ACTIVE COILS – Those coils which are free to deflect under load.
BAKING – Heating of electroplated springs to relieve hydrogen embrittlement.
BUCKLING – Bowing or lateral displacement of a compression spring. This effect is related to slenderness ratio L/D.
CLOSE WOUND – Adjacent coils are touching.
CLOSED AND GROUND ENDS – Same as closed ends, except the first and last coils are ground to provide a flat-bearing surface.
CLOSED ENDS – Compression spring ends with coil pitch angle reduced so they are square with the spring axis and touch the adjacent coils.
DEFLECTION – Motion imparted to a spring by application or removal of an external load.
FREE LENGTH – Overall length of a spring which is not under load.
HOOKS – Open loops or ends of extension springs.
INITIAL TENSION – A force that tends to keep coils of a closewound extension spring closed and which must be overcome before the coils start to open.
LOOPS – Formed ends with minimal gaps at the ends of extension springs.
MEAN DIAMETER – The average diameter of the mass of spring material, equal to one-half the sum of the outside and inside diameters. In a helical spring (compression), this is the equivalent to the outside diameter minus one wire diameter.
PITCH – Distance from center to center of wire in adjacent coils in a open-wound spring.
PLAIN ENDS – End coils of a compression spring having a constant pitch and ends not squared.
PLAIN ENDS, GROUND – Same as plain ends, except wire ends are ground square with the axis.
RATE – Spring gradient, or change in load per unit of deflection.
SET – Permanent change of length, height 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.
SOLID HEIGHT – Length of a compression spring when deflected under sufficient load to bring all adjacent coils into contact – no additional deflection is possible at this point.
SPIRAL SPRINGS – Springs formed from flat strip or wire wound in the form of a spiral, loaded by torque about an axis normal to the plane of the spiral.
SPRING INDEX – Ratio of mean diameter to wire diameter.
SQUARED AND GROUND ENDS – See closed and ground ends.
SQUARED ENDS – See closed ends.
STRESS RELIEF – A low temperature heat treatment given to springs to relieve residual stresses produced by prior cold forming.
TOTAL NUMBER OF COILS – The sum of the number of active and inactive coils in a spring body.