CH703343A2 - Unique hand i.e. chronograph hand, for use in luxury watch, has support whose length is larger than its width, where hand is made of completely amorphous material or partially amorphous material containing precious metal element - Google Patents

Abstract

The hand (2) has a support (3) whose length is larger than its width, where the hand is made of partially amorphous material containing precious metal element or completely amorphous material. An orifice (4) is formed at the proximity of an end (32) of the support, where the end serves as an unbalancing mass. The orifice allows ejection of the hand along an axis so as to permit the hand to be pivotably mounted around the axis for indicating information regarding hour, minute or second, on a dial of a timepiece (1). An independent claim is also included for a method for fabricating a hand.

Description

The present invention relates to a timepiece needle, said needle being pivotally mounted about an axis so as to indicate information.

The technical field of the invention is the technical field of fine mechanics.

BACKGROUND TECHNOLOGY

[0003] It is known that timepieces include needles. These needles consist of a beam whose length is much greater than the width, itself much larger than the thickness. These needles include an orifice to be driven on an axis so as to be pivotally mounted. In order to have fine and strong needles, it is planned to make them in crystalline metal such as steel, brass, gold or even silicon or ceramic. These needles can be machined or cut by laser or water jet from a plate. They can also be molded, sintered or made by growth by deposition of material. These hands are then used to indicate the hours, minutes and seconds but also when performing certain functions such as chronograph functions or date functions.

However, these needles undergo many constraints. One of these constraints is the weight of the needle itself. Indeed, the needle is usually driven on its axis at one of its ends. Therefore, it is quite normal, given the small size of a needle, that it bends, if only slightly, under its own weight. This weight constraint is also applied to the imbalance, serving as a counterweight, of the needle.

The needle also undergoes acceleration constraints. These constraints can be due, in the first place, to the movement controlled by the watch movement. This movement is linked to the display of the time or to a function of said timepiece such as the chronograph function, and can be retrograde. However, for a retrograde display or when using the chronograph function, an instantaneous reset of the hands is performed. This reset consists of a sudden return of the needle to its initial position. During this reset operation, the acceleration of the needle can reach 1.106 rad.s <-> <2>. Such acceleration involves a high stress applied to the needle during acceleration as well as during deceleration and stopping of the needle.

Second, the constraints related to the acceleration may be due to a shock applied to the watch. Indeed, when, for example, the watch falls, it undergoes an acceleration. The energy stored during this fall is transmitted to the hands during the contact of said watch with the ground. These shocks can then deform the needle or unbalance can then cause problems during the movement of the needle.

However, a disadvantage of the crystalline metal needles is their low mechanical strength when high stresses are applied. Indeed, each material is characterized by its Young's modulus E also called modulus of elasticity (generally expressed in GPa), characterizing its resistance to deformation. Each material is also characterized by its elastic limit σe (generally expressed in GPa) which represents the stress beyond which the material deforms plastically. It is then possible, for given dimensions, to compare the materials by establishing for each the ratio of their elastic limit on their Young's modulus σe / E, said ratio being representative of the elastic deformation of each material. Thus, the higher the ratio, the greater the elastic deformation of the material. Typically, for an alloy of the Cu-Be type, the Young's modulus E is equal to 130 GPa and the elastic limit σe is equal to 1 GPa, which gives a ratio σe / E of the order of 0.007 c that is to say, weak. Needles of metal or crystalline alloy have, therefore, limited elastic deformation. Consequently, when returning to zero or shock, the stresses applied to said needles can be so high that the needles deform plastically, that is to say they twist. This deformation then poses a problem of readability and reliability of the information.

This deformation phenomenon is even more accentuated for precious crystalline metals. Indeed, these have even lower mechanical characteristics. Precious metals in particular have a low elastic limit, of the order of 0.5 GPa for Au, Pt, Pd and Ag alloys, against about 1GPa for crystalline alloys conventionally used in the manufacture of needles. Since the elastic modulus of these precious metals is of the order of 120 GPa, we arrive at an ee / E ratio of about 0.004, which is even lower than for non-precious alloys. The risks of deformation, following the stresses applied during a strong acceleration such as a reset, are then increased. Therefore, the skilled person is not encouraged to use these precious metals for the realization of a timepiece needle.

In addition, current methods such as stamping, laser cutting or deposit growth are limited. They do not allow the realization of three-dimensional needles. Indeed, in the case of stamping or laser cutting, the needles are made from a plate. For the manufacture of needles by LIGA-type material growth, the disadvantage is that the walls of the needles are straight and that no inclination type chamfering is possible.

SUMMARY OF THE INVENTION

The invention aims to overcome the disadvantages of the prior art by proposing to provide a metal needle for sudden acceleration that does not deform during its movement to have a precise readability and significant durability.

For this purpose, the invention relates to the needle cited above which is characterized in that it is made of at least partially amorphous material and comprising at least one metal element.

A first advantage of the present invention is to allow the realization of precious metal needles that can withstand shocks or abrupt acceleration. Surprisingly, precious amorphous metals have more interesting elastic characteristics than their crystalline counterparts. The elastic limit σe is increased to increase the ratio σe / E so that the material sees the stress beyond which it does not resume its initial shape increase.

Another advantage of the present invention is to allow great ease in formatting for the development of complicated shapes with greater precision. In fact, the amorphous precious metals have the particular characteristic of softening while remaining amorphous for a certain time in a given temperature range [Tg - Tx] specific to each alloy (with Tx: crystallization temperature and Tg: transition temperature glass). It is thus possible to shape them under a relatively low stress and at a low temperature then allowing the use of a simplified process. The use of such a material also makes it possible to reproduce fine geometries very precisely because the viscosity of the alloy decreases sharply as a function of the temperature in the temperature range [Tg-Tx] and the alloy thus allies the details of a negative. The term "negative" is understood to mean a mold which has a hollow profile complementary to that of the desired needle. This then makes it possible to produce a needle in three dimensions, which the techniques of the prior art can not or hardly allow.

Advantageous embodiments of this needle are the subject of dependent claims 2 to 8.

One of the advantages of these embodiments is to make it possible to make precious metal needles supporting the stresses applied to the needle during a reset of a chronograph. It thus becomes possible to make needles of precious materials having dimensions similar to those of non-precious materials, without the risk that they will deform during a strong acceleration.

The invention also proposes to provide a method for producing the needle according to the present invention, said method comprising the following steps: <tb> a) <sep> get the negative of the needle to make; <tb> b) <sep> to provide a material comprising at least one metal element and being able to solidify at least partially in the amorphous phase. <tb> c) <sep> shaping said material in the negative so as to obtain said needle; <tb> d) <sep> separating said needle from said negative.

Advantageous embodiments of this method are the subject of dependent claims 10 to 15.

BRIEF DESCRIPTION OF THE FIGURES

The purposes, advantages and characteristics of the needle according to the present invention will appear more clearly in the following detailed description of at least one embodiment of the invention given solely by way of nonlimiting example and illustrated by the attached drawings in which: <tb> - fig. 1 <sep> schematically represents a timepiece with a chronograph function; <tb> - figs. 2 to 4 <sep> schematically represent sectional views of timepiece needles; <tb> - fig. <Sep> represents the deformation curves for a crystalline material and for an amorphous material; <tb> - figs. 6 to 9 <sep> schematically represent the process according to the present invention; <tb> - figs. 10 to 14 <sep> schematically represent a variant of the process according to the present invention, and <tb> - fig. <Sep> shown a top view of a needle variant according to the present invention.

DETAILED DESCRIPTION

In FIG. 1 shows a timepiece 1 comprising several needles 2 pointing information on the dial of said timepiece. These needles 2 may be the hands indicating the hours, minutes or seconds. They may be driven by a continuous or retrograde movement, said displacement may include sudden acceleration. One understands by sudden acceleration, a sudden acceleration, predictable or not and occurring during a limited time and whose value is very high, said acceleration succeeding a displacement having a null acceleration, constant or weak. The sudden accelerations that can be supported are at least 250,000 rad.s <-> <2> and preferably 1.10 <6> rad.s <-> <2>. These needles 2 can also be chronograph or date hand 2 or other. Such a needle 2, shown in FIG. 2, consists of a beam 3 whose length is much greater than the width of the beam 3, this width is itself much larger than the thickness. A first end 31 of the beam serves to point information. This first end 31 is preferably the thinnest end. An orifice 4 is provided to allow the needle to be driven on its axis 10. This orifice 4 is arranged near the second end 32 of the beam forming the needle 2. This second end 32 may be arranged so as to serve as an unbalance to ensure a good balance of the needle 2 during its displacement. It can also be envisaged that the second end 32 is arranged, as can be seen in FIG. 1, to be circular and to include the orifice 4 for hunting on its axis 10.

The needle 2 is mounted on an axis 10 by being directly driven on said axis 10 as shown in FIG. 2 or being reported on a barrel 5 itself driven on the axis 10 as shown in FIG. 4. It is also possible that the barrel 5 comes directly from material with the needle 2 as shown in FIG. 3.

Advantageously, at least one of the needles 2 is made of at least partially amorphous material comprising at least one metal element. This metal element may be valuable such as gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or osmium. It will be understood by at least partially amorphous material that the material is capable of solidifying at least partially in the amorphous phase, that is to say that it is capable of losing at least locally all of its crystalline structure.

Indeed, the advantage of these amorphous metal alloys comes from the fact that, during their manufacture, the atoms of these amorphous materials do not arrange according to a particular structure as is the case for crystalline materials. Thus, even if the Young's modulus E of a crystalline metal and an amorphous metal is identical, the elastic limit σe is different. An amorphous metal is then distinguished by an elastic limit σeA higher than σeC of the crystalline metal by a factor substantially equal to two, as shown in FIG. 5. This figure represents the curve of the stress a as a function of the deformation ε for an amorphous metal (in dotted lines) and for a crystalline metal (in solid line).

In addition, the maximum energy that can be stored elastically is calculated as being the ratio between the elastic limit σe squared and Young's modulus E. Or, with a higher elastic limit of a substantially equal factor at two, the energy that the amorphous metal can store elastically is therefore higher by a factor substantially equal to four. This allows the amorphous metals to be able to undergo a greater stress before reaching the elastic limit ae. Amorphous metals plastically deform more difficultly and break brittle, that is to say they break without prior plastic deformation and therefore their plastic deformation is very low or zero, when the applied stress exceeds the elastic limit.

A needle 2 amorphous metal allows, in the first place, to improve the reliability of the latter with respect to its crystalline metal equivalent. Indeed, the stress applied to the needle 2 is related to the moment of inertia of the needle 2, which is a function of mass and length. Therefore, the longer a needle will be or the longer the mass at the end of the needle 2 will be large and the moment of inertia of the pawl 2 will be high. The kinetic energy accumulated during the displacement of the needle 2 following a reset-or shock is dependent on the moment of inertia. This kinetic energy determines the stress applied to the wand 2 during the return movement to zero or during the shock. High kinetic energy leads to high stress and therefore a risk of significant deformation.

Since the elastic limit σe is higher for an amorphous metal than for a crystalline metal, the stress to be applied to obtain a plastic deformation is higher. Thus, at equivalent kinetic energy, a needle 2 of amorphous metal will be less likely to deform than a needle 2 crystalline metal.

A material may also be characterized by its specific resistance which is the ratio of the elastic limit to the density. An amorphous metal with a higher specific resistance than a crystalline metal because, on the one hand, for the same type of alloy, the amorphous metal has an elastic limit which is about twice as high and, on the other hand, for In a given composition, the amorphous structure has a density that is about 10% less than that of the crystal structure. As a result, a needle of amorphous metal alloy or amorphous metal will be lighter than a needle of the same dimensions made of a metal alloy of the same composition but of crystalline structure. The moment of inertia will therefore be lower for the amorphous metal needle, the moment of inertia being linked to the mass. The kinetic energy and therefore the stress applied to the amorphous metal needle, will be lower so that the needle will be able to withstand a higher stress before plastically deforming.

The characteristics of the amorphous metal allow, secondly, to consider forms of needles 2 more varied. Indeed, the moment of inertia is used to know the kinetic energy of the needle and the stress it will undergo when returning to zero. This moment of inertia is dependent on the mass and the length of the needle 2. These parameters are thus calculated to limit the risk of plastic deformation of the needle 2.

As the amorphous metal can withstand a higher stress, that is to say a higher kinetic energy and therefore a greater moment of inertia, the mass and the length of the needle 2 can be increased without to risk a plastic deformation. More particularly, the mass at the first end of the needle 2 can be increased, allowing access to possibilities of larger needle shapes 2. It is then possible to provide for this first end to comprise, for example, a zone with larger dimensions for applying a luminescent material, or for the second hand of the chronograph to take the form of a Breguet-type needle 2. It is also possible that the mass at the second end 32, which can serve as unbalance, be increased.

If the characteristics of the amorphous metal can increase the size of the needles 2, they also make it possible to make needles 2 with smaller dimensions. Indeed, at equivalent stress, the needle 2 may be of shorter length and / or less mass without plastically deforming, this being the consequence of a higher elastic limit This reduction in dimensions can also be applied to the unbalance of the needle 2 serving for the balance of said needle 2.

The amorphous metal has the double advantage of allowing to increase or decrease the size of the needles 2 without increasing the risk of plastic deformation. The reduction in the size and / or mass of the needle can be done by arranging recesses 11 passing through or not through the needles 2 as visible in FIG. 15. These recesses 11 make it possible to reduce, by removal of material, the mass needles 2 and thus reduce the moment of inertia while providing an interesting visual effect.

To make a needle 2 amorphous metal, several methods are possible.

In the first place, it is possible to use the traditional methods of stamping or cutting. The amorphous metal is thus previously arranged in the form of thin plates. These thin plates are then stamped in press or cut by water jet or laser.

However, it is possible to use the properties of the amorphous precious metal to shape it. Indeed, the amorphous metal allows great ease in shaping allowing the development of complicated shapes with greater precision. This is due to the particular characteristics of the amorphous metal which can soften while remaining amorphous for a certain time in a given temperature range [Tg - Tx] specific to each alloy (for example for a Zr41,24Ti13.75Cu12.5Ni10Be22 alloy. 5, Tg = 350 ° C and Tx = 460 ° C). It is thus possible to shape them under a relatively low stress and at a low temperature then allowing the use of a simplified process such as hot forming. The use of such a material also makes it possible to reproduce fine geometries very precisely because the viscosity of the alloy decreases sharply as a function of the temperature in the temperature range [Tg-Tx] and the alloy thus allies the details of the negative. For example, for a platinum-based material, the shaping is done around 300 ° C for a viscosity up to 10 <3> Pa.s for a stress of 1MPa, instead of a viscosity of 10 <12 > Pa.s at temperature Tg. The use of dies has the advantage of creating highly accurate three-dimensional parts, which can not be cut or stamped.

One method used is the hot forming of an amorphous preform. This preform 7 is obtained by melting the metal elements constituting the amorphous alloy in a furnace. This fusion is made under a controlled atmosphere with the aim of obtaining as low a contamination of the oxygen alloy as possible. Once these elements are melted, they are cast as a semi-finished product, such as for example a blade of dimension close to the needle, and then rapidly cooled in order to maintain the at least partially amorphous state or phase. Once the preform 7 has been made, the hot forming is performed in order to obtain a final piece. This hot forming is performed by pressing in a temperature range between its glass transition temperature Tg and its crystallization temperature Tx for a predetermined time to maintain a totally or partially amorphous structure. This is done in order to maintain the characteristic elastic properties of the amorphous precious metals. The different stages of definitive shaping of the needle 2 are then: <tb> a) <sep> Heating the matrices 8 having the negative form of the needle 2 to a temperature chosen as visible in FIG. 6 <tb> b) <sep> Introduction of the amorphous metal preform 7 between the hot matrices as shown in FIG. 7 <tb> c) <sep> Application of a closing force on the matrices 8 to replicate the geometry of the latter on the preform 7 amorphous precious metal as shown in FIG. eight, <tb> d) <sep> Waiting for a chosen maximum time, <tb> e) <sep> Opening matrices 8, <tb> f) <sep> Rapid cooling of the needle 2 below Tg so that the material keeps its phase at least partially amorphous, and <tb> g) <sep> Output of the needle 2 of the dies 8 as shown in FIG. 9.

The hot forming makes it possible to simplify the production of said needle 2, in particular to make the recesses 11 of the needle shown in FIG. 15.

In addition, it is possible to make the needle 2 directly with its barrel 5, using the hot forming technique as visible in FIGS. 6 to 9. It is therefore understood that the barrel 5 and the needle 2 are one and the same piece as visible in FIG. 3. The dies 8 forming the mold are then arranged to form the negative of the needle 2 and its integrated barrel 5. Steps a) to g) are then performed to form said needle 2. This arrangement of the needle 2 and its barrel 5 in one piece makes it possible not to have fixing problems between said needle 2 and its barrel 5.

In a variant, it is intended to make a needle 2 directly attached to the barrel 5. The barrel 5, shown in FIG. 4, consists of a cylindrical piece whose inner diameter d is equal to the diameter of the axis 10 on which the barrel 5 is driven. The barrel 5 comprises an outer diameter D greater than the inner diameter d, the outside diameter D may not be uniform over the entire barrel 5. The profile of this barrel 5 comprises an annular recess 6 in which needle 2 is placed. This recess, whose diameter is between the inner and outer diameters, allows axial retention of the needle 2. The barrel 5 is placed between the dies 8 in which the needle 2 will be made as visible in FIG. 11. Steps a) to g) previously described are then carried out and shown in FIGS. 12, 13 and 14. As a result, the needle 2 is overmolded directly on the barrel 5 and is therefore directly attached to the barrel 5. It can be provided that the wall of the annular recess comprises reliefs or other means to improve maintaining the needle 2 in the barrel 5 and in particular the angular support.

It will be understood that various modifications and / or improvements and / or combinations obvious to those skilled in the art can be made to the various embodiments of the invention described above without departing from the scope of the invention defined by the appended claims.

Of course, it will be understood that the needle 2 or the part forming the barrel 5 and the needle 2 can be made by casting or injection. This process involves casting the alloy obtained by melting the metal elements in a mold having the shape of the final piece. Once the mold is filled, it is rapidly cooled to a temperature below Tg in order to avoid the crystallization of the alloy and thus obtain a needle 2 of amorphous or partially amorphous precious metal.

Claims (15)

1. A special needle for sudden acceleration, said needle (2) being pivotally mounted about an axis (10) so as to be able to indicate information, characterized in that said needle is made of an at least partially amorphous material comprising at least less a metal element. 2. Needle according to claim 1, characterized in that the needle is made of totally amorphous material 3. Needle according to one of the preceding claims, characterized in that said needle (2) is a needle undergoing, at a given time, an acceleration of at least 250,000 rad / s "2. 4. Needle according to one of the preceding claims, characterized in that said needle (2) is a needle undergoing, at a given moment, an acceleration of the order of 1.106 rad / s "2. 5. Needle according to one of the preceding claims, characterized in that said needle is fixed on its axis (10) via a barrel (5). 6. Needle according to one of the preceding claims, characterized in that said needle is a chronograph hand. 7. Needle according to one of the preceding claims, characterized in that said needle is driven by a retrograde movement. 8. Needle according to one of the preceding claims, characterized in that said at least one metal element is of the precious type and selected from the group consisting of gold, platinum, palladium, rhenium, ruthenium, rhodium , silver, iridium or osmium. 9. A method of producing a needle, characterized in that said method comprises the following steps: a) equipping the negative (8) of the needle (2) to be produced; b) providing a material comprising at least one metal element of the precious type and being able to solidify at least partially in the amorphous phase. c) shaping said material in the negative so as to obtain said needle; d) separating said needle from said negative. 10. Production method according to claim 9, characterized in that step c) comprises the following steps: - Making a preform (7) with said material, said material being solidified at least partially in the amorphous phase, and placing the preform on the negative (8); heating said preform to a temperature between the glass transition temperature and the crystallization temperature of said material; - Pressing the preform to fill the negative with said material; - Cooling said material so that it keeps its at least partially amorphous phase. 11. Production method according to claim 9, characterized in that step c) comprises the following steps: heating said material above its melting point; - casting said material in said negative; - Cool the assembly so that said material solidifies at least partially amorphous phase. 12. The manufacturing method according to claim 10 or 11, characterized in that it comprises, before the step of cooling said material, the step of removing the excess material. 13. Production method according to one of the preceding claims, characterized in that said needle (2) is fixed on its axis by means of a barrel (5) and in that said needle and said barrel are a single and same piece made during step c) shaping. 14. Production method according to one of claims 9 to 12, characterized in that said needle (2) is fixed on its axis (10) via a barrel (5) and in that said needle is fixed to said barrel during the c) shaping step. 15. Production method according to one of claims 9 to 14, characterized in that said at least one metal element is of the precious type and selected from the group formed by gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or osmium.