A Constant Force Spring is usually mounted by first tightly wrapping it on a drum, then attaching the free end to the loading force such as in a counterbalance application. This relationship can be reversed, however, with the free end mounted stationary and the spring itself providing the working force, as with carbon brushes in electrical apparatus.

  • The drum diameter should be 10 to 20% larger than its natural diameter.
  • One and one-half wraps should remain on the drum at maximum extension.
  • The strip becomes unstable at long extensions and should be guided to prevent twisting or kinking on recoil.
  • Idler pulleys must be larger in diameter than the natural diameter and should never be used to cause back-bending against the natural radius of curvature.

Constant force springs may be mounted without a bushing in a cavity. This mounting is simple and inexpensive; however, friction encountered can result in relatively high hysteresis. Another variation, the "rolling action unit" has its free end fixed allowing the coil to push against a movable member.

Multiple mounting can be used to increase force. Constant force springs mounted back-to-back make the sum of their forces available at one point. This method also provides stable extension over long deflections. Tandem mounting makes the sum of two spring forces available at a single point but does not add stability. Pulley mounting doubles the force of a single constant force spring but reduces the cycle life. Laminar mounting, inter-winding of two or more springs as an assembly, offers the sum of their forces in a minimum of space.



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