GB739929A - Delay electric blasting caps - Google Patents

Abstract

739,929. Blasting fuzes. CANADIAN INDUSTRIES (1954), Ltd. Feb. 2, 1954 [Feb. 28, 1953], No. 3002/54. Classes 9(1) and 9(2). An electric blasting device is provided with a delay element placed between the igniter and the detonating charge, the element being a metallic cylinder 4 containing a fuze composition 5 arranged in a spiral. Fig. 1 shows a metal shell 1 of copper or aluminium, into which is introduced a base charge 2 and a priming charge 3 such as a lead azide-lead styphnate mixture. The delay cylinder 4 is of lead and above it is a matchhead 6 connecting lead wires 7, 8 which extend through a plug 9 of sulphur asphalt, rubber or other plastic insulating materials. The delay element may be made by drawing down a lead tube filled with the fuze composition, sealing the ends of the tube, then winding the tube on a mandrel with adjacent turns in contact. The mandrel is then removed and the helix cut to the required length and swaged in a die to produce the solid cylinder 4. The fuze composition may be 70 per cent red lead, 16 per cent silicon and 14 per cent silica. In a given example the swaged tube is wound around a piano wire to produce a helix of outer diameter 0À250 with 7 to 8 turns per inch. The wire being removed, the spiral is cut into 1À2 inch long sections which are placed in a steel die and pressed under a load of 600 pounds. A solid cylinder 0À92 inches long is thus produced and inserted in a copper shell containing a base charge of tetryl. The delay period can be altered by changing the length of the spiral or altering the fuze composition. An alternative composition given is 69 per cent potassium permanganate, 29À5 per cent antimony, 1À5 per cent boron. In place of the matchhead, a loose charge of igniting composition such as 70 parts red lead and 30 parts silicon may be used. The mandrel used to form the spiral may be of soft metal and allowed to remain within the delay element and be compressed with it.