Glossary of Spring Terminology.

Active Coils - Coils which are free to deflect under load.

Buckling - Bowing or lateral deflection of compression springs when compressed (related to the slenderness ratio).

Closed Ends -  Ends of a compression spring where pitch of the end coils are reduced so that the end coils touch.

Closed and Ground Ends - "As whith Closed Coils" but with the ends ground to a flat plain (generally for seating within an application).

Close Wound. - Coiled with adjacent coils touching.

Deflection - Motion of spring ends or legs under the application or removal of an external load.

Dead Coils - Coils at the end of a compression spring that do not contribute to the "Rate" of the spring

Endurance Limit - mMaximum stress at which any given material will operate indefinitely without failure for a given minimum stress.

Free Angle - Angle between the legs of a torsion spring when the spring is not loaded.

Free Length - The overall length of a spring in the unloaded position.

Free Angle - Angle between the legs of a Torsion Spring when spring is not loaded.

Helix - The spiral form (open or closed) of compression, extension & torsion springs.

Hooks - Open loops or ends of extension springs.

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

Initial Tension - The force that tends to keep the coils of an extension spring closed and which must be overcome before the coils start to function.

Load - The force applied to a spring that causes deflection.

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

Mean Coil Diameter - The Outside diameter of a spring minus one wire gauge.

Open Ends, Not Ground - Ends of a compression Spring with a constant pitch for each coil.

Passivating - Acid treatment of stainless steel to remove caonaminants and improve corrosion resistance.

Permanent Set - A material that is deflected so far that its elastic properties have exceeded and it does not return to its origional condition upon release of load is said to have taken a "permanent set".

Pitch - The distance from centre to centre of wire in adjacent active coils.

Rate - Change in load per unit of deflection (generally given in pounds per inch (Lb\Inch) or netwons per mm (N\mm).

Set - Permanent distortion which occurs when a spring is stresses beyond the elastic limit of the material.

Solid Height - Length of a compression Spring when under sufficient load to bring all coils into contact with adjacent coils.

Spring Index - Ration of Mean Coil Diameter to wire diameter.

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

Torque - A twistingaction in torsion springs which tends to produce rotation, equal to the load multiplied by the distance from the load to the axis of the spring body.

Total Number of Coils - Number of Active Coils plus the coils forming the ends (see Active Coils and Dead Coils).