Maxwell Laboratories, Inc.

G Mark Wilkinson

Steven G Pronko

A method and apparatus for blasting of hard rock using a highly insensitive energetic material ignited with a moderately high energy electrical discharge causing the fracturing and break up of the hard rock is provided. The blasting apparatus comprises a reusable blasting probe including a high voltage electrode and a ground return electrode separated by an insulating tube. The two electrodes of the blasting probe are in electrical contact with a continuous volume of highly insensitive yet combustible material such as a metal powder and oxidizer mixture. The metal particles within the metal powder and oxidizer mixture form a plurality of fusible metal paths between the high voltage electrode and the ground return when subjected to an electric current delivered from a large capacitor bank coupled to the high voltage electrode. The plurality of fused metal paths act much like a fuse in that they provide a sufficiently high electrical resistance to allow coupling of the electrical energy from the capacitor bank to the metal powder and oxidizer mixture causing an increased dissipation of heat which initiates an exothermic reaction of the metal powder and oxidizer mixture generating high pressure gases fracturing the surrounding rock.

Method and apparatus for blasting hard rock

An electrothermal chemical cartridge with a fuse of tapering cross section enables higher impulse energy to be imparted to a projectile by means of complete controlled burning of propellant. A long, narrow tube filled with propellant has a fuse on its inside surface with a cross section that tapers toward the discharge end, separated from the electrical ground of the cartridge casing by a layer of insulation sufficiently thin to be destroyed as the fuse ignites the propellant. A high-voltage electrode connected at the back end of the tube provides for application of a pulse of sufficient current density to ohmically heat or burn the fuse in a controlled fashion from the discharge end to the back end. Many such tubes can be bundled together in a large casing for wide barrel guns.

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San Diego, CA, United States of America

G Mark Wilkinson