Spring Terminology

Spring Terminology

Active Coils (N)
Coils that are free to deflect under load

Angular Relationship of Ends Degrees
Extension and torsion springs, relates to relative end positions of loops and legs respectively.

Anneal
Process of heating the material so that it becomes ductile and soft.

Baking
Heating of electroplated springs to relieve hydrogen embrittlement

Buckling
Compression spring, lateral displacement due to loading. This effect is a function of slenderness ratio L/D

Close Wound
Generally applies to tension & torsion springs where adjacent coils touch.

Closed and Ground Ends
End coils of a compression spring are closed and ground flat. See Closed End.

Closed End
End coils of compression spring are closed by reducing the coil pitch angle until they are square with the spring axis and touch the adjacent coil.

Closed Length mm
Compression springs, see Solid Height

Coils per mm
Number of coils per length, See Pitch

Dead Coils
Compression spring, Inactive coils

Deflection (F) mm
Distance moved due to an external load

Elastic Limit
The stress point at which the wire material, if subjected to higher stress, will no longer return to its original shape. Applied to a spring, the maximum stress at a given stress ratio at which material will operate in a given environment for a stated number of cycles without failure.

Free Angle (Θ) Degrees
Torsion spring, angle between legs when not under load.

Free Length (F/L) mm
Compression spring, overall length when not under load.

Rate (R) N/mm
Ratio of load [N] to deflection [mm].

Hot Setting
A process to improve spring relaxation when operating at elevated temperatures.

Helical Springs
Wire or bar wound to form a helical coil.

Hysteresis
The loss of mechanical energy during loading and unloading whilst operating in the elastic range. Ilustrated by the area between deflection curves.

Initial Tension N
Tension springs, the magnitude of force that is required to separate closely wound coils.

Loops
Tension springs, end coil formed into hooks or loops

Mean Diameter (D) mm
The average diameter of the mass of spring material

Modulus of Rigidity (G)
Coefficient of stiffness

Young’s Modulus (E)
Ratio of Stress/Strain

Moment (M) N/m
Product of the distance (m) and load (N), from the spring axis to the point of load application. The force component is at 90 degress to the distance line.

Natural Frequency (n) Hz
Frequency is the ratio of oscillations per unit of time. The natural frequency is the lowest inherent rate of free vibration of a spring oscillating between its own ends

Patenting
Heat treatment process where carbon steel is heated above its critical temperature followed by a controlled rate of cooling to produce a fine pearlitic microstructure.

Pitch (p) mm
Distance from wire centres of adjacent coils in an open-wound spring.

Plain Ends
Generally a compression spring where end coils have a constant pitch and not squared

Plain Ends, Ground
Same as Plain Ends, except wire ends are ground square to the axis

Rate (R) N/mm
Ratio of change of Load (N) / Deflection (mm)

Relaxation
For a compression spring, it is the permanent reduction in length and is a function of material, stress and temperature. The longer the time period a spring is exposed to higher stresses and higher temperature the greater the relaxation. Springs held at a constant stress relax more than if they are cycled between that stress and a lower stress.

Residual Stress N/mm2
Mechanically induced Stress by processes such set removal, shot-peening, cold working, or forming. It may be beneficial or not, depending on the spring application.

Set
Permanent change of length, height or position after a spring is stressed beyond material’s elastic limit.

Set Point
Stress at which some arbitrarily chosen amount of set (usually 2%) occurs. Set percentage is the set divided by the deflection which produced it.

Shot-Peening
Blasting the spring wire material surface with steel or glass beeds to induce compressive stresses to improve fatigue life.

Slenderness Ratio
Helical springs, the ratio of spring length to mean diameter L/D.

Solid Height (Ls) mm
Compression spring, when loaded to bring all adjacent coils into contact and no further deflection is possible.

Spiral Springs
Springs formed from flat strip, bar or wire wound into the form of a spiral. Load applied by torque about an axis normal to the plane of the spiral

Spring Index (C)
Ratio of mean diameter to wire diameter.

Squared and Ground Ends
See Closed and Ground Ends.

Squared Ends
See Closed Ends.

Squareness
Compression spring, angular measurement of the deviation between the axis in free state and a line at right angles to the end planes.

Stress Range N/mm2
The difference between the operating stresses at minimum and maximum loads.

Stress Ratio
Ratio of Minimum stress / Maximum stress.

Stress Relief
A low temperature heat treatment process to relieve residual stresses produced when the spring is cold formed.

Tempering
A low temperature heat treatment process to relieve residual stresses produced when the spring is cold formed.

Torque (M) N/m
See Moment.

Total Number of Coils (N)
Sum of active coils and dead coils