Non-magnetic Copper Alloy Pivot Axes for Watch Movements
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Solution Overview
Problem
Conventional horological pivot axes made of martensitic carbon steels are magnetic, sensitive to corrosion, and have insufficient hardness for wear resistance, while alternative non-magnetic materials like austenitic stainless steels and hardenable bronze lack the necessary hardness and machinability for watchmaking applications.
Innovation Solution
A non-magnetic copper alloy with specific compositions (10-20% Ni, 6-12% Sn, and additional elements) is used for the pivot axes, which can be machined by chip removal and further enhanced with surface hardening or deep hardening to achieve high hardness and resistance to corrosion and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If martensitic carbon steels are used for pivot axes, then machinability and mechanical properties are improved, but magnetic sensitivity and corrosion resistance worsen
Solution Approach 1:
The invention changes the material parameters by using a copper-based alloy with specific composition (6-12% Sn, 0.5-5% Ni, 0.5-2% Zn, 0.1-1% Si, 0.03-0.15% Pb, and 0.03% max Ti) instead of traditional martensitic steel, fundamentally altering the material's magnetic properties while maintaining machinability and improving corrosion resistance
Solution Approach 2:
The invention employs a composite alloy system combining copper with multiple elements (Sn, Ni, Zn, Si, Pb, Ti) to achieve a balance of properties: non-magnetic behavior, good machinability, high corrosion resistance, and sufficient hardness for horological applications
2Object-affected harmful factors
If austenitic stainless steels are used for pivot axes, then magnetic sensitivity is improved, but hardness and wear resistance worsen
Solution Approach 1:
The invention achieves sufficient hardness (HV 200-400) through specific alloy composition and heat treatment parameters, eliminating the need for work hardening while maintaining non-magnetic properties, thus resolving the hardness limitation of austenitic steels
Solution Approach 2:
The invention utilizes phase transition during heat treatment (solution treatment followed by aging) to precipitate hardening phases within the austenitic matrix, achieving the required hardness without compromising the non-magnetic austenitic structure
3Strength
If hard layers are deposited on pivot axes, then hardness is improved, but delamination risk worsens
Solution Approach 1:
The invention extracts the need for separate hard coating layers by achieving sufficient hardness directly in the base material through alloying and heat treatment, eliminating the interface between layers and thus the delamination risk entirely
Solution Approach 2:
The invention creates a homogeneous non-magnetic copper-based alloy with uniformly distributed strengthening elements, ensuring consistent mechanical properties throughout the material without requiring heterogeneous layered structures
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 solution provides a balance shaft with reduced magnetic sensitivity, improved hardness, and enhanced corrosion resistance, enabling effective operation in watchmaking without compromising on toughness or machinability.
Implementation Method 1
The element that can be machined by chip removal is subjected to a sequence of operations comprising a solution treatment, a cold deformation and a heat treatment for hardening known as spinodal decomposition
Implementation Method 2
One way to increase the hardness of these steels is work hardening
Data Source
Figure 1~2
AI summary
The invention relates to a watch component (1) comprising at least one part (3) machined by chip removal. This part (3) is made of a non-magnetic copper alloy to limit its sensitivity to magnetic fields, said copper alloy comprising by weight between 10% and 20% Ni, between 6% and 12% Sn, X% of additional elements, where X is between 0 and 5, and the remainder Cu. The invention relates to the field of watch movements.