CH703796B1 - Spring barrel for a timepiece, a watch or a clock, where the spring is made of a metal alloy including nitrogen, iron, carbon, manganese, chromium, niobium and niobium - Google Patents

Abstract

The spring barrel for a timepiece, is claimed. The spring is made of a metal alloy including nitrogen in a proportion of 0.75-1 wt.%, and iron. A ratio of an interior diameter of eye and a thickness of plate is less than 12. An independent claim is included for a timepiece.

Description

Technical area

The present invention relates to the field of micromechanics and relates to the field of springs. More particularly, the invention can be applied to the field of watchmaking, particularly to barrel springs used in mechanical watchmaking.

State of the art

[0002] A particular application of the invention relates to the barrel springs. In a mechanical watch movement, the energy required for its operation is generally stored in a spring, housed in a barrel and, in fact, called the mainspring. The force supplied is distributed by the escapement and regulated by an oscillator, which is generally a balance-spring.

The force that must transmit the spring is determined by the characteristics of the movement, from which the spring is dimensioned. The diameter of the barrel conditions the number of turns that can comprise the spring, this number of turn being the essential parameter determining the power reserve of the movement, that is to say the maximum duration during which the barrel can operate the movement in correct conditions.

At present, the barrel springs are made almost exclusively in Nivaflex <®>. Indeed, a barrel spring must meet several fundamental qualities. It must be stainless, non-magnetic, indefatigable, and have a very high coefficient of elasticity. At the moment, the Nivaflex <®> has all these qualities and offers remarkable performances. We note that they occupy a quasi-monopoly position in the market.

From a practical point of view, if we implement a barrel spring Nivaflex in an existing movement, the size available for the barrel and the force that the spring must provide being determined, there is no the possibility of improving the walking reserve of the movement, since one can not change the number of winding turn without resizing the place occupied by the barrel and thus change the movement.

The present invention is intended to provide a significant improvement in the power reserve of a movement, without changing the dimensions of the barrel or the elements of the regulating organ.

The invention also aims to propose a new type of spring, particularly interesting in the field of watchmaking.

Disclosure of the invention

To achieve these objects, the invention relates to a spring as defined in the claims. In a particularly advantageous application, the invention is applicable in a mainspring. Thus, the invention also relates to a barrel comprising such a spring and a timepiece equipped with such a barrel.

Brief description of the drawings

Other details of the invention will appear more clearly on reading the description which follows, given with reference to the accompanying drawing in which: <tb> figs. 1 and 2 <sep> are graphs illustrating the advantages of the invention in its application to a mainspring, and <tb> figs. 3a and 3b <sep> show another comparative example of an advantage of the invention in this same application.

Mode (s) of realization of the invention

The present invention is based on the use for producing a spring, an alloy of the following mass composition: <tb> - <sep> carbon: from 0.1% to 1%, <tb> - <sep> manganese: from 5% to 25%, <tb> - <sep> chromium: from 16% to 20%, <tb> - <sep> nitrogen: from 0.1% to 5%, <tb> - <sep> niobium: ≤ 0.25% <tb> - <sep> molybdenum: from 2.5% to 4.2%, <tb> - <sep> iron: the balance.

This kind of alloy is known under the steel reference 1.4452. It is generally used in medical applications, for prostheses, and even in the watch industry for dressing parts, such as bracelets or watch cases. Indeed, this alloy does not contain nickel and is, in fact, well tolerated in allergies. To the knowledge of the applicant, this alloy is not used for its elasticity qualities.

However, as we will show below, the applicant has noticed the extreme interest in using this alloy to make springs, applied to the watch or not. In particular, this alloy is extremely interesting for making a barrel spring with remarkable properties.

For the applications concerned, the alloy preferably contains less than 0.15% of carbon. It may also contain, more particularly, between 0.75% and 1% of nitrogen. In addition, the alloy may also contain between 12% and 16% manganese.

In order to demonstrate the advantages of the proposed alloy, the following description will highlight its qualities in the context of its application to a mainspring, without limiting the invention to this particular application.

Thus, to test in a comparative manner the performance of a barrel spring made in such an alloy, barrel springs were made to the dimensions of a standard barrel spring, in Nivaflex <®>. In the examples below, the tested springs have the following dimensions: 1.18 × 0.115 × 455 (mm). For the sake of clarity, it will be specified that these dimensions are, respectively, the height, the thickness and the length of the leaf spring.

For the manufacture, the first tests were carried out using a manufacturing method usually used with Nivaflex <®>, in order to be able to make a rigorous comparison. This method being known, it will not be described in detail.

To achieve a Nivaflex <®> spring to the required dimensions, one must have a wire diameter of 0.55 mm. To achieve this dimension, an annealed blank wire of 1.1 mm diameter is drawn, which corresponds to an optimum strain-hardening rate of 65% to 75% and a tensile strength of 2000 MPa at 2200 MPa. Optimal hardening means hardening to obtain an optimum in the ratio between the elasticity and fragility of the material. Thus, with Nivaflex <®>, it is known that wire drawing should not be maximum because the material becomes too fragile.

For 1.4452 steel, the optimum work hardening rate is greater than 98%. However, to date, the steel tell that used in the context of the invention is available on the market in the form of wire diameter of 1.29 mm, which corresponds to a work hardening rate of 82%. The following tests have therefore been carried out using such a wire, which points to possible additional improvements starting from a wire which has been hardened.

The son of Nivaflex <®> and 1.4452 steel are then laminated and thermally treated at a temperature of 380 ° for 4 hours.

The springs obtained, therefore having the same dimensions and having been obtained by the same method for the Nivaflex <®> spring and the 1.4452 steel spring, have the following results: Nivaflex <®> <tb> <sep> <sep> Steel 1.4452 <tb> Thread <sep> Springs 1.18 × 0.115 × 455 treated 380 ° C <sep> Thread <sep> Springs 1.18 × 0.115 × 455 Treated at 380 ° C. <tb> Ø 0.55 mm <sep> M 0.5 <sep> M 4.8 <sep> Ø 0.55 mm <sep> M 0.5 <sep> M 4.8 <tb> Rm 2018 MPa A 6.3% <sep> 7.88 mNm <sep> 6.35 mNm <sep> Rm 2480 MPa At 5.9% <sep> 8.25 mNm (+5%) <sep> 6.88 mNm (+ 8%)

In this table, Rm means the tensile strength of the spring, the force applied to break it. The value A is the relative elongation of the spring during this rupture. The values M0.5 and M4.8 are the torques provided by the cylinder integrating said spring, respectively when, after having been fully armed, the springs are discharged by 0.5 or 4.8 turns of barrel. Naturally, in terms of watchmaking, it is desired that the torque provided by the spring is as constant as possible during the disarming of the spring, and that the values M0.5 and M4.8 are as close as possible to one of the 'other.

We can already see a clear improvement in the mechanical characteristics of an alloy spring according to the invention compared to a Nivaflex spring <®>. It can be noted that the break is at a comparable elongation, but that the 1.4452 steel spring withstands much more traction (+ 22.9%). In addition, for a spring of the same dimensions, the transmitted torque is larger (+ 5% or + 8%, respectively at M0.5 and M4.8), especially with better stability during disarming.

In addition, as mentioned above, the alloy used to make a spring according to the invention can be further drawn. It was thus drawn to a diameter of 0.18 mm. The theoretical values which would be obtained with a cylinder spring of the required dimensions obtained from 0.18 mm drawn wire were calculated. <tb> Steel 1.4452 <sep> <sep> Theoretical properties calculated for treatment at 380 ° C <tb> Wire Ø 0.18 mm <sep> <sep> M0.5 <sep> M4.8 <tb> Rm 3010MPa A 5.9% <sep> <sep> 8.73mNm (11%) <September> 7.44mNm (+ 17%)

It can be seen that a 1.4452 steel spring having these dimensions makes it possible to obtain a greater breaking strength of 49% with respect to the reference spring in Nivaflex <®>. It will be recalled that a drawn Nivaflex <®> spring would give even worse results than the reference spring. In addition, the torque provided (theoretical values, calculated by modeling) is even better than in the tests obtained with a 0.55 mm diameter wire, with greater stability during disarming.

In addition, this wire still has an elongation at break of 5.9%, so it is likely that it can be drawn further, thus further improving its resistance to breakage.

Fig. 3 1 represents the curves of the applied tensile force (in MPa) as a function of the relative elongation. The sudden drop in force applied corresponds to the rupture of the blade. Curve a corresponds to a Nivaflex <®> wire with a diameter of 0.55 mm (75% hardening), the curve b corresponds to a steel wire 1.4452 with a diameter of 0.55 mm (82% hardening) and the curve c corresponds to a 1.4452 steel wire with a diameter of 0.18 mm (98% hardening).

With the springs obtained, it was also carried out fatigue tests. To do this, the spring is armed and disarmed successively between 10% and 90% of its power reserve, until the spring break. The following results were obtained. <tb> <sep> Nivaflex M0.5 to 8.40mNm <sep> Steel 1.4452 M0.5 to 8.25 mNm <tb> Coils Ø 2.40 mm <sep> 1269 cycles <sep> 2047 cycles (+ 61%)

We can see a very significant improvement in the fatigue resistance of the springs to the repetition of armor and disarmament.

Shells tests were performed to improve this point. The shelling consists of making the shell, that is to say the inner end of the mainspring, bent ring-shaped, which is intended to be attached to the barrel shaft. Today, all literature and experience impose a limit on the ratio between the diameter of the barrel shaft and the thickness of the blade forming the spring. This ratio is in principle less than 20. In other words, the ring formed by the shell should not be too small compared to the thickness of the leaf spring. The current limit is based on the ductility of Nivaflex <®>, since the quasi-exclusivity of the barrel springs is made in this material. Thanks to better ductility, 1.4452 steel makes it possible to reduce this ratio.

Tests were carried out with a ratio of 12 times, between the diameter of the barrel shaft and the thickness of the blade forming the spring. In the case tested, the reduction of this ratio is concretely translated by a reduction in the diameter of the barrel shaft from 2.40 mm to 1.35 mm.

Figs. 3a and 3b show respectively Nivaflex® and 1.4452 steel springs with a shell made with a ratio of 12 between the diameter of the barrel shaft on which the spring is intended to be mounted (this diameter corresponds substantially to the inside diameter of the ring formed by the shell), and the thickness of the leaf spring. We can see in fig. The ductility of Nivaflex® does not make it possible to obtain a perfectly circular shell at this size. The elliptical shape promotes the rupture of the blade at the level of the shell. On the contrary, fig. 3b illustrates the possibility of obtaining a shell having a satisfactory circular shape. Thus, despite the relationship between the diameter of the shaft and the thickness of the spring blade, the risk of breakage is not increased.

Additional tests were carried out. Fig. Figure 2 shows torque measurements provided at M0.5 and M4.8. They were made with springs obtained by heat treatments at different temperatures. The curves a and b, obtained with Nivaflex <®> respectively at pairs M0.5 and M4.8, are relatively steeper than the curves c and d obtained with steel 1.4452, respectively at pairs M0.5 and M4.8. The decrease in the M0.5-M4.8 deviation is 5% compared to the Nivaflex <®>, resulting in a slope differential of 25%. Tests carried out at different temperatures show that, beyond a certain area shown in the graph, the springs obtained are unsatisfactory, either because they are too brittle or because they are not elastic enough. It can be seen that 1.4452 steel offers a much larger working temperature range than Nivaflex <®>. In addition, 1.4452 steel can be worked at lower temperatures, which reduces the energy consumed for its treatment. In addition, the temperature range and the slope of the curves obtained with 1.4452 steel allow a simpler definition of the desired torque. Indeed, it is found that for the same tolerance, the temperature control is less strict to obtain a precise torque.

Concretely, all these improvements give the possibility, for a barrel of 11.50 mm in diameter with a blade of 1.18 × 0.115 × 455 mm, according to the example tested, to switch from a power reserve of 48 hours for a given movement, to a power reserve of 66.3 hours for the same movement, an increase of 38%.

Thus, the tests carried out show a very clear advantage in making steel barrel springs 1.4452. The test values given above are only non-limiting illustrations. Thus, thanks to the elastic qualities of the material, which are added to its qualities of resistance to oxidation and amagnetism, the improvement made to the barrel springs is notable. By replacing barrels with Nivaflex <®> springs in existing movements, by barrels with steel springs 1.4452 with a shaft adapted to the new geometry of the shell, we can expect an increase in the power reserve greater than 30% , which is considerable, especially since only the change of the barrel is to be envisaged, without any other modification on the movement, since this improvement is done with constant torque and external dimension of constant barrel.

The above description is not limiting. Thus, the advantages illustrated above can be transposed to other springs used in mechanics or micromechanics. Thanks to the qualities of a 1.4452 steel spring, miniaturization of the elastic systems used until now can be performed, reducing the size of the device incorporating these systems.

It may be added that the interest aroused by these improvements is further reinforced by the ease of implementation of this alloy, which allows optimization of manufacturing costs.

Claims (9)

1. Spring characterized in that it is made of an alloy of the following mass composition: <tb> - <sep> carbon: from 0.1% to 1%, <tb> - <sep> manganese: from 5% to 25%, <tb> - <sep> chromium: from 16% to 20%, <tb> - <sep> nitrogen: from 0.1 to 5%, <tb> - <sep> niobium: ≤ 0.25%, <tb> - <sep> molybdenum: from 2.5% to 4.2%, <tb> - <sep> iron: the balance. 2. Spring according to claim 1, characterized in that the alloy contains less than 0.15% carbon. 3. Spring according to one of the preceding claims, characterized in that the alloy contains between 0.75% and 1% nitrogen. 4. Spring according to one of the preceding claims, characterized in that the alloy contains between 12% and 16% of manganese. 5. Spring according to one of claims 1 to 4, characterized in that it is a mainspring. 6. Spring according to claim 5, characterized in that it has a shell diameter ratio / blade thickness less than 20. 7. Spring according to claim 6, characterized in that it has a report shell internal diameter / blade thickness of less than 12. Barrel with a spring according to one of claims 5 to 7. 9. Timepiece with a barrel according to claim 8.