Sergo Ordzhonikidze Russian State Geological Prospecting University, Moscow, Russia:

Yu. A. Arsentiev, Associate Professor, Candidate of Engineering Sciences, arsentev1956@yandex.ru
N. V. Soloviev, Head of Chair. Professor, Doctor of Engineering Sciences
A. P. Nazarov, Acting Head of Chair, Associate Professor, Candidate of Engineering Sciences
A. M. Limitovsky, Professor, Doctor of Engineering Sciences

Mining industry conventionally uses wing bits with tungsten carbide reinforcement for various purpose drilling. Recently tungsten/cobalt alloys have many times been modified with fine powders, additives of 2 % tantalic oxide, etc. However, the modifications enjoy no technical breakthrough. The advance has been reached with a new generation of extra-hard materials (slavutich, tvisal, elbor) as well as synthetic diamonds, and initiation of their series production. A shining example is the stratopaks alloy produced under brand PDC. PDC cutters enable considerable increase in the penetration rate and run speed of drilling in variable hardness rocks with medium hard interlayers at the considerably reduced cost. At the same time, some problems connected with PDC cutters are yet unsolved, e.g. optimization of PDC cutter rake with regard to properties of rocks. This problem is solved in the given study. After completing theoretical researches and bench testing, it has been found that: the recommend range of PDC cutter back-rake angle of 45–55° produces drilling cuttings in the form of chips, which conforms with the energy-best mode of breaking medium-hardness rocks—the mode of cutting–chipping; with the back-range angle more than 65°, drilling cuttings are power-like, which proves inefficiency of PDC cutter setup with the back-rake angle of 70–75° in medium-hardness rocks as this conforms with the energy-consuming mode of rock breaking–rubbing. Thus, in variable hardness rock drilling, it is recommended to use wing drill bits with PDC cutters set at the back-rake angle of 45–55° to reach minimum wearing of the front face of cutters and maximum penetration rate.

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