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
  • G04B17/04—Oscillators acting by spring tension
  • G04B17/06—Oscillators with hairsprings, e.g. balance
  • G04B17/066—Manufacture of the spiral spring

Definitions

• the invention relates to a method of manufacturing a spiral spring intended to equip a balance with a watch movement and the spiral spring resulting from the method.
• spiral springs are also centered on the concern for thermal compensation, so as to guarantee regular chronometric performance. This requires obtaining a thermoelastic coefficient close to zero. We are also looking to produce spiral springs exhibiting limited sensitivity to magnetic fields.
• This copper layer on the wire has a disadvantage. It does not allow fine control of the wire geometry during wire calibration and rolling. These dimensional variations of the Nb-Ti core of the wire result in significant variations in the torques of the balance springs.
• the present invention provides a method of manufacturing a spiral spring which makes it possible to facilitate shaping by deformation while avoiding the drawbacks associated with copper.
• the method of manufacturing the spiral spring according to the invention comprises a heat treatment step aimed at transforming part of the Cu layer coating the core in Nb-Ti into a layer of intermetallics Cu, Ti and remove the remaining Cu layer.
• This intermetallic layer then forms the outer layer which is in contact with the dies and the rolling rolls. It is chemically inert and ductile and makes it easy to draw and roll the spiral wire. It has the other advantage of facilitating the separation between the balance springs after the fixing step following the stretching.
• the intermetallic layer is retained on the hairspring at the end of the manufacturing process. It is sufficiently thin with a thickness between 20 nm and 10 microns, preferably between 300 nm and 1.5 miti, so as not to significantly modify the thermoelastic coefficient (CTE) of the hairspring. It is also perfectly adherent to the Nb-Ti core.
• CTE thermoelastic coefficient
• the invention is more specifically described for a Cu layer partially transformed into a Cu, Ti intermetallic layer.
• the present invention is applicable for other elements such as Sn, Fe, Pt, Pd, Rh, Al, Au, Ni, Ag, Co and Cr also able to form intermetallics with Ti. It is also applicable for an alloy of any of these elements.
• Figure 1 shows a microscopy of the blank with a core made of the NbTUz alloy coated with a layer of Cu partially transformed into intermetallics with the heat treatment of the process according to the invention.
• Figure 2 shows, according to the prior art, the XRD spectrum of this alloy with the Cu layer in the absence of the heat treatment according to the method of the invention.
• FIG. 3 represents the XRD spectrum of this same alloy with the Cu layer in the presence of the heat treatment according to the method of the invention.
• FIG. 4 is an enlargement of the XRD spectrum of FIG. 3 for the peaks relating to intermetallics.
• the invention relates to a method of manufacturing a spiral spring intended to equip a balance 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.
• the manufacturing process comprises the following steps: a) a step of providing a blank with an Nb-Ti core made from an alloy consisting of: - niobium: balance at 100% by weight,
• the blank of step a) comprises a layer around the Nb-Ti core of a material X chosen from Cu, Sn, Fe, Pt, Pd, Rh, Al , Au, Ni, Ag, Co and Cr or an alloy of these elements.
• a material X chosen from Cu, Sn, Fe, Pt, Pd, Rh, Al , Au, Ni, Ag, Co and Cr or an alloy of these elements.
• it can be Cu, Cu-Sn, Cu-Ni, etc.
• the method comprises a step of supplying said material X around the core in Nb-Ti to form the layer in X, said step being carried out between step a) and step c) of deformation .
• the manufacturing process also includes a heat treatment step to partially transform the X-shaped layer into an X, Ti intermetallic layer around the Nb-Ti core.
• the heat treatment is carried out at a temperature between 200 and 900 ° C during 15 minutes to 100 hours.
• the blank thus successively comprises the core in Nb-Ti, the layer of intermetallic X, Ti and the remaining part of the layer in X, said step being carried out between step b) and step c) or between two sequences of the deformation step c).
• the manufacturing process then comprises a step of removing the remaining part of the layer in X. This step is carried out between step b) and step c), between two sequences of the deformation step c) or between step c) and step d).
• step a the core is made from an Nb-Ti alloy comprising between
• the alloy used in the present invention comprises by weight between 40 and 60% of 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 a martensitic phase causing problems of fragility of the alloy during its use.
• the titanium content is reduced more significantly to avoid the formation of these hard phases.
• the titanium content is then less than 40% by weight. It is between 5 and 40% by weight (upper limit not included). More particularly, it is between 5 and 35%, preferably between 15 and 35% and more preferably between 27 and 33%.
• the Nb-Ti alloy used in the present invention does not include other elements except for possible and inevitable traces. This helps prevent the formation of fragile 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. More particularly, 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 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 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 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 less than or equal to 0.0005% by weight of the total. More particularly, the silicon content is less than or equal to
• 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. 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.
• 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 material X as listed above.
• the addition of the X-shaped layer around the core can be achieved by galvanic means, by PVD, CVD or by mechanical means.
• a tube of material X is fitted to a bar of the Nb-Ti alloy.
• the assembly is deformed by hammering, stretching and / or wire drawing to thin the bar and form the blank made available in step a).
• the present invention does not exclude providing the X-shaped layer during the method of manufacturing the spiral spring between step a) and step c) of deformation.
• the thickness of the layer in X is chosen so that the ratio of material surface X / surface area of the Nb-Ti core for a given wire section is less than 1, preferably less than 0.5, and more preferably included 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 beta-type quenching in step b) is a dissolving treatment. 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 specifically, this beta quench is a dissolving treatment at 800 ° C under vacuum for 5 minutes to 1 hour, followed by gas cooling.
• Deformation step c) is carried out in several sequences.
• deformation is meant a deformation by wire drawing and / or rolling.
• the deformation step comprises at least successively a first wire drawing sequence, a second calibration wire drawing sequence and a third rolling sequence, preferably with a rectangular profile compatible with the entry section of a stepping spindle. .
• Each sequence is carried out with a given strain rate between 1 and 5, this strain rate corresponding to the classic formula 2ln (d0 / d), where dO is the diameter of the last beta hardening, and where d is the diameter of the strain-hardened wire.
• the global accumulation of deformations over the whole of this succession of sequences leads to a total rate of deformation of between 1 and 14.
• the manufacturing process comprises the step of heat treatment to partially transform the X-shaped layer into a X, Ti intermetallic layer around the Nb-Ti core.
• This step is carried out for 15 minutes to 100 hours at a temperature between 200 and 900 ° C. Preferably, it is carried out for 5 to 20 hours between 400 and 500 ° C.
• This heat treatment step can be used to precipitate the titanium in the alpha phase.
• the intermetallic layer has a thickness between 20 nm and 10 miti, preferably between 300 nm and 1.5 miti, more preferably between 400 and 800 nm and even more preferably between 400 and 600 nm.
• the remaining layer of X has a thickness of between 1 and 25 ⁇ m.
• the intermetallic layer includes, for example, Cu4 ⁇ i, Cu2 ⁇ i, CuTi, CU3T12 and CuTÎ2.
• the microscopy in Figure 1 shows the structure of the blank after heat treatment at 450 ° C of a niobium-titanium alloy with 47% by weight of titanium covered with a layer of copper.
• FIG. 3 represents the XRD spectrum for this same alloy of the spiral spring according to the invention after removal of the Cu layer and after the steps of stretching and fixing.
• the XRD spectrum for this same alloy with the copper layer but in the absence of the heat treatment is shown in FIG. 2.
• a series of small peaks is observed next to the Nb peak which are shown in enlargement at Figure 4.
• This heat treatment aimed at forming intermetallics can be carried out before deformation step c) or between two deformation sequences during step c).
• it is carried out in step c) between the first wire drawing sequence and the second calibration wire drawing sequence.
• the remaining X-layer is removed so as to have the intermetallic layer as the outer layer.
• This step can be carried out by chemical attack in a solution based on cyanides or acids, for example nitric acid. It will be specified that the present invention does not exclude that certain intermetallics are also dissolved in the acid. This is for example the case with Cu4 ⁇ i in a nitric acid solution.
• the X-layer can be removed at different points in the process depending on the desired effect. Preferably, it is removed in step c) before the calibration wire drawing so as to very finely control the final dimensions of the spiral wire.
• the intermetallics present in the outer layer then prevent the sticking of the wire in the dies, against the rolling rolls and between the spirals during fixing. More preferably, it is removed between the first wire drawing sequence and the second calibration wire drawing sequence. According to a less advantageous variant, it is removed after the calibration wire drawing before the rolling, so as to prevent the wire sticking against the rolling rolls and between the spirals during fixing. According to a variant which is also less advantageous, it is removed at the end of the deformation step c) before the stretching step.
• Step d) to form the spiral spring is followed by step e) 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 process may include intermediate heat treatments between the deformation sequences in this same range of times and temperatures.
• 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 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 intermetallics X, Ti with X chosen from Cu, Sn, Fe, Pt, Pd, Rh, Al, Au, Ni, Ag, Co and Cr or an alloy of one of these elements, said intermetallic layer having a thickness between 20 nm and 10 ⁇ m, preferably between 300 nm and 1.5 ⁇ m, more preferably between 400 nm and 800 nm, or even between 400 nm and 600 nm.
• the intermetallic layer is a Cu, Ti layer.
• the spiral spring core has a two-phase microstructure comprising beta phase niobium and alpha phase titanium.
• the spiral spring produced according to the invention has a thermoelastic coefficient, also known as CTE, allowing it to guarantee the maintenance of chronometric performance despite the variation in the operating temperatures of a watch incorporating such a spiral spring.
• the method of the invention allows the production, and more particularly the shaping, of a balance spring made of a niobium-titanium type alloy, typically containing 47% by weight of titanium (40-60%).
• This alloy exhibits 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 80 GPa. This combination of properties is well suited for a spiral spring.
• such an alloy is paramagnetic.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Springs (AREA)
• Heat Treatment Of Steel (AREA)
• Laminated Bodies (AREA)

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• 2019
  • 2019-11-29 EP EP19212457.6A patent/EP3828642A1/de not_active Withdrawn
• 2020
  • 2020-11-27 WO PCT/EP2020/083622 patent/WO2021105352A1/fr unknown
  • 2020-11-27 CN CN202080082129.5A patent/CN114730155A/zh active Pending
  • 2020-11-27 US US17/779,659 patent/US20220413438A1/en active Pending
  • 2020-11-27 EP EP20811381.1A patent/EP4066066A1/de active Pending
  • 2020-11-27 JP JP2022531415A patent/JP7475447B2/ja active Active

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