Terminology
ACTIVE COILS
Those coils which are free to deflect under load.
ALLOW FOR SET
Spring is supplied longer than specified to compensate for length loss when fully compressed in assembly by customer.
ANGULAR RELATIONSHIP OF 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).
CLOSED ENDS
Ends of compression springs where pitch of the end coils is reduced so that the end coils touch.
CLOSED AND GROUND ENDS
Same as with closed ends, except that the end is ground to provide a flat plane.
CLOSE-WOUND
Coiled with adjacent coils in contact.
DEFLECTION MOTION
Of spring ends or arms under the application or removal of an external load.
ELASTIC LIMIT
Maximum stress to which a material may be subjected without producing permanent set.
EXPANDED OD
Diameter of spring in compressed position.
FREE ANGLE
Angle between the arms of a torsion spring when the spring is not loaded.
FREE LENGTH
The overall length of a spring in the unloaded position.
HELIX
The spiral form (open or closed) of compression, extension and torsion springs.
HOOKS
Open loops or ends of extension springs.
HYDROGEN EMBRITTLEMENT
Hydrogen absorbed in electroplating or pickling of carbon steels, tending to make the spring material brittle and susceptible to cracking and failure, particularly under sustained loads.
HYSTERESIS
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.
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 ends of extension springs that provide for attachment and force application.
MEAN COIL DIAMETER
Outside spring diameter minus one wire diameter.
MODULUS IN SHEAR OR TORSION
Coefficient of stiffness for extension and compression springs.
MODULUS IN TENSION OR BENDING
Coefficient of stiffness used for torsion and flat springs (Young's Modulus).
MOMENT
See Torque.
OPEN ENDS, NOT GROUND
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.
PASSIVATING
Acid treatment of stainless steel to remove contaminants and improve corrosion resistance.
PERMANENT SET
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”.
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).
RATE
Change in load per unit deflection, generally given in pounds per inch. Remove Set
full compression of a spring to solid state by manufacturer when needed to prevent length loss in operation.
RESIDUAL STRESS
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.
SET
Length loss in operation due to the high stress condition of the spring.
SHOT PEENING
A cold working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life.
SOLID HEIGHT
Height of a compression spring when under sufficient load to bring all coils into contact with adjacent coils.
SPRING INDEX
Ratio of the mean coil diameter to wire diameter.
STRESS RELIEVE
To subject springs to low-temperature heat treatment so as to relieve residual stresses.
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 in 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 in foot-pounds.
TOTAL NUMBER OF COILS
Number of active coils plus the coils forming the ends.
