a method of driving holes in which the rock is broken down at the face by the percussive effect of hydraulic mining machines operating directly within the hole.
The first patents on hydropercussion machines were taken out in the late 19th century, and practical models were produced in the period between 1900 and 1907 and used to drill for petroleum in the Caucasus.
A hydropercussion machine is actuated by the power in a stream of fluid pumped from the surface through a shaft of drill pipe. This fluid cleans the muck from the face and carries it to the surface. Core drilling is done with hard-alloy insert bits; when drilling an unbroken face, blade and rolling-cutter bits are used.
When hydropercussion machines are drilling hard minerals at a flushing fluid rate of 100 to 300 liters per min, the energy per impact is between 70 and 80 joules (7 to 8 kilograms-force m), and the impact rate is between 1,200 and 1,500 per minute. The axial load developed on the face ranges from 4,000 to 8,000 newtons (400 to 800 kilograms-force), and the tool turns at a rate of 25 to 100 rpm depending on the hardness and abrasiveness of the rock being penetrated.
The use of hydropercussion drilling is most efficient for rocks of medium and high hardness, which are broken down very effectively under percussive loads. Such machines increase the productivity of drilling by a factor of 1.5 to 1.8 with a cost reduction of 20 to 30 percent compared with rotary drilling with hard alloy and diamond bits.
REFERENCESUdarno-vrashchatel’noe burenie skvazhin gidroudarnikami. Moscow, 1963.
Teoriia ipraktika udarno-vrashchatel’nogo bureniia. Moscow, 1967.
L. E. GRAF and A. T. KISELEV