In mining industry during geological material extraction preparations are wide spread drilling-and blasting operations. One should spud a hole for blasting charge to explode a rock mass. Nowadays almost all blastholes at the open cast are bored in cylindrical form. However, if the well has, for example, a square or triangular cross section, then its lateral area per volume of blasting material in comparison to the circular one is 12% and 27% bigger. Moreover, the angles, formed by the borehole walls matching, represent the concentrator of tension stress. As a result, there might beobtained predicted quantity and initial main crack propagation direction, where gas is delivered during the explosion, providing the piston type effect. Test results sustain, that changes in the form of the borehole lead to the changes in the qualitative composition of exploded mass. It has been established that during explosion of sandy-cement blocks and changing circular form of the borehole to the rectangular or flat form decreases the output of fine and oversized fractions.
During the research on predrilling process at the Public Technical Univercity of Kuzbas n.a. T.F. Gorbachev was produced the prototype of two-roller bit with single-cone rolling cutter (pic. 1). There were predrilled (pic. 2) sand-cement blocks with the following volume of sand to cement ratio — 4:1.
The suggested drilling tool for forming of blastholes with noncircular cross-section has some significant distinctions and provides:
1. Noncircular wells drilling with tool rotation and avoiding changes in widely spread technology of drilling at the open-cast mining;
2. Series roller-bit drilling rig usage;
3. Wide range of rocks drilling according to the hardness.
Pic. 1. Prototype of square cross-section roller bit for well drilling.
Рiс. 2 The view of initially predrilled well.
Usage of suggested drilling tool will provide noncircular cross-sectional wells bursting effect with area. According to the preliminary tests, it will lead to significant decrease of explosive ratio and drilling volume reduction.
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