Power Spring

Your compact power source

Power spring, also known as clock springs, is formed by winding a strip of material around an arbor, inside a case or retaining ring to create a compact power source.

Our engineers will help you to design and manufacture the perfect power spring for your needs. This type of spring is used in applications requiring a large torque output and provides a curved load / deflection characteristic. This will not be smooth due to friction, as the coils lose frictional contact with their neighbor. The precise curve is difficult to predict because the amount of active material is constantly changing. Also, the unwinding torque is significantly less than the winding torque.

This type of spring is closely wound and is encased within a keeper, and is generally used without prestressing, although it is possible to prestress them. To optimize the design, it is necessary to avoid an arbor diameter to strip thickness ratio that falls outside the range 15 to 25. At less than 15 the spring will take a set and at greater than 25 the maximum torque attainable is not optimized.

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Advantages and benefits of power spring

  • High torque output, a compact, wound power source for applications needing large stored energy
  • Prestressing gains, stores 25–55% more energy and delivers up to 30% more torque than a non-prestressed spring
  • Flatter torque curve, prestressed designs give a more consistent torque/deflection profile

Measures

  • Strip thickness: 0.05-1 mm (0.002-0.04 in)
  • Strip width: 1.5-100 mm (0.06-3.9 in)
  • Other dimensions as required

Materials

The choice of the right material, surface treatment and coating are critical for the final quality and safety of the product. From stainless steels to the most specific materials bought in from the best suppliers. 

  • Carbon steel
  • Stainless steel
  • Inconel  
  • Elgiloy 
  • Hastelloy 
  • Chrome silicon
  • Other materials according to your special requirements

Industries / Applications

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Go to Other industries
Go to Bike and eBike

Frequently Asked Questions

What is a power spring, and how does it store energy?

A power spring (also called a clock spring or motor spring) is a flat strip coiled inside a housing. Winding the strip in either direction stores potential energy as a torsional force. When released, the spring unwinds and drives rotation. Power springs are used wherever rotational energy storage is needed, retracting tape measures, powering mechanical watch movements, driving seatbelt retractors, and actuating motorized window shades.

What automotive applications use power springs?

Automotive power springs include seatbelt retractors (which must meet strict safety force and retraction speed requirements), powered trunk and tailgate mechanisms, and cable retraction systems. Seatbelt retractor springs are safety-critical and require full compliance with IATF 16949.

What is the difference between a power spring and a constant force spring?

Both are flat strip springs wound into a coil. A power spring delivers torque (rotational force) and is housed in a drum or housing. A constant-force spring applies a linear pulling force as the strip unrolls from its mandrel. They store energy through the same mechanism but release it differently- through torque rather than linear tension.

Are power springs used in e-mobility applications?

Yes. EV charge port door actuators, cable management systems, and folding mirror return mechanisms can use power springs. As EVs adopt more motorized and retractable exterior elements, demand for custom power springs in these assemblies increases.

Get the most out of our expertise

Our engineers work alongside our customers to find the best solution for them, applying scientific methods and knowledge accumulated over almost 50 years.

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Do you need help for your next project?

Contact our engineering and sales teams. We will help you find the best solution for your applications.

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