Brief description

A spring is an elastic object that stores mechanical energy. Springs are typically made of spring steel. When a spring is compressed or extended from its resting position, it exerts an opposing force approximately proportional to its change in length.

Use / Function

Energy Storage: Stores potential energy to power mechanisms (e.g., mainspring in Mechanical Watches).
Regulation: Provides a restoring force for oscillators (e.g., hairspring in a Balance Wheel).
Shock Absorption: Absorbs impacts in vehicle suspensions.
Force Measurement: Measures weight or force in a Spring Scale.
Return Mechanism: Returns keys, levers, or handles to their original position.

Operating principle

Most springs obey Hooke’s Law, which states that the force ($F$) needed to extend or compress a spring by some distance ($x$) scales linearly with respect to that distance: $F = -kx$, where $k$ is the spring constant (stiffness).

Deformation: An external force deforms the material within its elastic limit.
Storage: The work done to deform the spring is stored as elastic potential energy.
Release: When the external force is removed, the spring returns to its original shape, releasing the stored energy.

How to create it

Creating a durable spring requires precise heat treatment.

Material Selection: Use high-carbon steel (Spring Steel) or work-hardened bronze.
Forming: Coil the wire around a mandrel (for coil springs) or flatten and shape it (for leaf springs).
Hardening: Heat the steel to its critical temperature (cherry red) and quench it in oil or water. The metal becomes very hard but brittle.
Tempering: Reheat the spring to a lower temperature (blue/purple oxide color) to reduce brittleness and impart toughness. This is the critical step for elasticity.

Materials needed

Essential: Spring Steel (high carbon steel).
Substitutes: Work-hardened Bronze or Brass (for non-magnetic or corrosion-resistant needs), Wood (bows), Bamboo.
Tools: Forge, pliers, mandrel, heat source for tempering.

Variants and improvements

Coil Spring: A wire wound into a helix (compression or extension).
Leaf Spring: Flat strips of metal layered together (suspension).
Torsion Spring: Stores energy by twisting (mousetraps).
Mainspring: A spiral ribbon of steel used to power timepieces.
Hairspring: A tiny spiral spring used to regulate a Balance Wheel.
Constant-force Spring: Exerts a constant force throughout its deflection.

Limits and risks

Fatigue: Repeated cycling can cause microscopic cracks, leading to failure over time.
Creep: Under constant load, a spring may slowly deform permanently (lose tension).
Elastic Limit: Stretching beyond this point causes permanent deformation.
Safety: Releasing a spring under high tension can cause injury.