G lossary of S pring T erms
Terms
Description
Active Coils Allow for Set
The coils that are free to deflect when under load.
Spring is supplied longer than specified to compensate for length loss when fully compressed.
Angular Relationship to Ends
The relative position of the plane of the hooks or loops of extension springs to each other.
Buckling
Bowing or lateral deflection of compression springs when compressed, related to the slenderness ratio (L/D). Ends of compression springs where pitch of the end coils is reduced so that the end coils touch.
Closed Ends
Closed & Ground Ends Same as with closed ends, except that the end is ground to provide a flat plane. Closed Length
Also called Solid Height. Height of a compression spring when under sufficient load to bring all the coils into contact with adjacent coils.
Close-Wound
Coiled with adjacent coils in contact.
Also called Pitch. The distance from center to center of the wire in adjacent active coils (recommended practice is to specify number of active coils rather than pitch).
Coils per Inch
Deflection
Motion of spring ends or arms under the application or removal of an external load. Maximum stress to which a material may be subjected without producing permanent set.
Elastic Limit
Endurance Limit
Maximum stress at which any given material will operate indefinitely without failure for a given minimum stress.
Free Length
The overall length of a spring in the unloaded position.
Gradient
Also called Rate. Change on load per unit deflection, generally given in pounds per inch or Newtons per millimeter.
Helix
The spiral form (open or closed) of compression, extension and torsion springs.
Hooks
Open loops or ends of extension springs.
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 to a spring.
Hysteresis
Initial Tension
The force that keeps the coils of an extension spring closed and which must be overcome before the coils start to open.
Load
The force applied to a spring that causes a deflection.
Loops
Coil-like wire shapes at the end of extension springs that provide for attachment and force application.
Mean Coil Diameter Modulus in Shear
Outside spring diameter (O.D.) minus one wire diameter.
Coefficient of stiffness for extension and compression springs. Modulus in Tension Coefficient of stiffness used for torsion and flat springs (Young’s Modulus). Moment End of a compression spring with a constant pitch for each coil. Open and Ground End “Open ends, not ground” followed by an end grinding operation. Permanent Set Open Ends. Not Ground
Also called Torque. 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 inch-oz., inch-pounds or foot-pounds.
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 number of active coils rather than pitch).
Pitch
Preset
Full compression of a spring to solid state by manufacturer when needed to prevent length loss in operation. Change on load per unit deflection, generally given in pounds per inch or Newtons per millimeter. Full compression of a spring to solid state by manufacturer when needed to prevent length loss in operation.
Rate
Remove Set
Stresses induced by set removal, shot peening, cold working, forming and other means. These stresses may or may not be beneficial, depending on the application.
Residual Stress
Set
Length loss in operation due to the high stress condition of the spring.
Slenderness Ratio
Ratio of spring length (L) to mean coil diameter (D).
Solid Height Spring Index Stress Range Stress Relieve Shot Peened
Height of a compression spring when under sufficient load to bring all the coils into contact with adjacent coils.
Ratio of the mean coil diameter (D) to wire diameter (d).
The difference in operating stress at minimum and maximum loads.
To subject springs to low-temperature heat treatment so as to relieve residual stresses.
A cold working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life.
Squareness of Ends Angular deviation between the axis of a compression spring and a normal to the plane of the ends. Squareness Under Load Same as Squareness of Ends, except with the spring under load. Torque
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 inch-oz., inch-pounds or foot-pounds.
Total Coils Wahl Factor
Number of active coils (n) plus the coils forming the ends.
A factor to correct stress in helical springs effects of curvation and direct shear.
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