It is known in the method of electrothermomechanical drilling and device for its implementation (see Inventor's Certificate No. 1,555,460 Int. Cl. E 21 7(15,1988), which consists in loosening the rock by the passage of current and then in drilling this loosened rock by a mechanical rock-breaking foot and excavating the drill sludge from the hole with an air mixture. This sludge is then divided on fraction, then the coarse fraction is separated, concentrated and broken down thermodynamically outside of the drill pipes.
The device that realizes this method includes a drill bit, a bit chamber, a current collector, an insulating adaptor and a multi-screw spiral, put on an external surface of the cylindrical bit chamber.
However, this method and device are only capable of loosening the rock with the further evacuation of the breakdown products. This method does not strengthen the hole shaft with a solid layer of compressed and thermally transformed rocks.
See also the known device for electrothermal hole drilling (see IC 1,608,340 Int. Cl. E 215 37(18,1988), which we took as a prototype. It includes a rotator, a jib holder, drill jib with waveguide, a compressor, a magnetron, a sludge pipe and a high-temperature penetrator.
This device does not provide sufficiently high drilling speed in loose rocks because the highest temperature is generated directly on the extended circular or conical end of the penetrator and is fed by contact through the melt layer to the rock. Besides, outside the liquid phase of the melt layer in loose rock there is inevitably formed an area of compressed and thermally transformed rock at the expense of its sintering and baking. The high density and strength of the crystalline phase formed in front of the stope, block the mechanical moving of the penetrator and considerably reduce the drilling speed.