To estimation of temperature fluctuations in diamond grains when drilling with diamond bits

Abstract

Abstract. If we consider the interacting pair: the matrix of a diamond crown, reinforced with protruding diamonds and rock, as a kind of system, then in the process of friction of the matrix against the bottom hole, external mechanical energy is converted into the energy of the heat and matter flows. The main concentration of the flows occurs in places where diamonds protrude above the matrix and take on an additional load. The rubbing system tries to smoothing itself by concentrating pressure and temperature on the diamonds. Diamonds, due to their higher hardness than the destructible medium, are pressed into the rock and destroy it. Since the process of cutting rocks is intermittent, the concentration of energy on diamonds occurs periodically, in the form of “flashes”. Each such “flash” is accompanied by a short-term increase in temperature in the contact zone (temperature fluctuation) and the spalling of a microparticle of the rock. In this work, from the standpoint of thermoelastic instability, the issue of temperature microflashes in single diamonds during the interaction of rough surfaces of the matrix of the diamond crown and the bottom of the borehole is considered, in order to take this factor into account in the mechanism of wear of the diamond of the drill bit. The value of temperature fluctuations on the surface of cutting diamonds was estimated and the size of the flash zone was determined. It is shown that temperature flashes of 400 (С < T* < 3650 (С are observed when drilling granite with a diamond crown on the diamond surface in an area of 5.8(10‑5 m, therefore, the presence of such “microflashes” on the diamond surface in a very small area in the process of interaction with the rock can lead to graphitization of the diamond in this place and separation from the surface of the grain. Such a mechanism should play a certain role in the wear and destruction of diamond surface areas during drilling. The magnitude of temperature fluctuations depends on the physical and mechanical properties of the contacting pair: diamond – rock, operating parameters of the tool and the nature of the placement of diamonds in the crown matrix. In this regard, the study of the assessment of temperature fluctuations in diamond grains when drilling with diamond bits may be of practical interest. Keywords: rock, thermal stresses, intensive cooling, macro- and microcrack system.