Regular Extension Springs

Extension springs are helical coil springs with tightly wound helical wire coils, designed to resist tension forces. They elastically deform as they absorb tension loads and displacements. As the name suggests, they extend in length upon loading as the coils separate. They store energy by resisting external pulling forces applied to the ends of the spring because the separation of the spring coils during extension creates a force that opposes the direction of the extension.

Extension springs attach to components that move away from each other along a single straight axis. The extension action creates a stored energy that generates a counterforce opposing the direction of extension, pulling the spring back to its original length upon unloading.  

Applications

Extension springs are found in mechanisms and components that move away from each other along a straight axis and require an axial pulling or return force.

For example, in a trampoline, the extension springs lining the perimeter of the trampoline extend under the weight of the jumper, and produce a counterforce upon unloading that propels the trampoline mat upward. Using the sample principles of operation, medical-grade stainless steel extension springs operate within medical devices such as stretchers, surgical lifts, and surgical instrumentation.

Custom extension springs can be configured to fit applications, such as industrial machinery or exercise equipment that require large load magnitudes or precision displacement control. High-performance custom extension springs are engineered into safety-critical aerospace components like landing gear door actuation systems.

Key Specifications

Generally, a few unique geometric features define extension springs, such as the Wire Diameter, Outside Diameter (OD), End Type, and Length inside Hooks (LIH). The extension spring’s Spring Rate parameter is a function of the wire diameter, outside diameter, and spring material. It is denoted in units of lb/in, representing the force required to extend the spring by 1 in.

Other performance specifications include Maximum Deflection, which is the maximum recommended length of the spring at maximum recommended extension, as well as Initial Tension, which is a measure of the force needed to move a helical coil to achieve the minimal coil separation required to observe light passing through the coils.

High carbon steel, such as music wire or spring steel, is commonly used for extension springs because they have excellent elasticity, durability, and strength, even under cyclic loading applications. In contrast, stainless steel springs are found in applications that require additional corrosion resistance. 

Extension springs can also receive additional surface coating treatments to increase corrosion resistance, such as plating or passivation, in addition to post-forming heat treatments to increase strength and hardness.  

Benefits

Extension springs provide repeatable displacement and precision return force control in tension applications where linear mechanism motion control is required. They offer smooth performance under static or dynamic loading profiles across a wide range of applications and markets.  

Dozens of varieties of extension springs for sale are available across many standard sizes and materials, as well as numerous customization options, including large wire diameters and customizable end types, such as hooks or loops.  Rapid order fulfillment times meet your tight development and procurement constraints.

More Tools
Extension Spring Selection Guide & Technical Information
Learn More About Extension Springs

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