Horological Spiral Spring Alloy for Low Secondary Error
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Solution Overview
Problem
Current binary Nb—Ti alloys used for watch spiral springs face challenges such as high secondary error, long production times due to titanium precipitation, and the formation of fragile martensitic phases, which affect their mechanical properties and chronometric performance.
Innovation Solution
A ternary alloy composition replacing part of niobium with tantalum or vanadium and part of titanium with zirconium or hafium, along with optional elements like tungsten and molybdenum, to reduce secondary error, accelerate precipitation, and enhance mechanical properties, while maintaining a low thermoelastic coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If binary Nb—Ti alloy is used for spiral spring, then thermoelastic coefficient is close to zero, but secondary error is high (4.5 s/d)
Solution Approach 1:
The patent uses a ternary Nb—Ti—V alloy composite material combining three elements with complementary properties. Niobium provides the base structure with positive TEC, titanium provides negative TEC through precipitation, and vanadium reduces secondary error while maintaining mechanical properties, achieving both low thermoelastic coefficient and low secondary error
Solution Approach 2:
The patent changes the chemical composition parameters by adding vanadium (5-25 wt%) to the binary Nb—Ti alloy system. This parameter change modifies the phase transformation characteristics and reduces secondary error from 4.5 s/d to within -3 to +3 s/d range, while maintaining the thermoelastic coefficient close to zero
2Reliability
If high percentage of titanium is used in Nb—Ti alloy, then precipitation occurs during fixing step, but production time increases significantly (8-30 hours)
Solution Approach 1:
Vanadium acts as an intermediary element that modifies the precipitation kinetics of titanium. It facilitates the precipitation process by creating favorable nucleation sites and diffusion pathways, enabling the same level of Ti precipitation (required for TC close to zero) to occur much faster, reducing fixing time from 8-30 hours to 2-10 hours
Solution Approach 2:
The addition of vanadium changes the thermodynamic and kinetic parameters of the precipitation process. It lowers the activation energy for titanium precipitation and increases the diffusion rate, allowing the precipitation to reach completion in significantly reduced time while maintaining the required microstructure for low thermoelastic coefficient
3Reliability
If high percentage of titanium is used in Nb—Ti alloy, then precipitation occurs during fixing step, but fragile martensitic phases form making deformation difficult
Solution Approach 1:
Vanadium changes the phase transformation parameters by suppressing martensitic transformation and promoting bainitic or pearlitic microstructures. It modifies the TTT diagram of the alloy, shifting the transformation curves to prevent fragile martensite formation while maintaining the necessary titanium precipitation for low thermoelastic coefficient, thereby preserving deformation capability
4Measurement precision
If small section spiral spring is manufactured, then chronometric performance is improved, but elastic limit is compromised
Solution Approach 1:
The ternary Nb—Ti—V alloy creates a composite microstructure with fine precipitates distributed in a ductile matrix. This composite structure provides both the strength needed for small sections and the elastic properties required for chronometric performance, overcoming the trade-off between size and elastic limit
Solution Approach 2:
The alloy exhibits local quality variations at the microstructural level, with hard Ti precipitates providing strength and elastic limit, while the softer Nb-V matrix provides ductility and energy storage capacity. This local differentiation allows small sections to maintain both high elastic limit and chronometric performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The new alloy composition significantly reduces secondary error, shortens production times, and improves the elastic limit and modulus of elasticity, ensuring stable chronometric performance and ease of deformation, with a thermoelastic coefficient close to zero, suitable for watchmaking applications.
Implementation Method 1
its composition is not optimised for the secondary error which is a measure of the curvature of the rate which is approximated above by a straight line passing through two points (8° C. and 38° C.). The rate can deviate from this linear behaviour between 8° C. and 38° C. and the secondary error at 23° C. is a measure of this deviation at the temperature of 23° C. Typically, for an NbTi47 alloy, the secondary error is 4.5 s/d whereas preferably it should be comprised between −3 and +3 s/d.
Implementation Method 2
ease of production, in particular drawing and rolling
Data Source
AI summary
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 O, 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.