Extension springs, or helical extension springs, store energy and exert a pulling force. They’re often made with round wire and are close-wound with initial tension. Applications include tape cassette players, garage doors, balance scales, and automatic washing machines.

Extension springs are used when there is a pulling force involved. Loops or hooks are used on the ends to ensure a secure hold.

With our full looping capabilities cost and lead time is reduced without the need of secondary operations. Electronic probes and sensors on machines ensure tolerances and loop positions are to print specification.

Extension springs are stressed in torsion in the body. The design is similar to that of compression springs with a few exceptions:

• Most extension springs are coiled with initial tension.
• These do not have a solid stop to prevent overloading, thus stress levels are usually lower than for compression springs.

Initial tension is equal to the minimum force required to separate adjacent coils. The amount that can be put into a spring depends on its index, material, manufacture method, and post-coiling stress relief treatment. Small diameter music wire is able to support higher levels of this than a lower strength material like large diameter hard-drawn wire. The higher the spring index, the less initial tension it will have. To have a spring with no
initial tension, it must be designed with space between the coils.

At no extra cost to the customer we can provide:
• Technical specifications at your request (i.e. tolerances for critical dimensions, proper size and type of material, etc.)
• SPC data on production runs.
• Design support and problem solving to ensure functionality of product at the most effective cost.