SPIRAL SPRING FOR A HOROLOGICAL MOVEMENT

Abstract

A spiral spring is configured to equip a balance of a horological movement. The spiral spring is made of an alloy consisting of: Nb, Ti and at least one element selected from V and Ta, optionally at least one element selected from Zr and Hf, optionally at least one element selected from W and Mo, possible traces of other elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al, with the following weight percentages: a total content of Nb, V and Ta comprised between 40 and 85%, a total content of Ti, Zr and Hf comprised between 15 and 55%, a content for W and Mo respectively comprised between 0 and 2.5%, a content for each of the elements selected from 0, H, C, Fe, N, Ni, Si, Cu, Al between 0 and 1600 ppm with the sum of the traces less than or equal to 0.3% by weight.

Claims

1. A spiral spring intended to equip a balance of a horological movement, wherein the spiral spring is made of an alloy consisting of: Nb, Ti and at least one element selected from V and Ta, optionally at least one element selected from Zr and Hf, optionally at least one element selected from W and Mo, possible traces of other elements selected from O, H, C, Fe, N, Ni Si, Cu, Al, with the following weight percentages: a total content of Nb, V and Ta comprised between 40 and 85%, a total content of Ti, Zr and Hf comprised between 15 and 55%, a content for W and Mo respectively comprised between 0 and 2.5%, a content for each of said elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al comprised between 0 and 1600 ppm with the sum of said traces less than or equal to 0.3% by weight.

2. The spiral spring according to claim 1, wherein the Nb content is greater than 45% by weight.

3. The spiral spring according to claim 1, wherein the Ti content is greater than or equal to 15% by weight.

4. The spiral spring according to claim 1, wherein the sum of the content of V and Ta is comprised between 5 and 25% by weight.

5. The spiral spring according to claim 1, wherein the sum of the content of V and Ta is comprised between 10 and 25% by weight.

6. The spiral spring according to claim 1, wherein the sum of the content of V and Ta is comprised between 15 and 25% by weight.

7. The spiral spring according to claim 1, wherein said spiral spring comprises Zr and/or Hf with the sum of the content of Zr and Hf comprised between 1 and 40% by weight.

8. The spiral spring according to claim 1, wherein said spiral spring comprises Zr and/or Hf with the sum of the content of Zr and Hf comprised between 5 and 25% by weight.

9. The spiral spring according to claim 1, wherein said spiral spring comprises Zr and/or Hf with the sum of the content of Zr and Hf comprised between 10 and 25% by weight.

10. The spiral spring according to claim 1, wherein said spiral spring comprises Zr and/or Hf with the sum of the content of Zr and Hf comprised between 15 and 25% by weight.

11. The spiral spring according to claim 1, having a microstructure comprising a beta phase of Nb, and of V and/or of Ta and an alpha phase of Ti, and of Zr and/or of Hf when the alloy includes Zr and/or Hf

12. The spiral spring according to claim 1, that it wherein said spiral spring has an elastic limit greater than or equal to 500 MPa, and a modulus of elasticity greater than or equal to 100 GPa.

13. A method for manufacturing a spiral spring intended to equip a balance of a horological movement, it wherein said method successively comprises: a step of producing a blank from an at least ternary alloy consisting of: Nb, Ti and at least one element selected from V and Ta, optionally at least one element selected from Zr and Hf, optionally at least one element selected from W and Mo, possible traces of other elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al, with the following weight percentages: a total content of Nb, V and Ta comprised between 40 and 85%, a total content of Ti, Zr and Hf comprised between 15 and 55%, a content for W and Mo respectively comprised between 0 and 2.5%, a content for each of said elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al comprised between 0 and 1600 ppm with the sum of said traces less than or equal to 0.3% by weight, a step of beta type quenching of said blank, so that titanium of said alloy is essentially in the form of a solid solution with niobium, and vanadium and/or tantalum in the beta phase, zirconium and/or hafnium of said alloy also being essentially in the form of a solid solution when the alloy includes zirconium and/or hafnium, a step of application to said alloy of a succession of sequences of deformation followed by an intermediate heat treatment, a winding step to form the spiral spring, a final heat treatment step.

14. The method for manufacturing a spiral spring according to claim 13, wherein the beta type quenching is a dissolution treatment, with a duration comprised between 5 minutes and 2 hours at a temperature comprised between 700° C. and 1000° C., under vacuum, followed by cooling under gas.

15. The method for manufacturing a spiral spring according to claim 13, wherein the final heat treatment as well as the intermediate heat treatment of each sequence is a precipitation treatment of Ti, and optionally of Zr and/or Hf when the alloy includes Zr and/or Hf, in the alpha phase, with a duration comprised between 1 hour and 200 hours at a holding temperature comprised between 300° C. and 700° C.

16. The method for manufacturing a spiral spring according to claim 13, wherein, when the alloy includes Zr and/or Hf, the final heat treatment is carried out at a holding temperature comprised between 400° C. and 600° C. for a duration comprised between 4 and 8 hours.

17. The method for manufacturing a spiral spring according to claim 13, wherein, after the step of producing the alloy blank, and before the step of applying a succession of sequences, a surface layer of ductile material taken from copper, nickel, cupro-nickel, cupro-manganese, gold, silver, nickel-phosphorus Ni—P and nickel-boron Ni—B is added to the blank to facilitate shaping into a wire shape and in that, before or after the winding step, said wire is stripped of its layer of said ductile material by chemical attack.

Description

DETAILED DESCRIPTION

[0030] The invention relates to a watch spiral spring made of an at least ternary alloy including niobium and titanium and one or more additional elements.

[0031] According to the invention, this alloy consists of: [0032] Nb, Ti and at least one element selected from V and Ta, [0033] optionally at least one element selected from Zr and Hf, [0034] optionally at least one element selected from W and Mo, [0035] possible traces of other elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al, [0036] with the following weight percentages for a total of 100%: [0037] a total content of Nb, V and Ta comprised between 40 and 85% with preferably an Nb content greater than 45%, or even greater than or equal to 50%, [0038] a total content of Ti, Zr and Hf comprised between 15 and 55% with preferably a minimum Ti content of 15%, [0039] a content for W and Mo respectively comprised between 0 and 2.5%, [0040] a content for each of said elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al comprised between O and 1600 ppm with the sum of said traces less than or equal to 0.3% by weight.

[0041] According to the invention, the Nb is partly replaced by Ta and/or V. The partial replacement of Nb by Ta and/or V is intended to reduce the secondary error. Tests were performed on binary Nb—V and Nb—Ta alloys to show the effect of V and Ta respectively on the secondary error. The secondary error is measured at 23° C. This is the difference in rate at 23° C. with respect to the straight line linking the rate at 8° C. to that at 38° C. For example, the rate at 8° C., 23° C. and 38° C. can be measured using a Witschi chronoscope-type apparatus.

[0042] Table 1 below shows reference data for pure Nb, pure V, pure Ta and the NbTi47 alloy and the values obtained as a function of the percentage by weight of V and Ta in a binary alloy Nb-V and Nb-Ta respectively. Pure Nb has a secondary error at 23° C. of −6.6 s/d. The precipitation of Ti in the alpha phase in the NbTi47 alloy compensates for the negative effect of Nb with, however, an excessive rise with a value reaching 4.5 s/d, that is to say a delta of 11.1 s/d, following the addition of Ti. Pure vanadium and pure tantalum have a significantly more negative secondary error than pure Nb with values of −24.9 and −28.7 s/d respectively. The partial replacement of Nb by V and/or Ta allows to lower the secondary error to negative values less than −7 s/d. Thus, the increasing replacement of Nb by V or Ta ranging from 5% to 25% lowers the secondary error from about −7 s/d to −12 s/d. Nb can thus be replaced by V or Ta or by a combination of V and Ta to reach this range of values. The secondary error is comprised between −7 s/d and −12 s/d for a content of Ta alone, of V alone or a total content of Ta and V comprised between 5% and 25% by weight. Preferably, the secondary error is comprised between −9 and −12 s/d for a content of Ta alone, of V alone or a total content of Ta and V comprised between 10 and 25% and more preferably between 15 and 25% by weight. The addition in the Nb—V/Ta alloy of one or more elements forming an alpha phase of precipitates during the fixing step allows to compensate for this negative value and to reach a value close to 0 s/d. Preferably, the content of the element(s) forming an alpha phase of precipitates is comprised for all of these elements between 15 and 55% by weight. The element forming an alpha phase is at least Ti with preferably a minimum content of 15%. It may, in addition to Ti, be Hf and/or Zr which forms with Ti a single alpha phase of precipitates during the fixing step. When the alloy comprises Zr and/or Hf, the total content of

[0043] Zr and Hf is comprised between 1 and 40%, preferably between 5 and 25%, more preferably between 10 and 25%, even more preferably between 15 and 25% by weight.

TABLE-US-00001 TABLE 1 % weight Secondary error Alloy: V/Ta at 23° C. Pure Niobium −6.6 s/d Pure Vanadium −24.9 s/d Pure Tantalum −28.7 s/d NbTi47 4.5 s/d Nb.sub.100  0% −6.6 s/d Nb.sub.95V.sub.5  5% −7.2 s/d Nb.sub.90V.sub.10 10% −8.6 s/d Nb.sub.85V.sub.15 15% −9.0 s/d Nb.sub.80V.sub.20 20% −11.0 s/d Nb.sub.75V.sub.25 25% −11.5 s/d Nb.sub.100  0% −6.6 s/d Nb.sub.95Ta.sub.5  5% −8.0 s/d Nb.sub.90Ta.sub.10 10% −8.7 s/d Nb.sub.85Ta.sub.15 15% −10.5 s/d Nb.sub.80Ta.sub.20 20% −11.6 s/d Nb.sub.75Ta.sub.25 25% −12.0 s/d

[0044] The alloy may further include W and Mo in a content by weight for each comprised between 0 and 2.5% in order to increase the Young's modulus of the alloy, which allows for a given torque of the spring to reduce the thickness of the spiral and thereby lighten the spiral.

[0045] In a particularly advantageous manner, the alloy used in the present invention does not comprise other elements except for possible and unavoidable traces.

[0046] 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.

[0047] 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 less than or equal to 0.0175% by weight of the total.

[0048] 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 less than or equal to 0.020% by weight of the total.

[0049] 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 less than or equal to 0.0075% by weight of the total.

[0050] More particularly, the hydrogen content is less than or equal to 0.01% by weight of the total, in particular less than or equal to 0.0035% by weight of the total, or even less than or equal to 0.0005% by weight of the total.

[0051] More particularly, the silicon content is less than or equal to 0.01% by weight of the total.

[0052] 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.

[0053] More particularly, the copper content 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.

[0054] More particularly, the aluminium content is less than or equal to 0.01% by weight of the total.

[0055] Advantageously, this spiral spring has a multi-phase microstructure including a single beta phase of niobium, vanadium and/or tantalum and a single alpha phase of titanium, and hafnium and/or zirconium when the alloy includes hafnium and/or zirconium. In the presence of tantalum and vanadium, the microstructure could also include an intermetallic of the type TaV.sub.2. To obtain such a microstructure, it is necessary to precipitate the alpha phase (Ti, Hf, Zr) by heat treatment as described below.

[0056] The spiral spring produced with this alloy has an elastic limit greater than or equal to 500 MPa and more precisely between 500 and 1000 MPa. Advantageously, it has a modulus of elasticity greater than or equal to 100 GPa and preferably greater than or equal to 110 GPa.

[0057] The invention also relates to the method for manufacturing the watch spiral spring, characterised in that the following steps are implemented successively:

[0058] a) production or provision of a blank made of an alloy consisting of: [0059] Nb, Ti and at least one element selected from V and Ta, [0060] optionally at least one element selected from Zr and Hf, [0061] optionally at least one element selected from W and Mo, [0062] possible traces of other elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al, with the following weight percentages for a total of 100%: [0063] a total content of Nb, V and Ta comprised between 40 and 85% with preferably an Nb content greater than 45%, [0064] a total content of Ti, Zr and Hf comprised between 15 and 55% with preferably a minimum Ti content of 15% (limit included), [0065] a content for W and Mo respectively comprised between 0 and 2.5%. [0066] a content for each of said elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al comprised between 0 and 1600 ppm with the sum of said traces less than or equal to 0.3% by weight, [0067] b) beta type quenching of said blank, so that titanium, and zirconium and hafnium when they are present, of said alloy is essentially in the form of a solid solution with niobium as well as tantalum and/or vanadium in the beta phase; [0068] c) application to said alloy of deformation sequences followed by heat treatment. Deformation means a deformation by drawing and/or rolling. Drawing may require the use of one or more dies during the same sequence or during different sequences if necessary. The drawing is carried out until a wire with a round section is obtained. Rolling can be performed in the same deformation sequence as the drawing or in another sequence. Advantageously, the last sequence applied to the alloy is a rolling preferably with a rectangular profile compatible with the entry section of a winding pin. [0069] d) winding to form a spiral spring, followed by a final fixing heat treatment.

[0070] In these coupled deformation-heat treatment sequences, each deformation is carried out with a given deformation amount comprised between 1 and 5, this deformation amount corresponding to the conventional formula 2In(d0/d), wherein d0 is the diameter of the last beta quenching, and where d is the diameter of the cold-worked wire. The global accumulation of the deformations on the whole of this succession of sequences brings a total deformation amount comprised between 1 and 14. Each coupled deformation-heat treatment sequence includes, each time, a heat treatment of precipitation of the alpha phase (Ti, Zr and/or Hf).

[0071] The beta quenching prior to the deformation and heat treatment sequences is a dissolution treatment, with a duration comprised between 5 minutes and 2 hours at a temperature comprised between 700° C. and 1000° C., under vacuum, followed by cooling under gas. Even more particularly, this beta quenching is a dissolution treatment, lasting 1 hour at 800° C. under vacuum, followed by cooling under gas.

[0072] To return to the coupled deformation-heat treatment sequences, the heat treatment is a precipitation treatment with a duration comprised between 1 hour and 200 hours at a temperature comprised between 300° C. and 700° C. More particularly, the duration is comprised between 5 hours and 30 hours with a holding temperature comprised between 400° C. and 600° C.

[0073] More particularly, the method includes between one and five coupled deformation-heat treatment sequences.

[0074] More particularly, the first coupled deformation-heat treatment sequence includes a first deformation with at least 30% reduction in section.

[0075] More particularly, each coupled deformation-heat treatment sequence, other than the first, includes one deformation between two heat treatments with at least 25% reduction in section.

[0076] More particularly, after this production of said alloy blank, and before the deformation-heat treatment sequences, in an additional step, a surface layer of ductile material taken from copper, nickel, cupro-nickel, cupro-manganese, gold, silver, nickel-phosphorus Ni-P and nickel-boron Ni—B, or the like is added to the blank to facilitate shaping into a wire shape during deformation. And, after the deformation-heat treatment sequences or after the winding step, the wire is stripped of its layer of ductile material, in particular by chemical attack.

[0077] Alternatively, the surface layer of ductile material is deposited so as to form a spiral spring whose pitch is not a multiple of the thickness of the blade. In another variant, the surface layer of ductile material is deposited so as to form a spring whose pitch is variable.

[0078] In a particular horological application, ductile material or copper is thus added at a given moment to facilitate shaping into a wire shape, so that a thickness of 10 to 500 micrometres remains on the wire with the final diameter of 0.3 to 1 millimetres. The wire is stripped of its layer of ductile material or copper in particular by chemical attack, then is rolled flat before the manufacture of the actual spring by winding.

[0079] The supply of ductile material or copper can be galvanic, or else mechanical, it is then a jacket or a tube of ductile material or copper which is adjusted on an alloy bar with a large diameter, then which is thinned during the steps of deformation of the composite rod.

[0080] The removal of the layer is in particular possible by chemical attack, with a solution based on cyanides or based on acids, for example nitric acid.

[0081] The final heat treatment is carried out for a duration comprised between 1 hour and 200 hours at a temperature comprised between 300° C. and 700° C. More particularly, the duration is comprised between 5 hours and 30 hours at a holding temperature comprised between 400° C. and 600° C. During this final heat treatment, the precipitation of the alpha phase is finalised. In the presence of hafnium and/or zirconium, the final treatment time can be reduced by a few hours with typically a precipitation time comprised between 4 and 8 hours at a holding temperature comprised between 400° C. and 600° C.

[0082] By a suitable combination of sequences of deformation and heat treatment, it is possible to obtain a very fine microstructure, which is in particular nanometric, composed of the beta phase of niobium, tantalum and/or vanadium and of the alpha phase of titanium, and zirconium and/or hafnium if the alloy contains one or two of these last two elements. This alloy combines a very high elastic limit, greater than at least 500 MPa and a modulus of elasticity greater than or equal to 100 GPa. This combination of properties is well suited for a spiral spring. In addition, this alloy according to the invention can easily be covered with ductile material or copper, which greatly facilitates its deformation by drawing.

[0083] An alloy of an at least ternary type including niobium, titanium, tantalum and/or vanadium of the type selected above for implementing the invention also has an effect similar to that of “Elinvar”, with a practically zero thermo-elastic coefficient in the range of temperatures commonly used in watches, and adapted for the manufacture of self-compensating spirals.