The Selection Of Rock Drill Bits

THE introduction of the tungsten-carbide bit and the single-use bit to the mining industry has had far-reaching effects on the advancement of drilling techniques. Six years of testing these new bits has disclosed new factors not previously considered. The mining industry, which is ordinarily slow to change, has accepted the new methods of drilling as a possible relief for the reduced manpower available to the mines. In 1950 an extensive program of testing was begun at the Calloway mine of the Tennessee Copper Co. to gather data on rock-drill bits and drill steel: When these tests are concluded the information should be sufficient to establish a drilling program. The scope of this article is a progress repor the years 1950 and 1951. The deposits of the Ducktown, Tenn. mining district are massive sulphide replacement lenses in folded and metamorphosed Cambrian schists and graywackes. The primary ore consists of pyrrhotite, pyrite, and chalcopyrite with minor amounts of zinc blende, bornite, specularite, magnetite, quartz, chlorite, and iron-magnesium-lime silicates. The deposits are high-temperature hydrothermal replacements. The drilling conditions vary from a hard highly siliceous rock to the softer material of the ore body, thereby giving a range of hardnesses to be considered. Single-Use Bits Test work was done first on two single-use bits to determine life expectancy, costs, rate rate of penetration, gage wear, and ease of use. At the same time a test was conducted for comparison using the conventional detachable steel bits to obtain the same for