Set­ting be­hav­iour

“Setting” is generally used to refer to the levelling of surface irregularities in the bolt head and nut contact surfaces as well as the flanks of nut and bolt threads and the joints between the stressed parts.

As levelling of surface irregularities already occurs when tightening the bolt, the amount of setting is generally less than would be assumed for the degree of roughness present. Even at room temperature, a loss of pretension can already occur after the assembly of a screwed connection via setting.

Micro-layer systems have scarcely any effect on setting behaviour

Essentially, the setting effects to be planned for are dependent on various factors. In addition to the rigidity of the stressed components, the roughness of the surfaces affected, the amount of surface pressure, the type and degree of stress as well as the temperature also play a role. The elastic resilience of the parts utilised also needs to be taken into consideration - particularly where plastic or rubber elements are used, but also in the application of very thick coatings. The influence of surface systems such as zinc flake technology or galvanic coating on the pretension of screwed fittings is marginal and negligible, however, for example in the automotive industry, sometimes barely achievable maximum coat thicknesses of 25 µm below the head are specified.