Extension and Torsion Springs

Extension and Torsion Springs store energy in a different direction from compression springs: extension springs resist pulling force along their axis, torsion springs resist rotation around their axis. Together they cover most of the return, latch and tensioning functions in mechanical products. Our extension springs are close coiled with initial tension, so the coils stay tight until a load is applied, and hook styles include machine hooks, cross-center hooks and side loops. Long slender versions are used for tensioning wires, gates and agricultural machinery; short hooked versions serve latch mechanisms, garage doors and appliances. Torsion springs are wound with legs bent to the required angle and length; single and double torsion types are standard, and complex wire forms bent from one piece of wire can replace multi-part brackets, saving assembly time in the final product. Material is SUS302 / SUS304 stainless steel or high-tensile carbon spring wire [TBC], stress relieved after coiling for a stable torque or load curve. Hook and leg positions are controlled by dedicated tooling, and load-length or torque-angle testing is documented for each batch. Surface treatments include black oxide, zinc and nickel plating for corrosion protection. We can produce customized springs according to your drawings and your requirements, processing all standard extension and torsion springs; if you only have a sample, we measure wire diameter, coil diameter, active coils, free angle and rate, then reproduce it and send a comparison report. Applications include door hinges, clothespins, levers, switches, garage doors, fitness equipment, agricultural tools and household devices. Trial quantities from a few hundred pieces are accepted so you can validate the design before committing to mass production. Extension and torsion springs are easy to get wrong at the design stage, in three predictable ways. First, initial tension: a close-coiled extension spring only starts to extend after the initial tension is overcome, so the working load must exceed it or the spring behaves like a rigid link. Second, hook stress: the hook is almost always the first part to fail, so we radius the bend and, where possible, use a cross-center hook that keeps load on the coil axis instead of bending the wire. Third, torsion leg angle: legs must be specified in the installed position, not the free position, because the spring is usually pre-wound during assembly. Tell us the installed angle and the torque at that angle, and we will design the free angle accordingly. Samples are produced with the exact wire lot that will be used in production, so measured rate matches the delivered parts.