Most extension springs are wound with initial tension. This is an internal force that holds the extension spring's coils together. The measure of the initial tension is the load necessary to overcome the internal force and begin coil separation. Unlike a compression spring that has zero load at zero deflection, an extension spring can have a preload at zero deflection (see graph). This built-in load, called initial tension, can be varied within limits, decreasing as the spring index increases.
Note that there is a range of stress (and, therefore, force) for any extension spring index that can be held without problems. If the designer needs an extension spring with no initial tension, the spring should be designed with space between the coils. Read more on initial tension.
Initial Tension (P1) is determined by extending the extension spring to a given length (L1) ensuring coil separation. The spring then is extended an equal distance to (L2). The amount of initial tension is equal to two (2) times the load achieved at (L1) minus the load at (L2). The formula for Initial Tension Simplified is (Pi) = 2P1 - P2.
While we have listed some of the most common sizes, materials and manufacturing specifications, Newcomb Spring provides completely customized production on all extension springs.
If you don't see the extension spring you need listed here, don't hesitate to contact us. Whatever your needs - Newcomb Kan-Do It!
Newcomb Spring extension springs can be produced with a variety of ends types, all of which can vary in distance from the spring body. We match all end types to your order specifications, and can change end hook shapes based on customer needs. As one of the industry's leading extension spring manufacturers, we recommend discussing your requirements with a Newcomb sales engineer who can verify manufacturing capabilities and will work to keep your production costs as low as possible.
Stresses on an extension spring’s ends are often higher than the stress on a spring’s body. A minimum bend radius of 1-1/2 times the wire diameter is recommended for extension springs. Designs should ensure the end’s torsional stress does not exceed 40-50% of the tensile strength and the end’s bending stress does not exceed 75% of the tensile strength.
As a custom extension spring manufacturer, Newcomb Spring can produce a wide variety of extension spring (tension spring) shapes, sizes and designs. Using material sizes from .007 to .625 inches in wire diameter, all Newcomb extension springs are precision manufactured to meet even the strictest order requirements.
We produce extension springs with varying body lengths, widths, and a virtually unlimited variety of end types. With over a century of spring design and manufacturing experience, we can provide design assistance on your extension spring order, helping lower production costs and review your part's fit and function
Below are just a small selection of the extension spring shapes we have produced, including:
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