The main method of preparation to rock extraction is the blasthole drilling. Specific consumption of explosives and drilling rigs increase in productivity according to drilled rocks. Nowadays almost all blastholes at the open casts are drilled in cylindrical form. We suggest changing the form of the well – provide drilling with square cross-section.
Why for such goals the square wells usage is suggested?
The wells with noncircular cross-section are meant to decrease the specific consumption of explosives. It might cause the drilling rigs increase in productivity according to drilled rocks and specific consumption of explosives decreasing.
There exist and are applied different methods of blasthole drilling by the means of technological changes in blasting and drilling operations. There hasn’t been applied a method of stress-raiser usage at the well side in practice. We suggest using this method in order to decrease the off-gauge rock pieces output.
Test results confirm, that wells’ form changing leads to the alteration of blasted mass qualitative composition. The fraction distribution diagram shows that quantity of medium size pieces is larger in comparison to the triangular or circle wells. Therefore, there was designed a special tool with rollers and square cross-section.
Construction of the tool is based on the following principles:
1. Drilling and concentrator formation combination, that helps to avoid drilling technology changing.
2. Serial roller drilling rig usage.
There was produced a prototype of two roller bit with single-cone rolling cutter in conformity with scientific experimental data. Bit dimensions fit the rectangular cross section well with round corners, 160 mm diagonal and gear ratio equal to 2.
There were predrilled some wells using this tool, one of which is represented on pic.1.
Рiс. 1 The view of initially predrilled well
As you can see on the picture – the well has a square form with round corners. It is a side view of the well.
Moreover, there was developed a drawing of cutting roller bit for noncircular cross section wells drilling.
Pic. 2 Cutting roller bit
Two rollers installed on the lugs welded onto the bit base. The rollers have a form of gage edge and, as you can see from the picture, provide a square cross section of the well. Cutting unit with cutters (2) and spring supported (3) might move in the axial direction. Spring compression is regulated by the screw (4). Сжатие пружины регулируется гайкой 4. Cutting edges are allocated in such a way as to follow the roller profile and provide bottomhole destruction around the circle inside the cross section of the well, formed by the rollers.
There was made a research (using t-flex analysis program) into compression strain, which appears during the static load over sides of cylindrical wells and wells with noncircular cross section. Firstly, there were examined the circular wells with 200mm diameter and 5х6 well pattern. первом Secondly, there were examined 190 mm square wells with 5,5х6 well pattern. It may be concluded, that lager damage area in case of bigger well pattern and smaller dimensions is provided by square cross section wells.
There were made economic calculations of such wells and drilling tools productivity. Specific consumption of explosives qualitative decrease might be gained trough well pattern increasing, this also will cause drilling volume decreasing.
According to the index conditions of the drilling and blasting operations at the graphic log Berezovsckiy might be decreased up to 12,5 %, as well as drilling volumes, which might also decrease up to 12,5 %.
According to this data the economic calculations of drilling and blasting operations productivity were made. The drawing shows that expenses on drilling and blasting operations of wells with square cross section are lower in comparison to circular cross section wells.
Pic. 3. Summary expenses on different types of drilling and blasting operations
1. There was suggested a drilling tool for square cross section wells, which might be applied to rock with 7-11 hardness. Noncircular cross section wells usage influences over drilling and blasting operations productivity at the open cast mining. It might cause drilling rig efficiency increasing and specific consumption of explosives decreasing.
2. There is required a production of bit prototypes in order to carry out drilling and blasting tests.
3. There is required a detailed research into square wells blasting for drilling and blasting parametric optimization and precise determination of economic potential.
4. There are required project investments.
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