Self-compensating balance spring for a mechanical oscillator of a balance-spring/balance assembly of a watch movement and process for manufacturing this balance-spring
AssigneeMontres Rolex S.A.
InventorsJacques Baur, Patrick Sol, Pierre-Alain Walder
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Abstract
A self-compensating spring for a balance-spring for a balance-spring/balance assembly of a mechanical oscillator of a horological movement or of any other precision instrument, made of a paramagnetic Nb--Zr alloy containing between 5% and 25% by weight of Zr, obtained by cold rolling or cold drawing, and having a Young's modulus whose temperature coefficient (TCY) is adjustable by precipitation of Zr-rich phases in the Nb--Zr solid-solution. It contains at least 500 ppm by weight of an interstitial doping agent at least partly formed of oxygen.
Claims20
A self-compensating balance-spring for a balance-spring/balance assembly of a mechanical oscillator of a precision instrument in particular a horological movement, made of a paramagnetic Nb--Zr alloy containing between 5% and 25% by weight of Zr and having a Young's modulus whose temperature coefficient (TCY) is such that it can substantially nullify the expression ##EQU4## where ##EQU5## E Young's modulus of the oscillator spring;
- .alpha..sub.s :
- coefficient of thermal expansion of the oscillator's spring;
- and
- .alpha..sub.b :
- coefficient of thermal expansion of the oscillator's balance,
- characterized by the fact that it contains at least 500 ppm by weight of an interstitial doping agent at least partly formed of oxygen.
The balance-spring according to any preceding claim, characterised in that it further comprises between 0.01% and 5% by weight of at least one element selected from :
- Be, Al, Si, Ge, Sc, Y, La, Ti, Hf, V, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au.
Process for manufacturing a self-compensating balance-spring made of a Nb--Zr alloy comprising 5% to 25% of Zr for a mechanical balance/balance-spring oscillator of a precision instrument in particular a horological movement, wherein a bar is formed from said alloy, this bar is transformed into a wire having a diameter comprised between 0.05 and 1.5 mm by cold rolling or cold drawing in the absence of oxygen, the diameter of this wire is reduced by cold rolling or cold drawing and shaped into a ribbon suitable for the balance-spring, this ribbon is wound into the shape of a spiral and submitted to at least one heat treatment under a controlled pressure and/or controlled atmosphere to reduce the temperature coefficient of the Young's modulus (TCY) by the controlled precipitation of Zr rich phases and to define the shape of the balance-spring, characterised in that the wire contains an interstitial agent in an amount producing the controlled precipitation of Zr rich phases, and the wire thus obtained is heated between 650.degree. C. and 880.degree. C. for 1 h to 24 h, to adjust the TCY to the desired value.
Dependencies are inferred from the claim text.