The following links have definitions with visual diagrams:
Compression Spring | Extension Spring | Torsion Spring
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 or the legs of
a torsion spring to each other.
Baking
Heating of electroplated springs
to relieve hydrogen embrittlement.
Buckling
Bowing or lateral deflection
of compression springs when compressed, related to the slenderness
ratio (Free Length/Mean Coil Diameter).
Closed ends and squared
Ends of compression
springs where pitch of the end coils is reduced so that the end
coils touch and are square with the spring axis.
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.
Compression
Spring
Helical
compression springs have applications to resist applied compression
forces or in the push mode, store energy to provide the "push".
Different forms of compression springs are produced. There are
conical, barrel, hourglass, or straight conical compression
springs. These compression springs can be made with or without
variable spacing between coils. Round wire springs can store
more energy than rectangular wire compression springs.
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Deflection (F)
Motion of spring ends
or legs under the application or removal of an external load (P).
Elastic limit
Maximum stress to which
a material may be subjected to without permanent set.
Endurance limit
Maximum stress at which
any given material will operate for a determined number of cycles
without failure for a given minimum stress.
Extension
Spring
Extension
Springs exert a pulling force or energy. They are usually close
wound with initial tension and are mostly made from round wire.
The design of the extension springs' ends are limitless. Hooks,
loops, bends, crossbars, etc.
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Free angle
Angle between the legs
of a torsion spring which is not under load.
Free length (L)
The overall length of
a spring which is not under load.
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. Proper baking is required
to relieve the hydrogen.
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
Formed wire shapes at
the ends of extension springs that provide for attachment and
force application.
Mean coil diameter (D)
Outside spring diameter
(OD) minus one wire diameter (d).
Modulus in shear or torsion
(G)
Coefficient of stiffness
for extension and compression springs. (Modulus of Rigidity)
Modulus in tension or
bending (E)
Coefficient of stiffness
used for torsion and flat springs (Young's Modulus E).
Moment (M)
A
product of the distance from the spring axis to the point of load
application, and the force component normal to the distance line. See Torque.
Open ends, not ground
End of a compression
spring with a constant pitch for each coil and the last coils
not touching adjacent coils.
Open ends ground
"Open ends, not
ground" followed by an end grinding operation.
Passivating
Acid treatment to remove
contaminants and improve corrosion resistance of stainless steel.
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 has
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).
Plain Ends
End coils of a compression spring having
a constant pitch and not squared.
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 mechanically
induced by set removal, shot peening, cold working, forming or
other means. These stresses may or may not be beneficial, depending
on the application of the spring.
Set
Permanent distortion
in length, height, or positon which occurs when a spring is stressed
beyond the elastic limit of the material.
Shot peening
Blasting the surfaces
of the spring with pellets 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; no additional deflection is possible.
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.
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 product of the distance from the spring
axis to the point of load application, and the force component
normal to the distance line. 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.
Torsion
Spring
A torsion
spring provides rotational energy or torque. You can have a
single bodied or double bodied torsion spring. You must have
three points of support and the body usually sits on a shaft
or arbor. Again, the design of the ends or legs of a torsion
spring are limitless. The stress in a torsion spring is bending.
Round wire is still the preferred material due to the cost of
rectangular wire, even though rectangular is more efficient
in bending.
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Total number of coils
(Nt)
Number of active coils (Na).
For compression springs, active coils (Na) plus the number of
dead coils forming the ends.
Wahl Factor
A factor to correct stress
in helical springs effects of curvature and direct shear.
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