Extension Coil Springs
A tension coil spring is a spring with tightly wound coils and hooks at both ends. When pulled, it generates a force that tries to contract, which is used to return or hold parts. The load is expressed as initial tension plus spring rate multiplied by extension, and the spring does not begin to extend until the initial tension is exceeded. Common materials include stainless steel wire SUS304WPB and piano wire SWP-B, and end hook styles include round hooks and reverse round hooks. Some products are low-temperature annealed after forming to remove strain. Long coil springs that are cut to length are also available. They are widely used in machinery and small equipment for tension retention, such as returning levers, maintaining tension in belts and chains, and pulling back covers and dampers.
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Extension Coil Springs
D Series Extension Coil Spring
Cold-formed extension coil springs with wire diameters of 0.1 to 2.5 mm, available in SUS304WPB and SWP-B piano wire.
KS Industries Co., Ltd.
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Extension Coil Springs
DS Series Extension Coil Spring
Extension coil springs made of SUS304WPB with wire diameters of 0.5 to 2.5 mm. Model numbers for SWP material are also included.
KS Industries Co., Ltd.
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Extension Coil Springs
Long-Coil Spring (Tension)
Long-coil tension springs with outer diameter 4 mm to 26 mm, developed for wire diameters 0.26 mm to 3.2 mm based on a free length of 500 mm.
KS Industries Co., Ltd.
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Extension Coil Springs
K Series Extension Coil Spring
Extension coil spring made of SUS304WPB stainless steel wire. Covers a wide range of sizes with outer diameters of approximately 2.0 to 20 mm.
KS Industries Co., Ltd.
How to choose Extension Coil Springs
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1. Select the spring rate from the required load
The operating load equals the initial tension plus the product of the spring rate and the extension. Calculate whether sufficient force is produced both at installation and at maximum extension. Listed spring rates range from 0.128 to 16.31 N/mm, and they vary widely with wire diameter and number of coils even at the same outer diameter.
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2. Operate within the maximum allowable load and length
Extending beyond the maximum allowable load or maximum allowable length can cause permanent deformation (set) or damage to the hooks. Confirm that the load and length at maximum stroke are below the allowable values and that there is sufficient margin.
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3. Free length that fits the installation space
Free length is the distance between the inner edges of the hooks under no load. It must be shorter than the spacing of the mounting holes or pins. Because initial tension applies load from the moment of installation, this must also be considered. Listed products range from 14.5 to 500 mm, and long coil products can be cut to adjust the length.
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4. Determine outer diameter and wire diameter based on fit
The outer diameter is determined by whether it fits through the hole or the clearance inside the housing. For a given outer diameter, a thicker wire diameter produces a stiffer spring, and a thinner wire diameter produces a softer spring. Listed products have outer diameters of 2 to 34.5 mm and wire diameters of 0.1 to 3.2 mm.
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5. Select the material for the environment
SUS304WPB offers excellent corrosion resistance and is suitable for humid or wet environments. Piano wire SWP-B has high strength but is prone to rust, so check whether surface treatment is applied. The operating temperature range also depends on the material, and an example for SUS304WPB products is -30 to +200 °C.
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6. Check hook shape and orientation
The end shape, such as round hook or reverse round hook, affects compatibility with the pin or hole being engaged and determines the orientation of the hooks at both ends. Damage tends to concentrate at the base of the hook, so select a shape that avoids excessive bending when hooked.
This guide was written by AI based on the listed products' documents and specification items. Check each manufacturer's documents before adopting.