CH714594A1 - Pivoting axis of a regulating organ of mechanical watchmaking movement. - Google Patents

Abstract

The invention relates to a pivot axis of a clockwork mechanical movement regulating member made of a material consisting of weight: between 25% and 55% of palladium between 25% and 55% of silver between 10% and 30% of copper between 0% and 5% of 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 selected from boron and nickel. The invention also relates to a method of manufacturing such an axis.

Description

Description

Technical Field [0001] The present invention relates to the field of watchmaking. It relates, more particularly, to a pivot axis of a regulating member of a mechanical clockwork movement and more particularly still to a pendulum, anchor or escapement mobile axis made of a non-magnetic material.

State of the art The manufacture of clockwork pivot axes such as a pendulum axis, anchor rod or escapement pinion consists in carrying out a succession of operations making it possible, from a bar of raw material, to form an axis having precise dimensional characteristics as well as sufficient mechanical strength with regard to the envisaged application.

Due to their general form of revolution, the watch pivoting axes are produced in a known manner by bar turning or precision turning operations, using 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, range of the plate, range of the ferrule , etc.). The neckline axis then undergoes a deburring operation and then one or more heat treatment operations comprising at least one quenching to improve the hardness of the axis and an income to improve its toughness. A rolling operation of the pivots, intended to improve the surface finish, the hardness and the geometric precision, is generally carried out during or at the end of manufacture. The rolling operation can be compared to a grinding and / or polishing operation of the pivots.

More specifically, the pivot axes, for example the pendulum axes, traditionally used in mechanical watch movements are made from carbon martensitic steel bars having type addition elements lead and / 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 bond to non-metallic inclusions 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 area interface and limits the formation of a deposit of material on the cutting edge of the tool. These additional elements therefore have the common objective of improving the machinability of steel. Steel of this type can be supplied from a large number of suppliers under the designation 20 AP or 1.1268 + Pb.

In addition to good machinability, lead martensitic steel has, after quenching and tempering treatments, high mechanical properties in line with the stresses encountered by the pivot axes during their operation. Typically, the pivots of an axis made of lead martensitic 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, lead martensitic steel has a major drawback: its sensitivity to magnetism. The environment in which watches evolve has evolved considerably in recent decades. Electronic devices and accessories incorporating permanent magnets have multiplied, thus exposing watches, and therefore the regulating organs of these, to increasingly high magnetic fields and more and more frequently. The lead martensitic steel commonly used for the production of pendulum axes 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 will be noted that martensitic carbon steels are also sensitive to corrosion. This drawback is a problem mainly during the manufacturing and storage stages of the axes. In use, the pivot axes of the mechanical movement normally remain confined within the waterproof zone of the watch, which does not represent a particularly restrictive medium for a material, even oxidizable.

Document CH 707 503 describes a pivot axis 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 of the latter, said matrix being charged with hard particles chosen from WC, TiC, TaC, TiN, TiCN, AI ₂ O ₃ , ZrO ₂ , Cr ₂ O ₃ , SiC, MoSi ₂ , AIN or a combination of these, in order to limit the sensitivity of the axis 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 cutting tool machining of metal matrices loaded with hard particles generates premature tool wear.

In operation, the pivoting of such an axis in a ruby bearing also generates premature wear at the bearing.

Document CH 707 504 describes a pivot axis made of titanium or titanium alloy in order to limit its sensitivity to magnetic fields. At least the external surface of the pivots is partially or completely hardened relative to the core

CH 714 594 A1 of the axis according to a predetermined depth, the external 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 pendulum axis. In addition, titanium alloys require special precautions during machining, especially with regard to the risk of fire.

Document CH 707 505 describes a pivot axis of steel of the austenitic type, of cobalt alloy of the austenitic type or of nickel alloy of the austenitic type in order to limit its sensitivity to magnetic fields. At least the outer surface of the pivots is hardened relative to the heart of the axis to a predetermined depth, the outer 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 pendulum axis. This hardening occurring after the stage or stages of termination of the pivots, the handling precautions taken during this treatment stage must be important so as not to risk marking or bending the pivots.

The object of the present invention is to provide an axis produced from a non-magnetic material as an alternative to the various solutions of the prior art and which at least partially remedy their drawbacks.

Disclosure of the invention [0012] More precisely, the invention relates to a pivot axis of a regulating member of a mechanical watch movement made of an alloy comprising by weight:

- between 25% and 55% of 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.

Preferably, the invention relates to an alloy of the type consisting of 41% palladium, 37.5% silver, 20% copper, 1% zinc and 0.5% platinum.

The invention also relates to a method of manufacturing a pivot axis of a regulating member of a mechanical clockwork movement comprising the following steps:

- Obtain an alloy bar comprising 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;

- Bar the axis with an extra thickness compared to a predetermined dimension;

- Carry out an operation to treat the surface condition of the axle with removal of the additional thickness to reach the predetermined dimension.

The manufacturing process may further comprise a step of heat curing treatment between the steps of bar turning and surface treatment.

Brief description of the drawings [0016] Other details of the invention will appear more clearly on reading the description which follows, made with reference to the attached drawing in which:

Fig. 1 is a representation of a pivot axis according to the invention, at the neckline stage;

Fig. 2 is a representation of a pivot axis according to the invention, in the rolled stage;

Fig. 3 is a representation of a pivot axis according to the invention, at the completed stage;

Fig. 4 is a representation of a pivot axis according to the invention, showing the different extra thicknesses which may be involved in the process.

Embodiment of the invention The invention relates to a pivot axis of a regulating member of a mechanical clockwork movement, and more particularly still to a pendulum, anchor or mobile axis exhaust.

The Applicant has identified an alloy family (resume R1) having particularly advantageous properties for an application to axes of organ regulating mechanical movement, in particular in terms of magnetism and resistance to oxidation.

More particularly among this family of alloy, an alloy of the type consisting of 41% palladium, 37.5% silver, 20% copper, 1% zinc and 0.5% platinum, has no action attractive detectable when exposed to a permanent magnet. Nor does it have any measurable remanent magnetization after exposure to the magnet.

CH 714 594 A1 The Applicant has also identified that the 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 from the group of platinum. Palladium makes it possible to improve the following characteristics of the alloy, which are particularly advantageous in the case of use for a pivot axis: chemical inertia, resistance to corrosion and to oxidation, low coefficient of thermal expansion and mechanical durability.

Another aspect of the invention relates to a method of manufacturing a pivot axis 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 for turning the Palladium-Silver-Copper alloy in the defined composition. Different shades are available from various suppliers. The latter carry out the alloying stages and the bar shaping stages (drawing, drawing, etc.) in order to provide a bar in the standard dimensions of bar turning. Generally 2-3 mm in diameter by 2000-3000 mm long.

The Vickers hardness of the stretched material used to produce the axis according to the invention is of the order of 260-310 HV1. After thermal hardening at 380-420 ° C for 1 h, the hardness value rises to 460-500 HV1. This value after hardening remains lower than what can be encountered on 20 AP steel after rolling, typically more than 700 HV1.

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 stage or stages of treatment of the surface state of the axis.

When we quantify the Hertz pressure at the pivoting of the axis, we note 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 the pivot stone. During a contact between two materials of Young's modulus Ε _Ί and E ₂ , the equivalent elastic modulus E used to determine the rigidity of the contact is calculated as follows:

i ₌ i / £ ₊ jA ^{E +} (1)

The maximum pressure observed at the contact level is given by the following formula:

Pmax - 0.418

F = normal force on contact

E = previously defined equivalent elastic modulus 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 Vë.

With a digital application, we realize that Æ is down by more than 20% when we go from a Steel contact (220 GPa) on rubies (350 GPa) to a PdAgCu alloy contact (100 GPa) on rubies (350 GPa) with equivalent geometry.

Case n ° 1 Steel - Ruby Case 2 PdAgCu - Ruby E1 220 GPa 100 GPa E2 350 GPa 350 GPa E calculated with (1) 270.2 GPa 155.6 GPa VE 16.4 12.5

Thus, despite a lower hardness, it is found that the resistance to wear of the contact is still satisfactory. This is explained by the drop in contact pressure, thus making it possible to use an axis with a lower hardness without compromising the wear resistance of the contact, typically 460-500 HV1 for the axis made of Palladium alloy- SilverCopper against 600-700 HV1 for a standard Martensitic Carbon steel axle. The use of a lower hardness alloy facilitates material removal and shaping operations.

The next step in the process of obtaining an axis according to the invention, consists of shaping it by a turning stage. This is carried out in the traditional way on the same equipment as that used to machine axes of 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 turning stage. In the case of the pendulum axis, its radius being very

CH 714 594 A1 small, even at high spindle speed, the cutting speeds achieved during machining are limited. Referring to fig. 1, the pendulum axis has two zones of small diameter, the pivots 10, located at the ends of the axis as well as several zones of larger diameter forming the body of the axis 20.

For example, at the pivots, it is possible to use a cutting speed of 20 to 23 m / min with an advance of 0.0015 mm / rev.

At the axis body, a cutting speed of 20 to 23 m / min and a feed of 0.002 mm / rev to 0.005 mm / rev can be used.

During this turning step, it is necessary to provide one or more extra thicknesses depending on the operations of treatment of the surface condition of the axis envisaged. If the turning step is sufficiently repeatable and allows to obtain a sufficient geometric tolerance for the envisaged application, a simple polishing of the functional areas should be carried out. An additional thickness (e1) corresponding to the quantity of material removed during polishing must be added to the part compared to the final dimensions. Fig. 2 illustrates, by way of example, a pendulum axis after the bar turning step. Fig. 3 illustrates, by way of example, a pendulum axis after the polishing step. Referring to fig 4, the turning step will allow profile 2 to be obtained at the pivot with an extra thickness (e1) compared to profile 1. The polishing step will bring the profile of the pivot to its final profile 1. The additional thickness (e1) is typically of the order of 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 of the pivots is envisaged for fine control of the dimensions and of the surface conditions, an additional thickness (e2) corresponding to the quantity of material removed during this step grinding or rolling must be added to the workpiece 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 must therefore be done at profile 3, as shown in fig. 4. The rolling will bring the pivot to the level of the profile 2 as shown in fig. 4. A surface finish treatment may be added at the end of the process to obtain profile 1.

Depending on the type of surface finish treatment chosen, in bulk or located at the pivots, the skilled person will consider an additional thickness over the entire axis if the treatment is carried out in bulk or only on the areas affected by the removal of material if it is a localized treatment.

Other steps for processing the surface state of the axis or pivots with removal of material 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 allowance to be taken into account during the bar turning stage.

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

Other types of parts integrated into a mechanical watch movement or quartz, and likely to disrupt the operation of the movement in the event of magnetization, can be made of an alloy of the type described above without being part of the perimeter of protection claimed. This type of part can in particular be of the pin, screws and bolts type, axes of the gear train, etc. without, however, presenting problems similar to those encountered for the pivot axis of a regulating member.

Claims (13)

claims 1. Pivot axis of a regulating mechanical watch movement member made of a material consisting of 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. axis of regulating member according to claim 1, characterized in that said material comprises by weight between 38% and 43% of palladium. 3. axis of regulating member according to one of the preceding claims, characterized in that said material comprises by weight between 35% and 40% of silver. 4. axis of regulating member according to one of the preceding claims, characterized in that said material comprises by weight between 18% and 23% of copper. 5. axis of regulating member according to one of the preceding claims, characterized in that said material comprises by weight between 0.5% and 1.5% of zinc 6. axis of regulating member according to one of the preceding claims, characterized in that said axis is a pendulum axis, an anchor axis or an escapement mobile axis. CH 714 594 A1 7. Mechanical movement for a timepiece, characterized in that it comprises an axis of a regulating member according to one of the preceding claims. 8. Method for manufacturing a pivot axis of a regulating member comprising the following steps: - Obtain an alloy bar comprising 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; - Bar the axis with an extra thickness compared to a predetermined dimension; - Carry out an operation to treat the surface condition of the axle with removal of the additional thickness to reach the predetermined dimension. 9. The manufacturing method according to the preceding claim, characterized in that it further comprises a hardening heat treatment step. 10. The manufacturing method according to the preceding claim, characterized in that said hardening heat treatment step is carried out between the steps of obtaining said alloy bar and bar turning or between the bar turning and surface treatment steps. 11. Method for manufacturing a pivot axis of a regulating member comprising a body provided with pivots at its ends, said method comprising the following steps: - Obtain an alloy bar comprising 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; - Cutting off the body of the axis with a first additional thickness relative to a first predetermined dimension, and the pivots of the axis with a second additional thickness compared to a second predetermined dimension, said second additional thickness being greater than the first additional thickness; - Roll the pivots to bring them to the first additional thickness compared to the second predetermined dimension; - Carry out an operation to treat the surface finish of the body and the pivots with removal of the first additional thickness to reach the first and second predetermined dimensions respectively. 12. The manufacturing method according to the preceding claim, characterized in that it further comprises a step of hardening heat treatment. 13. The manufacturing method according to the preceding claim, characterized in that said hardening heat treatment step is carried out between the steps of obtaining said alloy bar and bar turning or between the bar turning and surface treatment steps.