the thermoelastic coefficient, it is possible to carry out one or more heat treatments with the wire, before and / or after the shaping of step b).

• un recuit, par exemple à une température supérieure à 300°, de préférence entre 600°C et 1200°C, pendant 5 minutes à 1 heure, suivi par un refroidissement à un taux entre 100°C/h et 400°C/h, ou par une trempe dans de l'eau à partir d'une température entre 600°C et 1200°C ;
• un chauffage à une température entre 250°C et 600°C, de préférence entre 300°C et 450°C, encore de préférence entre 350°C et 450°C, cette température étant maintenue pendant un laps de temps entre 1 heure et 20 heures, de préférence entre 5 heures et 15 heures, encore de préférence entre 10 heures et 15 heures.

In both cases, the heat treatment can include one or more of:

• annealing, for example at a temperature above 300 °, preferably between 600 ° C and 1200 ° C, for 5 minutes to 1 hour, followed by cooling at a rate between 100 ° C / h and 400 ° C / h , or by quenching in water from a temperature between 600 ° C and 1200 ° C;
• heating to a temperature between 250 ° C and 600 ° C, preferably between 300 ° C and 450 ° C, more preferably between 350 ° C and 450 ° C, this temperature being maintained for a period of time between 1 hour and 20 hours, preferably between 5 a.m. and 3 p.m., more preferably between 10 a.m. and 3 p.m.

If two heat treatments are carried out, one before and the other after step b), the latter may be identical or different.

In the case where a heat treatment is carried out after step b), the latter can optionally be carried out by introducing the wire into a jig which defines the final profile of the hairspring 1, the heat treatment step serving to fix the profile of the hairspring. spring 1 in a known manner. The latter may optionally be followed by quenching and / or heating as described above.

It should also be noted that the spiral spring 1 according to the invention is typically monolithic, that is to say without any layer provided on its surface, it can nevertheless be provided with at least one outer layer of metal, carbon. adamantine (DLC), silicon oxide or the like.

Although the invention has been previously described in connection with specific embodiments, other additional variants are also conceivable without departing from the scope of the invention as defined by the claims.

Claims (16)

Spiral spring (1) for a watch balance-sprung oscillator, the material of said spring (1) comprising a binary alloy comprising: - a mass percentage of gold between 45% and 55%; - any impurities up to 0.5% by mass percentage; - the palladium scale. Spiral spring (1) according to the preceding claim, in which the mass percentage of gold is between 48% and 55%. Spiral spring (1) according to the preceding claim, in which the mass percentage of gold is between 48% and 52% Spiral spring (1) according to the preceding claim, in which the mass percentage of gold is between 49% and 51%, preferably substantially 50%. Spiral spring (1) according to one of the preceding claims, wherein said spiral spring (1) is monolithic. Spiral balance oscillator comprising a balance rotatably attached to one end of a spiral spring (1) according to one of the preceding claims. Timepiece movement comprising a sprung balance oscillator according to the preceding claim. Timepiece comprising a movement according to the preceding claim. A method of manufacturing a spiral spring (1), comprising the following steps: a) use a binary palladium-gold alloy wire comprising: - a mass percentage of gold between 45% and 55%, preferably between 48% and 52%, more preferably substantially 50%; - any impurities up to 0.5% by mass percentage; - the palladium scale; b) shaping said spiral spring (1). Manufacturing process according to claim 9, further comprising, before step b), a step of:
a1) performing a heat treatment on said wire. Manufacturing process according to one of claims 9 and 10, further comprising, after step b), a step of:
b1) performing a heat treatment of said spiral spring (1). A method according to one of claims 10 and 11, wherein said heat treatment comprises annealing. A method according to the preceding claim, wherein said annealing is followed by quenching. Process according to one of claims 10-13, wherein said heat treatment comprises heating to a temperature between 250 ° C and 600 ° C, preferably between 300 ° C and 450 ° C, more preferably between 350 ° C and 450 ° C. Process according to the preceding claim, in which said temperature of said heating is maintained for a period of time lying between 1 hour and 20 hours, preferably between 5 hours and 15 hours, more preferably between 10 hours and 15 hours. A method according to one of claims 9 to 15, wherein step b) comprises calendering said yarn.

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