EP3743538B1 - Pivoting pin of a regulator and manufacturing method therefor - Google Patents

Description

Technical area

The present invention relates to the field of watchmaking. It relates, more particularly, to a pivot axis of a regulating member of a mechanical watch movement and even more particularly to a balance, lever or escapement mobile axis made of a non-magnetic material.

State of the art

The manufacture of watchmaking pivot axes of the balance shaft, anchor rod or escapement pinion type consists of carrying out a succession of operations allowing, from a bar of raw material, to form an axis having precise dimensional characteristics. as well as sufficient mechanical strength with regard to the intended application.

Owing to their general shape of revolution, watch pivot axes are produced in a known manner by precision turning or turning operations, from a martensitic carbon steel bar. These machining operations make it possible to define the functional surfaces necessary for the proper functioning of the axis (clearances, stops, pivots, etc.) and for the assembly of the various components (balance seat, plate bearing, ferrule bearing , etc.). The turned pin then undergoes a deburring operation and then one or more heat treatment operations comprising at least quenching to improve the hardness of the pin and tempering to improve its toughness. A rolling operation of the pivots, intended to improve the surface condition, the hardness and the geometric precision, is generally carried out during or at the end of manufacturing. The rolling operation can be compared to a grinding and/or polishing operation of the pivots.

More specifically, the pivot axes, for example balance axes, traditionally used in mechanical watch movements are made from martensitic carbon steel bars having lead-type addition elements and/or or manganese. Manganese is generally present in steels in the form of manganese sulphides and allows regular fragmentation of the cutting chip. Lead tends to bind to non-metallic inclusions present in steel, or is found in the form of elementary particles. It acts as a lubricant, reduces the coefficient of friction at the tool/cutting zone interface and limits the formation of a material deposit on the cutting edge of the tool. These addition elements therefore have the common objective of improving the machinability of the steel. A steel of this type can be supplied by a large number of suppliers under the name 20AP or 1.1268+Pb.

In addition to good machinability, martensitic lead steel has, after quenching and tempering treatments, high mechanical properties in line with the stresses encountered by the pivot pins during their operation. Typically, the pivots of an axle made of martensitic lead steel have a hardness exceeding 600 HV1 after heat treatment and rolling. Such hardness values guarantee optimum wear resistance for the proper functioning of the oscillator over time.

Despite the advantages of machinability and mechanical strength, martensitic lead steel has a major drawback: its sensitivity to magnetism. The environment in which watches operate has greatly evolved in recent decades. Electronic devices and accessories incorporating permanent magnets have multiplied, thus exposing watches, and therefore their regulating organs, to increasingly high and increasingly frequent magnetic fields. The martensitic leaded steel commonly used for the production of balance shafts has a non-negligible residual field after exposure to an external magnetic field. The proximity of the axis to the hairspring, generally made of ferromagnetic material, makes it a particularly strategic component when it is desired to improve the resistance to magnetism of watches.

It should be noted that martensitic carbon steels are also sensitive to corrosion. This drawback poses a problem mainly during the stages of manufacture and storage of the axles. In use, the pivot axes of the mechanical movement normally remain confined within the sealed zone of the watch, which does not represent a particularly constraining environment for a material, even oxidizable.

The document CH707503 describes a pivot pin formed from a composite material having a metal matrix comprising at least one metal chosen from nickel, titanium, chromium, zirconium, silver, gold, platinum, silicon, molybdenum , aluminum or an alloy thereof, said matrix being loaded with hard particles chosen from among WC, TiC, TaC, TiN, TiCN, Al2O3, ZrO2, Cr2O3, SiC, MoSi2, AlN or a combination thereof, in order to limit the shaft's sensitivity to magnetic fields. The hardness of said composite material is greater than or equal to 1000 HV1. The solution described here is not optimal. The machining by cutting tool of metal matrices loaded with hard particles generates premature wear of the tools. In operation, the pivoting of such an axis in a ruby bearing also generates premature wear at the level of the bearing.

The document CH707504 describes a titanium or titanium alloy pivot pin to limit its sensitivity to magnetic fields. At least the outer surface of the pivots is partially or totally hardened with respect to the core of the axle according to a predetermined depth, the outer surface has a hardness greater than 800 HV1. The solution described here is not optimal. The surface hardening of the pivots adds a step in the already complex process of obtaining a balance shaft. In addition, titanium alloys require special precautions during machining, particularly with regard to the risk of fire.

The document CH707505 describes a pivot pin made of austenitic-type steel, austenitic-type cobalt alloy or austenitic-type nickel alloy in order to limit its sensitivity to magnetic fields. At least the external surface of the pivots is hardened with respect to the core of the axle according to a predetermined depth, the external surface has a hardness greater than 1000 HV1. The solution described here does not seem optimal. The surface hardening of the pivots adds a step in the already complex process of obtaining a balance shaft. This hardening occurring after the pivot termination step(s), the handling precautions taken during this processing step must be important so as not to risk marking or twisting the pivots.

The document EP3273303 describes a balance shaft made of a non-magnetic copper alloy. During the production of the axle, the pivots are rolled or polished in order to remove an extra thickness of material and thus achieve the final dimensions and surface finish. In addition, the surface is hardened by means of a thermal and/or thermochemical diffusion treatment or an ion implantation of other atoms, down to a predetermined depth. This alloy, after treatment, can have an interesting hardness, greater than 600 HV, but the treatment methods used are complicated, require specialized equipment and are difficult to control, in particular with regard to ionic diffusion. The document EP3273304 also describes an axle made of a similar alloy, which has a layer of hard material deposited on its surface. Ideally, the aim is to avoid additional surface deposition, which again is complicated to perform and requires specialized equipment.

The document US9194024 describes an alloy for jewelry, the composition of which is chosen to obtain a substantially white color, comparable to platinum alloys. After hardening by aging, the alloy only reaches a hardness of up to around 240 HV, which is insufficient for a watch axis.

The document WO 98/45489 reveals alloys intended for electrical contacts, but does not teach anything and is not relevant to a watchmaking axis.

The object of the present invention is to propose a shaft made of a non-magnetic material as an alternative to the various solutions of the prior art and overcoming, at least partially, their drawbacks.

Disclosure of invention

The invention is described in the appended claims.

Brief description of the drawings

• La fig. 1 est une représentation d'un axe de pivotement selon l'invention, au stade décolleté;
• La fig. 2 est une représentation d'un axe de pivotement selon l'invention, au stade roulé;
• La fig. 3 est une représentation d'un axe de pivotement selon l'invention, au stade terminé;
• La fig. 4 est une représentation d'un axe de pivotement selon l'invention, montrant les différentes surépaisseurs susceptibles d'intervenir dans le processus.

Other details of the invention will appear more clearly on reading the following description, made with reference to the appended drawing in which:

• The fig. 1 is a representation of a pivot pin according to the invention, at the neckline stage;
• The fig. 2 is a representation of a pivot pin according to the invention, in the rolled stage;
• The fig. 3 is a representation of a pivot pin according to the invention, at the finished stage;
• The fig. 4 is a representation of a pivot axis according to the invention, showing the different extra thicknesses likely to occur in the process.

Embodiment of the invention

The invention relates to a pivot axis of a regulating member of a mechanical watch movement, and more particularly still to a balance, lever or escapement mobile axis.

The applicant has identified a family of alloys having particularly advantageous properties for application to the axes of regulating members of mechanical movements, in particular in terms of magnetism and resistance to oxidation.

• entre 25% et 55% de palladium
• entre 25% et 55% d'argent
• entre 10% et 30% de cuivre
• entre 0% et 5% de zinc
• entre 0% et 2% d'un ou plusieurs éléments choisis parmi rhénium, ruthénium, or et platine
• entre 0% et 1% d'un ou plusieurs éléments choisis parmi bore et nickel.

The alloys of this family have, by weight:

• between 25% and 55% palladium
• between 25% and 55% silver
• between 10% and 30% copper
• between 0% and 5% zinc
• between 0% and 2% of one or more elements selected from rhenium, ruthenium, gold and platinum
• between 0% and 1% of one or more elements chosen from boron and nickel.

• entre 38% et 43% de palladium ; et/ou
• entre 35% et 40% d'argent ; et/ou
• entre 18% et 23% de cuivre ; et/ou
• entre 0.5% et 1.5% de zinc.

Preferably, the alloys in question comprise by weight:

• between 38% and 43% palladium; and or
• between 35% and 40% silver; and or
• between 18% and 23% copper; and or
• between 0.5% and 1.5% zinc.

More particularly among this family of alloys, an alloy of the type consisting of 41% palladium, 37.5% silver, 20% copper, 1% zinc and 0.5% platinum does not have a detectable attractive action when it is exposed to a permanent magnet. It also shows no measurable remanent magnetization after exposure to the magnet.

The Applicant has also identified that Palladium-Silver-Copper alloys have a higher resistance to oxidation than that of martensitic carbon steels thanks in particular to the presence of palladium, a chemical element of the platinum group. Palladium makes it possible to improve the following characteristics of the alloy, which are particularly interesting in the case of use for a pivot pin: chemical inertness, resistance to corrosion and oxidation, low coefficient of thermal expansion and mechanical durability.

Another aspect of the invention relates to a method of manufacturing a pivot pin of a regulating member, the steps of which we will now describe.

The first step in the process of obtaining an axis according to the invention consists in obtaining a bar of bar turning of the Palladium-Silver-Copper alloy having a composition belonging to the family of alloys as defined below. above. Different shades are available from various suppliers. The latter carry out the alloying steps and the bar shaping steps (drawing, drawing, etc.) in order to offer a bar in standard bar-turning dimensions. Typically 2-3mm in diameter by 2000-3000mm long. It goes without saying that the chemical composition of the bar will be the same as that of the axis made from this bar.

The Vickers hardness of the stretched material used to make the shaft is preferably of the order of 260-310 HV1. After heat hardening at 380-420°C, the hardness value can rise to 460-500HV1. This heat treatment can last between 30 minutes and 2 hours, more particularly for between 45 minutes and 1h30, even more particularly for 1h, and the hardness value after hardening remains lower than what can be encountered on a 20AP steel after rolling, typically more than 700HV1.

The hardening heat treatment can be carried out at any time during the process of obtaining the axis. This hardening can be carried out on the bar upon receipt if the machining requires high hardness. Preferably, the hardening is carried out after machining and before the step or steps of treating the surface state of the pin.

When one quantifies the Hertz pressure at the level of the pivoting of the axis, one notices that the low Young's modulus of the Palladium-Silver-Copper alloy makes it possible to lower the maximum pressure observed at the level of the contact of the axis with pivot stone. During a contact between two materials of Young's modulus E ₁ and E ₂ , the equivalent modulus of elasticity E used to determine the rigidity of the contact is calculated as follows: $$\frac{1}{E}=\frac{1}{2}\left(\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="imgf0004.png"\; state="\{\{state\}\}">E</figure-callout>}}_1}+\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="imgf0004.png"\; state="\{\{state\}\}">E</figure-callout>}}_2}\right)$$

• F = effort normal sur le contact
• E = module d'élasticité équivalent précédemment défini rr et I = sont des paramètres géométriques du contact.

The maximum pressure observed at the level of the contact is given by the following formula: $$\mathit{Pmax}-0.418\sqrt{\frac{F.E}{\mathit{rr}.I}}$$

• F = normal force on the contact
• E = equivalent modulus of elasticity previously defined rr and I = are geometric parameters of the contact.

.For a given normal force F, and with equivalent contact geometry, we observe that the maximum pressure is proportional to $\sqrt{E}$

.

est en baisse de plus de 20% lorsque nous passons d'un contact Acier (220GPa) sur rubis (350GPa) à un contact alliage PdAgCu (100GPa) sur rubis (350GPa) à géométrie équivalente. Cas n°1 Acier - Rubis Cas n°2 PdAgCu - Rubis E1 220 GPa 100 GPa E2 350 GPa 350 GPa E calculé avec (1) 270.2 GPa 155.6 GPa √E 16.4 12.5 With a numerical application, we find that $\sqrt{E}$

is down by more than 20% when we go from a Steel contact (220GPa) on ruby (350GPa) to a PdAgCu alloy contact (100GPa) on ruby (350GPa) with equivalent geometry. Case n°1 Steel - Ruby Case n°2 PdAgCu - Ruby E1 220GPa 100GPa E2 350GPa 350GPa E calculated with (1) 270.2GPa 155.6GPa √E 16.4 12.5

Thus, despite a lower hardness, it is found that the wear resistance of the contact is still satisfactory. This is explained by the drop in contact pressure, thus allowing the use of a pin with a lower hardness without compromising the wear resistance of the contact, typically 460-500HV1 for the pin made of Palladium-Silver alloy -Copper versus 600-700HV1 for a standard Carbon Martensitic Steel axle. The use of a lower hardness alloy facilitates material removal and shaping operations.

The next step in the process for obtaining an axis according to the invention consists in shaping it by a turning step. This is carried out in the traditional way on the same equipment as those used to machine pins in martensitic carbon steel according to the prior art. An adaptation of the cutting parameters is necessary in order to optimize the quality and the yield of the bar turning step. In the case of the pendulum axis, its radius being very small, even at high spindle speed, the cutting speeds reached during machining are limited. By referring to the figure 1 , the balance shaft has two small diameter zones, the pivots 10, located at the ends of the shaft as well as several larger diameter zones forming the body of the shaft 20.

For example, at the level of the pivots, it is possible to use a cutting speed of 20 to 23 m/min with a feed of 0.0015 mm/rev. At the spindle body, a cutting speed of 20 to 23 m/min and a feed rate of 0.002 mm/rev to 0.005 mm/rev can be used.

During this step of turning, it is necessary to provide one or more additional thicknesses depending on the treatment operations of the surface state of the axis envisaged. If the turning step is sufficiently repeatable and makes it possible to obtain a sufficient geometric tolerance for the application envisaged, a simple polishing of the functional zones will have to be carried out. An extra thickness (e1) corresponding to the quantity of material removed during polishing must be added to the part compared to the final dimensions. The figure 2 illustrates, by way of example, a balance staff after the cutting step. The picture 3 illustrates, by way of example, a balance staff after the polishing step. Referring to fig 4, the step of turning will make it possible to obtain profile 2 at the level of the pivot with an extra thickness (e1) compared to profile 1. The polishing step will bring the profile of the pivot to the level of its final profile 1. The extra thickness (e1) is typically around 2 µm in diameter but can be adapted according to the polishing envisaged (duration, type of abrasive particles used, etc.).

According to another variant of the method, if a step of grinding or rolling the pivots is envisaged for a fine control of the dimensions and the surface states, an extra thickness (e2) corresponding to the quantity of material removed during this grinding or rolling step must be added to the part or to the pivots at the turning stage. The additional thickness (e2) is typically of the order of 20 μm over the length and 5 μm over the diameter but can be adapted according to the rolling or grinding function envisaged. The turning should therefore be done at the level of profile 3, as shown in figure 4 . Rolling will bring the pivot to the level of profile 2 as shown in figure 4 . A surface treatment can be added at the end of the process to obtain profile 1.

Depending on the type of treatment of the surface state chosen, in bulk or localized at the level of the pivots, the person skilled in the art will consider an extra thickness on the entire axis if the treatment is carried out in bulk or only on the areas involved in the removal of material if it is a localized treatment.

Other steps for treating the surface state of the pin or pivots with material removal can be envisaged without departing from the scope of the invention: electrolytic polishing or laser polishing for example. A person skilled in the art will adapt the extra thickness to be taken into account during the turning step.

Intermediate washing and dimensional control steps can be integrated into the process.

Other types of parts integrated into a mechanical or quartz watch movement, and liable to disturb the operation of the movement in the event of magnetization, may be made of an alloy of the type described above without being part of the claimed scope of protection. . This type of part may in particular be of the pin type, fasteners, axles of the gear train, etc. without however presenting problems similar to those encountered for the pivot axis of a regulating member.

Claims (14)

1. Pivot staff of a mechanical timepiece movement regulating member, made of a non-magnetic material consisting of, by weight:

   - between 25% and 55% palladium

   - between 25% and 55% silver

   - between 10% and 30% copper

   - between 0% and 5% zinc

   - between 0% and 2% of one or more elements chosen from rhenium, ruthenium, gold and platinum

   - between 0% and 1% of one or more elements chosen from boron and nickel.
2. Regulating member staff according to Claim 1, characterized in that said material comprises, by weight, between 38% and 43% palladium.
3. Regulating member staff according to either of the preceding claims, characterized in that said material comprises, by weight, between 35% and 40% silver.
4. Regulating member staff according to one of the preceding claims, characterized in that said material comprises, by weight, between 18% and 23% copper.
5. Regulating member staff according to one of the preceding claims, characterized in that said material comprises, by weight, between 0.5% and 1.5% zinc.
6. Regulating member staff according to one of the preceding claims, characterized in that said staff is a balance staff, an anchor staff or an escapement wheel staff.
7. Regulating member staff according to one of the preceding claims, characterized in that it has a Vickers hardness of 460 HV1 to 500 HV1.
8. Mechanical movement for a timepiece, characterized in that it comprises a regulating member staff according to one of the preceding claims.
9. Method for manufacturing a pivot staff of a regulating member, comprising the following steps:

   - obtaining a bar of non-magnetic alloy consisting of between 25% and 55% palladium, between 25% and 55% silver, between 10% and 30% copper, between 0% and 5% zinc, between 0% and 2% of one or more elements chosen from rhenium, ruthenium, gold and platinum, and between 0% and 1% of one or more elements chosen from boron and nickel;

   - profile-turning the staff with an overthickness with respect to a predetermined dimension;

   - performing an operation of treating the surface state of the staff with removal of the overthickness so as to reach the predetermined dimension;

   - performing a hardening heat treatment step at a temperature of 380°C to 420°C.
10. Manufacturing method according to the preceding claim, wherein said bar has a Vickers hardness of between 260 HV1 and 310 HV1.
11. Manufacturing method according to either of Claims 9 and 10, wherein said hardening heat treatment step lasts between 30 minutes and 2 hours, more particularly between 45 minutes and 1 h 30, even more particularly for 1 h.
12. Manufacturing method according to one of Claims 9 to 11, wherein, after said hardening heat treatment step, said staff has a Vickers hardness of between 460 HV1 and 500 HV1.
13. Manufacturing method according to one of Claims 9 to 12, characterized in that said hardening heat treatment step is performed between the steps of obtaining said alloy bar and of profile-turning or between the steps of profile-turning and of surface treatment.
14. Manufacturing method according to one of Claims 9 to 13, said pivot staff of a regulating member having a body provided at its ends with pivots, said method comprising the following steps:

    - obtaining said alloy bar;

    - profile-turning the body of the staff with a first overthickness with respect to a first predetermined dimension, and the pivots of the staff with a second overthickness with respect to a second predetermined dimension, said second overthickness being greater than the first overthickness;

    - burnishing the pivots so as to bring them to the first overthickness with respect to the second predetermined dimension;

    - performing an operation of treating the surface state of the body and of the pivots with removal of the first overthickness so as to reach the first and second predetermined dimensions respectively.

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