How does spring stiffness affect couplings selection?

By Zak Khan

Spring stiffness affects couplings in a few ways. Because many couplings act as springs or use the concepts behind springs in their construction and operation, spring stiffness affects their selection.

When a coupling experiences a load in a direction that places it in tension or compression, its spring stiffness comes into effect. This is usually described by using Hooke’s Law. This law relates the force and displacement of a spring using its spring constant. This value varies for different materials. Hooke’s law does not work for every displacement and load situation because materials are not always perfectly elastic in every load condition. Nevertheless, it works well for the kinds of conditions most couplings operate in.

If the coupling is expected to find use in situations that involve compression or tension, then the relationship governing their expansion and contraction is F=kX. Where X is the displacement of the coupling or spring, k is the spring constant and F is the force applied. The units are either metric (meters and Newtons) or American (pounds-force and feet). Rearranging this equation gives =F/k . This is useful in systems using couplings because knowing the force and spring constant, it is simple to find the expected amount of displacement the coupling will experience. Because this is a linear relationship, to stretch a coupling twice as far requires twice as much force and so on.

When engineers select couplings, a using Hooke’s law to quickly check if the amount of displacement is acceptable can help determine if a certain coupling is right for a system or not. While not a perfect description of spring behavior, for must use cases, this calculation provides a simple check that can prevent headaches in the future.