Spring is supplied longer than specified to compensate for length loss when fully compressed in assembly by customer. Usually recommended for large quantity orders to reduce cost.
Angular Relationship of Ends
The relative position of the plane of the hooks or loops of extension springs to each other.
Blue
A thin blue film of oxide on ferrous alloys, sometimes used to indicate that the material has been stress relieved.
Baking
Heating of electroplated springs to relieve hydrogen embrittlement.
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.
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 (F).
Loops
Coil-like wire shapes at the end of extension springs that provide for attachment and force application.
Mean Coil Diameter
Outside spring diameter (O.D.) 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).
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 contaminates 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).
Change on 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 and 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.
Slenderness Ratio
Ratio of spring length (L) to mean coil diameter (D).
Solid Height
Height of a compression spring when under sufficient load to bring all the coils into contact with adjacent coils.
Spring Index
Ratio of the mean coil diameter (D) to wire diameter (d).
The difference in operating stress at minimum and maximum loads.
Stress Relieve
To subject springs to low-temperature heat treatment so as to relieve residual stresses.
Shot Peened
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 Number of Coils
Number of active coils (n) plus the coils forming the ends.