Glossary
of Spring Terminology
Active
Coils (na)
Those coils
which are free to deflect under load.
Angular
relationship of ends
The relative
position of the plane of the hooks or loops of extension springs to each
other.
Baking
Heating of
electroplated springs to relieve hydrogen embrittlement.
Buckling
Bowing or
lateral deflection of compression springs when com pressed, 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
As with
closed ends, except that the end is ground to provide a flat plane.
Closed
length
See Solid
height
Close-wound
Coiled with
adjacent coils touching.
Coils per
inch
See Pitch.
Deflection
(F)
Motion of
spring ends or arms under the application or removal of an external load
(P).
Elastic
limit
Maximum
stress to which a material may be subjected without permanent set.
Endurance
limit
Maximum
stress at which any given material will operate indefinitely without
failure for a given minimum stress.
Free angle
Angle between
the arms of a torsion spring when the spring is not loaded.
Free length
(L)
The overall
length of a spring in the unloaded position.
Frequency (natural)
The lowest
inherent rate of free vibration of a spring itself (usually in cycles per
second) with ends restrained.
Gradient
See Rate (R).
Heat
setting
Fixturing a
spring at elevated temperature to minimize loss of load at operating
temperature.
Helix
The spiral
form (open or closed) of compression, extension, and torsion springs.
Hooke's Law
Load is
proportional to displacement.
Hooks
Open loops or
ends of extension springs.
Hot
pressing
See Heat
Setting.
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 of a spring.
Initial
tension (Pi)
The force
that tends to keep the coils of an extension spring closed and which must
be overcome before the coils start to open.
Load (P)
The
force applied to a spring that causes a deflection (F).
Loops
Coil-like
wire shapes at the ends of extension springs that provide for attachment
and force application.
Mean coil
diameter (D)
Outside
spring diameter (O.D.) minus one wire diameter (d).
Modulus in
shear or torsion (G)
Coefficient
of stiffness for extension and compression springs.
Modulus in
tension or bending (E)
Coefficient
of stiffness used for torsion and flat springs (Young's Modulus).
Moment (M)
See Torque.
Open ends,
not ground
End of a
compression spring with a constant pitch for each coil.
Open ends
ground
"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 (p)
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).
Poisson's
Ratio
The
ratio of the strain in the transverse direction to the strain in the
longitudinal direction.
Preset
See Remove
set.
Rate (R)
Change in
load per unit deflection, generally given in pounds per inch. (N/mm)
Remove set
The process
of closing to solid height a compression spring which has been coiled
longer than the desired finished length, so as to increase the apparent
elastic limit.
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
Permanent
distortion which occurs when a spring is stressed beyond the elastic limit
of the material.
Shot
peening
A cold-working
process in which the material surface is peened to induce compressive
stresses and thereby improve fatigue life.
Slenderness
ratio
Ratio of
spring length (L) to mean coil diameter (D).
Solid
height (H)
Length of a
compression spring when under sufficient load to bring all coils into
contact with adjacent coils.
Spring
index
Ratio of mean
coil diameter (D) to wire diameter (d).
Squared and
ground ends
See Closed
and ground ends.
Squared
ends
See Closed
ends.
Squareness
of ends
Angular
deviation between the axis of a compression spring and a line normal to
the plane of the ends.
Squareness
under load
As in
Squareness of ends, except with the spring under load.
Stress
range
The
difference in operating stresses at minimum and maximum loads.
Stress
relieve
To subject
springs to low-temperature heat treatment so as to relieve residual
stresses.
Torque (M)
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 oz./in., lb./in., lb./ft., or in.
N/mm.
Total
number of coils (Nt)
Number of
active coils (Na) plus the coils forming the ends.
Wahl Factor
A factor to
correct stress in helical springs effects of curvature and direct shear.
![[]](servic1.jpg)
SPRING
GLOSSARY
EMAIL FOR FREE METAL DATA BOOK IF YOU'RE IN OUR FREE
* DELIVERY ZONE