coiled to the straightened and back to the coiled condition. As a guide in determining size, force, and
fatigue requirements, these relationships are tabulated in the design charts on the last pages of this
section.
BACKBEND
Unless specifically designed to do so, the constant-force extension spring cannot normally be back-bent
or reverse wound without permanent deformation.
TENSILE LOAD
Normally, the spring material should not be loaded in tension by restraining the coil and increasing the
load. If it is necessary to place a stop on the travel, it should be applied in the mechanism in such a way as
to avoid using the spring itself to transmit a holding force other than that exerted by its natural re-coiling
force.
TEMPERATURE
Engineering assistance should always be requested when springs of this type are expected to operate in
temperatures in excess of 160ºF.
SPEED AND ACCELERATION
There is a limit to the speed or suddenness of the coiling and uncoiling action of this type of spring. If
the two members to be connected by the coiled-band spring are expected to approach each other or
separate at high speed or acceleration, testing may be necessary to determine whether or not the spring
will perform favorably under such conditions.
EXTENSION
A long, unsupported strip of spring material may be unstable - particularly in cases where the free end is
not properly anchored. In many cases where an extremely long stroke is required, the motor form of the
constant-force spring, see Figure 12, is recommended. Use of the constant-torque motor form permits the
use of a simple and effective cable and pulley System. Design information on the motor form of the
NEG'ATOR Spring is given in Section B.
Figure 12 In Some Applications, the Motor Form of the Coiled-Band, Constant-Force Spring is Preferred.
TORQUE
The drum and coiled body of the extension spring must be completely free to rotate. No torque load or
friction load should be applied to the spool or shaft, as the extended portion must be taken up by the coil
readily to maintain full tension. Relaxation of the extended material |
