Hairspring Materials: Phosphor Bronze, Beryllium Copper and Stainless Steel
A material name is the starting point of a hairspring specification. Phosphor bronze, beryllium copper and stainless steel each include grades and supply conditions with different properties. The decision should consider the finished spring's geometry, torque requirements, operating environment and manufacturing route.
For purchasing, the useful question is: which exact material and condition can meet the agreed requirements for this part?
Phosphor bronze: identify the grade and temper
Phosphor bronze is a copper-tin-phosphorus alloy family used in spring applications. Material property data distinguish between grades, product forms and tempers. “Phosphor bronze” alone therefore leaves important information unspecified.
When discussing this option, provide the grade and temper from the existing drawing, if known. Include strip dimensions and the required finished-part torque. If the original specification is incomplete, ask which material conditions can be reviewed for the intended geometry.
Do not assume that all phosphor bronze strip will produce the same spring performance.
Beryllium copper: clarify the final material condition
Beryllium copper is a precipitation-hardening copper alloy family. Available options include materials intended for age hardening after forming and materials supplied in mill-hardened conditions. Grade, condition and the processing route influence the balance between strength and formability.
For an inquiry, specify the required final condition when it is known. If it is not known, provide the finished spring requirements and ask the supplier to clarify the proposed material and processing route.
A general description such as “high-strength copper” does not fully define the material or the acceptance requirements for a finished hairspring.
Stainless steel: review the grade and environment together
Stainless spring strip is available in different grades and conditions. Spring-steel comparisons distinguish properties such as formability, fatigue strength, corrosion resistance and relaxation resistance; one grade does not lead in every category.
For many austenitic spring grades, cold working is important to the mechanical properties. A grade name without its supply condition may therefore be incomplete.
Describe the temperature, humidity and any relevant chemical exposure around the installed spring. If low magnetic response is required, state that requirement separately. Do not assume that every stainless grade has the same magnetic or corrosion behaviour.
What to confirm for each material family
| Material family | Information to confirm | Question for the supplier |
|---|---|---|
| Phosphor bronze | Exact grade, temper and strip dimensions | Which specified material condition is being proposed for this spring? |
| Beryllium copper | Grade, final condition and processing route | Is the proposed condition compatible with the required forming and finished-part performance? |
| Stainless steel | Grade, supply condition and operating environment | Which grade and condition are proposed for the stated spring and environmental requirements? |
Phosphor bronze
Information to confirm: Exact grade, temper and strip dimensions
Question for the supplier: Which specified material condition is being proposed for this spring?
Beryllium copper
Information to confirm: Grade, final condition and processing route
Question for the supplier: Is the proposed condition compatible with the required forming and finished-part performance?
Stainless steel
Information to confirm: Grade, supply condition and operating environment
Question for the supplier: Which grade and condition are proposed for the stated spring and environmental requirements?
Compare finished parts under agreed conditions
A material datasheet describes material properties under stated conditions. It does not, by itself, establish the torque, accuracy or service life of a particular hairspring.
When comparing proposals, keep the drawing revision and acceptance requirements clear. Specify torque at the relevant rotation angles, dimensional tolerances and any required environmental or durability evaluation. If stress relaxation matters, define the temperature, held deflection and duration to be evaluated.
When changing a material, do not assume the existing geometry is automatically interchangeable. Review the assembled movement and agree how samples will be evaluated before approving the change.
Prepare a material discussion that leads to a useful quotation
Start with the material on the current drawing, the reason for considering alternatives and the requirements that must remain unchanged. Include any restrictions on material substitution.
If the grade is unknown, identify it as an open question. A photograph or sample may support the discussion, but it should not be presented as proof of alloy grade or temper.
You can review our materials information and use the pressure gauge hairspring specification checklist to organise an inquiry. For a discussion with Kunshan Xintao, send the available drawing, operating conditions and quantities.
Technical references
These references describe general material properties and processing considerations. They do not establish the stock, supply capability or test results of a particular finished product.