GB640514A - Improvements in or relating to delay electric blasting caps - Google Patents

Abstract

640,514. Blasting-cartridges. ATLAS POWDER CO. April 1, 1947, No. 8779. Convention date, July 12, 1946. [Class 9 (i)] An electric delay blasting cap or fuze comprises a charge of compressed blackpowder placed in a tubular member between an electric initiating element and a detonating charge, the blackpowder charge being small enough to give delay times between 10 and 250 milliseconds, a ventless casing or shell enclosing all the parts of the fuze. The shell 10 of internal diameter 0.260 inch is of drawn metal 0.007 inch thick and holds a base charge 12 of tetryl, a primary detonator charge 14 of nitromannite and a flash charge 16, which is 75 per cent diazodinitrophenol and 25 per cent nitromannite pressed under a capsule 18. A delay tube 20 has a 9/64 inch bore 22 containing a charge 24 of 0.04 grams of blackpowder compressed under a pressure of 31,000 lb. per sq. inch to a height of 0.068 inch. An electric match assembly placed above the delay tube comprises an insulating tube 26 in which sulphur is cast around an electric match 30 carrying a copper acetylide match head 31 and attached to leg wires 32, 34. The shell 10 is sealed by an asphaltic plug 36 and a sulphur plug 38. This delay cap is stated to have a delay average of 40 milliseconds with a standard deviation of 16 milliseconds. A modified cap is described with a delay of 115 milliseconds, and standard deviation about 15 milliseconds. The Specification gives alternative powders for the delay element, and alternative compositions for the base charge, primary detonator charge and flash charge and for the ignition element. The shell 10 may be of aluminium or a plastic composition.