Rock Blasting / A Practical Treatise on the Means Employed in Blasting Rocks for Industrial Purposes

by George G. André

Auxiliary Tools.

—Besides the drill and the hammer, other tools are needed in preparing the hole for the blasting charge. If the bore-hole is inclined downwards, the débris or “bore-meal” made by the drill remains on the bottom of the hole, where it is converted into mud or “sludge” by the water there present. This sludge has to be removed as the work progresses, to keep the rock exposed to the action of the drill. The removal of the sludge is effected by a simple tool called a “scraper.” It consists of a rod of iron from ¹⁄₄ inch to ¹⁄₂ inch in diameter, and of sufficient length to reach the bottom of the bore-hole. One end of the rod is flattened out on the anvil and made circular in form, and then turned up at right angles to the stem. The disc thus formed must be less in diameter than the bore-hole, to allow it to pass readily down. When inserted in the hole, the scraper is turned round while it is being pressed to the bottom; on withdrawing the instrument, the sludge is brought up upon the disc. The operation, two or three times repeated, is sufficient to clear the bore-hole. The other end of the scraper is sometimes made to terminate in a ring for convenience in handling, as shown in [Fig. 18]. Instead of the ring, however, at one end, a disc may be made at each end, as shown in [Fig. 19], the discs in this case being of different diameter, to render the scraper suitable for different size bore-holes. Sometimes the scraper is made to terminate in a spiral hook or “drag-twist,” as represented in [Fig. 20]. The use of the drag is to thoroughly cleanse the hole before inserting the charge. A wisp of hay is pushed down the hole, and the drag end of the scraper introduced after it, and turned round till it has become firmly entangled. The withdrawal of the hay by the drag wipes the bore-hole clean. Instead of the twist drag, the “loop” drag is frequently employed. This consists of a loop or eye, through which a piece of rag or tow is passed. The rag or tow is used for the same purpose as the hay, namely, to thoroughly cleanse and dry the bore-hole previous to the introduction of the charge. Very frequently the “swab-stick” is used instead of the scraper to clear out the bore-hole. This is simply a deal rod bruised at one end by blows with a hammer until the fibres separate to form a kind of stumpy brush or “swab.” When this is pushed down the hole, the sludge passes up around and between the fibres, which are then spread out by being pressed against the bottom of the hole. On withdrawing the swab, the sludge is brought out with it.

Fig. 18.

Fig. 19.

Fig. 20.

When the charge has been placed in the bore-hole, and the fuse laid to it, the hole needs to be tamped, that is, the portion above the charge has to be filled up with some suitable substance. For this purpose, a “rammer,” “stemmer,” or “tamping iron,” as the instrument is variously called, is required. This instrument is illustrated in [Fig. 21]. It consists of a metal bar, the tamping end of which is grooved to receive the fuse lying against the side of the bore-hole. The other end is flat, to afford a pressing surface for the hand, or a striking face for the hammer when the latter is needed. To prevent the danger of accidental ignition from sparks caused by the friction of the metal against silicious substances, the employment of iron stemmers has been prohibited by law. They are usually made of copper or phosphor-bronze, the latter substance being more resisting than the former.

Fig. 21.