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 Resonance is an issue for springs used in a dynamic cyclic loading environment, where the compressive force varies between two values. For example, the valve springs used in a car engine are subject to dynamic loads. By design intent, a spring is a static mechanism. However, a spring will no longer behave as a static mechanism if the frequency of operation approaches the spring's first resonant frequency. Worse, the force the spring exerts on its boundaries will tend to decrease, which could have disastrous implications for the spring assembly. In light of this, a rule of thumb for spring design is to make sure the frequency of operation is 15 to 20 times less than the first resonant frequency of the spring in question. Use this calculator to find the first resonant frequency of a compression spring when you know its spring constant and its mass. (The spring mass can be found by weighing the spring.)
Inputs
 Spring constant, k: N/m dyne/cm lbf/in Mass of spring, M: kg g lbm oz
 Lowest spring resonant frequency, fres: 296  Hz Hz kHz cpm

Equations Behind the Calculator
 The frequency of the lowest spring resonance (in Hz) is found from the equation, where k is the spring constant and M is the spring mass (see derivation). The spring mass M can be found by weighing the spring. If you do not know the mass of the spring, you can calculate it by multiplying the density of the spring material times the volume of the spring. Inserting this product into the above equation for the resonant frequency gives, which may be a familiar sight from reference books. This equation is implemented in the Compression Spring Designer calculator, which includes a definition of all its terms.
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