— Springs
See the Spring Design calculator to compute spring rate, stress, and deflection from wire diameter, coil diameter, and number of coils.
Spring Types
| Type | Loading Direction | Typical Use | Energy Storage / Space |
|---|---|---|---|
| Compression | Axial, compressive (pushes apart) | Valves, pens, mattresses, suspension | Baseline; moderate energy density |
| Extension | Axial, tensile (pulls together) | Garage doors, trampolines, counterbalances | Similar to compression; needs hooks/loops, adds length |
| Torsion | Rotational/twisting about coil axis | Door hinges, garage doors, clothespins, clocks | High torque per volume; long fatigue life under repeated twist |
| Belleville (disc) washer | Axial, compressive | High load in small axial space — bolted joints, clutches | Highest load-per-space of the group; low deflection per disc |
| Wave spring | Axial, compressive | Bearing preload, space-constrained compression | Occupies ~30–50% of the axial height of an equivalent round-wire compression spring |
| Constant-force | Extension (uncoiling of pre-stressed flat strip) | Counterbalances, retractors, tape measures, seatbelts | Constant load over long travel in a compact rolled package |
Common Spring Wire Materials
| Material | Tensile Strength | Max Service Temp | Typical Use |
|---|---|---|---|
| Music wire (ASTM A228) | ~230–399 ksi | 250°F (121°C) | General-purpose, highest strength/fatigue life of common wires; not for corrosive/hot environments |
| Stainless steel 302/304 | ~130–325 ksi | 550°F (288°C) | Corrosion resistance, moderate heat — food/medical/marine |
| Chrome silicon | ~224–300 ksi | 475°F (246°C) | Shock/impact loads, moderately elevated temperature (valve springs) |
| Chrome vanadium | ~190–300 ksi | 425°F (218°C) | Shock loads, fatigue/impact resistance, moderate heat |
| Beryllium copper | ~160–230 ksi | 400°F (204°C) | Non-magnetic, conductive, corrosion-resistant — electronic contacts/connectors |
| Inconel X-750 | ~155–220 ksi | ~1100–1300°F (593–704°C) | High-temperature, corrosion/oxidation-resistant — aerospace, exhaust, nuclear |
Spring Index
Spring index C = D/d, where D is the mean coil diameter and d is the wire diameter. Recommended practical range: 4 ≤ C ≤ 12, with a preferred sweet spot around C ≈ 6–12. A low index (tight coil, wire nearly as thick as the coil) is difficult/expensive to form and produces high stress concentration at the wire's inner fiber. A high index (loose, "floppy" coil) becomes prone to buckling under compression and tangling with adjacent coils during handling.
Belleville Washer Stacking
| Stack Type | Disc Orientation | Effect |
|---|---|---|
| Parallel stack | Same orientation, nested, in direct contact | Increases load capacity at the same deflection (2 discs = double the load of one) |
| Series stack | Alternating (opposing) orientation, rim-to-rim/hub-to-hub | Increases deflection at the same load (2 discs = double the deflection of one) |
Series-parallel combinations (e.g. parallel pairs repeated in series) let a designer tune load-vs-deflection between the two pure cases. Both stack types should be mechanically guided (rod, sleeve, or self-centering fixture) to prevent lateral misalignment during cycling.