Abstract
This paper systematises the theoretical background of fire-jet (thermal) destruction of strong rocks and substantiates the rational operating parameters of thermo-gas-jet tools for the extraction and surface finishing of granite blocks. An analytical description of the “heat carrier – rock” system is built on the basis of the thermoelastic problem for an elastic isotropic half-space with first-kind boundary conditions. The convective and radiant components of the heat flux from a supersonic gas jet are analysed; the radiant contribution from a high-temperature jet is shown to be more than an order of magnitude lower than the convective one. Analytical expressions are obtained for the destruction temperature, separating-layer thickness, cut depth and volumetric destruction rate. Experimentally, a drop in quartz content in the rock from 40-60 % to 15-20 % is shown to reduce the productivity of thermal cutters by a factor of 1.5; the exponent n in the empirical relationship for surface-processing efficiency versus combustion-chamber pressure decreases from 1.28 (coarse-grained granites) to 0.93 (fine-grained). Rational ranges of operating parameters are established: combustion-chamber pressure 0.5-0.7 MPa, oxidiser excess coefficient 0.7-0.9, jet-to-rock impingement angle 45-60°, tool travel speed 0.6-1.2 m/min. The results are applicable to the design of thermo-gas-jet tools and to the substantiation of technological schemes for combined preparation of granite blocks for extraction.