EP3736639B1 - Method for manufacturing a hairspring for clock movement - Google Patents

Description

Field of the invention

The invention relates to a method of manufacturing a spiral spring intended to equip a balance wheel with a watch movement. It also relates to the spiral spring resulting from this process made in an Nb-Hf alloy.

Background of the invention

• nécessité d'obtention d'une limite élastique élevée,
• facilité d'élaboration, notamment de tréfilage et de laminage,
• excellente tenue en fatigue,
• stabilité des performances dans le temps,
• faibles sections.

The manufacture of spiral springs for watchmaking must face constraints that are often at first glance incompatible:

• need to obtain a high elastic limit,
• ease of production, in particular drawing and rolling,
• excellent fatigue resistance,
• stability of performance over time,
• weak sections.

The production of spiral springs is also centered on the concern for thermal compensation, so as to guarantee regular chronometric performance. To do this, it is necessary to obtain a thermoelastic coefficient close to zero. We are also seeking to produce spiral springs with limited sensitivity to magnetic fields.

Hairsprings were developed from niobium and hafnium alloys. However, these alloys pose sticking and seizing problems in the drawing or drawing dies (diamond or hard metal) and against the rolling rolls (hard metal or steel), which makes them almost impossible to transform into wires. fine by standard processes used for example for steel.

Any improvement on at least one of these points, and in particular on the ease of production, in particular of wire drawing and rolling, therefore represents a significant advance.

The document EP1258786A1 discloses a spiral spring formed in an Nb-Hf alloy and whose characteristics correspond to those set out in the preamble to claim 1.

The document CH713924A2 concerns an Nb-Ti spiral spring and it teaches covering a blank of such a spiral spring with a layer of ductile material, to facilitate its shaping into wire form.

Summary of the invention

An object of the present invention is to propose a method of manufacturing a spiral spring intended to equip a balance wheel with a clockwork movement making it possible to facilitate deformations, and more particularly to obtain easy rolling.

To this end, the invention relates to a method of manufacturing a spiral spring intended to equip a balance wheel with a clock movement, this method being defined in independent claim 1 appended.

Preferred embodiments are defined in the dependent claims.

Description of the invention

The invention relates to a method of manufacturing a spiral spring intended to equip a balance wheel with a watch movement and made from an alloy comprising niobium and hafnium.

• une étape d'élaboration d'une ébauche dans un alliage de niobium et d'hafnium constitué de :
  • niobium : balance à 100% en poids,
  • hafnium: entre 5 et 60% en poids, de préférence entre 5 et 30%, et plus préférentiellement entre 8 et 12% en poids,
  • un ou plusieurs éléments choisis parmi le Ti, Zr, Ta, W avec un pourcentage pour chaque élément compris entre 0 et 2%, de préférence entre 0.2 et 1.5% en poids,
  • impuretés avec un pourcentage total de ces dernières compris entre 0 et 0.5% en poids. Plus précisément, les impuretés peuvent être des traces d'éléments sélectionnés parmi le groupe constitué de O, H, C, Fe, N, Ni, Si, Cu, AI, Cr, Mn, V, Sn, Mg, Mo, Pb, Co, B, chacun desdits éléments étant présent dans une quantité comprise entre 0 et 1000 ppm en poids,
• une étape de recuit suivi d'un refroidissement de ladite ébauche,
• une étape de dépôt d'un matériau ductile sur l'ébauche,
• au moins une étape de déformation de l'ébauche pour former un fil, avec une étape de recuit et refroidissement entre les étapes de déformation lorsqu'il y a plusieurs étapes de déformation,
• une étape d'estrapadage pour former le ressort spiral,
• une étape finale de traitement thermique permettant de fixer la forme du ressort spiral et d'ajuster le coefficient thermoélastique.

The process includes the following steps:

• a step of developing a blank in an alloy of niobium and hafnium consisting of:
  • niobium: balance at 100% by weight,
  • hafnium: between 5 and 60% by weight, preferably between 5 and 30%, and more preferably between 8 and 12% by weight,
  • one or more elements chosen from Ti, Zr, Ta, W with a percentage for each element of between 0 and 2%, preferably between 0.2 and 1.5% by weight,
  • impurities with a total percentage of the latter between 0 and 0.5% by weight. More precisely, the impurities may be traces of elements selected from the group consisting of O, H, C, Fe, N, Ni, Si, Cu, AI, Cr, Mn, V, Sn, Mg, Mo, Pb, Co, B, each of said elements being present in a quantity between 0 and 1000 ppm by weight,
• an annealing step followed by cooling of said blank,
• a step of depositing a ductile material on the blank,
• at least one step of deformation of the blank to form a wire, with an annealing and cooling step between the deformation steps when there are several deformation steps,
• a step of strapping to form the spiral spring,
• a final heat treatment step allowing the shape of the spiral spring to be fixed and the thermoelastic coefficient to be adjusted.

Particularly preferably, the blank comprises by weight between 8 and 12% of hafnium, Ti, Zr, Ta and W with a percentage for each element of between 0.2 and 1.5%, and more preferably Ti included in a percentage between 0.5 and 1.5%, Zr in a percentage between 0.5 and 0.9%, Ta in a percentage between 0.3 and 0.7%, W in a percentage between 0.3 and 0.7%.

Preferably, the NbHf alloy blank used in the present invention does not include other elements with the exception of possible and inevitable traces. This makes it possible to avoid the formation of fragile phases.

More particularly, the oxygen content is less than or equal to 0.10% by weight of the total, in particular less than or equal to 0.05% by weight of the total, or even less than or equal to 0.03% by weight of the total.

More particularly, the carbon content is less than or equal to 0.04% by weight of the total, in particular less than or equal to 0.02% by weight of the total, or even less than or equal to 0.015% by weight of the total.

More particularly, the iron content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.02% by weight of the total, or even less than or equal to 0.005% by weight of the total.

More particularly, the nitrogen content is less than or equal to 0.04% by weight of the total, in particular less than or equal to 0.02% by weight of the total, or even less than or equal to 0.015% by weight of the total.

More particularly, the hydrogen content is less than or equal to 0.01% by weight of the total, in particular less than or equal to 0.0035% by weight of the total, or even less than or equal to 0.001% by weight of the total.

More particularly, the silicon content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.02% by weight of the total, or even less than or equal to 0.005% by weight of the total.

More particularly, the nickel content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.002% by weight of the total.

More particularly, the content of element in ductile solid solution, such as copper, in the alloy, is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.05% by weight of the total. equal to 0.004% by weight of the total.

More particularly, the aluminum content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.002% by weight of the total.

More particularly, the chromium content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.002% by weight of the total.

More particularly, the manganese content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.002% by weight of the total.

More particularly, the vanadium content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.002% by weight of the total.

More particularly, the tin content is less than or equal to 0.01% by weight of the total, in particular less than or equal to 0.0035% by weight of the total, or even less than or equal to 0.001% by weight of the total.

More particularly, the magnesium content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.002% by weight of the total.

More particularly, the molybdenum content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.002% by weight of the total.

More particularly, the lead content is less than or equal to 0.05% by weight of the total, in particular less than or equal to 0.01% by weight of the total, or even less than or equal to 0.002% by weight of the total.

More particularly, the cobalt content is less than or equal to 0.01% by weight of the total, in particular less than or equal to 0.0035% by weight of the total, or even less than or equal to 0.001% by weight of the total.

More particularly, the boron content is less than or equal to 0.005% by weight of the total, in particular less than or equal to 0.0001% by weight of the total.

The annealing step is a solution treatment, with a duration of preferably between 5 minutes and 2 hours at a temperature of between 650°C and 1750°C, under vacuum, followed by quenching for example under gas to obtain Hf in supersaturated solid solution in Nb ß. According to a variant, natural cooling under vacuum can also be considered.

The deposition step which is more particularly the subject of the invention consists of depositing a layer of a ductile material chosen from the group comprising copper, nickel, cupro-nickel, cupro-manganese, gold , silver, nickel-phosphorus Ni-P and nickel-boron Ni-B, to facilitate shaping into wire form. The thickness of the layer of ductile material deposited is chosen so that the surface ratio of ductile material/surface of the NbHf alloy for a given wire section is less than 1, preferably less than 0.5, and more preferably between 0.01 and 0.4. For example, for a total wire diameter of 0.1 mm, the layer of ductile material can have a thickness of 7 µm for an NbHf alloy section of 0.086 mm in diameter. This corresponds to a ratio between the copper surface area (0.002 mm ² ) and the NbHf surface area (0.0058 mm ² ) of 0.35.

Such a thickness of ductile material, and in particular of copper, makes it possible to easily stretch, draw and roll the Cu/NbHf composite material. In fact, the copper thickness is optimized so that the tip, created by filing or by hot drawing, necessary for introducing the wire into the die during drawing or drawing, is covered with copper.

The ductile material, preferably copper, is thus deposited at a given moment to facilitate the shaping of the wire by drawing, drawing and rolling, in such a way that a thickness remains, preferably between 1 and 500 micrometers on the wire with a total diameter of 0.2 to 1 millimeter.

The addition of ductile material can be galvanic, by PVD or CVD, or mechanical, it is then a jacket or a tube of ductile material such as copper which is adjusted to an NbHf alloy bar with a large diameter, then which is thinned during the step(s) of deformation of the composite bar. Thus, one possibility is to form a composite billet by assembling a Nb-Hf bar and a copper jacket which is then extruded.

The deformation step generally designates one or more deformation treatments, which may include wire drawing and/or rolling. Wire drawing may require the use of one or more dies during the same deformation stage or during different deformation stages if necessary. Drawing is carried out until a round section wire is obtained. Rolling can be carried out in the same deformation step as wire drawing or in another subsequent deformation step. Advantageously, the last deformation treatment applied to the alloy is rolling, preferably with a rectangular profile compatible with the entry section of a strapping pin.

The process may comprise one step or several deformation steps with a deformation rate for each step of between 1 and 5, preferably between 2 and 5, the deformation rate corresponding to the classic formula 2ln(d0/d) where d0 and d are respectively the diameter before and after deformation. The total strain rate can be between 1 and 14.

The process may include intermediate annealing stages between the different deformation stages.

The method of the invention comprises, after the deformation step, and before the stepping step, a step of eliminating said layer of ductile material.

Preferably, the ductile material is eliminated once all the deformation operations have been carried out, that is to say after the last rolling, before strapping. However, it is not excluded to eliminate the layer of ductile material before having finalized all the deformation operations. It is therefore possible during rolling in several passes to eliminate the layer of ductile material before the last rolling pass. Preferably, the wire is freed from its layer of ductile material, such as copper, in particular by chemical attack, with a solution based on cyanides or based on acids, for example nitric acid.

The annealing prior to the deformation stage as well as the intermediate annealing carried out between the deformation stages is carried out during a duration of between 5 minutes and 2 hours, preferably between 10 minutes and 1 hour at a temperature of between 650°C and 1750°C.

The final heat treatment after strapping is carried out at a temperature between 500 and 1250°C for a time between 30 minutes and 30 hours. Depending on the composition of the alloy and the temperatures, a single-phase structure of centered cubic type or two-phase with a centered cubic structure and a compact hexagonal structure can be obtained at the end of this heat treatment.

The method of the invention allows the production, and more particularly the shaping, of a spiral spring for a balance wheel made of a niobium-hafnium type alloy. This alloy has high mechanical properties, combining a very high elastic limit, greater than 600 MPa, and a very low modulus of elasticity, of the order of 60 GPa to 100 GPa. This combination of properties is well suited for a spiral spring. In addition, such an alloy is paramagnetic.

A binary type alloy comprising niobium and hafnium, of the type selected above for the implementation of the invention, also has an effect similar to that of "Elinvar", with a thermo-elastic coefficient practically zero in the usual temperature range of watches, and suitable for the manufacture of self-compensating hairsprings.

Claims (6)

1. Method for manufacturing a balance spring intended to equip a balance of a horological movement, comprising:

   - a step of producing a blank made of a niobium and hafnium alloy containing:

   - niobium: the remainder to 100 wt%,

   - hafnium: between 5 and 60 wt%, preferably between 5 and 30 wt%, and more preferably between 8 and 12 wt%,

   - one or more elements selected from Ti, Zr, Ta and W, the percentage of each element lying in the range 0 to 2 wt%, preferably in the range 0.2 to 1.5 wt%,

   - impurities, the total percentage whereof lies in the range 0 to 0.5 wt%.

   - a step of annealing and cooling the blank,

   - at least one step of deforming the annealed blank in order to form a wire,

   - a winding step for forming the balance spring,

   - a final step of heat treating the balance spring,

   characterised in that it comprises, before the deformation step, a step of depositing, on the blank, a layer of a ductile material chosen from the group consisting of copper, nickel, cupronickel, cupro-manganese, gold, silver, nickel-phosphorus Ni-P and nickel-boron Ni-B, in order to facilitate the wire shaping operation, in that the thickness of the ductile material layer deposited is chosen such that the ratio of the area of ductile material to the area of the alloy for a given wire cross-section is less than 1, preferably less than 0.5, and more preferably lies in the range 0.01 to 0.4 and in that it comprises, before the winding step, a step of eliminating said layer of ductile material.
2. Method according to one of the preceding claims, characterised in that the deformation step is carried out by wire drawing and/or rolling.
3. Method according to one of the preceding claims, characterised in that it includes one or more deformation steps with, for each step, a deformation carried out with a deformation ratio that lies in the range 1 to 5, the total cumulation of the deformations over all of the steps producing a total deformation ratio that lies in the range 1 to 14.
4. Method according to the preceding claim, characterised in that it includes an annealing and cooling step between the deformation steps.
5. Method according to one of the preceding claims, characterised in that each annealing and cooling step is a dissolving treatment, with a duration that lies in the range 5 minutes to 2 hours at a temperature that lies in the range 650°C to 1,750°C, in a vacuum, followed by quenching, in a gas or by natural cooling in a vacuum, to obtain a supersaturated solid solution of Hf in Nb.
6. Method according to any one of the preceding claims, characterised in that the final heat treatment step is carried out for a duration that lies in the range 30 minutes to 30 hours at a temperature that lies in the range 500°C to 1,250°C.