CH703343B1 - Needle of timepiece. - Google Patents

Abstract

The invention relates to a special needle for sudden acceleration. Said needle (2) is pivotally mounted about an axis so as to be able to indicate information. Said needle is made of at least partially amorphous material comprising at least one metallic element. The invention also relates to a method of manufacturing such a needle, as well as its use in a chronograph or in a retrograde display.

Description

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

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

Technological background [0003] It is known that timepieces include hands. These needles consist of a beam whose length is much greater than the width, itself much greater than the thickness. These needles include an orifice in order to be driven out on an axis so as to be pivotally mounted. In order to have fine and resistant needles, it is planned to produce them in crystalline metal such as steel, brass, gold or even in 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 produced by growth by depositing material. These hands are then used to indicate the hours, minutes and seconds but also when performing certain functions such as the chronograph functions or the date functions.

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

The needle also undergoes acceleration constraints. These constraints may be due, firstly, to the movement controlled by the watch movement. This movement is linked to the time display 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 instant reset of the hands is carried out. 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 1.10 ⁶ rad.s ^-2 . Such acceleration implies a high stress applied to the needle during acceleration as well as during deceleration and stopping of the needle.

Second, the stresses associated with 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 when the watch contacts the ground. These shocks can then deform the needle or unbalance, which can then cause problems when the needle moves.

However, a disadvantage of crystalline metal needles is their poor mechanical strength when high stresses are applied. Indeed, each material is characterized by its Young E modulus also called elastic modulus (generally expressed in GPa), characterizing its resistance to deformation. Each material is also characterized by its elastic limit σθ (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 to their Young's modulus σθ / Ε, said ratio being representative of the elastic deformation of each material. Thus, the higher this ratio, the higher 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 σθ is equal to 1 GPa, which gives a ratio σθ / Ε of the order of 0.007, that is to say, weak. Metal or crystal alloy needles therefore have limited elastic deformation. Consequently, during a return to zero or an impact, the stresses applied to said needles can be so high that the needles deform plastically, that is to say that they twist. This distortion 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 weaker mechanical characteristics. Precious metals notably have a low elastic limit, of the order of 0.5 GPa for Au, Pt, Pd and Ag alloys, compared to around 1GPa for crystalline alloys conventionally used in the manufacture of needles. Since the elastic modulus of these precious metals is around 120 GPa, we arrive at a σθ / Ε ratio of around 0.004, an even lower figure than for non-precious alloys. The risks of deformation, following the constraints applied during a strong acceleration such as a reset, are then increased. Consequently, a person skilled in the art is not encouraged to use these precious metals for the production of a timepiece hand.

In addition, current methods such as stamping, laser cutting or deposition growth are limited. They do not allow the production 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 material growth of the LIGA type, the disadvantage is that the walls of the needles are straight and thus no inclination of the bevelling type is possible.

CH 703 343 B1

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

To this end, 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 metallic element.

A first advantage of the present invention is to allow the production of precious metal needles that can withstand shock or sudden acceleration. Indeed, surprisingly, precious amorphous metals have more interesting elastic characteristics than their crystalline equivalents. The elastic limit σθ is increased making it possible to increase the ratio σθ / Ε 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 shaping allowing the production of parts with complicated shapes with greater precision. Indeed, amorphous precious metals have the particular characteristic of softening while remaining amorphous for a certain time in a given temperature interval (T g-Tx) specific to each alloy (with Tx: crystallization temperature and T g: temperature glass transition). 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 very precisely fine geometries because the viscosity of the alloy decreases strongly as a function of the temperature in the temperature range (Tg-Tx) and the alloy thus marries all details of a negative. By negative is meant 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 cannot or hardly allow.

Advantageous embodiments of this needle are the subject of dependent claims 2 to 6.

One of the advantages of these embodiments is that it makes it possible to produce precious metal needles supporting the stresses applied to the hand when resetting a chronograph. It therefore 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 use of such a needle in a chronograph or in a retrograde display.

The invention also proposes to provide a method for producing the needle according to the present invention, said method comprising the following steps:

a) bring the negative of the needle to be produced;

b) be provided with a material comprising at least one metallic element and being capable of solidifying 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.

Advantageous embodiments of this process are the subject of dependent claims 9 to 15.

Brief Description of the Figures The objects, 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 appended drawings in which:

fig. 1 schematically represents a timepiece with a chronograph function; fig. 2 to 4 schematically represent sectional views of timepiece hands; fig. 5 represents the deformation curves for a crystalline material and for an amorphous material; fig. 6 to 9 schematically represent the method according to the present invention; fig. 10 to 14 schematically represent a variant of the process according to the present invention, and fig. 15 shows a top view of a variant needle according to the present invention.

CH 703 343 B1

Detailed description In FIG. 1 shows a timepiece 1 comprising several hands 2 pointing to information on the dial of said timepiece. These hands 2 can be the hands indicating the hours, the minutes or the seconds. They can be driven by a continuous or retrograde movement, said movement possibly comprising sudden accelerations. Sudden acceleration is understood to mean sudden acceleration, predictable or not, occurring during a limited time and the value of which is very high, said acceleration succeeding a displacement having zero 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 hands 2 can also be chronograph or calendar hands 2 or the like. Such a needle 2, shown in FIG. 2, consists of a beam 3 whose length is much greater than the width of this beam 3, this width itself being much greater than the thickness. A first end 31 of the beam is used to point information. This first end 31 is preferably the thinnest end. A hole 4 is provided to allow the needle to be driven on its axis 10. This hole 4 is arranged near the second end 32 of the beam forming the needle 2. This second end 32 can be arranged so as to serve as an unbalance in order to ensure a good balancing of the needle 2 during its displacement. It is also conceivable that the second end 32 is arranged, as visible in FIG. 1, to be circular and to understand the orifice 4 allowing it to be driven out on its axis 10.

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

Advantageously, at least one of the needles 2 is made of an at least partially amorphous material comprising at least one metallic element. This metallic element can be precious such as gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or osmium. It will be understood by material at least partially amorphous 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 making up these amorphous materials do not arrange themselves 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 of an amorphous metal is identical, the elastic limit a _eA is different. An amorphous metal is then differentiated by an elastic limit a _eA higher than that σθ ₀ of the crystalline metal by a factor substantially equal to two, as shown in fig. 5. This figure represents the curve of the stress σ as a function of the deformation ε for an amorphous metal (dotted line) and for a crystalline metal (in solid line). Furthermore, the maximum energy which can be stored elastically is calculated as being the ratio between the elastic limit σθ squared and the Young's modulus E. Now, with a higher elastic limit by a factor substantially equal to two, the energy that the amorphous metal can store elastically is therefore higher by a factor substantially equal to four. This allows amorphous metals to be able to undergo a higher stress before arriving at the elastic limit σθ. Amorphous metals are more difficult to deform plastically and break in a fragile manner, that is to say that they break without prior plastic deformation and therefore their plastic deformation is very low or even zero, when the applied stress exceeds the elastic limit.

A needle 2 of amorphous metal allows, first, to improve the reliability of the latter compared to its equivalent in crystalline metal. Indeed, the stress applied to needle 2 is linked to the moment of inertia of needle 2, which is a function of mass and length. Consequently, the longer the needle or the greater the mass at the end of needle 2, the greater the moment of inertia of needle 2. The kinetic energy accumulated during movement of needle 2 following a reset or a shock is dependent on the moment of inertia. This kinetic energy determines the stress applied to the pin 2 during the return to zero movement or during the impact. A high kinetic energy causes a high stress and therefore a significant risk of deformation.

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

A material can 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 approximately twice higher and, on the other hand, for a given composition, the amorphous structure has a density which is about 10% lower 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 mass. The kinetic energy and therefore the stress applied to the amorphous metal needle, will be weaker so that the needle will be able to withstand a greater stress before being deformed plastically.

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

CH 703 343 B1 will suffer when it returns to zero. This moment of inertia is dependent on the mass and length of the needle 2. These parameters are therefore 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 however risking 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 that this first end comprises, for example, an area with larger dimensions allowing the application of luminescent material, or that the second hand of the chronograph takes the form of a Breguet type hand 2. It is also possible that the mass at the second end 32, which can serve as an unbalance, is increased. If the characteristics of the amorphous metal make it possible to increase the dimensions of the needles 2, they also make it possible to produce needles 2 with smaller dimensions. Indeed, at equivalent stress, the needle 2 may be of length and / or of lower 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 therefore has the double advantage of making it possible to increase or decrease the size of the needles 2 without increasing the risk of plastic deformation. The reduction in the size and / or the mass of the needle can be done by arranging recesses 11 passing through or not on the needles 2 as visible in FIG. 15. These recesses 11 make it possible to reduce, by removing material, the mass of the needles 2 and therefore to reduce the moment of inertia while providing an interesting visual effect.

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

First, it is possible to use the traditional methods of stamping or cutting. The amorphous metal is therefore previously arranged in the form of thin plates. These thin plates are then stamped in a 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 parts with 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 interval (Tg-Tx) specific to each alloy (for example for an alloy Zr ₄₁ .24Ti ₁ 3.75Cu ₁ 2.5Ni ₁₀ Be22.5, 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 very precisely fine geometries because the viscosity of the alloy decreases strongly as a function of the temperature in the temperature range (Tg-Tx) and the alloy thus marries all details of the negative. For example, for a material based on platinum, the shaping is done around 300 ° C for a viscosity reaching 10 ³ Pa.s for a stress of 1 MPa, instead of a viscosity of 10 ¹² Pa. s at the temperature Tg. The advantage of using dies is the creation of high-precision three-dimensional parts, which cutting or stamping does not make it possible to obtain.

One method used is the hot forming of an amorphous preform. This preform 7 is obtained by melting the metallic elements constituting the amorphous alloy in an oven. This fusion is carried out under a controlled atmosphere with the aim of obtaining the lowest possible contamination of the oxygen alloy. Once these elements have melted, they are cast in the form of a semi-finished product, such as for example a blade of dimension close to the needle, then cooled quickly in order to preserve the state or the phase at least partially amorphous. Once the preform 7 has been produced, the hot forming is carried out with the aim of obtaining a final part. This hot forming is carried out by pressing in a temperature range between its glass transition temperature Tg and its crystallization temperature Tx for a determined time to maintain a totally or partially amorphous structure. This is done in order to maintain the elastic properties characteristic of amorphous precious metals. The different stages of final shaping of needle 2 are then:

a) heating the dies 8 having the negative shape of the needle 2 to a chosen temperature as shown in FIG. 6

b) introduction of the preform 7 of amorphous metal between the hot dies as visible in FIG. 7

c) application of a closing force on the dies 8 in order to replicate the geometry of the latter on the preform 7 of amorphous precious metal as shown in FIG. 8

d) waiting for a selected maximum time,

e) opening of the dies 8,

f) rapid cooling of the needle 2 below Tg so that the material keeps its phase at least partially amorphous, and

CH 703 343 B1

g) outlet of the needle 2 from the dies 8 as visible in FIG. 9.

Hot forming makes it possible to simplify the production of said needle 2, in particular for producing the recesses 11 of the needle shown in FIG. 15.

In addition, it is possible to produce the needle 2 directly with its barrel 5, using the hot forming technique as shown in Figs. 6 to 9. It is therefore understood by this that the barrel 5 and the needle 2 are only 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 carried out to form said needle 2. This arrangement of needle 2 and its barrel 5 in one piece makes it possible to have no problems of attachment between said needle 2 and its barrel 5.

Alternatively, provision is made for a needle 2 directly attached to the barrel 5. The barrel 5, shown in FIG. 4, consists of a cylindrical part whose internal diameter d is equal to the diameter of the axis 10 on which the barrel 5 is driven. The barrel 5 comprises an outside diameter D greater than the inside diameter d, the outside diameter D possibly not being uniform over the whole of the barrel 5. The profile of this barrel 5 comprises an annular recess 6 in which needle 2 is placed. This recess, the diameter of which is between the inside and outside diameters, allows axial maintenance of the needle 2. The barrel 5 is placed between the dies 8 in which the needle 2 will be produced as shown in FIG. 11. The steps a) to g) previously described are then carried out and shown in FIGS. 12, 13 and 14. It follows that the needle 2 is molded directly on the barrel 5 and therefore is directly fixed to the barrel 5. It can be provided that the wall of the annular recess includes reliefs or other means for improving the maintenance of the needle 2 in the barrel 5 and in particular the angular maintenance.

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 produced by casting or by injection. This process consists in casting the alloy obtained by melting the metallic elements in a mold having the shape of the final part. Once the mold is filled, it is quickly cooled to a temperature below T _{g in} order to avoid crystallization of the alloy and thus obtain a needle 2 made of amorphous or partially amorphous precious metal.

claims

Claims (15)

1. Needle for sudden acceleration, said needle (2) being pivotally mounted about an axis (10) of said needle 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 one metallic element. 2. Needle according to claim 1, characterized in that the needle is made of completely amorphous material. 3. Needle according to one of the preceding claims, characterized in that said needle (2) is capable of withstanding 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 capable of withstanding an acceleration of the order of 1.10 ⁶ rad.s ^-2 . 5. Needle according to one of the preceding claims, characterized in that it further comprises a barrel, said needle being fixed on its axis (10) by means of said barrel (5). 6. Needle according to one of the preceding claims, characterized in that said at least one metallic element is chosen from the group formed by gold, platinum, palladium, rhenium, ruthenium, rhodium, silver , iridium or osmium. 7. Use of a needle according to one of claims 1 to 6, in a chronograph. 8. Use of a needle according to one of claims 1 to 6, in a retrograde display. 9. Method for producing a needle (2) pivotally mounted about an axis (10) of said needle so as to be able to indicate information, characterized in that said method comprises the following steps: a) bring the negative (8) of the needle (2) to be produced; b) be provided with a material comprising at least one metallic element being capable of solidifying at least partially in the amorphous phase; c) shaping said material in the negative; d) separating said needle obtained during the shaping step from said negative. 10. Production method according to claim 9, characterized in that step c) comprises the following steps: - Make a preform (7) with said material, said material being solidified at least partially in the amorphous phase, and place the preform on the negative (8); - Heating said preform to a temperature between the glass transition temperature and the crystallization temperature of said material; CH 703 343 B1 - exert pressure on the preform in order to fill the negative with said material; - Cooling said material while keeping it in 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; -dissolving said material in said negative; - cooling the whole by solidifying said material at least partially in the amorphous phase. 12. Production 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 claims 9 to 12, characterized in that said needle (2) further comprises a barrel, this needle (2) being fixed on its axis by means of said barrel (5) and in that said needle and said barrel are one and the same part produced during step c) of shaping. 14. Production method according to one of claims 9 to 12, characterized in that said needle (2) further comprises a barrel, this needle (2) being fixed on its axis (10) by means of a barrel (5) and in that said needle is fixed to said barrel during step c) of shaping. 15. Production method according to one of claims 9 to 14, characterized in that said at least one metallic element is chosen from the group formed by gold, platinum, palladium, rhenium, ruthenium, rhodium , silver, iridium or osmium.