CH714494B1 - Spiral clockwork spring, in particular a barrel spring or a spiral spring. - Google Patents

Abstract

The invention relates to a method of manufacturing a spiral clockwork spring with a two-phase structure, made of an alloy of niobium and titanium, comprising the steps: - production of a binary alloy comprising niobium and titanium, with: - niobium : 100% balance; - titanium between 45.0% and 48.0% by mass of the total, - traces of components among O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, between 0 and 1600 ppm, with an accumulation of less than 0.3 % by mass; - application of alternating deformations to heat treatments to obtain a two-phase microstructure comprising a solid solution of niobium with titanium in β phase and a solid solution of niobium with titanium in α phase, the titanium content in α phase being greater than 10% by volume, elastic limit greater than 1000 MPa, modulus of elasticity less than 80 GPa; - wire drawing to obtain calenderable wire; - Calendering or ringing to form a barrel spring, in treble clef before its first winding, or straddling to form a balance spring. The invention also relates to a spiral clockwork spring with a two-phase structure, made of an alloy of niobium and titanium, comprising between 45% and 48% by total mass of titanium.

Description

Field of the invention

The invention relates to a spiral clockwork spring, in particular a barrel spring or a spiral spring, with a two-phase structure.

[0002] The invention also relates to a method of manufacturing a spiral clockwork spring.

The invention relates to the field of the manufacture of clockwork springs, in particular coil springs for energy storage, such as barrel springs or motor or striking balance springs, or oscillator springs, such as spiral springs.

Background of the invention

[0004] The manufacture of spiral energy storage springs for watchmaking must face constraints that are often incompatible at first sight: need to obtain a very high elastic limit, need to obtain a low modulus of elasticity, ease of production, especially wire drawing, excellent resistance to fatigue, held over time, low sections, arrangement of the ends: bung hook and sliding flange, with local weaknesses and difficulty in processing.

[0005] The production of spiral springs is for its part centered on the concern for thermal compensation, so as to guarantee regular chronometric performance. This requires obtaining a thermoelastic coefficient close to zero.

Any improvement on at least one of the points, and in particular on the mechanical strength of the alloy used, therefore represents a significant advance.

Summary of the invention

The invention proposes to define a new type of clockwork spiral spring, based on the selection of a particular material, and to develop the appropriate manufacturing process.

[0008] To this end, the invention relates to a spiral clockwork spring with a two-phase structure, according to claim 1.

[0009] The invention also relates to a method of manufacturing such a spiral clockwork spring, according to claim 6.

Brief description of the drawings

Other characteristics and advantages of the invention will become apparent on reading the detailed description which follows, with reference to the accompanying drawings, where: FIG. 1 shows, schematically and in plan view before its first winding, a barrel spring which is a spiral spring according to the invention; FIG. 2 shows, schematically, a spiral spring which is a spiral spring according to the invention; FIG. 3 represents the sequence of the main operations of the method according to the invention.

Detailed description of the preferred embodiments

The invention relates to a spiral clockwork spring with a two-phase structure.

According to the invention, the material of this spiral spring is a binary type alloy comprising niobium and titanium.

This alloy comprises: niobium: 100% balance; a proportion by mass of titanium greater than or equal to 45.0% of the total and less than or equal to 48.0% of the total, traces of other components among O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said trace components being between 0 and 1600ppm, and the sum of these traces being less than or equal to 0.3 % by mass.

Advantageously, this coil spring has a two-phase microstructure comprising centered cubic beta niobium and compact hexagonal alpha titanium. More particularly, this coil spring has a two-phase microstructure comprising a solid solution of niobium with titanium in β phase (centered cubic structure) and a solid solution of niobium with titanium in α phase (compact hexagonal structure), the titanium content in α phase being greater than 10% by volume.

To obtain such a structure, and suitable for the development of a spring, it is necessary to precipitate part of the alpha phase by heat treatment.

The higher the titanium content, the higher the maximum proportion of alpha phase which can be precipitated by heat treatment, which encourages the search for a high proportion of titanium. But on the contrary, the higher the titanium content, the more difficult it is to obtain only a precipitation of the alpha phase at the intersections of the grain boundaries. The appearance of intragranular Widmastatten alpha-Ti type precipitates or the intragranular ω phase makes the deformation of the material difficult, if not impossible, which is then not suitable for producing a spiral spring, and it is therefore advisable not to incorporate too much titanium in the alloy. The development of the invention made it possible to determine a compromise, with an optimum between these two characteristics close to 47% titanium by mass.

[0017] Also, more particularly, the proportion by mass of titanium is greater than or equal to 46.5% of the total.

More particularly, the proportion by mass of titanium is less than or equal to 47.5% of the total.

In an alternative, the balance at 100% of the total by mass is made by titanium, and the proportion by mass of niobium is greater than or equal to 51.7% of the total and less than or equal to 55.0% of the total.

In another variant of the composition, the proportion by mass of titanium is greater than or equal to 46.0% of the total and less than or equal to 50.0% of the total.

In yet another variant of the composition, the proportion by mass of titanium is greater than or equal to 53.5% of the total and less than or equal to 56.5% of the total, and the proportion by mass of niobium is greater than or equal to 43.5% of the total and less than or equal to 46.5% of the total.

More particularly, in each variant, the total of the proportions by mass of titanium and niobium is between 99.7% and 100% of the total.

More particularly, the proportion by mass of oxygen is less than or equal to 0.10% of the total, or even less than or equal to 0.085% of the total.

More particularly, the proportion by mass of tantalum is less than or equal to 0.10% of the total.

More particularly, the proportion by mass of carbon is less than or equal to 0.04% of the total, in particular less than or equal to 0.020% of the total, or even less than or equal to 0.0175% of the total.

More particularly, the proportion by mass of iron is less than or equal to 0.03% of the total, in particular less than or equal to 0.025% of the total, or even less than or equal to 0.020% of the total.

More particularly, the proportion by mass of nitrogen is less than or equal to 0.02% of the total, in particular less than or equal to 0.015% of the total, or even less than or equal to 0.0075% of the total.

More particularly, the proportion by mass of hydrogen is less than or equal to 0.01% of the total, in particular less than or equal to 0.0035% of the total, or even less than or equal to 0.0005% of the total.

More particularly, the proportion by mass of nickel is less than or equal to 0.01% of the total.

More particularly, the proportion by mass of silicon is less than or equal to 0.01% of the total.

More particularly, the proportion by mass of nickel is less than or equal to 0.01% of the total, in particular less than or equal to 0.16% of the total.

More particularly, the proportion by mass of ductile or copper material is less than or equal to 0.01% of the total, in particular less than or equal to 0.005% of the total.

More particularly, the proportion by mass of aluminum is less than or equal to 0.01% of the total.

This spiral spring has an elastic limit greater than or equal to 1000 MPa.

More particularly, the spiral spring has an elastic limit greater than or equal to 1500 MPa.

More particularly still, the spiral spring has an elastic limit greater than or equal to 2000 MPa.

Advantageously, this spiral spring has a modulus of elasticity greater than 60GPa and less than or equal to 80GPa.

The alloy thus determined allows, depending on the treatment applied during development, the making of spiral springs which are spiral springs with an elastic limit greater than or equal to 1000 MPa, or barrel springs, in particular when the elastic limit is greater than or equal to 1500MPa.

The application to a hairspring requires properties capable of guaranteeing the maintenance of chronometric performance despite the variation in the temperatures of use of a watch incorporating such a hairspring. The thermoelastic coefficient, also called CTE, of the alloy is then of great importance. The hardened beta phase alloy exhibits a strongly positive CTE, and the precipitation of the alpha phase, which has a strongly negative CTE, makes it possible to bring the two-phase alloy to a CTE close to zero, which is particularly favorable. To form a chronometric oscillator with a CuBe or nickel silver balance, a CTE of +/- 10.10 <-6> / ° C must be reached.

The formula which links the CTE of the alloy and the expansion coefficients of the hairspring and the balance is as follows:

The variables M and T are the rate and the temperature, respectively. E is the Young's modulus of the hairspring, and, in this formula, β and α are expressed in ° C <-1>.

CT is the thermal coefficient of the oscillator, (1 / E. DE / dT) is the CTE of the balance spring alloy, β is the expansion coefficient of the balance and α that of the balance spring.

The invention also relates to a method of manufacturing a spiral clockwork spring, characterized in that the following steps are successively implemented: (10) production of a blank in an alloy comprising niobium and titanium, which is a binary type alloy comprising niobium and titanium, and which comprises: niobium: 100% balance; a proportion by mass of titanium greater than or equal to 45.0% of the total and less than or equal to 48.0% of the total, traces of other components among O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said trace components being between 0 and 1600ppm, and the sum of said traces being less than or equal to 0.3% en masse; (20) application to said alloy of coupled sequences of deformation-heat treatment of precipitation, comprising the application of alternating deformations to heat treatments, until a two-phase microstructure comprising a solid solution of niobium with titanium in β phase and a solid solution of niobium with titanium in α phase, the titanium content in α phase being greater than 10% by volume, with an elastic limit greater than or equal to 1000 MPa, and a modulus of elasticity greater than 60GPa and less than or equal to 80GPa; (30) drawing until a wire with a round section is obtained, and rolling with a rectangular profile compatible with the entry section of a calender or of a stripping spindle or with a ring setting in the case of a mainspring; (40) treble calendering of the turns to form a barrel spring before its first winding, or straddling to form a spiral spring, or ringing and heat treatment for a barrel spring.

In particular, the application to this alloy of coupled sequences 20de deformation-heat treatment of precipitation is carried out, comprising the application of deformations (21) alternating with heat treatments (22), until obtaining of a two-phase microstructure comprising a solid solution of niobium with titanium in β phase and a solid solution of niobium with titanium in α phase, the content of titanium in α phase being greater than 10% by volume, with an upper elastic limit or equal to 2000MPa. More particularly, the treatment cycle then comprises beforehand a beta quenching (15) at a given diameter, so that the entire structure of the alloy is beta, then a succession of these coupled sequences of deformation-heat treatment of precipitation. .

In these coupled sequences of deformation-heat treatment of precipitation, each deformation is carried out with a given deformation rate between 1 and 5, this deformation rate corresponding to the conventional formula 2ln (d0 / d), where d0 is the diameter of the last beta hardening, and where d is the diameter of the hardened wire. The global accumulation of the deformations over the whole of this succession of phases brings a total rate of deformation between 1 and 14. Each coupled sequence of deformation-heat treatment of precipitation comprises, each time, a heat treatment of precipitation of the alpha phase. Ti (300-700 ° C, 1h-30h).

This variant of the process comprising a beta quenching is particularly suitable for the manufacture of barrel springs. More particularly, this beta quenching 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.

More particularly still, this beta quenching is a solution treatment, with 1 hour at 800 ° C. under vacuum, followed by cooling under gas.

To return to the coupled sequences of deformation-heat treatment of precipitation, more particularly each coupled sequence of deformation-heat treatment of precipitation comprises a precipitation treatment lasting a precipitation treatment lasting between 1 hour and 80 hours at a temperature between 350 ° C and 700 ° C. More particularly, the duration is between 1 hour and 10 hours at a temperature between 380 ° C and 650 ° C. More particularly still, the duration is from 1 hour to 12 hours, at a temperature of 380 ° C. Preferably, long heat treatments are applied, for example heat treatments carried out for a period of between 15 hours and 75 hours at a temperature of between 350 ° C and 500 ° C. For example, heat treatments are applied from 75h to 400h at 350 ° C, from 25h to 400 ° C or from 18h to 480 ° C.

More particularly, the method comprises between one and five, preferably three to five, coupled sequences of deformation-heat treatment of precipitation.

More particularly, the first coupled sequence of deformation-heat treatment of precipitation comprises a first deformation with at least 30% reduction in section.

More particularly, each coupled sequence of deformation-heat treatment of precipitation, other than the first, comprises a deformation between two heat treatments of precipitation with at least 25% reduction in section.

More particularly, after this preparation of said alloy blank, and before wire drawing, in an additional step 25, a surface layer of ductile material is added to the blank from among copper, nickel, cupro-nickel , cupro-manganese, gold, silver, nickel-phosphorus Ni-P and nickel-boron Ni-B, or the like, to facilitate wire forming by drawing and drawing and rolling. And, after wire drawing, or after rolling, or after a subsequent calendering or stretching operation, or even ringing and heat treatment in the case of a barrel spring, the wire is freed from its layer of ductile material. , in particular by chemical attack, in a step 50.

For the barrel spring, it is in fact possible to carry out the production by ringing and heat treatment, where the ringing replaces the calendering. The barrel spring is still generally heat treated after ringing or after calendering.

A spiral spring is, for its part, generally still heat-treated after slipping.

More particularly, the last phase of deformation is carried out in the form of a flat rolling, and the last heat treatment is carried out on the calendered or ringed or estrapadé spring. More particularly, after drawing, the wire is rolled flat, before the manufacture of the spring proper by calendering or slipping or ringing.

In a variant, the surface layer of ductile material is deposited so as to constitute a spiral spring, the pitch of which is not a multiple of the thickness of the blade. In another variant, the surface layer of ductile material is deposited so as to constitute a spring whose pitch is variable.

In a particular horological application, ductile or copper material is thus added at a given time to facilitate the shaping of the wire by drawing and drawing, so that there remains a thickness of 10 to 500 micrometers on the wire to the final diameter of 0.3 to 1 millimeters. The wire is stripped of its layer of ductile or copper material in particular by chemical attack, then is rolled flat before the manufacture of the spring itself.

The supply of ductile or copper material can be galvanic, or else mechanical, it is then a jacket or a tube of ductile or copper material which is fitted to a bar of niobium-titanium alloy with a large diameter, then which is thinned during the stages of deformation of the composite bar.

Removal of the layer can in particular be carried out by chemical attack, with a solution based on cyanides or based on acids, for example nitric acid.

The invention thus makes it possible in particular to produce a coil spring made of a niobium-titanium type alloy, typically containing 47% by mass of titanium (46-50%). By a suitable combination of deformation and heat treatment steps, it is possible to obtain a very fine, in particular nanometric, two-phase lamellar microstructure, comprising a solid solution of niobium with titanium in the β phase and a solid solution of niobium with titanium in the α phase, the titanium content in the α phase being greater than 10% by volume. This alloy combines a very high elastic limit, greater than at least 1000 MPa, or greater than 1500 MPa, or even 2000 MPa on wire, and a very low modulus of elasticity, of the order of 60Gpa to 80GPa. This combination of properties works well for a barrel or hairspring. This niobium-titanium type alloy can easily be covered with ductile material or copper, which greatly facilitates its deformation by drawing.

Such an alloy is known and used for the manufacture of superconductors, such as magnetic resonance imaging devices, or particle accelerators), but is not used in watchmaking. Its fine and two-phase microstructure is sought after in the case of superconductors for physical reasons and has as a welcome side effect an improvement in the mechanical properties of the alloy.

An alloy of the NbTi47 type is particularly suitable for the production of a barrel spring, and also for the production of spiral springs.

A binary type alloy comprising niobium and titanium, of the type selected above for the implementation of the invention, is also capable of being used as a spiral wire, it has an effect similar to that of the "Elinvar", with a thermoelastic coefficient practically zero in the temperature range of usual use of watches, and suitable for the manufacture of self-compensating balance-springs, in particular for niobium-titanium alloys with a mass proportion 40%, 50%, or 65% titanium.

The selection of composition according to the invention was also imposed, moreover, for the superconducting application, and is favorable because of the titanium content, which avoids the drawbacks: alloys too loaded with titanium, where a martensitic phase appears, and where shaping difficulties are encountered; alloys that are too low in titanium, which result in less alpha phase during the heat treatment (s) of precipitation.

The shaping of the lace of a spiral spring involves avoiding high titanium alloys, and the need to achieve thermal spring compensation involves avoiding low titanium alloys.

Claims (6)

1. Clockwork spiral spring with a two-phase structure, characterized in that the material of said spiral spring is a binary type alloy comprising niobium and titanium, and which comprises: - niobium: 100% balance, - a proportion by mass of titanium greater than or equal to 45.0% of the total and less than or equal to 48.0% of the total, - traces of other components among O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said trace components being between 0 and 1600 ppm, and the sum of said traces being less than or equal to 0.3 % by mass; said coil spring being further characterized in that it has a two-phase microstructure comprising a solid solution of niobium with titanium in β phase and a solid solution of niobium with titanium in α phase, the content of titanium in α phase being greater at 10% by volume. 2. Spiral spring according to claim 1, characterized in that the proportion by mass of titanium is greater than or equal to 46.5% of the total. 3. Spiral spring according to claim 1, characterized in that the proportion by mass of titanium is less than or equal to 47.5% of the total. 4. Spiral spring according to one of claims 1 to 3, characterized in that said spiral spring is a barrel spring. 5. Spiral spring according to one of claims 1 to 3, characterized in that said spiral spring is a spiral spring. 6. A method of manufacturing a spiral clockwork spring, characterized in that the following steps are successively implemented: - preparation of a blank in a binary type alloy comprising niobium and titanium, and which comprises: - niobium: 100% balance, - a proportion by mass of titanium greater than or equal to 45.0% of the total and less than or equal to 48.0% of the total, - traces of other components among O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said trace components being between 0 and 1600 ppm, and the sum of said traces being less than or equal to 0.3 % by mass; - execution of a treatment cycle comprising beforehand a beta quenching at a given diameter, so that the entire structure of the alloy is beta, then application to said alloy of a succession of coupled sequences of deformation-heat treatment of precipitation, comprising the application of alternating deformations to heat treatments, until a two-phase microstructure is obtained comprising a solid solution of niobium with titanium in the β phase and a solid solution of niobium with titanium in the α phase, the α-phase titanium content being greater than 10% by volume, with an elastic limit greater than or equal to 1000 MPa, and a modulus of elasticity greater than 60GPa and less than or equal to 80GPa; - drawing until a wire of round section is obtained, and rolling with a rectangular profile compatible with the entry section of a calender or of a slitting spindle or with a ring setting; - Treble calendering of the turns to form a barrel spring before its first winding, or slipping to form a spiral spring, or ringing and heat treatment for a barrel spring.