Extension spring calculator
Calculate the rate, initial tension and maximum load of extension springs with hooks. Enter the dimensions and the hook-to-hook length.
Formula
Simboli
Esempio calcolato
Calcolato dallo stesso motore del calcolatore sopra, con i valori iniziali del modulo.
Extension springs work under pull load and carry an initial tension that must be overcome before the coils separate.
The tool estimates initial tension from geometry and validates that the hooks fit within the overall length.
Hooks are usually the weak point: bending stress at the loop limits the load before the spring body does. The full designer computes that limit for each hook style.
Come misurare la molla
- Measure the wire diameter (d) on the body, not on the hook.
- Measure the outer diameter (OD) across the closed coils.
- Measure the hook-to-hook length (end to end, inside the hooks) with no load.
- Count the body coils. On extension springs every body coil is active.
- Identify the hook style: machine loop, crossover loop, side loop, extended hook or swivel eye.
Moduli e densità dei materiali
| Materiale | Modulo di taglio G | Modulo elastico E | Densità |
|---|---|---|---|
| Acciaio al carbonio (MW) | 11.5 × 10⁶ psi (79.3 GPa) | 29.5 × 10⁶ psi (203.4 GPa) | 7.85 g/cm³ |
| Inox 302 (SS302) | 10.0 × 10⁶ psi (69.0 GPa) | 28.0 × 10⁶ psi (193.0 GPa) | 7.90 g/cm³ |
| Inox 17-7 PH (SS177) | 11.0 × 10⁶ psi (75.8 GPa) | 29.4 × 10⁶ psi (203.0 GPa) | 7.81 g/cm³ |
| Inox 316 (SS316) | 10.0 × 10⁶ psi (69.0 GPa) | 28.0 × 10⁶ psi (193.0 GPa) | 7.98 g/cm³ |
| Temprato in olio (OT) | 11.2 × 10⁶ psi (77.2 GPa) | 29.5 × 10⁶ psi (203.4 GPa) | 7.85 g/cm³ |
| Cromo-silicio (CS) | 11.2 × 10⁶ psi (77.2 GPa) | 29.5 × 10⁶ psi (203.4 GPa) | 7.85 g/cm³ |
| Trafilato duro (HD) | 11.5 × 10⁶ psi (79.3 GPa) | 29.5 × 10⁶ psi (203.4 GPa) | 7.85 g/cm³ |
| Bronzo fosforoso (PB) | 6.0 × 10⁶ psi (41.4 GPa) | 14.9 × 10⁶ psi (103.0 GPa) | 8.86 g/cm³ |
| Rame berillio (BC) | 7.0 × 10⁶ psi (48.3 GPa) | 18.6 × 10⁶ psi (128.0 GPa) | 8.25 g/cm³ |
| Cromo-vanadio (CV) | 11.2 × 10⁶ psi (77.2 GPa) | 29.5 × 10⁶ psi (203.4 GPa) | 7.85 g/cm³ |
Domande frequenti
What is initial tension in an extension spring?
It is the force wound into the spring that holds the coils closed. The spring only starts to extend once the load exceeds that force, so F = IT + k·x.
How do I measure the rate of an extension spring?
Measure the force at two different lengths and divide the force difference by the travel difference. Using two points cancels initial tension out of the math.
Do hooks affect the strength of the spring?
Yes. The loop concentrates bending stress and typically fails before the body. Extended hooks and swivel eyes change both the usable length and the load limit.
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