Application of the hydrostatic piston device for testing the force of tightening and screw dilatation in a screw connection

Abstract

For the most responsible screw connections (especially those with large prestressing) it is very important to precisely define the required tightening force Fp which must not be less than the minimum necessary force Fpmin, nor greater than the maximum permissible force Fpmax . If Fp< Fpmin then there would be a real danger of shifting between connected parts, while in the opposite case if Fp > Fmax plastic deformations may occur and consequently permanent damage of some elements of screw connection.Therefore, the tightening force should be defined as precisely as possible, and then in practice it needs to be adequately measured and controlled in a screw connection. The paper presents an original laboratoryexperimental method for measuring the forces and dilatations of the screw during tightening based on the application of a special hydrostatic piston device as well as a brief description and operating principle of the device. The device was designed at the Higher Technical School of Mechanical Engineering in Trstenik and it can be used for laboratory exercises in technical schools and faculties, as well as in the industry for checking the mechanical properties of the screws before being mounted, and also for various experiments in research laboratories and institutes.