Papers by Keyword: Tightening

Abstract: The axial tension remaining in a bolt after the hydraulic tightening is less than the initial tension from the hydraulic load, and the ratio of the residual tension to the initial tension, an effective tensile coefficient, is the most critical factor to securely tighten a pressure vessel. In this study, an analysis model simulating the hydraulic joint processes by using a finite element model was developed to clarify the effects of various joint parameters on the effective tensile coefficient. The analysis model could estimate the effective tensile coefficient within a 5% error compared to the hydraulic tightening experimental results. The simulated results of the analysis model showed that the effective tensile coefficient changed largely depending on the thickness and the surface pressure of the flange, and that the coefficient hardly changed by the height of the nut and the friction coefficient at the bearing surface.

Abstract: To evaluate the mechanical deformation phenomena of dental abutment screw after tightening and loosening, five species of abutments were selected (3i-three, Avana- two) respectively by two pieces. The abutment screws were repeatedly tightened and removed 20 times with a digital controller. Field emission scanning electron microscope (FE-SEM) was used to observe changes of each part caused by repeatedly tightening and loosening experiment. As the number of tightening and loosening was increased, the wear or distortion of hexed or squared slot that contacted with the driver tip was more severely progressed. Wear or distortion of hexed slot was more severe than that of squared slot and it was more remarkable in the titanium screw than in the gold screw. All the tested screws showed that the width in the crest of their screw thread decreased gradually as the test was proceeded.