Preload (engineering)
Preload is an engineering term with several meanings. In the general sense, it refers to the internal application of stress to certain mechanical systems. Fastener preload The most common usage is to describe the load applied to a fastener as a result of its being installed, i.e., before any external loads are applied (e.g., tightening the nut on a bolt). Preload in such cases is important for several reasons. First, a tightened bolt experiences only a small fraction of any external load that will be applied later, so that a fully tightened bolt can (depending on the exact application) sustain a much greater load than a loosely tightened bolt. Second, a nut that is correctly tightened will resist becoming loose under the influence of vibration, temperature cycling, etc. Bearing preload Internal stress to a bearing through application of negative clearance is known as bearing preloading. Advantages of preloading include the following: maintain axial and radial position for accurate displacements of angular movements; increase bearing rigidity; prevent sliding or gyroscope-like movements, especially with high acceleration or rotation rates; maintain relative position of bearing elements. Preloading methods include position preload and constant pressure preload. Testing preload It is also used in testing