Extension Springs
The ends of extension springs are typically hooked or loop-shaped. One end of the spring is fixed, while the other is pulled to store energy. When the applied force is released, the spring uses this stored energy to return to its original length by exerting a tensile (pulling) force.
Extension springs are generally manufactured as preloaded and close-coiled. To prevent failures due to bending or torsional stress at the hooks, critical shear stress levels must be carefully analyzed. Hooks should be free from notches, small radii, or cross-section reductions that may cause stress concentration and fracture.
Extension springs, also known as closed-coil springs, vary according to hook types. Hooks can be formed from the spring’s own material or produced separately from different materials and designs. This allows for various configurations such as reduced (necked) extension springs or pinned extension springs.
In these types of springs, the hook wire diameter should be larger than the spring wire diameter. Under normal conditions, an extension spring should be able to extend to at least its closed length without deformation. The
