Spring wire: what really matters.
Standard, spring rate and straightness quality — a guide for purchasing and development.
- Stainless spring wire is governed by EN 10270-3; the base material is 1.4310 — it covers around 80% of market volume.
- The spring rate is tuned to the application via strength (alloy) and surface (tribology) — the chemistry is fixed in the melt and cannot be changed afterwards.
- Decisive for processing is straightness quality: defined torsion (target: zero) can only be produced reliably in the drawing die, not corrected afterwards via rollers.
- For medical applications such as auto-injectors, demand is rising for the special spring steel 1.4568.
- BenderWire manufactures spring wire in the optimised dimension range of 0.2–6 mm.
A spring has exactly one job: store force and release it again, exactly reproducibly. Whether in a ballpoint pen, a valve, or an auto-injector that injects a medicine at the push of a button — if the wire behind it isn't right, nothing is right. This guide sorts out the materials, the standard, and the often underestimated topic of straightness quality.
The standard and the base material
Stainless spring wire is governed by EN 10270-3. By far the most important material is 1.4310 — spring-hard, high-strength, available in several analysis and strength variants: more toughness, maximum strength, or the compromise in between. Standard grades such as 1.4301 or 1.4401 can also be deliberately “tuned” towards spring properties: the standard allows ranges — setting the strength-increasing elements towards the upper limit of the standard gives spring character; at the lower limit stands better cold formability. Important: this chemistry is fixed in the melt. It cannot be changed afterwards.
Spring rate: the actual product
What is bought is wire — what is needed is a spring rate. It arises from two levers: strength (tailored via alloying elements) and surface (tuned tribologically to the application). The manufacturing method of the spring also plays a role: a spring wound over a mandrel needs different surface properties than a bent part formed in a tool.
Straightness quality: why the drawing die decides
Spring wire must run straight — with defined torsion, ideally zero. This straightness can only be produced reliably in the drawing die; it cannot be reliably corrected afterwards via straightening rollers. Every processor knows the counterexample: the “pig's tail” — a wire with a multi-axial stress state that twists on unwinding and becomes unusable in the coiling machine. BenderWire has specifically optimised its straightening capability for the 0.2–6 mm dimension range over the last twelve months.
Special case: medicine
Demand is growing strongly for the special spring steel 1.4568 — above all for ventilators and auto-injectors, where a pre-tensioned spring triggers the injection. Here, alongside the spring rate, the purity of the material counts.
Why BenderWire
We source the material ourselves — free sourcing instead of being tied to a single melter. That means: the chemistry of the melt can be tuned to the application before the first metre is drawn. From sample to series, with documented batches.
Frequently asked questions.
Which material is the standard for stainless spring wire?
1.4310 to EN 10270-3 — around 80% of market volume, in several strength variants.
What does straightness quality mean for spring wire?
The straightness of the wire with defined torsion (target: zero). It is achieved reliably only in the drawing die and determines whether the wire runs cleanly in the coiling machine.
Which spring steel for medical applications?
Often 1.4568, e.g. for auto-injectors and ventilators — high strength combined with high purity.
Can a standard steel acquire spring properties?
Yes, within the standard's limits: strength-increasing elements at the upper limit give e.g. 1.4301 spring character. The setting happens in the melt.
Which dimensions does BenderWire supply?
Optimised range 0.2–6 mm, market-standard surfaces and dimensions.
Let's discuss your application.
We advise independently and find the right wire solution together with you.