Springs
Springs are elastic
members that exert forces, or torques, and absorb energy,
which
is usually stored and later released. The force produced by a spring can be
compressive
or tensile and linear or radial.
Springs are
usually,
but not necessarily, made of metal. Plastics can be used when loads are
light.
Modern structural composites are being introduced for some
applications
requiring minimum spring mass. Blocks of rubber often constitute springs, as
in
bumpers and in vibration isolation mountings of various machines such
as
electric motors and internal combustion engines. Pneumatic springs of
various
types take advantage of the elastic compressibility of gases, as compressed
air
in automotive "air shocks" and as hermetic ally sealed high-pressure
nitrogen gas in the hydro-pneumatic suspensions of French Citroen
automobiles.
For applications requiring compact springs providing very large forces
with
small deflections, hydraulic springs have proved effective. These work on
the
basis of the slight compressibility of liquids, as indicated by their
bulk
modulus of elasticity. Product cost can sometimes be reduced by designing
the
required elasticity into other parts, rather than making those parts rigid
and
adding a separate spring.
Springs can be
classified
by the direction and nature of the force exerted when they are
deflected.
Several types of spring are listed in Table 1 according to the nature of
force
or torque exerted. The principal characteristics of various classes of
springs
are summarized in Table 2.
Table 1
Classification of springs according to
the
nature of force or torque exerted
|
Actuation
|
Type of spring
|
|
Compressive
|
Helical compression
springs
Belleville springs
Flat springs, e.g. cantilever or leaf springs
|
|
Tensile
|
Helical extension
springs
Flat springs, e.g. cantilever of leaf springs
Drawbar springs
Constant force springs
|
|
Radial
|
Garter springs
Elastomeric bands
Spring clamps
|
|
Torque
|
Torsion springs
Power springs
|
Table 2 Principle characteristics of a variety
of
types of spring
|
Type of spring
|
Principle
characteristics
|
|
Helical compression
springs
|
These are usually
made from round wire wrapped into a straight cylindrical form with a
constant
pitch between adjacent coils
|
|
Helical extension
springs
|
These are usually
made from round wire wrapped into a straight cylindrical form but with
the
coils closely spaced in the no -load condition. As an axial load is
applied
the spring will extend but resisting the motion
|
|
Drawbar springs
|
A helical spring is
incorporate into an assembly with two loops of wire. As a load is applied
the
spring is compressed in the assembly resisting the motion
|
|
Torsion springs
|
These exert a
torque
as the spring id deflected by rotation about their axis. A common example
of
the application of a torsion spring is the clothes peg
|
|
Leaf springs
|
Leaf springs are
made from flat strips of material and loaded as cantilever beams. They
can
produce a tensile or compressive force depending on the mode of loading
applied
|
|
Belleville springs
|
These comprise
shallow conical discs with a central hole
|
|
Garter spring
|
These consist of
coiled wire formed into a continuous ring so that they can exert radial
inward force when stretched
|
|
Volute springs
|
These consist of a
spiral wound strip, that functions in compression. They are subject to
significant friction and hysteresis
|
Compression Spring
Extension Spring
Torsion Spring
Types
and configurations and spring action:
|
|
Helical
Compression
Round and Rectangular Wire
|
|
Push
- wide load and deflection range - constant rate.
Push - wide load and deflection range.
Conical springs can be made with minimum
solid height and with constant or increasing rate.
Barrel, hourglass, and variable pitch
springs used to minimize resonant surging and vibration.
|
|
|
Spring Washer
Column 1:
1)Belleville
2)Wave
3)Slotted
Column 2:
4)Finger
5)Curved
|
 
|
1)
Push - high loads, low deflections - choice of rates (constant,
increasing or
decreasing)
2) Push - Light Loads, low deflection-uses
limited radial space.
3) Push - Higher deflections than
bellevilles.
4) Push - for axial loading of bearings.
5) Push - uesd to absorb axial end play.
|
|
|
Volute
|
|
Push
- may have inherently high friction damping.
|
|
|
Beam
1) Cantilever, Retangular Section
2) Cantilever, Trapezoidal Section
3) Simple Beam
|
1
2
3
|
Push
or pull - wide range of loads, low dflection range.
|
|
|
Helical Torsion
Round or Rectangular Wire
|
|
Twist
- constant rate.
|
|
|
Spiral
1) Hairspring
2) Brush
|
1
2
|
Twist
Twist or Push
|
|
|
Constant Force Spring Motor
Level Torque
|
|
Twist
- exerts close-to-constant torque over many turns.
|
|
|
Helical Extension
|
|
Pull
- wide load and deflection range - constant rate.
|
|
|
Drawbar
|
|
Pull
- extension to a solid stop.
|
|
|
Constant Force
|
|
Pull
- very long deflection at constant load or low rate.
|
|
|
Retaining Rings
Round or Rectangular Wire
|
|
Pull
or push - to resist axial loads.
|
|
|
Garter Springs
1) Extension
2) Compression
|
1
2
|
1)
Pull with radial pressure.
2) Push with radial pressure.
|
Types of car suspension
springs