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Active coils
- 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.
Blue -
See Stress relieve.
Bucking -
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 - 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
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.
Hystereis
- 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 elaastic range of a
spring.
Initial
tension (P) - 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 (E) -
Coefficient of stiffness used
for torsion and flat springs.
Modulus in
tension or bending (E) -
Coefficient of stiffness used
for torsion and flat springs.
Moment -
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 traverse 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.
Remove set
- Process of closing to solid
height a compression spring
which has been coiled longer
than the desired finish length,
so as to increase the apparent
elastic limit.
Residual
stress - Stresses included
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 normal
to the plane of the ends.
Squareness
under load - As in the
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 spring
to low-temperature heat
treatment so as to relieve
residual stress.
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.
Total number
of active coils (N) - Number
of active coils (n) 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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