Hammer Drill(redirected from hammer drills)
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hammer drill[′ham·ər ‚dril]
a percussion boring machine for drilling blast holes (less frequently well holes). The hammer drill is usually a pneumatic machine; power drills with gasoline engines are seldom used. In the first hammer drills (mid-19th century) the cutter performed its operation with a piston (so-called piston drills). These were later replaced by drills of the hammer type, in which the piston strikes the drill shaft, to which a rock-crushing drill bit is fastened. The bit turns 10°-15° on each return stroke of the piston. (The rotation is transmitted from the piston to the drill by a swivel gear.) Hammer drills with independent rotation, in which the drill is turned by a special air compressor, have been developed. Piston motion is controlled by an air-distribution device that supplies consecutive charges of air to the front and rear cylinder cavities. The crushed rock is removed from the blast hole by water or compressed air.
Hammer drills are classified as follows: hand-held jack-hammers (light, medium, and heavy-duty), weighing 10-30 kg, which are held in the drill operators’ hands or are mounted on a pneumatic support during the drilling operation; core hammer drills, weighing 50-70 kg, which are mounted on mobile drilling rigs or on columns with an automatic power supply; and telescoping borehammers, weighing 30-40 kg, for drilling upward-directed blast holes.
Hammer drills are rated according to the energy of a single impacts A= mv2/2 (m is the piston mass, and v is the velocity before impact), the number of impacts per minute n, the air flow rate, and the mass of the drill. The most efficient hammer drills are those with higher impact energy and an n rating of up to 2,000 impacts per minute. High-frequency hammer drills with n ratings above 2,500 impacts per minute are used only when mounted on mobile drilling rigs or manipulators, owing to their excessive noise level (up to 120 decibels) and high vibrations. Vibration-damping handles and mufflers have been developed to lessen the harmful effects of the vibration and noise on the drill operators.
REFERENCESTekhnika bureniia pri razrabotke mestorozhdenii poleznykh iskopaemykh. Moscow, 1966.
Pnevmaticheskie ruchnye mashiny: Spravochnik. Leningrad, 1968.
B. N. KUTUZOV