Written by Jerry Ratzlaff on . Posted in Fastener

Springs are mechanical devices of flat wire or round wire that can store potential energy because of its elasticity in a spiral coil used to compress, extend, pull, or rotate using an applied force.


Spring Types


Spring Terms

  • Active coils  (\(n_a\))  -  Coils that are free to move under load.
  • Baking  -  Heating of electroplated springs to relieve hydrogen embrittlement.
  • Buckling  -  Bowing or lateral displacement of a compression spring when compressed, related to slenderness ration L/D.
  • Close wound  -  Adjacent coils are touching.
  • Closed ends  -  The ends of a compression springs with coil pitch angle reduced to touch the adjacent coil, can be one or more coils.
  • Closed and ground ends  -  Same as closed ends except the ends are ground to have a flat surface.
  • Deflection or displacement  (\(d_s\))  -  The motion of spring ends by adding or removal of an external load.
  • Extension hook  -  The hook is made from the end coil and bent at the center opening extended from the coil.
  • Free length  (\(h_f\))  -  Overall length of a spring which is not under load.
  • Initial Tension  -  A force that keep coils of an extension spring closed and must be overcome before the coils start to open.
  • Load  (\(P\))  -  The force applied to a spring that causes a deflection.
  • Number of active coils  (\(n_a\))  -  Active coils are the open wound coils exerting energy while under a load of compression, extending, or deflection.
  • Pitch  (\(p\))  -  Distance from center to center of wire in adjacent coils.
  • Plain end  -  End coils of a compression spring having a constant pitch and ends not squared.
  • Set  -  Permanent change in height, length, or position after a spring is stressed beyond material's elastic limit.
  • Shot peening  -  Blasting surfaces of spring material with steel or glass pellets to induce compressive stresses that improve fatigue life.
  • Side hook  -  The hook is made from the end coil and bent at the side opening close to the coil.
  • Solid height  (\(h_s\))  -  Length of a compression spring when under sufficient load to bring all adjacent coils into contact.
  • Spiral spring  -  Springs formed on a wound spiral plane from a flat strip or wire.
  • Slenderness ratio  -  The ratio of spring length to mean coil diameter. 
  • Spring index  (\(C\))  -  The ratio of mean diameter to wire diameter.
  • Spring rate  (\(n_s\))  -  The change in load per unit of deflection.
  • Stress relief  -  A low temperature heat treatment given to springs to relieve residual stresses produced by prior cold forming.
  • Total number of coils  (\(n_t\))  -  The sum of the number of active and inactive coils in a spring body.


Tags: Equations for Spring