新型二重ねじボルトの転造加工と性能評価

―並一条・並多条二重ねじ機構に基づく緩み止め ボルト締結体の開発に関する研究 第1報―

抄録

We have devised new double-thread bolt fasteners (DTB) based on an innovative mechanism composed of a coarse single thread and a coarse multiple thread (called the multithread DTB). In the present work, thread-rolling experiments, FEM simulations, and performance evaluation tests were carried out. The number of coarse multithreads was set to 2, 3, and 4, which were called 2-thread, 3-thread, and 4-thread DTBs, respectively. The rolling dies have special profile grooves that follow the same outline as the thread profiles of each multithread DTB. Using these dies, the 3-thread DTB was successfully formed, although the height of the lower screw-thread portion of the 2-thread and 4-thread DTBs did not achieve the target level. The FE simulations well reproduced the actual deformation state. The tensile strength of the new DTB tended to decrease with increasing number of multithreads, and the 3-thread and 4-thread DTBs were damaged by shear failure of the screw thread in the double-nut mounted state. The loosening test results obtained using a Junker vibration test bench show that multithread DTB can withstand a certain amount of axial tensile force after the prescribed number of load cycles when controlling only the tightening torque of the outer nut.