The mathematical model of mechanical drilling speed for fractured rocks for serial and experimental bits (bits with solid matrix and flushing channels in the body) was built. As a result of the analysis of mathematical models, methodological recommendations for drilling with pilot bits, for which the existing recommendations for drilling fractured rocks with serial (with sectoral matrix) diamond bits can be used, are proposed. In order to build a regression model of mechanical drilling rate for fractured rocks, prototype and production drill bits were made. The matrix of the pilot bit was made solid, and radial flushing channels were made in the body. The drill bits were tested at the drilling stand of the St. Petersburg Mining Institute.
It is known from the practice of diamond drilling that during drilling of hard fractured rocks of 1X-XP categories of drillability, the mechanism of their occurrence is explained by self-jamming of the core in the matrix ring and the drill bit body. As a rule, self-jamming of the core is associated with settling of large cuttings that, as they accumulate, overlap the annular gap between the cores and the inner wall of the core barrel and clog the flushing channels in the matrix. In such cases the normal circulation of the cleaning agent is disturbed, and in order to restore it the drilling tool has to be pulled away from the bottom hole. If this operation is not performed in time, there is a risk of burning the diamond core bit. If there are additional flushing channels in the body in case of core self-jamming, the cleaning agent continues to circulate through these channels, which prevents the tool from getting into a situation of increased wear or burning. In our opinion, it is especially reasonable to use such crowns in case of automated drilling process control; in this case the control algorithm and control over the drilling process in fractured rocks are simplified.
In order to assess the performance of diamond drill bits under different conditions more fully, it is important to correctly determine the nature and features of their wear. We propose a classification of diamond drill bit types when drilling fractured rocks. The classification is based on two prevailing types of wear: mechanical and thermophysical. The mechanical type of wear includes: grooves on the matrix face and side surface; cracks on the matrix body; chipping of matrix sectors and normal wear. The thermal-physical type of wear includes burnout of the diamond crowns. The proposed classification reflects the main types of wear when drilling fractured rocks and creates the basis for the development of rock destruction tools more resistant to mechanical and thermophysical wear.
