Common Spring and Wire Form Terminology

The relative position of the plane of the hooks or loops of extension springs to each other

Heating of electroplated springs to relieve hydrogen embrittlement

Bowing or lateral deflection of compression springs when compressed, related to the slenderness ratio (L/D)

Examples of Compression Springs:

Location on extension springs where pitch of the end coils is reduced so that the end coils touch

Examples of Extension Springs

As with closed ends, except that the end is ground to provide a flat plane

See Solid Height

Coiled with adjacent coils touching

See Pitch

Motion of spring ends or arms under the application or removal of an external load (P)

Examples of Torsion Springs

Maximum stress to which a material may be subjected without permanent set

Maximum stress to which any given material will operate indefinitely without failure for a given minimum stress

Angle between the arms of a torsion spring when the spring is not loaded

The overall length of a spring in the unloaded position

The lowest inherent rate of free vibration of a spring itself (usually in cycles per second) with ends restrained

See Rate (R)

Fixturing a spring at elevated temperature to minimize loss of load at operating temperature

The spiral form (open or closed) of compression, extension, and torsion springs

Load is proportional to displacement

Open loops or ends of extension springs

See Heat setting

Hydrogen absorbed in electroplating or pickling of carbon steels, tends to make the spring material brittle and susceptible to cracking and failure, particularly under sustained loads.

The mechanical energy loss that always occurs under cyclic loading and unloading of a spring, proportional to the area between the loading and unloading load-deflection curves within the elastic range of a spring

The force that tends to keep the coils of an extension spring closed and which must be overcome before the coils start to open

The force applied to a spring that causes a deflection (F)

Coil-like wire shapes at the ends of extension springs that provide for attachment and force application

Outside spring diameter (O.D.) minus one wire diameter (d)

Coefficient of stiffness for extension and compression springs

Coefficient of stiffness used for torsion and flat springs (Young’s Modulus)

See Torque

End of a compression spring with a constant pitch for each coil

“Open ends, not ground” followed by an end grinding operation

Acid treatment of stainless steel to remove contaminants and improve corrosion resistance

A material that is deflected so far that its elastic properties have been exceeded and it does not return to its original condition upon release of load is said to have taken a “permanent set”

The distance from center to center of the wire in adjacent active coils. Recommended practice is to specify the number of active coils rather than pitch.

The ratio of the strain in the transverse direction to the strain in the longitudinal direction

See Remove set

Change in load per unit deflection, generally given in pounds per inch (or in metric, N/mm)

The process of closing to solid height a compression spring which has been coiled longer than the desired finished length, to increase the apparent elastic limit

Stresses induced by set removal, shot peening, cold working, forming or other means. These stresses may or may not be beneficial, depending on the application.

Permanent distortion which occurs when a spring is stressed beyond the elastic limit of the material

A cold-working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life

Ratio of spring length (L) to mean coil diameter (D)

Length of compression spring when under sufficient load to bring all coils into contact with adjacent coils

Ratio of mean coil diameter (D) to wire diameter (d)

See Closed and ground ends

See Closed ends

Angular deviation between the axis of a compression spring and a normal to the plane of the ends

As in Squareness of ends, except with the spring under load

The difference in operating stresses at minimum and maximum loads

To subject springs to low-temperature heat treatment to relieve residual stresses

A twisting action in torsion springs which tends to produce rotation, equal to the load multiplied by the distance (or moment arm) from the load to the axis of the spring body. Usually expressed in oz * in., lb. * in., lb. * ft., or in N * mm.

Number of active coils (n_a) plus the coils forming the ends

A factor to correct stress in helical spring’s effects of curvature and direct shear