GB689440A - Improved blasting means - Google Patents

Abstract

689,440. Blasting devices. DU PONT DE NEMOURS & CO., E. I. July 11. 1951 [July 20, 1950], No. 16401/51. Class 9(i) A blasting device comprising a pressureresistant tube with a disc adapted to rupture under pressure contains a gasgenerating ammonium nitrate composition, which is so disposed in the tube as to maintain lengthwise channels for the escape of gas throughout the length of the composition, heating means being provided for initiating the charge. Fig. 1 shows a steel tube 1 with a steel rupture disc 2 shearing at a predetermined pressure and held in place by a hollow threaded cap 3 provided with vents 4, 5 through which the gases escape after rupturing the disc. At the opposite end of the tube is a firing head 6 comprising a threaded plug within which is a ridged member 7 bearing against an insulating plug 8 with a flange resting on a shoulder of the con tainer 1. Through bores 9, 10 in the insulating plug 8 are passed the ends of a nickel-chromium ribbon 11, one end being connected to an electrode 12 carrying a terminal 13 and insulated within a channel passing through the firing head. The other end of the ribbon contacts the ridged member 7 and is thus connected through the firing head to. a terminal 14, the terminals 13, 14 being connected to a source of current. Attached to the insulating plug 8 is a cardboard container 15 enclosing the gas generating charge and spaced from the inner wall of the tube 1, the ribbon 11 being carried through openings 16 in the base of the container 15 into a bag 17 of polythene plastic containing granular ammonium nitrate. The mixture in the container comprises 90 per cent ammonium nitrate and 10 per cent starch, parts being by weight. In a modification the charge is not divided into two portions and is contained in a tube of flame-resistant paper. The charge may be a mixture of granular ammonium nitrate 88 per cent, starch 10 per cent and sodium thiosulphate 2 per cent, all parts being by weight. Piezo gauge records are given of pressures developed after initiation of the charges. Vent holes may be provided in the side of the tube 15. The loading density of the ammonium nitrate may be less than 0.3 gram/c.c. and at any cross-section of the steel tube 1 less than 0.5 gram/c.c. The compositions may be varied by the addition of Na 2 S, 0, .5 H 2 O as an anti-segregating agent or by omitting the starch or by altering the proportions, or by replacing the starch by some other fuel such as wood pulp, petroleum, engine oil or calcium stearate. In one example the charge of ammonium nitrate was rendered electrically conducting by the addition of graphite, the conducting mixture being placed in a copper tube surrounding a copper electrode. A polythene bag containing a mixture of ammonium nitrate and starch was arranged around the copper tube. The disc 2 may be of fibre, brass or thermosetting plastic material. Cooling salts such as sodium chloride, borax, or metallic carbonates may be added to the charge. A permanent heating element such as a copper coil may be used to decompose the charge. The diameter of the charge container may be less than 75 per cent of the internal diameter of the pressure-resistant tube.