What Volute Springs Are and Their Usages

All volute springs work like a conical compression spring. They consist of tapered metal strips wound on flat and each turn (coil) telescopes inside the preceeding one.

Normally there is some friction between the coils. This could be an advantage for damping vibration or absorbing impact energy.

When you think aboout spring fatigue you must consider the rubbing between the coils. This rubbing may introduce a stress concentration leading to failure.

For long life you must design with space between the coils.

These springs are preferred over normal helical springs because of their-

superior lateral stability
non-linearity of their load/deflection curve

The larger coils will bottom out sooner than the smaller coils. This causes an increasing rate since the gradient varies as the cube of the diameter. This is a good feature for shock absorbers.

If you want all the coils to bottom out at the same time just design the part so the larger coils have a larger helix angle. This will also provide a linear load/deflection curve.

Design stresses can be determined by looking at the type of material used and considering the operating stress. volute spring

The formula shown will determine the rate when all coils are active. If the coils bottom the rate must be calculated by combining the rates of each active coil.

If a variable pitch is used the higher stress will occur in the outer coil. In this case use this diameter instead of D_i.

In variable pitch springs P must be the highest load attained. This takes into account the increased gradient that results from the bottoming of the larger coils. The higher stress always occurs in the outer coil in this case. You must use this diameter instead of D_i.

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