What is preload, and how much should be applied?

“Preload” is the amount of tension in a bolt or joint when it is first tightened. To ensure the integrity of the joint during operation, the amount of preload must exceed the expected external load that will be applied to it.

In other words, the joint has to be stronger than the force that will act on it.

Adding a spring to a bolt will increase the preload of the bolt. Since Belleville disc springs are flat conical springs, they are ideal for adding preload to bolts in limited spaces. Added in series, Bellevilles will increase preload, while requiring only minimal space.

Inevitably, bolts and joints loosen during the course of mechanical operation. Properly designed and installed, Belleville disc springs can increase preload to maintain joint integrity and endurance.