Materials are held together through the compressive force of a bolt-nut combination. The nut’s threads act with the screw’s threads to apply force to the fastener, working on both ends. The resulting tension is referred to as Bolt Preload. To put it simply, it is the compression produced by the tightening of a nut against a bolt.
The amount of weight that is placed on a bolt is, naturally, limited to how much it is capable of withstanding before coming apart. However, when tightened against a material, force is distributed through the material such that the bolt only takes a certain part of the load upon itself. However, it can hold more with the right preload.
Distinguishing the Terms
Load refers to the level of force acting upon a fastener assembly.
Preload is the compression required to distribute the force of a load throughout an assembly.
Working Load is the load taken by the assembly at the time when it is to perform.
Bolt Preload is a term that refers to the tension created when a nut works with a bolt to hold together two materials. As the tension hits the optimal preload, the working load acting on a bolt is distributed across the assembly, in order to prevent the bolt from bearing the complete load.
The Role of Bolt Preload Cannot be Overlooked
A fully tightened bolt is allowed to survive in a system where a loose assembly would easily come apart. Upon tightening, the bolted joint serves as a conduit for the force to distribute itself through the materials. Hence, the assembly bears only a part of the working load force. Preload is especially useful for rigorous applications where bolts are unlikely to survive. Bolted joints are strengthened because of the preload.
The Importance of Preload
If not for bolt preload, all of the burden would be shifted to the bolt to hold the weight. The introduction of the preload ensures that less number of bolts are needed, with the support plates playing an important role in holding the load. However, you should be certain that the working load is less than the preload of the bolts to ensure the support plates, and consequently, the bolt, doesn’t fail.
Preload is an essential concept in larger mechanical and high-performance instruments such as Telescopes. It helps raise the natural frequency of a system, safeguarding it against external disruptions. It helps you avoid buckling in case of changes in the stress caused by shifts in the position.
