The principle of the down-the-hole drilling is a reduction of energy loss, which is a result of the impact transmitted by the drill rod. The reduction is achieved by an impactor diving into the hole, so as to promote the efficiency of a deep hole drilling.
The DHT drilling equipment is a DHT drill, which is favorable for holes with a diameter of 20 ~100mm and a depth within 20m in medium hard rocks or the above ones. By their motive power, the DHT drills can be categorized into the pneumatic, the internal combustion, the hydraulic and the electric, among which the pneumatic is the most widely used one.
The DTH drilling equipment
is a percussive rotary drill with an internal structure different from that of the general rock drill. The reciprocating mechanism of air distribution and piston, its impactor is independent, of which the head is directly connected with the drill bit while the end is attached with the drill rod.
Into the hole goes the impactor, in which the piston (the hammer body) controlled by the distribution device (the valve) moves back and forth to strike the bit tail, which impact the rock at the bottom. The high-speed rotation of the impactor in the hole is motivated by a independent rotating mechanism, that is, the rotation is controlled by an electric motor or a pneumatic rotating device, which is connected to the drill rod at the end of the impactor.
The rock powder produced by the drilling is washed out of the hole by the air-water mixture. Injected into the center of the drill rod by the powder removal mechanism, the mixture goes to the bottom of the hole through the air slot on the impactor cylinder.