Percussion Drilling

the process of drilling blastholes and boreholes by percussive destruction of rock with a boring tool whose working cutters are usually wedge-shaped.

Cable-tool percussion drilling of vertical blastholes and exploratory, hydrogeological, and ventilation wells 150–600 mm in diameter to depths of 20–500 m and more is done with drillrigs that use a cutter weighing 0.5–3.0 tons. The cutter delivers 40–60 blows per minute to the face. Percussion-rotary drilling of blast-holes 36–85 mm in diameter is done using hammer drills with dependent (discontinuous) rotation of the bit, striking 1,800–2,000 blows per minute with an axial force of 0.5–1.2 kilonewtons (kN), or 50–120 kilograms-force (kgf). Rotary-air-percussion drilling of blastholes and boreholes is done using hammer drills with independent rotation of a bit 36–85 mm in diameter and bottom-hole pneumatic strikers (seePNEUMATIC PERCUSSION DRILLING). The tool rotates at 20–75 rpm and has a specific striking force of 10–25 joules per cm (J/cm) of diameter and an axial forward force of 1–3 kN (100–300 kgf). Rotary-percussion drilling of blastholes is done by special machines mounted on frames; the machines rotate at 100–150 rpm, delivering 1,500–4,000 blows per minute, with a specific striking force of 5–20 J/cm of diameter and an axial force of 10–15 kN (1,000–1,500 kgf). Hydraulic percussion machines and bottom-hole hydraulic strikers are also used. Electric hammer drills are being developed (1977).