EP4009114A1 - Hairspring for clock movement and method for manufacturing same - Google Patents

Hairspring for clock movement and method for manufacturing same Download PDF

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Publication number
EP4009114A1
EP4009114A1 EP21218349.5A EP21218349A EP4009114A1 EP 4009114 A1 EP4009114 A1 EP 4009114A1 EP 21218349 A EP21218349 A EP 21218349A EP 4009114 A1 EP4009114 A1 EP 4009114A1
Authority
EP
European Patent Office
Prior art keywords
weight
niobium
layer
spiral spring
core
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP21218349.5A
Other languages
German (de)
French (fr)
Inventor
Christian Charbon
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nivarox Far SA
Nivarox SA
Original Assignee
Nivarox Far SA
Nivarox SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nivarox Far SA, Nivarox SA filed Critical Nivarox Far SA
Priority to EP21218349.5A priority Critical patent/EP4009114A1/en
Publication of EP4009114A1 publication Critical patent/EP4009114A1/en
Pending legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B17/00—Mechanisms for stabilising frequency
    • G04B17/20—Compensation of mechanisms for stabilising frequency
    • G04B17/22—Compensation of mechanisms for stabilising frequency for the effect of variations of temperature
    • G04B17/227—Compensation of mechanisms for stabilising frequency for the effect of variations of temperature composition and manufacture of the material used
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B17/00—Mechanisms for stabilising frequency
    • G04B17/04—Oscillators acting by spring tension
    • G04B17/06—Oscillators with hairsprings, e.g. balance
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21F—WORKING OR PROCESSING OF METAL WIRE
    • B21F3/00—Coiling wire into particular forms
    • B21F3/02—Coiling wire into particular forms helically
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C14/00—Alloys based on titanium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
    • C22C27/02—Alloys based on vanadium, niobium, or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18—High-melting or refractory metals or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18—High-melting or refractory metals or alloys based thereon
    • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B17/00—Mechanisms for stabilising frequency
    • G04B17/04—Oscillators acting by spring tension
    • G04B17/06—Oscillators with hairsprings, e.g. balance
    • G04B17/063—Balance construction
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B17/00—Mechanisms for stabilising frequency
    • G04B17/04—Oscillators acting by spring tension
    • G04B17/06—Oscillators with hairsprings, e.g. balance
    • G04B17/066—Manufacture of the spiral spring
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B17/00—Mechanisms for stabilising frequency
    • G04B17/32—Component parts or constructional details, e.g. collet, stud, virole or piton
    • G04B17/34—Component parts or constructional details, e.g. collet, stud, virole or piton for fastening the hairspring onto the balance
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B45/00—Time pieces of which the indicating means or cases provoke special effects, e.g. aesthetic effects
    • G—PHYSICS
    • G04—HOROLOGY
    • G04D—APPARATUS OR TOOLS SPECIALLY DESIGNED FOR MAKING OR MAINTAINING CLOCKS OR WATCHES
    • G04D3/00—Watchmakers' or watch-repairers' machines or tools for working materials
    • G04D3/0002—Watchmakers' or watch-repairers' machines or tools for working materials for mechanical working other than with a lathe
    • G04D3/0035—Watchmakers' or watch-repairers' machines or tools for working materials for mechanical working other than with a lathe for components of the regulating mechanism
    • G04D3/0041—Watchmakers' or watch-repairers' machines or tools for working materials for mechanical working other than with a lathe for components of the regulating mechanism for coil-springs
    • G—PHYSICS
    • G04—HOROLOGY
    • G04D—APPARATUS OR TOOLS SPECIALLY DESIGNED FOR MAKING OR MAINTAINING CLOCKS OR WATCHES
    • G04D3/00—Watchmakers' or watch-repairers' machines or tools for working materials
    • G04D3/0069—Watchmakers' or watch-repairers' machines or tools for working materials for working with non-mechanical means, e.g. chemical, electrochemical, metallising, vapourising; with electron beams, laser beams

Definitions

  • the invention relates to a process for manufacturing a spiral spring intended to equip a balance wheel of a timepiece movement and the spiral spring resulting from the process.
  • spiral springs are also centered on the concern for thermal compensation, so as to guarantee regular chronometric performances. This requires a thermoelastic coefficient close to zero. It is also sought to produce spiral springs having a limited sensitivity to magnetic fields.
  • New hairsprings have been developed using niobium and titanium alloys.
  • these alloys cause problems of sticking and seizing in the drawing or drawing dies and against the rolling rolls, which makes them almost impossible to transform into fine wires by the standard processes used, for example, for the 'steel.
  • This layer of copper on the wire has a disadvantage: it must be deposited in a thick layer (typically 10 microns for an Nb-Ti diameter of 0.1 mm) to play its role as an anti-sticking agent during the deformation stages. It does not allow a fine control of the geometry of the wire during the calibration and rolling of the wire. These dimensional variations of the Nb-Ti core of the wire result in significant variations in the torque of the hairsprings.
  • the present invention proposes a process for manufacturing a spiral spring which makes it possible to facilitate shaping by deformation while avoiding the drawbacks associated with the copper layer.
  • the blank As the blank undergoes a large number of deformation passes to bring it to dimensions and a determined geometry, the blank must be coated with a layer preventing sticking in the successive dies sufficiently thick not to be damaged during these successive deformations.
  • the thickness of the copper layer for producing watch spiral springs is of the order of 10 microns. The applicant has however found that the external dimensions of the blank covered with the copper layer were well controlled during the successive deformation passes of the blank but on the other hand that the dimensions of the Nb-Ti core were not not mastered.
  • the applicant therefore had the inventive idea which consists in coating the Nb-Ti blank with a thin layer (typically chosen between 800 nm and 1.2 microns when the blank has reached a diameter of between 15 and 50 microns) of a first anti-sticking material and preferably compatible with the thermo-elastic coefficient (CTE) of the Nb-Ti core, before coating the blank with a layer of a second ductile material thicker than the layer of the first material to carry out the first stages of deformation then to eliminate the "thick" layer of the second material before the final stages while retaining the "thin” layer of the first material.
  • This "thin" layer will make it possible to carry out the final stages of deformation of the wire without sticking in the dies while perfectly controlling the dimensions of the Nb-Ti core.
  • the first material is preferably chosen from the group comprising niobium, gold, tantalum, vanadium, austenitic stainless steels, 316L grade steel
  • the second material is chosen from the group comprising copper , silver, copper and nickel alloys, single phase alpha copper and zinc alloys (eg CuZn30).
  • the first material is niobium and the second material is copper (ETP (electrolytic tough pitch), OF (oxygen-free) or OFE (oxygen-free electronic) grade, for example).
  • ETP electrolytic tough pitch
  • OF oxygen-free
  • OFE oxygen-free electronic grade
  • a preferred embodiment of the process for manufacturing the spiral spring according to the invention therefore comprises a step aimed at forming a thin layer of niobium coating the Nb-Ti core, then at forming a thick layer of copper, partially deforming the coated core, removing the remaining Cu layer, and then completing the deformation of the Nb-Ti core simply coated with niobium.
  • This layer of niobium then forms the outer layer which is in contact with the dies and rolling rolls. It is chemically inert and ductile and allows easy drawing and rolling of the spiral wire. It has the further advantage of facilitating the separation between the hairsprings after the fixing step following the strapping step.
  • the niobium layer is retained on the hairspring after the manufacturing process. It is sufficiently thin with a thickness comprised between 50 nm and 5 ⁇ m and preferably 200 nm and 1.5 ⁇ m and more preferably between 800 nm and 1.2 ⁇ m, so as not to significantly modify the thermoelastic coefficient (CTE) of the hairspring.
  • CTE thermoelastic coefficient
  • Nb has a CTE similar to that of Nb-Ti, which makes it easier to obtain a compensating hairspring.
  • Nb-Ti core It is also perfectly adherent to the Nb-Ti core.
  • These niobium layer thicknesses are typically suitable for Nb-Ti cores having diameters of between 15 and 100 ⁇ m.
  • step d1) of the method of the invention consists in cold deforming by hammering and/or stretching and/or drawing the blank obtained in step c).
  • a step of beta-type quenching of said blank is carried out, so that the titanium of said alloy is essentially in the form of a solid solution with niobium in the beta phase and preferably, the ⁇ quenching step is a solution treatment, with a duration of between 5 minutes and 2 hours at a temperature of between 700°C and 1000 °C, under vacuum, followed by cooling under gas.
  • the step of removing the layer of the second material is carried out by etching chemical in a solution based on cyanides or acids, for example nitric acid.
  • the final heat treatment of step g) is a titanium precipitation treatment in the alpha phase lasting between 1 hour and 80 hours at a temperature between 350° C. and 700° C., preferably between 5 hours and 30 hours between 400°C and 600°C.
  • step g) consists of a heat treatment for the precipitation of titanium in the alpha phase for a duration of between 1 hour and 80 hours at a temperature of between 350° C. and 700° C., preferably between 5 hours and 30 hours between 400°C and 600°C.
  • an intermediate heat treatment for the precipitation of titanium in the alpha phase for a duration of between 1 hour and 80 hours at a temperature of between 350° C. and 700° C., preferably between 5 hours and 30 hours between 400° C. C and 600°C can also be carried out after each or certain sequences of the deformation step d1) and/or d2)
  • the layer of the second material typically copper formed in step c) has a thickness of between 1 ⁇ m and 100 ⁇ m when the diameter of the core of the Nb-Ti wire is 100 ⁇ m.
  • each sequence of steps d1) and/or d2) is carried out with a deformation rate comprised between 1 and 5, the overall accumulation of the deformations over all the sequences leading to a total deformation rate comprised between 1 and 14.
  • the strain rate for each sequence g) corresponding to the classical formula 2In(d0/d), where d0 is the diameter of the last beta quench, and where d is the diameter of the work-hardened wire
  • step b) of forming the layer of the first material is carried out by winding a strip of the first material, eg. of niobium, around the Nb-Ti core
  • step c) of forming the layer of the second material is carried out by introducing the blank obtained at the end of step b) in a tube of the second material, e.g. of copper, followed by drawing and/or hammering and/or drawing of the entire tube and of the blank obtained at the end of step b).
  • the layer of the first material has a thickness comprised between 300 nm and 1.5 ⁇ m and preferably comprised between 400 nm and 800 nm.
  • the first material is niobium.
  • the Ti content is between 40 and 65% by weight, preferably between 40 and 49% by weight and more preferably between 46 and 48% by weight.
  • the Nb-Ti core has a two-phase microstructure comprising niobium in the beta phase and titanium in the alpha phase.
  • the spring has an elastic limit greater than or equal to 500 MPa, preferably 600 MPa, and a modulus of elasticity less than or equal to 120 GPa, preferably less than or equal to 100 GPa.
  • the invention relates to a method of manufacturing a spiral spring intended to equip a balance wheel of a timepiece movement.
  • This spiral spring is made of a binary type alloy comprising niobium and titanium. It also relates to the spiral spring resulting from this process.
  • niobium as a first material and copper as a second material.
  • the method of the invention further comprises a step h) consisting in removing said layer of copper formed in step c), at a moment in step c) at which the blank has reached a diameter such that one can still pass said blank at least through one die and preferably through two dies with an elongation rate of the blank of approximately 10% at each die before the first rolling step d2) or at the latest before the last pass of step d2).
  • the core is made of an Nb-Ti alloy comprising between 5 and 95% by weight of titanium.
  • the alloy used in the present invention comprises by weight between 40 and 60% titanium.
  • it comprises between 40 and 49% by weight of titanium, and more preferably between 46% and 48% by weight of titanium.
  • the percentage of titanium is sufficient to obtain a maximum proportion of Ti precipitates in the form of alpha phase while being reduced to avoid the formation of martensitic phase leading to problems of brittleness of the alloy during its implementation.
  • the Nb-Ti alloy used in the present invention does not include other elements except for possible and unavoidable traces. This prevents the formation of brittle phases.
  • the oxygen content is less than or equal to 0.10% by weight of the total, or even less than or equal to 0.085% by weight of the total.
  • the tantalum content is less than or equal to 0.10% by weight of the total.
  • the carbon content is less than or equal to 0.04% by weight of the total, in particular less than or equal to 0.020% by weight of the total, or even even less than or equal to 0.0175% by weight of the total.
  • the iron content is less than or equal to 0.03% by weight of the total, in particular less than or equal to 0.025% by weight of the total, or even even less than or equal to 0.020% by weight of the total.
  • the nitrogen content is less than or equal to 0.02% by weight of the total, in particular less than or equal to 0.015% by weight of the total, or even even less than or equal to 0.0075% by weight of the total.
  • 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 even less than or equal to 0.0005% by weight of the total.
  • the silicon content is less than or equal to 0.01% by weight of the total.
  • the nickel content is less than or equal to 0.01% by weight of the total, in particular less than or equal to 0.16% by weight of the total.
  • the content of ductile material, such as copper, in the alloy is less than or equal to 0.01% by weight of the total, in particular less than or equal to 0.005% by weight of the total.
  • the aluminum content is less than or equal to 0.01% by weight of the total.
  • the Nb-Ti core of the blank in step a) is coated with a layer of niobium.
  • the addition of the niobium layer around the core can be carried out by galvanic means, by PVD, CVD or by mechanical means. In the latter case, a niobium tube is fitted to a bar of the Nb-Ti alloy. The assembly is deformed by hammering, stretching and/or drawing to thin the bar and form the blank which was made available in step a).
  • the thickness of the niobium layer is chosen so that the niobium surface area/Nb-Ti core surface area ratio 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, the thickness is preferably between 1 and 500 micrometers for a wire having a total diameter of 0.2 to 1 millimeter.
  • the niobium layer can be produced by winding a strip of niobium around the Nb-Ti core, the niobium strip/Nb-Ti core assembly then being deformed by hammering, stretching and/or drawing. to thin the bar and form the blank which was made available at the end of step a).
  • the Nb-Ti core of the blank obtained in step b) is coated with a layer of copper during a step c) .
  • the contribution of the copper layer around the core can be carried out by galvanic way, by PVD, CVD or by mechanical way. In the latter case, a copper tube is fitted to a bar of the Nb-Ti alloy coated with the niobium layer. The assembly is deformed by hammering, stretching and/or drawing to thin the bar and form the blank which was made available at the end of step b).
  • the thickness of the copper layer is chosen so that the copper surface/surface ratio of the Nb-Ti core covered with the niobium layer for a given wire section is less than 1, preferably less than 0.5 , and more preferably between 0.01 and 0.4.
  • the thickness is preferably between 1 and 500 micrometers for a wire having a total diameter of 0.2 to 1 millimeter.
  • the copper layer can be made by winding a copper strip around the Nb-Ti core covered with the niobium layer, the niobium strip/Nb-Ti core assembly then being deformed by hammering. , drawing and/or drawing to thin the bar and form the blank which was made available at the end of step b).
  • the Nb-Ti core covered with the niobium strip can be introduced into a copper tube, the assembly being hot co-extruded at a temperature of the order of 600 to 900 degrees through a pathway.
  • Beta-type quenching consisting of a solution heat treatment is performed at least before the subsequent deformation steps. This treatment is carried out so that the titanium of the alloy is essentially in the form of a solid solution with the niobium in the beta phase. Preferably, it is carried out for a period of between 5 minutes and 2 hours at a temperature of between 700° C. and 1000° C., under vacuum, followed by cooling under gas. More particularly, this beta quenching is a solution treatment at 800° C. under vacuum for 5 minutes to 1 hour, followed by cooling under gas.
  • Step d) of deformation is carried out in several sequences.
  • deformation is meant a deformation by drawing and/or rolling.
  • the deformation step comprises at least successive sequences of deformation, preferably cold, by hammering and/or stretching and/or calibration wire drawing designated by step d1 ).
  • Step d1) makes it possible to bring the blank obtained at the end of step c) to a determined diameter called the wire calibration diameter.
  • the method further comprises a step h) which consists in removing the layer of copper formed in step c), when during step d1), the blank has reached a diameter such that one can still pass said blank at least through a die with an elongation rate of the blank of about 10% before the first subsequent rolling step d2).
  • This step of removing the copper layer is carried out by chemical attack in a solution based on cyanides or acids, for example in a bath of nitric acid at a concentration of 53% by weight in water.
  • a sequence of rolling operations preferably with a rectangular profile compatible with the entry section of a strapping pin, is then carried out, this sequence forming step d2 ).
  • Each sequence of steps d1) and d2) is carried out with a given deformation rate between 1 and 5, this deformation rate corresponding to the classic formula 2In(d0/d), where d0 is the diameter of the last beta temper, and where d is the diameter of the hardened wire.
  • the global cumulation of the deformations on the whole of this succession of sequences brings a total rate of deformation included between 1 and 14.
  • the niobium layer coating the Nb-Ti core at a thickness of between 20 nm and 10 ⁇ m, preferably between 300 nm and 1.5 ⁇ m, more preferably between 400 and 800 nm .
  • the blade-rolled wire obtained at the end of step d2) is then cut to a length determined during step e) .
  • Step f) of strapping to form the spiral spring is followed by step g) of final heat treatment on the spiral spring.
  • This final heat treatment is a precipitation treatment of Ti in the alpha phase lasting between 1 and 80 hours, preferably between 5 and 30 hours, at a temperature between 350 and 700° C., preferably between 400 and 600 °C.
  • the method may also comprise, between each sequence or between certain sequences of the deformation steps d1) and/or d2), an intermediate heat treatment for the precipitation of the titanium in the alpha phase for a duration of between 1 hour and 80 hours at a temperature between 350°C and 700°C, preferably between 5 hours and 30 hours between 400°C and 600°C.
  • this intermediate processing is carried out in step d1) between the first drawing sequence and the second calibration drawing sequence.
  • the spiral spring produced according to this method has an elastic limit greater than or equal to 500 MPa, preferably greater than 600 MPa, and more precisely comprised between 500 and 1000 MPa.
  • it has a modulus of elasticity less than or equal to 120 GPa, and preferably less than or equal to 100 GPa.
  • the spiral spring comprises an Nb-Ti core coated with a layer of niobium, said layer having a thickness of between 50 nm and 5 ⁇ m, preferably between 200 nm and 1.5 ⁇ m, more preferably between 800 nm and 1.2 ⁇ m .
  • the spiral spring core has a two-phase microstructure comprising beta-phase niobium and alpha-phase titanium.
  • the spiral spring made according to the invention has a thermoelastic coefficient, also called CTE, enabling it to guarantee the maintenance of chronometric performance despite the variation in the temperatures of use of a watch incorporating such a spiral spring.
  • the method of the invention allows the production, and more particularly the shaping, of a spiral spring for a balance wheel in an alloy of the niobium-titanium type, typically containing 47% by weight of titanium (40-60%).
  • This alloy has high mechanical properties, by combining a very high elastic limit, greater than 600 MPa, and a very low modulus of elasticity, of the order of 60 Gpa to 80 GPa. This combination of properties is well suited for a spiral spring.
  • such an alloy is paramagnetic.

Abstract

La présente invention concerne notamment un ressort spiral destiné à équiper un balancier d'un mouvement d'horlogerie, comprenant une âme en Nb-Ti réalisée dans un alliage constitué de :- niobium : balance à 100% en poids,- titane : entre 5 et 95% en poids,- traces d'éléments sélectionnés parmi le groupe constitué de O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, chacun desdits éléments étant présent dans une quantité comprise entre 0 et 1600 ppm en poids, la quantité totale constituée par l'ensemble desdits éléments étant comprise entre 0% et 0.3% en poids,dans lequel l'âme en Nb-Ti est enrobée d'une couche de niobium, ladite couche de niobium ayant une épaisseur comprise entre 20 nm et 10 µm.The present invention relates in particular to a spiral spring intended to equip a balance wheel of a watch movement, comprising an Nb-Ti core made of an alloy consisting of:- niobium: balance at 100% by weight,- titanium: between 5 and 95% by weight,- traces of elements selected from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of the said elements being present in an amount between 0 and 1600 ppm by weight, the total quantity constituted by all of said elements being between 0% and 0.3% by weight, in which the Nb-Ti core is coated with a layer of niobium, said niobium layer having a thickness between 20 nm and 10 µm.

Description

Domaine de l'inventionField of invention

L'invention concerne un procédé de fabrication d'un ressort spiral destiné à équiper un balancier d'un mouvement d'horlogerie et le ressort spiral issu du procédé.The invention relates to a process for manufacturing a spiral spring intended to equip a balance wheel of a timepiece movement and the spiral spring resulting from the process.

Arrière-plan de l'inventionBackground of the invention

La fabrication de ressorts spiraux pour l'horlogerie doit faire face à des contraintes souvent à première vue incompatibles :

  • 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 incompatible at first sight:
  • need to obtain a high elastic limit,
  • ease of production, in particular drawing and rolling,
  • excellent fatigue resistance,
  • stable performance over time,
  • weak sections.

La réalisation de ressorts spiraux est en outre centrée sur le souci de la compensation thermique, de façon à garantir des performances chronométriques régulières. Il faut pour cela obtenir un coefficient thermoélastique proche de zéro. On recherche également à réaliser des ressorts spiraux présentant une sensibilité aux champs magnétiques limitée.The production of spiral springs is also centered on the concern for thermal compensation, so as to guarantee regular chronometric performances. This requires a thermoelastic coefficient close to zero. It is also sought to produce spiral springs having a limited sensitivity to magnetic fields.

De nouveaux spiraux ont été développés à partir d'alliages de niobium et de titane. Toutefois, ces alliages posent des problèmes de collement et de grippage dans les filières d'étirage ou de tréfilage et contre les rouleaux de laminage, ce qui les rend quasiment impossibles à transformer en fils fins par les procédés standards utilisés, par exemple, pour l'acier.New hairsprings have been developed using niobium and titanium alloys. However, these alloys cause problems of sticking and seizing in the drawing or drawing dies and against the rolling rolls, which makes them almost impossible to transform into fine wires by the standard processes used, for example, for the 'steel.

Pour remédier à cet inconvénient, il a été proposé de déposer, avant la mise en forme dans les filières et le laminoir, une couche d'un matériau ductile, et en particulier de cuivre, sur l'ébauche en Nb-Ti.To overcome this drawback, it has been proposed to deposit, before shaping in the dies and the rolling mill, a layer of a ductile material, and in particular of copper, on the Nb-Ti blank.

Cette couche de cuivre sur le fil présente un désavantage : elle doit être déposée en couche épaisse (typiquement 10 microns pour un diamètre de Nb-Ti de 0.1 mm) pour jouer son rôle d'agent anti collement lors des étapes de déformation. Elle ne permet pas un contrôle fin de la géométrie du fil lors de la calibration et du laminage du fil. Ces variations dimensionnelles de l'âme en Nb-Ti du fil se traduisent par des variations importantes du couple des spiraux.This layer of copper on the wire has a disadvantage: it must be deposited in a thick layer (typically 10 microns for an Nb-Ti diameter of 0.1 mm) to play its role as an anti-sticking agent during the deformation stages. It does not allow a fine control of the geometry of the wire during the calibration and rolling of the wire. These dimensional variations of the Nb-Ti core of the wire result in significant variations in the torque of the hairsprings.

Résumé de l'inventionSummary of the invention

Pour remédier aux inconvénients précités, la présente invention propose un procédé de fabrication d'un ressort spiral qui permette de faciliter la mise en forme par déformation tout en évitant les inconvénients liés à la couche de cuivre.To remedy the aforementioned drawbacks, the present invention proposes a process for manufacturing a spiral spring which makes it possible to facilitate shaping by deformation while avoiding the drawbacks associated with the copper layer.

A cet effet, l'invention concerne un procédé de fabrication d'un ressort spiral destiné à équiper un balancier d'un mouvement d'horlogerie, comprenant :

  1. a) une étape de mise à disposition d'une ébauche avec une âme en Nb-Ti réalisée dans un alliage constitué de :
    • niobium : balance à 100% en poids,
    • titane : entre 5 et 95% en poids,
    • traces d'un ou plusieurs éléments sélectionnés parmi le groupe constitué du O, H, C, Fe, Ta, N, Ni, Si, Cu et de l'Al, chacun desdits éléments étant présent dans une quantité comprise entre 0 et 1600 ppm en poids, la quantité totale constituée par l'ensemble desdits éléments étant comprise entre 0% et 0.3% en poids,
  2. b) une étape de formation d'une couche d'un premier matériau ayant une première épaisseur autour de l'ébauche avec l'âme en Nb-Ti,
  3. c) une étape de formation d'une couche d'un deuxième matériau ayant une deuxième épaisseur supérieure à l'épaisseur de la couche du premier matériau autour de l'ébauche obtenue de l'étape b), les premiers et deuxième matériaux étant choisis pour que le deuxième matériau puisse être sélectivement éliminé physiquement ou chimiquement sans substantiellement attaquer le premier matériau d) une étape de déformation en plusieurs séquences de l'ébauche comprenant :
    • d1) une succession d'étapes de passe de déformations pour amener l'ébauche obtenue à l'étape c) à une ébauche ronde d'un diamètre déterminé dit diamètre de calibration et
    • d2) une succession d'étapes de laminage à plat de l'ébauche ronde obtenue à l'étape d1)
      • e) une étape de découpe du fil laminé en lames d'une longueur déterminée
      • f) une étape d'estrapadage pour former le ressort spiral,
      • g) une étape de traitement thermique final sur le ressort spiral, et dans lequel ledit procédé comprend en outre une étape h) consistant à enlever ladite couche du deuxième matériau formée à l'étape c), lorsque l'ébauche a atteint un diamètre tel que l'on puisse encore passer ladite ébauche au moins à travers une filière et de préférence à travers deux filières avec un taux d'allongement de l'ébauche d'environ 10% à chaque filière avant la première étape de laminage d2) ou au plus tard avant la dernière passe de l'étape d2).
To this end, the invention relates to a method of manufacturing a spiral spring intended to equip a balance wheel of a clockwork movement, comprising:
  1. a) a step of providing a blank with an Nb-Ti core made of an alloy consisting of:
    • niobium: 100% balance by weight,
    • titanium: between 5 and 95% by weight,
    • traces of one or more elements selected from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu and Al, each of said elements being present in an amount between 0 and 1600 ppm by weight, the total quantity constituted by all of said elements being between 0% and 0.3% by weight,
  2. b) a step of forming a layer of a first material having a first thickness around the blank with the Nb-Ti core,
  3. c) a step of forming a layer of a second material having a second thickness greater than the thickness of the layer of the first material around the blank obtained from step b), the first and second materials being chosen so that the second material can be selectively eliminated physically or chemically without substantially attacking the first material d) a step of deformation in several sequences of the blank comprising:
    • d1) a succession of deformation pass steps to bring the blank obtained in step c) to a round blank of a determined diameter called calibration diameter and
    • d2) a succession of flat rolling steps of the round blank obtained in step d1)
      • e) a step of cutting the rolled wire into strips of a determined length
      • f) a strapping step to form the spiral spring,
      • g) a final heat treatment step on the spiral spring, and in which said method further comprises a step h) consisting in removing said layer of the second material formed in step c), when the blank has reached a diameter such that said blank can still be passed at least through one die and preferably through two dies with an elongation rate of the blank of approximately 10% at each die before the first rolling step d2) or at later before the last pass of step d2).

Comme l'ébauche subit un grand nombre de passes de déformation pour l'amener à des dimensions et une géométrie déterminée, l'ébauche doit être revêtue d'une couche prévenant le collement dans les filières successives suffisamment épaisse pour ne pas être détériorée lors de ces déformations successives. Pour ce faire il est prévu selon l'invention d'enrober l'ébauche d'une couche d'un matériau ductile tel que le cuivre. L'épaisseur de la couche de cuivre pour la réalisation de ressorts spiral horlogers est de l'ordre de 10 microns. La demanderesse a toutefois constaté que les dimensions extérieures de l'ébauche recouvertes de la couche de cuivre étaient bien maitrisées au cours des passes de déformation successives de l'ébauche mais en revanche que les dimensions de l'âme en Nb-Ti n'étaient pas maitrisées. La demanderesse a donc eu l'idée inventive qui consiste à revêtir l'ébauche en Nb-Ti d'une fine couche (typiquement choisie entre 800 nm et 1.2 microns lorsque l'ébauche a atteint un diamètre compris entre 15 et 50 microns) d'un premier matériau anti collement et de préférence compatible avec le coefficient thermo élastique (CTE) de l'âme en Nb-Ti, avant de revêtir l'ébauche d'une couche d'un deuxième matériau ductile plus épaisse que la couche du premier matériau pour réaliser les premières étapes de déformation puis à éliminer la couche « épaisse » du deuxième matériau avant les étapes finales tout en conservant la couche « fine » du premier matériau. Cette couche « fine » va permettre de réaliser les étapes finales de déformation du fil sans collement dans les filières tout en maitrisant parfaitement les dimensions de l'âme en Nb-Ti.As the blank undergoes a large number of deformation passes to bring it to dimensions and a determined geometry, the blank must be coated with a layer preventing sticking in the successive dies sufficiently thick not to be damaged during these successive deformations. To do this, provision is made according to the invention to coat the blank with a layer of a ductile material such as copper. The thickness of the copper layer for producing watch spiral springs is of the order of 10 microns. The applicant has however found that the external dimensions of the blank covered with the copper layer were well controlled during the successive deformation passes of the blank but on the other hand that the dimensions of the Nb-Ti core were not not mastered. The applicant therefore had the inventive idea which consists in coating the Nb-Ti blank with a thin layer (typically chosen between 800 nm and 1.2 microns when the blank has reached a diameter of between 15 and 50 microns) of a first anti-sticking material and preferably compatible with the thermo-elastic coefficient (CTE) of the Nb-Ti core, before coating the blank with a layer of a second ductile material thicker than the layer of the first material to carry out the first stages of deformation then to eliminate the "thick" layer of the second material before the final stages while retaining the "thin" layer of the first material. This "thin" layer will make it possible to carry out the final stages of deformation of the wire without sticking in the dies while perfectly controlling the dimensions of the Nb-Ti core.

Le premier matériau est de préférence choisi parmi l'ensemble comprenant le niobium, l'or, le tantale, le vanadium, les aciers austénitiques inoxydables, l'acier de nuance 316L, et le deuxième matériau est choisi parmi l'ensemble comprenant le cuivre, l'argent, les alliages de cuivre et de nickel, les alliages de cuivre et de zinc monophasé alpha (par exemple CuZn30).The first material is preferably chosen from the group comprising niobium, gold, tantalum, vanadium, austenitic stainless steels, 316L grade steel, and the second material is chosen from the group comprising copper , silver, copper and nickel alloys, single phase alpha copper and zinc alloys (eg CuZn30).

De manière avantageuse le premier matériau est le niobium et le deuxième matériau est le cuivre (nuance ETP (electrolytic tough pitch), OF (oxygen-free) ou OFE (oxygen free electronic), par exemple).Advantageously, the first material is niobium and the second material is copper (ETP (electrolytic tough pitch), OF (oxygen-free) or OFE (oxygen-free electronic) grade, for example).

Un mode de réalisation préféré du procédé de fabrication du ressort spiral selon l'invention comporte donc une étape visant à former une couche fine de niobium enrobant l'âme en Nb-Ti, puis à former une couche épaisse de cuivre, à déformer partiellement l'âme revêtue, à enlever la couche de Cu restante, puis à terminer la déformation de l'âme en Nb-Ti simplement revêtues de niobium. Cette couche de niobium forme alors la couche externe qui est en contact avec les filières et les rouleaux de laminage. Elle est chimiquement inerte et ductile et permet aisément de tréfiler et laminer le fil spiral. Elle présente pour autre avantage de faciliter la séparation entre les spiraux après l'étape de fixage suivant l'étape d'estrapadage.A preferred embodiment of the process for manufacturing the spiral spring according to the invention therefore comprises a step aimed at forming a thin layer of niobium coating the Nb-Ti core, then at forming a thick layer of copper, partially deforming the coated core, removing the remaining Cu layer, and then completing the deformation of the Nb-Ti core simply coated with niobium. This layer of niobium then forms the outer layer which is in contact with the dies and rolling rolls. It is chemically inert and ductile and allows easy drawing and rolling of the spiral wire. It has the further advantage of facilitating the separation between the hairsprings after the fixing step following the strapping step.

La couche de niobium est conservée sur le spiral à l'issue du procédé de fabrication. Elle est suffisamment fine avec une épaisseur comprise entre 50 nm et 5 µm et de préférence 200 nm et 1.5 µm et plus préférentiellement entre 800nm et 1,2µm, pour ne pas significativement modifier le coefficient thermoélastique (CTE) du spiral. De plus, le Nb présente un CTE similaire à celui du Nb-Ti, ce qui facilite l'obtention d'un spiral compensateur.The niobium layer is retained on the hairspring after the manufacturing process. It is sufficiently thin with a thickness comprised between 50 nm and 5 μm and preferably 200 nm and 1.5 μm and more preferably between 800 nm and 1.2 μm, so as not to significantly modify the thermoelastic coefficient (CTE) of the hairspring. In addition, Nb has a CTE similar to that of Nb-Ti, which makes it easier to obtain a compensating hairspring.

Elle est par ailleurs parfaitement adhérente à l'âme en Nb-Ti. Ces épaisseurs de la couche de niobium sont typiquement adaptées pour des âmes en en Nb-Ti présentant des diamètres compris entre 15 et 100 µm.It is also perfectly adherent to the Nb-Ti core. These niobium layer thicknesses are typically suitable for Nb-Ti cores having diameters of between 15 and 100 μm.

Avantageusement, l'étape d1) du procédé de l'invention consiste à déformer à froid par martelage et/ou étirage et/ou tréfilage l'ébauche obtenue à l'étape c).Advantageously, step d1) of the method of the invention consists in cold deforming by hammering and/or stretching and/or drawing the blank obtained in step c).

Selon un mode préféré de mise en œuvre du procédé de l'invention on réalise au moins avant l'étape d1) et/ou d2) une étape de trempe de type bêta de ladite ébauche, de façon à ce que le titane dudit alliage soit essentiellement sous forme de solution solide avec le niobium en phase bêta et de préférence, l'étape de trempe β est un traitement de mise en solution, avec une durée comprise entre 5 minutes et 2 heures à une température comprise entre 700°C et 1000°C, sous vide, suivi d'un refroidissement sous gaz.According to a preferred embodiment of the method of the invention, at least before step d1) and/or d2), a step of beta-type quenching of said blank is carried out, so that the titanium of said alloy is essentially in the form of a solid solution with niobium in the beta phase and preferably, the β quenching step is a solution treatment, with a duration of between 5 minutes and 2 hours at a temperature of between 700°C and 1000 °C, under vacuum, followed by cooling under gas.

De préférence, lorsque le deuxième matériau est le cuivre, l'étape d'enlèvement de la couche du deuxième matériau est effectuée par attaque chimique dans une solution à base de cyanures ou d'acides, par exemple acide nitrique.Preferably, when the second material is copper, the step of removing the layer of the second material is carried out by etching chemical in a solution based on cyanides or acids, for example nitric acid.

Avantageusement, le traitement thermique final de l'étape g) est un traitement de précipitation du titane en phase alpha d'une durée comprise entre 1 heure et 80 heures à une température comprise entre 350°C et 700°C, de préférence entre 5 heures et 30 heures entre 400°C et 600°C.Advantageously, the final heat treatment of step g) is a titanium precipitation treatment in the alpha phase lasting between 1 hour and 80 hours at a temperature between 350° C. and 700° C., preferably between 5 hours and 30 hours between 400°C and 600°C.

De préférence, l'étape g) consiste en un traitement thermique de précipitation du titane en phase alpha d'une durée comprise entre 1 heure et 80 heures à une température comprise entre 350°C et 700°C, de préférence entre 5 heures et 30 heures entre 400°C et 600°C. Selon une variante, un traitement thermique intermédiaire de précipitation du titane en phase alpha d'une durée comprise entre 1 heure et 80 heures à une température comprise entre 350°C et 700°C, de préférence entre 5 heures et 30 heures entre 400°C et 600°C peut en outre être réalisé après chaque ou certaines séquences de l'étape de déformation d1) et/ou d2)Preferably, step g) consists of a heat treatment for the precipitation of titanium in the alpha phase for a duration of between 1 hour and 80 hours at a temperature of between 350° C. and 700° C., preferably between 5 hours and 30 hours between 400°C and 600°C. According to a variant, an intermediate heat treatment for the precipitation of titanium in the alpha phase for a duration of between 1 hour and 80 hours at a temperature of between 350° C. and 700° C., preferably between 5 hours and 30 hours between 400° C. C and 600°C can also be carried out after each or certain sequences of the deformation step d1) and/or d2)

Selon un mode de mise en oeuvre du procédé la couche du deuxième matériau, typiquement de cuivre formé à l'étape c) a une épaisseur comprise entre 1 µm et 100 µm lorsque le diamètre de l'âme du fil en Nb-Ti vaut 100 µm.According to one embodiment of the method, the layer of the second material, typically copper formed in step c) has a thickness of between 1 μm and 100 μm when the diameter of the core of the Nb-Ti wire is 100 µm.

De préférence, chaque séquence des étapes d1) et/ou d2) est effectuée avec un taux de déformation compris entre 1 et 5, le cumul global des déformations sur l'ensemble des séquences amenant un taux total de déformation compris entre 1 et 14. Le taux de déformation pour chaque séquence g) répondant à la formule classique 2In(d0/d), où d0 est le diamètre de la dernière trempe bêta, et où d est le diamètre du fil écrouiPreferably, each sequence of steps d1) and/or d2) is carried out with a deformation rate comprised between 1 and 5, the overall accumulation of the deformations over all the sequences leading to a total deformation rate comprised between 1 and 14. The strain rate for each sequence g) corresponding to the classical formula 2In(d0/d), where d0 is the diameter of the last beta quench, and where d is the diameter of the work-hardened wire

Avantageusement l'étape b) de formation de la couche du premier matériau typiquement d'une couche de niobium, est réalisée par enroulage d'une bande du premier matériau, par ex. de niobium, autour de l'âme en Nb-Ti et l'étape c) de formation de la couche du deuxième matériau, typiquement d'une couche de cuivre est réalisée par introduction de l'ébauche obtenue à l'issue de l'étape b) dans un tube du deuxième matériau, par ex. de cuivre, suivi d'un tréfilage et/ou martelage et/ou étirage de l'ensemble du tube et de l'ébauche obtenue à l'issue de l'étape b).Advantageously, step b) of forming the layer of the first material, typically a layer of niobium, is carried out by winding a strip of the first material, eg. of niobium, around the Nb-Ti core and step c) of forming the layer of the second material, typically a layer of copper, is carried out by introducing the blank obtained at the end of step b) in a tube of the second material, e.g. of copper, followed by drawing and/or hammering and/or drawing of the entire tube and of the blank obtained at the end of step b).

L'invention concerne également un ressort spiral destiné à équiper un balancier d'un mouvement d'horlogerie, comprenant une âme en Nb-Ti réalisée dans un alliage constitué de :

  • niobium : balance à 100% en poids,
  • titane : entre 5 et 95% en poids,
  • traces d'éléments sélectionnés parmi le groupe constitué de O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, chacun desdits éléments étant présent dans une quantité comprise entre 0 et 1600 ppm en poids, la quantité totale constituée par l'ensemble desdits éléments étant comprise entre 0% et 0.3% en poids, dans lequel l'âme en Nb-Ti est enrobée d'une couche d'un premier matériau choisi parmi l'ensemble comprenant le niobium, l'or, le tantale, le vanadium, les aciers austénitiques inoxydables, (acier de nuance 316L), ladite couche du premier matériau ayant une épaisseur comprise entre 20 nm et 10 µm.
The invention also relates to a spiral spring intended to equip a balance wheel of a watch movement, comprising an Nb-Ti core made of an alloy consisting of:
  • niobium: 100% balance by weight,
  • titanium: between 5 and 95% by weight,
  • traces of elements selected from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said elements being present in an amount between 0 and 1600 ppm by weight, the total amount constituted by all of said elements being between 0% and 0.3% by weight, in which the Nb-Ti core is coated with a layer of a first material chosen from the group comprising niobium, gold , tantalum, vanadium, austenitic stainless steels (steel of grade 316L), said layer of the first material having a thickness of between 20 nm and 10 μm.

Avantageusement, la couche du premier matériau a une épaisseur comprise entre 300 nm et 1.5 µm et de préférence comprise entre 400 nm et 800 nm.Advantageously, the layer of the first material has a thickness comprised between 300 nm and 1.5 μm and preferably comprised between 400 nm and 800 nm.

Selon un mode réalisation préféré, le premier matériau est le niobium.According to a preferred embodiment, the first material is niobium.

Avantageusement, la teneur en Ti est comprise entre 40 et 65% en poids, de préférence entre 40 et 49% en poids et plus préférentiellement entre 46 et 48% en poids.Advantageously, the Ti content is between 40 and 65% by weight, preferably between 40 and 49% by weight and more preferably between 46 and 48% by weight.

Avantageusement, l'âme en Nb-Ti a une microstructure bi-phasée comportant du niobium en phase bêta et du titane en phase alpha.Advantageously, the Nb-Ti core has a two-phase microstructure comprising niobium in the beta phase and titanium in the alpha phase.

De préférence le ressort a une limite élastique supérieure ou égale à 500 MPa, de préférence à 600 MPa, et un module d'élasticité inférieur ou égal à 120 GPa, de préférence inférieur ou égal à 100 GPa.Preferably, the spring has an elastic limit greater than or equal to 500 MPa, preferably 600 MPa, and a modulus of elasticity less than or equal to 120 GPa, preferably less than or equal to 100 GPa.

Description détaillée de l'inventionDetailed description of the invention

L'invention concerne un procédé de fabrication d'un ressort spiral destiné à équiper un balancier d'un mouvement d'horlogerie. Ce ressort spiral est réalisé dans un alliage de type binaire comportant du niobium et du titane. Elle se rapporte également au ressort spiral issu de ce procédé.The invention relates to a method of manufacturing a spiral spring intended to equip a balance wheel of a timepiece movement. This spiral spring is made of a binary type alloy comprising niobium and titanium. It also relates to the spiral spring resulting from this process.

Le procédé va être décrit plus précisément ci-après avec le niobium comme un premier matériau et le cuivre comme deuxième matériau.The method will be described more precisely below with niobium as a first material and copper as a second material.

Selon l'invention, le procédé de fabrication comporte les étapes suivantes :

  1. a) une étape de mise à disposition d'une ébauche avec une âme en Nb-Ti réalisée dans un alliage constitué de :
    • niobium : balance à 100% en poids,
    • titane : entre 5 et 95% en poids,
    • traces d'un ou plusieurs éléments sélectionnés parmi le groupe constitué du O, H, C, Fe, Ta, N, Ni, Si, Cu et de l'Al, chacun desdits éléments étant présent dans une quantité comprise entre 0 et 1600 ppm en poids, la quantité totale constituée par l'ensemble desdits éléments étant comprise entre 0% et 0.3% en poids,
  2. b) une étape de formation d'une couche de niobium autour de l'ébauche avec l'âme en Nb-Ti,
  3. c) une étape de formation d'une couche de cuivre autour de l'ébauche obtenue de l'étape b)
  4. d) une étape de déformation en plusieurs séquences de l'ébauche comprenant :
    • d1) une succession d'étapes de passe de déformations pour amener l'ébauche obtenue à l'étape c) à un diamètre déterminé dit diamètre de calibration et
    • d2) une succession d'étapes de laminage à plat de l'ébauche ronde obtenue à l'étape d1)
    • e) une étape de découpe du fil laminé en lames d'une longueur déterminée
    • f) une étape d'estrapadage pour former le ressort spiral,
    • g) une étape de traitement thermique final sur le ressort spiral.
According to the invention, the manufacturing process comprises the following steps:
  1. a) a step of providing a blank with an Nb-Ti core made of an alloy consisting of:
    • niobium: 100% balance by weight,
    • titanium: between 5 and 95% by weight,
    • traces of one or more elements selected from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu and Al, each of said elements being present in an amount between 0 and 1600 ppm by weight, the total quantity constituted by all of said elements being between 0% and 0.3% by weight,
  2. b) a step of forming a niobium layer around the blank with the Nb-Ti core,
  3. c) a step of forming a layer of copper around the blank obtained from step b)
  4. d) a step of deformation in several sequences of the blank comprising:
    • d1) a succession of deformation pass steps to bring the blank obtained in step c) to a determined diameter called the calibration diameter and
    • d2) a succession of flat rolling steps of the round blank obtained in step d1)
    • e) a step of cutting the rolled wire into strips of a determined length
    • f) a strapping step to form the spiral spring,
    • g) a final heat treatment step on the spiral spring.

Le procédé de l'invention comprend en outre une étape h) consistant à enlever ladite couche de cuivre formée à l'étape c), à un moment de l'étape c) auquel l'ébauche a atteint un diamètre tel que l'on puisse encore passer ladite ébauche au moins à travers une filière et de préférence à travers deux filières avec un taux d'allongement de l'ébauche d'environ 10% à chaque filière avant la première étape de laminage d2) ou au plus tard avant la dernière passe de l'étape d2).The method of the invention further comprises a step h) consisting in removing said layer of copper formed in step c), at a moment in step c) at which the blank has reached a diameter such that one can still pass said blank at least through one die and preferably through two dies with an elongation rate of the blank of approximately 10% at each die before the first rolling step d2) or at the latest before the last pass of step d2).

Le procédé est maintenant décrit plus en détail.The process is now described in more detail.

A l'étape a), l'âme est réalisée dans un alliage Nb-Ti comportant entre 5 et 95% en poids de titane. D'une manière avantageuse, l'alliage utilisé dans la présente invention comprend en poids entre 40 et 60% de titane. De préférence, il comporte entre 40 et 49% en poids de titane, et plus préférentiellement entre 46% et 48% en poids de titane. Le pourcentage de titane est suffisant pour obtenir une proportion maximale de précipités de Ti sous forme de phase alpha tout en étant minoré pour éviter la formation de phase martensitique entraînant des problèmes de fragilité de l'alliage lors de sa mise en œuvre. In step a) , the core is made of an Nb-Ti alloy comprising between 5 and 95% by weight of titanium. Advantageously, the alloy used in the present invention comprises by weight between 40 and 60% titanium. Preferably, it comprises between 40 and 49% by weight of titanium, and more preferably between 46% and 48% by weight of titanium. The percentage of titanium is sufficient to obtain a maximum proportion of Ti precipitates in the form of alpha phase while being reduced to avoid the formation of martensitic phase leading to problems of brittleness of the alloy during its implementation.

D'une manière particulièrement avantageuse, l'alliage Nb-Ti utilisé dans la présente invention ne comprend pas d'autres éléments à l'exception d'éventuelles et inévitables traces. Cela permet d'éviter la formation de phases fragiles.In a particularly advantageous way, the Nb-Ti alloy used in the present invention does not include other elements except for possible and unavoidable traces. This prevents the formation of brittle phases.

Plus particulièrement, la teneur en oxygène est inférieure ou égale à 0.10% en poids du total, voire encore inférieure ou égale à 0.085% en poids du total.More particularly, the oxygen content is less than or equal to 0.10% by weight of the total, or even less than or equal to 0.085% by weight of the total.

Plus particulièrement, la teneur en tantale est inférieure ou égale à 0.10% en poids du total.More particularly, the tantalum content is less than or equal to 0.10% by weight of the total.

Plus particulièrement, la teneur en carbone est inférieure ou égale à 0.04% en poids du total, notamment inférieure ou égale à 0.020% en poids du total, voire encore inférieure ou égale à 0.0175% en poids du 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 0.020% by weight of the total, or even even less than or equal to 0.0175% by weight of the total.

Plus particulièrement, la teneur en fer est inférieure ou égale à 0.03% en poids du total, notamment inférieure ou égale à 0.025% en poids du total, voire encore inférieure ou égale à 0.020% en poids du total.More particularly, the iron content is less than or equal to 0.03% by weight of the total, in particular less than or equal to 0.025% by weight of the total, or even even less than or equal to 0.020% by weight of the total.

Plus particulièrement, la teneur en azote est inférieure ou égale à 0.02% en poids du total, notamment inférieure ou égale à 0.015% en poids du total, voire encore inférieure ou égale à 0.0075% en poids du total.More particularly, the nitrogen content is less than or equal to 0.02% by weight of the total, in particular less than or equal to 0.015% by weight of the total, or even even less than or equal to 0.0075% by weight of the total.

Plus particulièrement, la teneur en hydrogène est inférieure ou égale à 0.01% en poids du total, notamment inférieure ou égale à 0.0035% en poids du total, voire encore inférieure ou égale à 0.0005% en poids du 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 even less than or equal to 0.0005% by weight of the total.

Plus particulièrement, la teneur en silicium est inférieure ou égale à 0.01% en poids du total.More particularly, the silicon content is less than or equal to 0.01% by weight of the total.

Plus particulièrement, la teneur en nickel est inférieure ou égale à 0.01% en poids du total, notamment inférieure ou égale à 0.16% en poids du total.More particularly, the nickel content is less than or equal to 0.01% by weight of the total, in particular less than or equal to 0.16% by weight of the total.

Plus particulièrement, la teneur en matériau ductile, tel que le cuivre, dans l'alliage, est inférieure ou égale à 0.01% en poids du total, notamment inférieure ou égale à 0.005% en poids du total.More particularly, the content of ductile material, such as copper, in the alloy, is less than or equal to 0.01% by weight of the total, in particular less than or equal to 0.005% by weight of the total.

Plus particulièrement, la teneur en aluminium est inférieure ou égale à 0.01% en poids du total.More particularly, the aluminum content is less than or equal to 0.01% by weight of the total.

Au cours d'une étape b) l'âme en Nb-Ti de l'ébauche à l'étape a) est enrobée d'une couche de niobium. L'apport de la couche de niobium autour de l'âme peut être réalisé par voie galvanique, par PVD, CVD ou par voie mécanique. Dans ce dernier cas, un tube de niobium est ajusté sur une barre de l'alliage en Nb-Ti. L'ensemble est déformé par martelage, étirage et/ou tréfilage pour amincir la barre et former l'ébauche qui a été mise à disposition à l'étape a). L'épaisseur de la couche de niobium est choisie de sorte que le rapport surface de niobium/surface de l'âme en Nb-Ti pour une section de fil donnée est inférieur à 1, de préférence inférieur à 0.5, et plus préférentiellement compris entre 0.01 et 0.4. Par exemple, l'épaisseur est de préférence comprise entre 1 et 500 micromètres pour un fil ayant un diamètre total de 0.2 à 1 millimètre.During a step b) the Nb-Ti core of the blank in step a) is coated with a layer of niobium. The addition of the niobium layer around the core can be carried out by galvanic means, by PVD, CVD or by mechanical means. In the latter case, a niobium tube is fitted to a bar of the Nb-Ti alloy. The assembly is deformed by hammering, stretching and/or drawing to thin the bar and form the blank which was made available in step a). The thickness of the niobium layer is chosen so that the niobium surface area/Nb-Ti core surface area ratio 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, the thickness is preferably between 1 and 500 micrometers for a wire having a total diameter of 0.2 to 1 millimeter.

Alternativement, la couche de niobium peut être réalisée par enroulage d'une bande de niobium autour de l'âme en Nb-Ti, l'ensemble bande de niobium/âme en Nb-Ti étant ensuite déformé par martelage, étirage et/ou tréfilage pour amincir la barre et former l'ébauche qui a été mise à disposition à l'issu de l'étape a).Alternatively, the niobium layer can be produced by winding a strip of niobium around the Nb-Ti core, the niobium strip/Nb-Ti core assembly then being deformed by hammering, stretching and/or drawing. to thin the bar and form the blank which was made available at the end of step a).

L'âme en Nb-Ti de l'ébauche obtenue à l'étape b) est enrobée d'une couche de cuivre au cours d'une étape c). L'apport de la couche de cuivre autour de l'âme peut être réalisé par voie galvanique, par PVD, CVD ou par voie mécanique. Dans ce dernier cas, un tube de cuivre est ajusté sur une barre de l'alliage en Nb-Ti revêtue de la couche de niobium. L'ensemble est déformé par martelage, étirage et/ou tréfilage pour amincir la barre et former l'ébauche qui a été mise à disposition à l'issue de l'étape b). L'épaisseur de la couche de cuivre est choisie de sorte que le rapport surface de cuivre/surface de l'âme en Nb-Ti recouverte de la couche de niobium pour une section de fil donnée est inférieur à 1, de préférence inférieur à 0.5, et plus préférentiellement compris entre 0.01 et 0.4. Par exemple, l'épaisseur est de préférence comprise entre 1 et 500 micromètres pour un fil ayant un diamètre total de 0.2 à 1 millimètre.The Nb-Ti core of the blank obtained in step b) is coated with a layer of copper during a step c) . The contribution of the copper layer around the core can be carried out by galvanic way, by PVD, CVD or by mechanical way. In the latter case, a copper tube is fitted to a bar of the Nb-Ti alloy coated with the niobium layer. The assembly is deformed by hammering, stretching and/or drawing to thin the bar and form the blank which was made available at the end of step b). The thickness of the copper layer is chosen so that the copper surface/surface ratio of the Nb-Ti core covered with the niobium layer 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, the thickness is preferably between 1 and 500 micrometers for a wire having a total diameter of 0.2 to 1 millimeter.

Alternativement, la couche de cuivre peut être réalisée par enroulage d'une bande de cuivre autour de l'âme en Nb-Ti recouverte de la couche de niobium, l'ensemble bande de niobium/âme en Nb-Ti étant ensuite déformé par martelage, étirage et/ou tréfilage pour amincir la barre et former l'ébauche qui a été mise à disposition à l'issu de l'étape b).Alternatively, the copper layer can be made by winding a copper strip around the Nb-Ti core covered with the niobium layer, the niobium strip/Nb-Ti core assembly then being deformed by hammering. , drawing and/or drawing to thin the bar and form the blank which was made available at the end of step b).

Selon encore une autre alternative, l'âme en Nb-Ti recouverte de la bande niobium peut être introduite dans un tube de cuivre, l'ensemble étant co-extrudé à chaud à une température de l'ordre de 600 à 900 degrés à travers une filière.According to yet another alternative, the Nb-Ti core covered with the niobium strip can be introduced into a copper tube, the assembly being hot co-extruded at a temperature of the order of 600 to 900 degrees through a pathway.

Une trempe de type bêta consistant en un traitement de mise en solution est pratiquée au moins avant les étapes de déformation ultérieures. Ce traitement est réalisé de façon à ce que le titane de l'alliage soit essentiellement sous forme de solution solide avec le niobium en phase bêta. De préférence, il est effectué pendant une durée comprise entre 5 minutes et 2 heures à une température comprise entre 700°C et 1000°C, sous vide, suivi d'un refroidissement sous gaz. Plus particulièrement, cette trempe bêta est un traitement de mise en solution à 800°C sous vide pendant 5 minutes à 1 heure, suivi d'un refroidissement sous gaz.Beta-type quenching consisting of a solution heat treatment is performed at least before the subsequent deformation steps. This treatment is carried out so that the titanium of the alloy is essentially in the form of a solid solution with the niobium in the beta phase. Preferably, it is carried out for a period of between 5 minutes and 2 hours at a temperature of between 700° C. and 1000° C., under vacuum, followed by cooling under gas. More particularly, this beta quenching is a solution treatment at 800° C. under vacuum for 5 minutes to 1 hour, followed by cooling under gas.

L'étape d) de déformation est réalisée en plusieurs séquences. On entend par déformation une déformation par tréfilage et/ou laminage. Step d) of deformation is carried out in several sequences. By deformation is meant a deformation by drawing and/or rolling.

Avantageusement, l'étape de déformation comporte au moins successivement des séquences de déformation, de préférence à froid, par martelage et/ou étirage et/ou tréfilage de calibration désignées par l'étape d1). L'étape d1) permet d'amener l'ébauche obtenue à l'issue de l'étape c) à un diamètre déterminé dit diamètre de calibration du fil.Advantageously, the deformation step comprises at least successive sequences of deformation, preferably cold, by hammering and/or stretching and/or calibration wire drawing designated by step d1 ). Step d1) makes it possible to bring the blank obtained at the end of step c) to a determined diameter called the wire calibration diameter.

Selon l'invention, le procédé comprend en outre une étape h) qui consiste à enlever la couche de cuivre formée à l'étape c), lorsque durant l'étape d1), l'ébauche a atteint un diamètre tel que l'on puisse encore passer ladite ébauche au moins à travers une filière avec un taux d'allongement de l'ébauche d'environ 10% avant la première étape de laminage d2) ultérieure. Cette étape d'enlèvement de la couche de cuivre est effectuée par attaque chimique dans une solution à base de cyanures ou d'acides, par exemple dans un bain d'acide nitrique à une concentration de 53% massique dans l'eau.According to the invention, the method further comprises a step h) which consists in removing the layer of copper formed in step c), when during step d1), the blank has reached a diameter such that one can still pass said blank at least through a die with an elongation rate of the blank of about 10% before the first subsequent rolling step d2). This step of removing the copper layer is carried out by chemical attack in a solution based on cyanides or acids, for example in a bath of nitric acid at a concentration of 53% by weight in water.

Une séquence d'opérations de laminage, de préférence à profil rectangulaire compatible avec la section d'entrée d'une broche d'estrapadage est ensuite réalisée, cette séquence formant l'étape d2).A sequence of rolling operations, preferably with a rectangular profile compatible with the entry section of a strapping pin, is then carried out, this sequence forming step d2 ).

Chaque séquence des étapes d1) et d2) est effectuée avec un taux de déformation donné compris entre 1 et 5, ce taux de déformation répondant à la formule classique 2In(d0/d), où d0 est le diamètre de la dernière trempe bêta, et où d est le diamètre du fil écroui. Le cumul global des déformations sur l'ensemble de cette succession de séquences amène un taux total de déformation compris entre 1 et 14.Each sequence of steps d1) and d2) is carried out with a given deformation rate between 1 and 5, this deformation rate corresponding to the classic formula 2In(d0/d), where d0 is the diameter of the last beta temper, and where d is the diameter of the hardened wire. The global cumulation of the deformations on the whole of this succession of sequences brings a total rate of deformation included between 1 and 14.

A l'issue de l'étape d2), la couche de niobium enrobant l'âme de Nb-Ti à une épaisseur comprise entre 20 nm et 10 µm, de préférence entre 300 nm et 1.5 µm, plus préférentiellement entre 400 et 800 nm.At the end of step d2), the niobium layer coating the Nb-Ti core at a thickness of between 20 nm and 10 μm, preferably between 300 nm and 1.5 μm, more preferably between 400 and 800 nm .

Le fil laminé en lame obtenu à l'issue de l'étape d2) est ensuite découpé à une longueur déterminée lors de l'étape e).The blade-rolled wire obtained at the end of step d2) is then cut to a length determined during step e) .

L'étape f) d'estrapadage pour former le ressort spiral est suivie de l'étape g) de traitement thermique final sur le ressort spiral. Ce traitement thermique final est un traitement de précipitation du Ti en phase alpha d'une durée comprise entre 1 et 80 heures, de préférence entre 5 et 30 heures, à une température comprise entre 350 et 700°C, de préférence entre 400 et 600°C. Step f) of strapping to form the spiral spring is followed by step g) of final heat treatment on the spiral spring. This final heat treatment is a precipitation treatment of Ti in the alpha phase lasting between 1 and 80 hours, preferably between 5 and 30 hours, at a temperature between 350 and 700° C., preferably between 400 and 600 °C.

Selon une variante avantageuse le procédé peut comporter en outre, entre chaque séquence ou entre certaines séquences des étapes de déformation d1) et/ou d2) un traitement thermique intermédiaire de précipitation du titane en phase alpha d'une durée comprise entre 1 heure et 80 heures à une température comprise entre 350°C et 700°C, de préférence entre 5 heures et 30 heures entre 400°C et 600°C. Avantageusement, ce traitement intermédiaire est réalisé à l'étape d1) entre la première séquence de tréfilage et la deuxième séquence de tréfilage de calibration.According to an advantageous variant, the method may also comprise, between each sequence or between certain sequences of the deformation steps d1) and/or d2), an intermediate heat treatment for the precipitation of the titanium in the alpha phase for a duration of between 1 hour and 80 hours at a temperature between 350°C and 700°C, preferably between 5 hours and 30 hours between 400°C and 600°C. Advantageously, this intermediate processing is carried out in step d1) between the first drawing sequence and the second calibration drawing sequence.

Le ressort spiral réalisé selon ce procédé a une limite élastique supérieure ou égale à 500 MPa, de préférence supérieure à 600 MPa, et plus précisément comprise entre 500 et 1000 MPa. De manière avantageuse, il a un module d'élasticité inférieur ou égal à 120 GPa, et de préférence inférieur ou égal à 100 GPa.The spiral spring produced according to this method has an elastic limit greater than or equal to 500 MPa, preferably greater than 600 MPa, and more precisely comprised between 500 and 1000 MPa. Advantageously, it has a modulus of elasticity less than or equal to 120 GPa, and preferably less than or equal to 100 GPa.

Le ressort spiral comporte une âme en Nb-Ti enrobée d'une couche de niobium, ladite couche ayant une épaisseur comprise entre 50 nm et 5 µm, de préférence entre 200 nm et 1.5 µm, plus préférentiellement entre 800 nm et 1,2 µm.The spiral spring comprises an Nb-Ti core coated with a layer of niobium, said layer having a thickness of between 50 nm and 5 μm, preferably between 200 nm and 1.5 μm, more preferably between 800 nm and 1.2 μm .

L'âme du ressort spiral a une microstructure bi-phasée comportant du niobium en phase bêta et du titane en phase alpha.The spiral spring core has a two-phase microstructure comprising beta-phase niobium and alpha-phase titanium.

En outre le ressort spiral réalisé selon l'invention présente un coefficient thermoélastique, dit aussi CTE, lui permettant de garantir le maintien des performances chronométriques malgré la variation des températures d'utilisation d'une montre incorporant un tel ressort spiral.In addition, the spiral spring made according to the invention has a thermoelastic coefficient, also called CTE, enabling it to guarantee the maintenance of chronometric performance despite the variation in the temperatures of use of a watch incorporating such a spiral spring.

Le procédé de l'invention permet la réalisation, et plus particulièrement la mise en forme, d'un ressort spiral pour balancier en alliage de type niobium-titane, typiquement à 47 % en poids de titane (40-60%). Cet alliage présente des propriétés mécaniques élevées, en combinant une limite élastique très élevée, supérieure à 600 MPa, et un module d'élasticité très bas, de l'ordre de 60 Gpa à 80 GPa. Cette combinaison de propriétés convient bien pour un ressort spiral. De plus, un tel alliage est paramagnétique.The method of the invention allows the production, and more particularly the shaping, of a spiral spring for a balance wheel in an alloy of the niobium-titanium type, typically containing 47% by weight of titanium (40-60%). This alloy has high mechanical properties, by combining a very high elastic limit, greater than 600 MPa, and a very low modulus of elasticity, of the order of 60 Gpa to 80 GPa. This combination of properties is well suited for a spiral spring. Moreover, such an alloy is paramagnetic.

Claims (7)

Ressort spiral destiné à équiper un balancier d'un mouvement d'horlogerie, comprenant une âme en Nb-Ti réalisée dans un alliage constitué de : - niobium : balance à 100% en poids, - titane : entre 5 et 95% en poids, - traces d'éléments sélectionnés parmi le groupe constitué de O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, chacun desdits éléments étant présent dans une quantité comprise entre 0 et 1600 ppm en poids, la quantité totale constituée par l'ensemble desdits éléments étant comprise entre 0% et 0.3% en poids, caractérisé en ce que l'âme en Nb-Ti est enrobée d'une couche d'un premier matériau choisi parmi l'ensemble comprenant le niobium, le tantale, le vanadium, un acier austénitique inoxydable, (acier de nuance 316L), ladite couche du premier matériau ayant une épaisseur comprise entre 20 nm et 10 µm. Spiral spring intended to equip a balance wheel of a watch movement, comprising an Nb-Ti core made of an alloy consisting of: - niobium: 100% balance by weight, - titanium: between 5 and 95% by weight, - traces of elements selected from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said elements being present in an amount between 0 and 1600 ppm by weight, the amount total constituted by all of said elements being between 0% and 0.3% by weight, characterized in that the Nb-Ti core is coated with a layer of a first material chosen from the group comprising niobium, tantalum, vanadium, an austenitic stainless steel (316L grade steel), said layer of the first material having a thickness of between 20 nm and 10 μm. Ressort spiral selon la revendication 16, caractérisé en ce que la couche du premier matériau a une épaisseur comprise entre 300 nm et 1.5 µm.Spiral spring according to Claim 16, characterized in that the layer of the first material has a thickness of between 300 nm and 1.5 µm. Ressort spiral selon la revendication 16 ou 17, caractérisé en ce que la couche du premier matériau a une épaisseur comprise entre 400 nm et 800 nm.Spiral spring according to Claim 16 or 17, characterized in that the layer of the first material has a thickness of between 400 nm and 800 nm. Ressort spiral selon l'une des revendications 16 à 18, caractérisé en ce que le premier matériau est le niobium.Spiral spring according to one of Claims 16 to 18, characterized in that the first material is niobium. Ressort spiral selon l'une des revendications 16 à 19, caractérisé en ce que la teneur en Ti est comprise entre 40 et 65% en poids, de préférence entre 40 et 49% en poids et plus préférentiellement entre 46 et 48% en poids.Spiral spring according to one of Claims 16 to 19, characterized in that the Ti content is between 40 and 65% by weight, preferably between 40 and 49% by weight and more preferably between 46 and 48% by weight. Ressort spiral selon l'une des revendications 16 à 20, caractérisé en ce que l'âme en Nb-Ti a une microstructure bi-phasée comportant du niobium en phase bêta et du titane en phase alpha.Spiral spring according to one of Claims 16 to 20, characterized in that the Nb-Ti core has a two-phase microstructure comprising niobium in the beta phase and titanium in the alpha phase. Ressort spiral selon l'une des revendications 16 à 21, caractérisé en ce qu'il a une limite élastique supérieure ou égale à 500 MPa, de préférence à 600 MPa, et un module d'élasticité inférieur ou égal à 120 GPa, de préférence inférieur ou égal à 100 GPa.Spiral spring according to one of Claims 16 to 21, characterized in that it has an elastic limit greater than or equal to 500 MPa, preferably 600 MPa, and a modulus of elasticity less than or equal to 120 GPa, preferably less than or equal to 100 GPa.
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US20210200153A1 (en) 2021-07-01
JP2021110726A (en) 2021-08-02

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