Improvements in stemming plugs for use in coal mines, quarries and the like when shot-firing

摘要

491,506. Blasting ; tampings. WHITE, R. March 2, 1937, No. 6248. [Class 9 (i)] A stemming - plug adapted to form an air space of fixed predetermined capacity between the explosive and the tamping in a shot hole, comprises a cylindrical shell a and a solid end b which constitutes the outer end of the plug. The whole forms a cup with an internal cavity c of more than half its length. The cavity, which may be of the same diameter throughout or, as shown, of tapered formation, is usually concentric with the plug, although it may be eccentric thereto and may be of oval, semicircular or other desired section. A groove d is formed from end to end of the plug to receive the electric wires leading to the detonator or fuze. This groove may penetrate into the cavity c as shown or its depth may be less than the thickness of the wall of the shell a. The plug may be composed of an inert or incombustible material, such as " soured " clay which collapses into light non-inflammable dust when the explosion occurs, which dust functions as a flame-quenching element.