HK1241475A1 - Timepiece hand - Google Patents

Description

Clock hand

The present application is a divisional application of patent application No.201180040718.8 entitled "timepiece hands" having application date of 2011, 6 and 21.

Technical Field

The invention relates to a timepiece hand, wherein the hand is mounted to pivot about an axis in order to indicate a piece of information.

The invention belongs to the technical field of precision machinery.

Background

Timepieces with hands are known. These fingers are constituted by bars whose length is much greater than the width, which is itself much greater than the thickness. These hands comprise openings for pressing them against the shaft so as to be mounted so as to be able to pivot. In order to have a thin and robust pointer, pointers formed of crystalline metals such as steel, copper, gold or even silicon or ceramics are provided. These pointers may be produced by laser or water jet machining or cutting the sheet. They may also be molded, sintered, or formed by material growth or deposition. These pointers are then used, for example, to indicate hours, minutes and seconds, but also to perform certain functions, such as a timing function or a calendar function.

In fact, these hands are subjected to various stresses. One of these stresses is the weight of the needle itself. In fact, the pointer is usually pressed on its shaft at one of its ends. In view of the small size of the pointer, its slight bending is entirely normal due to its own weight. Weight stress is also applied to the unbalance (balourd) acting as a counterweight for the pointer.

The pointer is also subjected to an acceleration stress. These stresses are due above all to the displacements controlled by the timepiece movement. The above-mentioned displacement is associated with a time indication or a function of the timepiece, for example a timekeeping function, and can be reversed. The return of the pointer to zero occurs in the case of a back display or during the use of the timekeeping function. The return to zero includes the pointer suddenly returning to its original position. During the above-mentioned return-to-zero operation, the acceleration of the pointer may reach 1.10⁶rad·s^-2. During acceleration of the pointer and during deceleration and stopping of the pointer, such acceleration involves high stresses applied to the pointer.

Secondly, the stress associated with acceleration may be due to a shock applied to the watch. In fact, for example, when a table falls, the table accelerates. The energy accumulated during this drop is transferred to the pointer when the watch is in contact with the ground. These shocks may then deform the pointer or unbalance, which may cause problems during the displacement of the pointer.

A disadvantage of pointers made of crystalline materials is their low mechanical resistance when high stresses are applied. In fact, each material is characterized by its young's modulus E, also called the elastic modulus (usually expressed in GPa), which characterizes its resistance to deformation. Each material is further defined by its elastic limit σ_eCharacterisation (usually expressed in GPa) and the elastic limit represents the maximum stress to which the material is subjected in its elastic deformation. Thus, for a given size, one can establish the ratio σ of their elastic limit to their elastic modulus_eCompare materials, the ratio represents the elastic deformation of each material. Thus, the higher the ratio, the higher the elastic deformation of the material. Typically, for alloys such as Cu-Be, the Young's modulus E is equal to 130GPa, the elastic limit σ_eIs equal to 1GPa, thus σ_ethe/E is about 0.007, i.e., a very small ratio. Thus, pointers made of crystalline metals or alloys have limited elastic deformation. Thus, during the return to zero or shock, the stresses applied to the hands may be so high that the hands are plastically deformed, i.e. they are twisted. Therefore, the above-mentioned deformation causes problems of readability and reliability of the information.

In the case of crystalline noble metals, this deformation phenomenon can even be severe. In fact, they have even worse mechanical properties. The noble metals in particular have a low elastic limit, which is about 0.5GPa for alloys of Au, Pt, Pd and Ag compared to about 1GPa for crystalline alloys classically used for pointer production. It is assumed that the elastic modulus of these noble metals is about 120GPa, which results in a_ethe/E ratio is about 0.004, that is to say an even lower value than for the non-noble alloys. Thus, the risk of deformation due to stresses applied during significant acceleration, e.g. return to zero, is increased. The use of these precious metals for the manufacture of timepiece hands is therefore discouraged to those skilled in the art. However, these precious metals are required because they have a remarkable special aesthetic value and give off a sense of qualityHigh.

Furthermore, current methods such as stamping, laser cutting or growth by deposition are limited. They do not allow the formation of three-dimensional pointers. In fact, in the case of stamping or laser cutting, the pointer is formed by a sheet. In the case of the manufacture of the hands by growth of LIGA-type material, the drawback is that the walls of the hands are straight and therefore no inclination of the angular type is possible.

Disclosure of Invention

The object of the present invention is to overcome the drawbacks of the prior art by proposing a metal pointer for sudden acceleration that does not deform during its displacement, so as to have precise readability and remarkable durability.

On this basis, the invention relates to the above-mentioned pointer, which is characterized in that it is made of a completely amorphous metal alloy comprising at least one metal element selected from the group consisting of gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or osmium.

A first advantage of the invention is that it is possible to form a pointer made of precious metal that can withstand shocks or sudden accelerations. It is therefore possible to form pointers made of noble metals with similar dimensions to pointers formed of non-noble metals or crystalline noble metals, but without the risk of deformation during significant acceleration. In fact, surprisingly, amorphous noble metals have more interesting elastic properties than their crystalline equivalents. Increase of the elastic limit sigma_eAllowing an increase of σ_ethe/E ratio such that the stress above which the material does not return to the original shape of the material increases.

Another advantage of the present invention is that it enables extremely easy shaping to allow complex-shaped parts to be manufactured with greater precision. In fact, the amorphous noble metal has the following special characteristics: within a given temperature range [ Tg-Tx ] (where Tx is the crystallization temperature and Tg is the glass transition temperature) specific to each alloy, amorphous metals can soften but remain amorphous for a certain period of time. Thus, these metals can be shaped under relatively low compressive stress and at moderate temperatures, allowing simplified methods to be used. Furthermore, the use of such materials additionally enables the repeated machining of fine geometries with high precision, since the viscosity of the alloy drops sharply as a function of temperature in the temperature range [ Tg-Tx ] and the alloy therefore molds all details of the master (n) piece. A master is understood to mean a mold having a contour in the cavity that is complementary to the contour of the desired component. This then makes it possible to form three-dimensional pointers, which is not allowed or only very difficult with the prior art techniques.

Advantageous embodiments of the pointer are subject matter of the dependent claims.

In a first advantageous embodiment, the pointer is fixed on its shaft by means of a motion work.

In a second advantageous embodiment, said hand and said motion work form a single piece.

In a third advantageous embodiment, the pointer is arranged to be driven by a backward movement.

The invention also proposes to provide a chronograph mechanism comprising at least one hand according to the invention.

The invention also proposes to provide an application of a pointer according to the invention for an application in which, at a given moment, said pointer is subjected to at least 250000rad · s^-2And preferably about 1.10⁶rad·s^-2Acceleration of (2).

The invention also proposes to provide a method for manufacturing a pointer according to the invention, said method comprising the following steps:

a) providing a master of a pointer to be formed;

b) providing a metal alloy comprising at least one metal element and capable of at least partial solidification into an amorphous phase;

c) shaping the metal alloy in the master piece so as to obtain the pointer;

d) separating the pointer from the substrate.

In a first advantageous embodiment, step c) comprises the following steps:

● forming a preform from the material, wherein the metal alloy at least partially solidifies into an amorphous phase, and placing the preform on the substrate member (8);

● heating the preform to a temperature in a range between the glass transition temperature and the crystallization temperature of the metal alloy;

● applying pressure to the preform to fill the substrate piece with the metal alloy;

● cools the metal alloy so that it retains its at least partially amorphous phase.

In a second advantageous embodiment, step c) comprises the following steps:

● adding the metal alloy above its melting point;

● injecting the metal alloy into the substrate;

●, the entire body is cooled so that the metal alloy at least partially solidifies into an amorphous phase.

In a third advantageous embodiment, the method comprises a step of removing excess material before the step of cooling said material.

In another advantageous embodiment, the pointer is fixed on its shaft by means of a needle travel mechanism, and the pointer and the needle travel mechanism are a single piece formed during the forming step c).

In another advantageous embodiment, the pointer is fixed on its shaft by means of a needle travel mechanism and the pointer is fixed to the needle travel mechanism during the forming step c).

In another advantageous embodiment, the at least one noble metal element is selected from the group consisting of gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or osmium.

Drawings

The objects, advantages and features of the pointer according to the present invention will be more clearly seen from the following detailed description of at least one embodiment of the invention, given purely by way of non-limiting example, illustrated in the accompanying drawings, in which:

fig. 1 schematically shows a timepiece with a chronograph function;

fig. 2 to 4 schematically show cross-sectional views of a timepiece hand;

FIG. 5 shows deformation curves for crystalline and amorphous materials;

fig. 6 to 9 schematically illustrate a method according to the invention;

fig. 10 to 14 schematically show a variant of the method according to the invention; and

fig. 15 is a plan view of a variant of the pointer according to the invention.

Detailed Description

Fig. 1 shows a timepiece 1, this timepiece 1 comprising several hands 2 indicating information on the dial of the timepiece. These hands 2 may be hands indicating hours, minutes or seconds. They may be driven by a continuous or backward displacement, wherein the displacement may comprise a sudden acceleration. Sudden acceleration is understood to mean a sudden acceleration, whether foreseeable or not, which occurs within a limited time and is of very large magnitude, wherein said acceleration is followed by a zero displacement, a constant acceleration orLow acceleration. The minimum bearable sudden acceleration is 250000rad & s^-2And is preferably 1.10⁶rad·s^-2. These hands 2 can also be the hands of a chronograph or calendar mechanism or other mechanism. The hands 2 as shown in fig. 2 are constituted by a bar 3, the bar 3 having a length much greater than the width of the bar 3 and the width itself much greater than the thickness. The first end 31 of the wand is used to indicate a message. The first end 31 is preferably the narrowest end. An opening 4 is provided to allow the pointer to press on its shaft 10. The opening 4 is arranged close to the second end 32 of the rod forming the pointer 2. This second end 32 can be arranged to act as an unbalance to ensure a good balance of the pointer 2 during displacement of the pointer 2. It is also contemplated that the second end 32 is circular and includes an opening 4 that allows the second end 32 to be pressed onto its shaft 10, as shown in fig. 1.

The pointer 2 is mounted on the shaft 10 by pressing directly on said shaft 10, as shown in fig. 2, or the pointer 2 is connected to a motion work 5, which motion work 5 itself presses on the shaft 10, as shown in fig. 4. The motion work 5 can be directly formed by a single piece with the hand 2, as shown in fig. 3.

Advantageously, at least one of the hands 2 is made of an at least partially amorphous material containing at least one metallic element. The metal element may be a noble metal element such as gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium, or osmium. An at least partially amorphous metal alloy is understood to mean that the material is capable of at least partially solidifying into an amorphous phase, i.e. it is capable of at least locally losing all of its crystalline structure.

In fact, the advantages of these amorphous metal alloys stem from the fact that: during their formation, the atoms forming these amorphous materials are not arranged in a particular structure like a crystalline material. Therefore, even if the Young's modulus E of the crystalline metal and that of the amorphous metal are substantially the same, the elastic limit σ is_eAs well as different. Thus, the significant differences between amorphous and crystalline metals are: elastic limit sigma of amorphous metal_eAIs a knotElastic limit of crystalline metal σ_eCSubstantially twice as shown in fig. 5. The graph shows the stress σ versus strain curves for amorphous metal (dashed line) and crystalline metal (solid line). Furthermore, the maximum elastic energy that can be stored is calculated as the elastic limit σ_eThe square of (d) and the young's modulus E. Since the elastic limit of amorphous metals is substantially twice that of crystalline metals, amorphous metals can store substantially four times as much elastic energy as crystalline metals. This means that the amorphous metal reaches its elastic limit σ_eAnd may previously be subjected to greater stresses.

First, the pointer 2 made of amorphous metal can improve its reliability as compared to the pointer made of crystalline metal. In fact, the stresses exerted on the pointer 2 are related to the moment of inertia of the pointer 2, which moment of inertia of the pointer 2 depends on the mass and on the length. Thus, the longer the pointer or the greater the mass at the end of the pointer 2, the higher the moment of inertia of the pointer 2. The kinetic energy accumulated by the pointer 2 during the displacement after returning to zero or shaking depends on the moment of inertia. This kinetic energy determines the stress exerted on the pointer 2 during the return to zero movement or during the shock. High kinetic energy leads to high stresses and thus to a significant risk of deformation.

Due to the elastic limit σ of amorphous metals_eAbove the elastic limit sigma of the crystalline metal_eThe stress that needs to be applied to obtain plastic deformation is therefore high. Thus, for a considerable kinetic energy, the fingers 2 made of amorphous metal are less at risk of plastic deformation than the fingers 2 made of crystalline metal.

A material can also be characterized by its specific strength, which is the ratio of the elastic limit to the density. Amorphous metals have a higher specific strength than crystalline metals, because, on the one hand, the elastic limit of amorphous metals is twice that of crystalline metals for the same type of alloy, and, on the other hand, the density of amorphous structures is about 10% lower than that of crystalline structures for a given composition. The result of this situation is: pointers made from amorphous metal alloys or amorphous metals are lighter than pointers of the same size made from metal alloys of the same composition but having a crystalline structure. Therefore, the moment of inertia of the pointer made of amorphous metal is lower because the moment of inertia is related to the mass. The kinetic energy and therefore the stress exerted on the fingers made of amorphous metal are low, so that the fingers can withstand higher stresses before plastic deformation.

The advantage of density in combination with the ability of amorphous metals to withstand higher stresses prior to plastic deformation allows the use of amorphous noble metal alloys. In fact, the elastic limit of amorphous noble metal alloys is twice that of their crystalline equivalents. Thus, the amorphous noble metal alloy is able to withstand higher stresses than its crystalline equivalent prior to plastic deformation. Stress is related to kinetic energy, which itself is related to moment of inertia, which depends on mass and length. Thus, since amorphous metal alloys, whether noble or not, are lower in density than their crystalline equivalents, their displacements exhibit lower kinetic energies and therefore lower stresses. Thus, a pointer made of amorphous noble metal having the same dimensions as a pointer made of crystalline noble metal alloy has a lower mass, the displacement of which will produce lower stresses. It is possible to use amorphous noble metal alloys to form pointers that must withstand significant and sudden accelerations, as the stresses are lower and the maximum withstand stress is higher, contrary to the prejudice of the person skilled in the art.

Secondly, the properties of the amorphous metal make it possible to envisage more variants of the pointer 2. In fact, the moment of inertia is used to determine the kinetic energy of the pointer and the stresses to which the pointer will be subjected during its return to zero. The moment of inertia depends on the mass and length of the pointer 2. These parameters are therefore taken into account to limit the risk of plastic deformation of the pointer 2.

Since amorphous metals are able to withstand higher stresses, i.e. higher kinetic energies and therefore higher moments of inertia, the mass and length of the pointer 2 can be increased without the risk of plastic deformation. More specifically, the mass at the first end of the pointer 2 can be increased, which allows the use of a pointer 2 of a larger shape. Therefore, it is possible to set: said first end portion comprises an area with a larger size, which for example allows the use of luminous material, or the long second hand of the chronograph mechanism takes the form of breguet hand 2. The mass at the second end 32, which may act as an unbalance, may also be increased.

While the properties of amorphous metals allow increasing the size of the fingers 2, they also allow forming fingers 2 with smaller dimensions. In fact, for equivalent stresses, the pointer 2 can have a smaller length and/or a smaller mass without plastic deformation, which is caused by a higher elastic limit. The above-mentioned size reduction can also be applied to the unbalance of the hand 2 for balancing said hand 2.

Thus, amorphous metals, whether noble or not, have the double advantage of allowing the size of the hands 2 to be increased or decreased without increasing the risk of plastic deformation. The reduction in size and/or mass of the pointer can be achieved by providing a groove 11 on the pointer 2, which groove 11 may or may not be through-going, as is evident from fig. 15. These grooves 11 allow to reduce the mass of the pointer 2 by removing material and therefore to reduce the moment of inertia, while providing interesting visual effects.

Several methods are conceivable for manufacturing the pointer 2 using amorphous metal.

First, a conventional method of punching or cutting may be used. Thus, the amorphous metal is first provided in the form of flakes. These sheets are then stamped by pressing or cut by water jets or laser.

However, the properties of the amorphous noble metal can be used for shaping. In fact, amorphous metals are very easy to shape, which makes it possible to manufacture parts with complex shapes with high precision. This is because the following special characteristics of amorphous metals: in a given temperature range [ Tg-Tx ] specific to each alloy](for example, for Zr)_41.24Ti_13.75Cu_12.5Ni₁₀Be_22.5Alloys, with Tg 350 ℃, Tx 460 ℃, amorphous metals can soften but remain amorphous for a certain period of time. Thus, these metals can be formed at relatively low stress and moderate temperatures, allowing simplified methods such as thermoforming to be used. Because the viscosity of the alloy is in the temperature range Tg-Tx]The use of such materials additionally enables fine geometries to be repeatedly machined with high precision, since the internal temperature drops sharply as a function of the temperature and the alloy therefore molds all the details of the substrate part. For example, for platinum-based materials, the forming occurs at a temperature of about 300 ℃ at which the viscosity of the alloy reaches 10³Pa.s, stress of 1MPa, and viscosity of 10 at temperature Tg¹²Pa.s. The use of a die has the advantage of producing three-dimensional high precision parts that do not allow cutting or stamping.

The method used is the thermoforming of amorphous preforms. This preform 7 is obtained by melting in a furnace the metallic elements intended to form the amorphous alloy. The melting is carried out in a controlled atmosphere so that any combination of alloy and oxygen is as low as possible. Once these elements are melted, they are cast in the form of a semi-finished product, for example a rod having dimensions close to those of the pointer, and then rapidly cooled so as to remain at least partially amorphous. Once the preform 7 is made, thermoforming is carried out in order to obtain the final part. The thermoforming is carried out by pressing in a temperature range between its glass transition temperature Tg and its crystallization temperature Tx for a predetermined time to maintain a fully or partially amorphous structure. This is done to maintain the elastic performance characteristics of the amorphous noble metal. The different steps of the final shaping of the cursor 2 are therefore:

a) the mould 8 of the master with the hands 2 is heated to a chosen temperature, as shown in figure 6,

b) the amorphous metal preform 7 is inserted between hot dies, as shown in figure 7,

c) a closing force is applied to mold 8 to replicate the geometry of mold 8 onto amorphous noble metal preform 7, as shown in figure 8,

d) waiting for a selected maximum time of the time,

e) the mould part 8 is opened and the mould part is opened,

f) rapidly cooling the pointer 2 below Tg so that the material retains its at least partially amorphous state, and

g) the pointer 2 is removed from the module 8 as shown in figure 9.

Thermoforming allows to simplify the formation of said cursor 2, in particular for the groove 11 forming the cursor shown in fig. 15.

Furthermore, the hands 2 can be formed directly with the motion work 5 using thermoforming techniques, as is clear from fig. 6 to 9. This means, therefore, that the motion work 5 and the hands 2 are made of the same piece only, as is clear from fig. 3. Thus, a mold (mold) 8 forming a mold (moule) is provided in the shape of a master having the hand 2 and its integrated needle travel mechanism 5. Thus, steps a) to g) are carried out to form said hand 2. Because of the arrangement in which the hands 2 and their travel mechanisms 5 are made as a single piece, there is no problem with the fixation between said hands 2 and their travel mechanisms 5.

In a variant, the hands 2 are formed directly fixed to the motion work 5. The motion work 5 shown in fig. 4 consists of a cylindrical part having an inner diameter d equal to the diameter of the shaft 10, the motion work 5 pressing on the shaft 10. The feed mechanism 5 has an outer diameter D which is larger than the inner diameter D and the outer diameter D may be non-uniform over the feed mechanism 5. The outer contour of the motion work 5 has an annular groove 6, in which groove 6 the pointer 2 is positioned. The above-mentioned groove, having a diameter between the above-mentioned inner and outer diameters, enables the pointer 2 to be axially retained. The motion work 5 is placed between the mould parts 8 and the hands 2 will be formed in the mould parts 8, as shown in fig. 11. The above-described steps a) to g) are then carried out, which steps a) to g) are shown in fig. 12, 13 and 14. As a result, the pointer 2 is directly moulded onto the needle travel mechanism 5 and is therefore directly fixed to the needle travel mechanism 5. The following can be set: the wall of the annular groove has projections or other structures to improve the retention and in particular the annular retention of the pointer 2 in the motion work 5.

It will be appreciated that various alterations and/or modifications and/or combinations, which are obvious to a person skilled in the art, may be made to the various embodiments of the invention discussed above without departing from the scope of the invention as defined by the appended claims.

It will of course be appreciated that the hands 2 or the parts forming the motion work 5 and the hands 2 may be formed by casting or by injection. The method comprises casting an alloy obtained by melting a metal element in a mould having the shape of the final part. Once the mold has been filled, it is rapidly cooled to a temperature below Tg to prevent the alloy from crystallizing and thus obtain the pointer 2 made of noble metal in amorphous or partially amorphous state.

Claims (7)

1. Use of a pointer (2) arranged to be mounted around an axis (10) so as to be able to indicate a piece of information, said pointer being made of an at least partially amorphous metal alloy comprising at least one metal element, characterized in that said pointer is used in a situation in which said pointer is subjected to at least 250000rad · s at a given moment^-2Acceleration of (2).

2. Use of a pointer according to claim 1 characterized in that the pointer is fixed on the shaft (10) with a pointer mechanism (5).

3. Use of a pointer according to claim 1 characterized in that the pointer and the motion work (5) form a single piece.

4. Use of a pointer as claimed in claim 1, characterized in that the pointer is arranged to be driven by a backward movement.

5. Use of a pointer according to claim 1 characterized in that the pointer is made of a metal alloy that is completely amorphous.

6. Use of a pointer as in claim 1 wherein the metallic element is selected from the group consisting of gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or osmium.

7. Use of a pointer as claimed in claim 1, characterized in that the pointer is used in an application in which the pointer is subjected to about 1.10 at a given moment in time⁶rad·s^-2Acceleration of (2).