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Glossary of Spring
Terminology |
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- 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.
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