Patent GB-727128-A (GB)
Title: Improvements in fluid-pressure blasting cartridges
Inventor: HESSON JAMES CHALMER
IPC: F42B3/06
Filed: 1953-09-15
Abstract: 727,128. Blasting cartridges. CARDOX CORPORATION. Sept. 15, 1953, No. 25470/53. Class 9(1).  A fluid-pressure blasting cartridge is provided with a shear element adapted to rupture at a given pressure, the element being clamped between inner and outer members which form a passageway for the release of gas and the inner clamping member being movable by the gas pressure within the cartridge to vary the clamping forces in direct proportion to the gas pressure. The cartridge has a body 12 containing a pressure chamber 13 closed at the rear by a charging cap 14 through which compressed gas is fed by a pipe line 21, Figs. 1 and 2. Alternatively the charge in the chamber may be a liquefied gas or a solid emitting gas when burned or heated. An adapter 26 screwed into the forward end of the body 12 and bearing against a gasket 27 seated on a shoulder 24 acts as a valve seating at its forward end. A discharge head 31 having screw-threaded connection with the adapter has a row of discharge ports 33 surrounding a main valve 34, which is slidable in the head to uncover the ports. A spring 42 holding the valve on its seating bears against a plunger 38. Screwed on to the head 31 is a double-ended venting cap 43 with an axial passage engaging the reduced end 45 of the plunger. Communicating between the pressure chamber 13 and the discharge head is a passage 47 having a diameter between 1/2 and 1/3 the diameter of an axial bore 48 in the plunger. Diametrically opposed slots 51 in the cap 43 house a shear element 52, which may be of brass, steel or fibre, held against the plunger end to close the bore 48 by a plug 53. An axial passage 54 in the plug is aligned with the bore 48 and opens into a transverse passage 55. Radial ports 56, 57 leading from the passage 54 are provided so that dust may be blown out of the threads of the plug and the space at the inner end of the plug. In operation, the unchanged cartridge is inserted into a borehole and gas is supplied through the feed line 21. Pressure in the chambers 13, 46 rises until the strip 52 is blown through the passages 54, 55, whereupon due to the smaller diameter of the passage 47, the pressure in the chamber 46 falls more rapidly than in the chamber 13. Consequently the valve 34 moves forwards to uncover the ports 33. The supply of gas is then discontinued. To reset the cartridge, the plug 53 is loosened and the strip 52, which may be long enough for two to six operations, moved in the slots 51 to bring an undamaged portion over the passage 48. The discharge head may have two rows of discharge ports, the ports in the two rows being respectively staggered. In a further modification, Fig. 7, the valve 85 is arranged with its open end directed forwardly to receive an extension of the plunger 87, which has radial ports 101 to facilitate venting from the chamber 97. Fig. 9 shows a cartridge with a discharge extension 105 having a row of venting ports 107 surrounding a pilot valve 115 bearing against a spring 114 which holds the main valve 109 on its seating. A second spring 119 bearing against a plunger 121 holds the pilot valve in position. In the venting cap 124 are recesses 127, Fig. 10, which house rotatable reels 139 carrying strip material 140, so that after each operation of the cartridge a new shear element may be brought into position by rotating the reels.