How Power Springs Work

Power springs work or function by tightly winding a strip of spring-tempered material onto an arbor housed within a circular case (keeper). When wound, the spring stores mechanical energy and releases it as torque when unwound.

As the spring unwinds, it expands toward the keeper’s maximum allowed curvature, delivering rotational force to the free-rotating portion of the assembly. This unique motion makes power springs ideal for controlled torque delivery in compact spaces.

A group of coiled power springs of varying sizes arranged on a flat surface, showcasing their tightly wound design.

However, the torque-deflection characteristics of a power spring are nonlinear. This is due to:

  • Changing amounts of active material during operation
  • Inter-coil friction
  • Hysteresis effects within the assembly

Design Guidelines for Optimal Performance

To ensure performance and durability:

  • The strip length should be less than 15,000 times the material thickness
  • The arbor diameter should be 15–25 times the thickness to reduce inter-coil friction and avoid excessive stress

It is possible to pre-stress power springs, where the strip is formed and back-wound into the case. This process can increase the number of useful revolutions from around 15 up to 35 turns, delivering more consistent torque across the operating range.

Graph showing the torque curve of a power spring, illustrating torque output versus the number of turns. The curve typically starts high, gradually levels off, and then rises again as the spring nears full extension.

Understanding the torque curve of a power spring is key to precision design. This curve highlights the spring’s torque output over its deflection range, providing predictable force for consistent performance in your application.

 

One tightly coiled power spring on a flat surface, displaying its compact and durable design.

Power Spring Applications:

Whether your application requires rotational energy or linear motion (using a pulley or cable system), our power springs can be tailored to meet your needs.

John Evans’ power springs are used across a wide range of industries:

Medical Devices

Industrial

  • Counterbalances
  • Cord retractors
  • Wind-up devices
  • Timers and escapements

Aerospace & Defense

  • Electrical/mechanical reels
  • Static discharge reels

Commercial

  • Wind-up toys
  • Timers
  • Cord and cable reels

 

3D line drawing of a power spring in its casing, with labeled dimensions including outer diameter (OD) and inner diameter (ID) of the case, as well as the spring’s width.

Power Springs (Clock Springs) – Precision-Engineered by John Evans’ Sons

John Evans’ Sons designs and manufactures high-performance power springs, also known as clock springs, for applications requiring reliable rotational energy storage.

We produce power springs from material as thin as .002″ to as thick as .080″, with widths ranging from fractions of an inch to multiple inches. Our team of expert engineers will work with you to deliver custom spring solutions that match your exact requirements.

 

Need a Custom Power Spring?

John Evans’ Sons has been delivering precision spring solutions for over 175 years. Contact our engineering department today to discuss how we can help you optimize your power spring design for performance, efficiency, and durability.

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