A constant force spring (also referred to as power springs or constant torque springs) is a roll of pre-stressed strip that exerts a nearly constant restraining force to resist uncoiling. The force is constant because the change in the radius of curvature is constant. This is true if the change in coil diameter due to buildup is disregarded. Long extension capabilities, constant torque, and a virtual absence of intercoil friction have led many designers to specify constant force springs in such applications as brush springs for motors, counterbalance springs for window sashes, and carriage return springs for typewriters.
Constant force springs are used to drive mechanisms for timers, movie cameras, and cable retractors. It is recommended to leave at least two wraps of the spring coiled at all times during use. The cycle life is approximately 2000 cycles.
We specialize in the production of constant force springs that can be used for several applications, many times as motor or power springs, but are found most often in POP (point-of-purchase) displays and other product merchandising units. Some examples include electronic, cosmetic, pharmaceutical, and food or beverage displays.
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CUSTOM MANUFACTURING
Custom Constant Force Springs
We produce several springs with standard end fittings; however, if none of these suit your needs, we are happy to custom design an end fitting for your specified application. From a few springs, to millions, we ship in any quantity and offer some of the fastest lead times in the industry.
If you would like to request a free sample kit to test our Constant Force Springs for your design or application or coordinate shipping an example of your existing trays and product for us to assist in making a recommendation, fill out our Custom Quote form.
Select request a quote to send us your specs or configure a spring.
Constant Force Springs Manufacturing
MW is a leader in the spring manufacturing industry. We provide standard and specialty processes to ensure your requested product meets your goals for quality and aesthetics. Some examples include heat treating, CNC machining, stamping, and laser etching.
Tolerances
Width tolerances for constant force springs are dictated by strip tolerances, and diameter tolerances are determined by storage and output drum tolerances. Torque tolerances are ±10% and I.D. tolerances are ±25%. Strip thickness and length should be considered reference dimensions.
Not sure where to start? Our highly trained staff of engineers and specialists are always on hand to assist with design, development, and manufacturing.
Direction of Helix (Wind)
We can configure your variable force springs in either a left or right wind configuration to suit your specific application.
Wire Types, Specs & Size For Coiling
We stock several material widths and thicknesses and can produce constant force springs in the below specifications.
Ends
We produce springs in several end configurations. Some of the most popular requested end configurations are listed; however, customizations can be accommodated as well.
Manufacturing Services
Our variable force springs can be manufactured with a selection of commonly requested services.
Quality Standards & Certifications
At MW, we pride ourselves on creating quality products that meet or exceed industry standards. Not only do our facilities perform rigorous quality assurance testing to your specified ranges, but we also maintain several key certifications to ensure that only the best products are shipped to you.
View the full list of certifications available for our products here.
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Frequently Asked Questions about Constant Force Springs
What is a Constant Force Spring Used For?
You will frequently see constant force springs used to in the drive mechanisms for timers, movie cameras, cable retractors and other mechanical devices that require a constant amount of force.
How Do You Mount Constant Force Springs?
There are several different ways to install, or mount, constant force springs. Two of the most common methods include drum mounting and cavity mounting. With drum mounting, you will secure the spring to a rotating drum. Start by attaching the spring’s inner end to the drum using a slot, clamp, or adhesive. Wrap the spring tightly around the drum in the correct orientation, ensuring smooth and even winding.
For cavity mounting, attach the spring’s outer end to the cavity wall or a fixed point, allowing the coil to unwind freely within the cavity. Ensure proper alignment and spacing to avoid friction or interference during operation for both mounting methods. Always verify the spring is mounted per design specifications for optimal performance.
How Long Do Constant Force Springs Last?
Constant force springs are highly durable and can last for thousands of cycles when properly installed and used within their design limits. Their lifespan depends on factors such as operating environment, load, and material quality. Regular maintenance and avoiding overextension or misalignment can further extend their longevity. Most constant force springs last for approximately 2,000 cycles.
How Are Constant Force Springs Made? What Is the Constant Force of a Spring?
Constant force springs are typically made from stainless steel, coiled tightly into a flat spiral. During operation, the spring exerts a nearly uniform force throughout its extension due to the consistent curvature of the material. The constant force is a result of the spring’s design, which allows it to store and release energy evenly over its range of motion.
What Is the Difference Between a Clock Spring and a Constant Force Spring?
A clock spring, also known as a spiral spring, stores rotational energy and is used in applications requiring torque, such as steering wheels and timers. In contrast, a constant force spring provides a steady linear force during extension, making it ideal for applications like counterbalances and retractable mechanisms. The main difference lies in their energy storage and force delivery methods: rotational for clock springs and linear for constant force springs.
Shop Constant Force Spring Products
Explore our wide range of constant force spring products to find the perfect solution for your application. Request a quote for a custom design or visit our online store to learn more about our high-quality, durable springs designed to meet your needs.