Bolt tightening techniques: Hydraulic bolt extension

The method of tightening by hydraulic extension of bolts

A third method of tightening bolts, particularly used for large installations, is hydraulic expansion. This tightening technique employs a hydraulic cylinder to pull on the screw, thereby elongating it. Then the nut is tightened and the rod is released, transferring the force applied by the jack to the screw via the nut. Knowing the force provided by the cylinder, we can deduce the force applied to the assembly.

Actuator accuracy varies between 1% and 5% depending on models and various factors. However, we measure a final uncertainty of ±15% in the fixtures, mainly due to uncertainties related to tightening the nut. Although this method is more precise than the previous ones, it has several disadvantages. Not all screws in an assembly are accessible for hanging on the cylinder. Pulling the screw requires access to the ends of the screw, which is not always possible in complex assemblies.

To learn more about hydraulic bolt tensionning , check out our article on this subject!

The remainder of this article will focus on alternatives to hydraulic tightening and in particular induction tightening.