Patent GB-313333-A (GB)
Title: Improvements in blasting cartridges
IPC: F42B3/06
Filed: 1928-07-05
Abstract: 313,333. Marks, E. C. R., (Safety Mining Co.). July 5, 1928. Blasting cartridges for use in mines contain liquid carbon dioxide and means for raising the temperature of the liquid above its critical temperature whereby it is rapidly converted into gas and acts explosively, as described in Specifications 259,799, 260,440 and 262,941. The force of the explosion is directed through transverse openings in the cartridge cap, and the cartridge has a smooth exterior surface to fit the drill hole accurately. The cartridge consists of a hollow container 10 having removable heads 20, 54, one enclosing a rupturable washer while the other encloses a filling valve and the firing means. The valve 43 is adjustable to and from a hollow plug 30 containing passages 32, 33 through which the liquid carbon dioxide is supplied from a passage 42 and a nozzle, and the plug is insulated from the cartridge casing and acts as the conductor of an electric current from a terminal 61 mounted on a cover disc 65, but insulated therefrom, a spring 51 serving to conduct the current from the terminal to the plug. An adjustable contact rod 69<1> is disposed in the forward end of the plug to contact with a fusible helical wire passing through the firing charge contained in a container 80 placed within a perforated shell 67 disposed centrally within the cartridge case. A spring contact 79<1> at the other end of the firing charge leads to a hollow plug 71 insulated in its mounting 75 and which contains a spring 81 and contact red 83 which presses at its other end against a metal disc 18 pressed against eccentric ribs 17 on the reduced end of the cartridge case 10, by a shearing washer 19 and the head 20. This head is provided with an outer end wall having a narrow aperture 25 and with side apertures 24 through which the explosive force is directed. The pressure of explosion ruptures the metal disc 18 and acting on the end wall prevents the cartridge from rising in the drill hole, the circuit of the firing current being completed through the cartridge case to a terminal 60 disposed on the cover-plate 65. The explosion end of the cartridge may have an enlarging nozzle opening and the end wall of the cap may be bulged in order to direct the explosive forces through the radial openings 224, Fig. 6, more effectively. A container of water may also be positioned in the nozzle to damp out any sparks which might be formed during the firing of the charge. Instead of the rupturable disc. a plug 301 supported by a rupturable cylinder 306, Fig. 5, may be used, or the rupturable disc may contact with eccentric projections on one face of a washer having eccentric projections also on its other face to contact with the end of the cartridge. The firing charge may be formed of a mixture having aluminium and potassium chlorate in the proportion of 45 to 120 with suitable amounts of accelerating or catalyzing agents such as sulphur, antimony trisulphide, ferric oxide, and manganese dioxide, varying from 2 to 20 per cent of the chlorate content. The charge is designed to raise the temperature of the liquid to and above its critical temperature within an interval of <1>/20th of a second, and is contained within a paraffined paper tube or sack.