Development of self-locking transfer mechanism for coal samples from pressure-preserved coring in deep mining

Pressure-preserved coring technology can directly store the collected deep coal samples at the bottom of the hole, so as to minimize the gas loss during the coring process. Besides, pressure transfer and testing of the pressure-preserved rock core is a technical prerequisite for the accurate determination of gas content. Then, how to achieve the precise docking from pressure-preserved coring to pressure transfer and testing has become a key technical difficulty that needs to be overcome urgently. Therefore, the research was carried out around the self-locking transfer mechanism, which is the core component of the docking transfer between the pressure-preserved coring system and the testing system. Specifically, the assembly relationship, motion characteristics and bearing capacity of the self-locking transfer mechanism were analyzed based on the theoretical calculation and laboratory test. Firstly, a self-locking transfer mechanism integrated into the pressure-preserved coring system was innovatively designed in the study. Meanwhile, the critical conditions for the smooth passage and safe bearing of the locking shaft were revealed based on the actual working conditions of the coring operation. The optimal assembly interference between the locking ring and the locking shaft was theoretically calculated to be 0.1 mm, at which the good mechanical properties could be maintained in terms of the passability and tensile bearing characteristics. In addition, the laboratory passability and tensile bearing tests were carried out to verify the working security of the locking mechanism under 5 kN tensile load. Finally, the prototype of the self-locking transfer mechanism was trial manufactured and assembled, with the downhole function, as well as the pressure transfer and testing completed, which verified the operation reliability of the self-locking transfer mechanism. The research results provide technical basis and equipment support for the in-situ pressure-preserved coring, pressure transfer and testing.