In our experience working with numerous customers and their diverse concepts, our representatives often learn that a spring sample is improperly utilized in a design. This misused spring prototype may work for a short time, but it will not perform long-term as well as a properly engineered solution.
The following are a few ways springs are often misused and how the situation can be resolved courtesy of Vulcan Spring’s experienced and knowledgeable custom spring engineering experts.
Winding the Inner Coil of a Constant Force Spring onto an Arbor:
A constant force spring is placed in a cavity, and the outer end is fastened to the inside diameter. An inner arbor is attached to the inner coil of the spring, usually by manipulating the inner end. The arbor then rotates, winding up the inner coils of the spring and using the torque to return the arbor to its starting position.
In this situation, a constant force spring is incorrectly used as a power spring. A constant force spring is designed to be used in a linear motion, not rotational. After discussing with one of our engineers, a properly designed power spring or Conpower® pre-stressed power spring can be created to optimize the available torque and turns. This solution will ease final assembly, provide more available turns, increase life cycles and increase torque options.
Back-Bending a Constant Force Spring:
A constant force spring is wound opposite to the coil set onto a spool to create torque.
There are subtle differences between a Conforce® constant force spring and a Contorque® constant torque spring. The main problem with back winding a Conforce® spring in this manner is that the spring could “take a set,” meaning the original coil diameter can expand once used. The result is a larger outside diameter and a loss of torque. A better design utilizes a Contorque® spring. This type of spring is designed to be wound opposite the coil set onto a recommended spool diameter. The number of turns, torque and life cycles can then be accurately calculated.
Extending a Power Spring from its Case:
A power or Conpower® spring is wound into a case. The spring’s outer end is extended out of the case and expected to retract, like how a tape measure rolls back into its case upon release. The issue with this scenario is that a spring made for rotational torque is improperly used for linear force.
There are a few ways to accomplish the linear action this situation requires. One way would be to design a Conforce® constant force spring to meet the extension, force and life cycle requirements, as the constant force spring is made for a linear extension.
In other situations, a better option may be to utilize the torque of the Conpower® spring by attaching a cable or cord of some type to the case housing the spring. When the cable is extended, the spring will wind onto an arbor, creating torque that will retract the cable when released.
A third option is to create a Contorque® spring assembly, which requires an output spool to wind the spring and cable. The advantage of this method is that the torque is relatively constant compared to the Conpower® spring.
Attaching the Inner End of a Constant Force Spring to a Spool:
A constant force spring is modified to attach the inner end to the spool. Sometimes this is done to utilize the rotation of the spool to drive a mechanism. A constant force spring is also commonly used to provide a stop for the extension of the spring.
Using the spring as a stop is not recommended, and we’ve even written a detailed blog on this concept—Springs Used as a Stopping Mechanism.
A constant force spring does not need to be attached to a spool. An external stop needs to be put into place, and the spring is designed long enough to have at least 1-1/2 wraps of material on the spool once fully extended. If torque from a spool is required, reviewing options such as a Conpower® spring or a Contorque®spring design is best.
Using a Constant Torque Spring for Extension Due to the Long Spring Length:
A stock Contorque® constant torque spring is used for a linear application to take advantage of the long length of the spring.
While the Contorque® spring will provide linear force, it is neither calculated nor controlled. This type of spring is designed and manufactured based on torque requirements. In addition, a general rule is the extended length of a constant force spring should not exceed 50X the inside diameter of the spring. If used in this manner, the Contorque® spring will exceed this rule and could twist along its extended length. A better solution for long extension would be to use a cable assembly mounted to a Contorque® Spring.
When in Doubt, Call in the Custom Spring Design Experts
Not everyone is a spring specialist, so it’s understandable when mistakes are made due to improper spring usage. Luckily, our Vulcan Engineers are spring experts, and they have the experience and knowledge to select and custom design the exact spring you need for your intended application.
Get in touch with Vulcan today, and let’s curate a custom spring to work correctly for your next design or to find out if one is already available from our collection of premade springs.Contact Us