jet-piercing drill[′jet ¦pir·siŋ ‚dril]
a device for the directed destruction of solid mineral mediums through the thermal and mechanical action of one or more supersonic, high-temperature gas jets.
The design and operation of a jet-piercing drill are analogous to those of a jet engine. The fuel—for example, diesel oil, kero-sine, gasoline, methane, or natural gas—is usually fed in atomized form into the combustion chamber, where it is mixed with the oxidizer (usually oxygen and compressed air) and ignited. The combustion products are ejected through a de Laval nozzle, which increases the speed of ejection to 1,500–2,000 m/sec. The thermodynamic parameters of the gas jets decrease with increasing distance from the nozzle opening. At a distance on the order of 100–200 mm, jet-piercing drills using air as the oxidizer have a stagnation temperature of 1,700°–2000°K and heat transfer of 3,500–4,500 watts (W) per (m2·deg) from the gas to the rock; for drills using oxygen, these values are 2,400°–2700°K and 4,000–5,000 W/m2·deg, respectively. Water, air, or a combination of the two may be used for cooling jet-piercing drills. In the case of water cooling and combined cooling, the used water is usually used for the reduction and catching of dust.
Jet-piercing drills may have one or more nozzles and may be hand-held or bench-mounted. Hand-held drills are used in driving boreholes, for secondary reduction of oversize pieces, and for cutting and working pieces of stone. Such drills are 20–50 mm in diameter and 150–350 mm long, with a fuel consumption of 10–15 kg/hr. Bench-mounted drills are used in special machines for boring and expanding wells. They are 100–160 mm in diameter and 400–800 mm long, with a fuel consumption of 100–120 kg/hr.
Means of increasing the operational efficiency of jet-piercing drills involve improvement of the thermodynamic parameters of the gas jets, simplification of design, increasing the wear-resistance of the working parts, and the design of machines that produce a combined action on the medium to be broken down, such as heating/cooling or heating/mechanical action.
REFERENCESIagupov, A. V. Teplovoe razrushenie gornykh porod i ognevoe burenie. Moscow, 1972.
Dmitriev, A. P., S. A. Goncharov, and G. A. Ianchenko. Termoelektrofizicheskoe razrushenie gornykh porod, part 2. Moscow, 1975.
K. I. NAUMOV, A. P. DMITRIEV, and G. A. IANCHENKO