Identifying Opportunities for Using Rotary-Percussive Machines for Borehole Drilling at the Khaidarkan Mine

O. D. Alimov, V. F. Gorbunov, A. P. Mironenko, M. A. Saruev, A. N. Shipunov

The high labor intensity and duration of drilling exploration boreholes is one of the main factors restraining the increase of labor productivity and the intensity of development of the Khaidarkan ore deposit, which is characterized for the most part by rocks of medium and high strength.

At present, at the mines of the Southern Mining and Metallurgical Combine named after Frunze, exploration boreholes are drilled by the percussive-rotary method, namely with column-type rock drills KTsM-4 and KS-50, which, under the existing mining-and-geological conditions, do not provide the required machine drilling rates.

EBG electric drills, which over several years underwent testing at the mine, although they make it possible to achieve higher drilling rates in rocks with strength up to 10–12 on the scale of Prof. M. M. Protodyakonov, have not found application here because of the great variability of the rocks in their strength.

Taking into account that the ore bodies, as a rule, are bounded by rocks with strength greater than \(f = 12\), exploration by boreholes using rotary-drilling machines, with the present durability of cutters, is practically impossible.

One of the promising methods for drilling exploration boreholes at the Khaidarkan mine is the rotary-percussive method of rock destruction.

The present investigations had the following aims:

1. To determine the effectiveness of drilling boreholes by the rotary-percussive method (with the BU-1 machine) in comparison with column-type rock drills and electric drills with hydraulic feed under the mining-and-geological conditions characteristic of the Khaidarkan mine of the YuGMK named after Frunze.

2. To determine the serviceability of the drilling tool when drilling exploration boreholes.

To make it possible to use the drilling machine of the BU-1 installation for drilling a fan of boreholes from workings of limited dimensions, the feeder of the BU-1 machine was shortened from 4200 to 2200 mm. The shortening of the feeder was carried out in the mine workshops without any substantial change in the machine design; as a result, the useful feed stroke proved to be only 800 mm, and the rod length 640 mm. The tool set included rods of two standard sizes, 640 and 1340 mm long.

The mounting device for the BU-1 machines was manufactured in the mechanical shops of the mine and consists of an A-shaped thrust column with three screw jacks: one upper jack and two for thrusting against the ground.

Drilling of exploratory boreholes with the KTsM-4 rock drill was carried out using cross bits 64 and 59 mm in diameter, and with the EBG drill and the BU-1 machine using RKS and BU-1-900 cutters 42 mm in diameter.

The methodology for experimental drilling of underground exploratory boreholes determined the location, conditions, and scope of the work; the method for determining the hardness of the rocks being drilled; the conduct of the necessary observations and measurements during drilling; the processing of the results of the experimental work; and the criteria for evaluating the machines.

Drilling of the experimental boreholes was carried out in the experimental section of the Khaidarkan mine. The drilling rig was located in a working; drilling was carried out through jasperoids, limestones, and quartz.

In order to obtain, as far as possible, a more objective comparison of the machines (KTsM-4 and BU-1), they were placed side by side under the same mining and geological conditions. The boreholes were drilled parallel to one another. During drilling, sludge was collected from borehole intervals equal to the length of the rod extension, which made it possible to compile geological sections for each borehole; these are a necessary supplement to the drilling-rate graphs along the length of the boreholes.

In these industrial tests, the BU-1 machine in its modified version was used for the first time for drilling underground exploratory boreholes. The great variability of the rocks, whose hardness sometimes exceeded \(f = 16\), did not make it possible to determine immediately the optimum drilling regimes under these conditions. For this purpose, several boreholes 2.5 to 5.5 m deep were drilled in advance. After that, in these rocks, two representative boreholes were drilled with the BU-1 machine: borehole No. 5, 15.8 m deep, with a drill string made of rods manufactured from drill steel (25 mm hexagon), and borehole No. 7, 30.4 m deep, with a round drill string 32 mm in diameter. Beside these boreholes, a 25 m deep borehole was drilled with a KTsM-4 column-mounted rock drill.

When drilling in the rocks through which the boreholes passed, the drilling rate of the BU-1 machine ranged from 84 cm/min to 11.5 cm/min, and that of the KTsM-4 from 13 cm/min to 3.4 cm/min. Thus, one of the main productivity indicators of the machine—the mechanical drilling rate—of the BU-1 exceeds, under the same mining and geological conditions, the drilling rate of the KTsM-4 rock drill by a factor of 3.9. The life of the BU-1-900 bits before becoming dull was 6 linear m of borehole, and that of the KTsM cross bits was 12 linear m. The test data are summarized in Table 1. As can be seen from Table 1, when drilling with the BU-1 machine, auxiliary operations take up almost 2/3 of the total drilling time. In percentage terms, the time of auxiliary operations when drilling with the BU-1 machine is 3.7 times greater than for the KTsM-4. But with small design changes to the BU-1 machine, the time for auxiliary operations can be made equal to that of the KTsM-4. This would make it possible to reduce the total time for drilling a borehole with the BU-1 machine by an additional 40%.

Despite the fact that in these industrial tests the time of auxiliary operations for the BU-1 machine exceeded the auxiliary operations of the KTsM-4 by more than 2 times, the total drilling time per 1 meter of borehole for the BU-1 was 1.72 times less than for the rock drill. Thus, rotary-percussive machines have great potential capabilities for drilling both blastholes and boreholes.

Table 1

Data from time-and-motion observations during borehole drilling

The comparison of the rotary-percussive drilling method (BU-1 machine) and rotary drilling (EBG drill) was carried out when drilling massive limestones with hardness \(f = 8—12\) in the same experimental area.

The average drilling rate with the EBG electric drill (per borehole) was 21 cm/min, while with the BU-1 machine it was 27.4 cm/min, i.e., 30% higher.

For drilling a 30-meter borehole with the BU-1 machine, 3 BU-1-900 bits were consumed without resharpening, i.e., the average life of a bit was 10 m. For drilling a 27-meter borehole with the EBG machine, 7 cutters were consumed, i.e., the average life of a cutter was 3.86 m. According to the data obtained, the life of one BU-1-900 bit in rocks with \(f = 8—12\) is 2.6 times higher than the life of an RKS cutter.

The comparatively low life of RKS cutters is explained partly by the poor quality of brazing.

As can be seen from Table 1, 58% of the total borehole drilling time is spent on auxiliary operations with the BU-1, while when drilling with the EBG electric drill the time for auxiliary operations was only 44%. The reduction in the time for auxiliary operations with the EBG drill in comparison with the BU-1 occurs mainly due to the reduction in the time for adding rods, which for the EBG, calculated per 1 running meter of borehole, is 4.4 times less than for the BU-1. The time spent on replacing cutters and disassembling the tool string, calculated per 1 running meter, is 35% greater for the EBG than for the BU-1, because the EBG drill string had to be disassembled 7 times instead of three times when drilling with the BU-1. Thus, taking into account that when replacing bits it is also necessary to add rods, reducing the time for these operations on the BU-1 machine is a major reserve that can increase its productivity.

In addition to the comparative tests, the BU-1 machine was tested in drilling a borehole in quartz. At a borehole depth of 442 cm, the average drilling rate was 16.7 cm/min. Three bits were consumed in drilling the borehole. The bit life in quartz was 1.5 m. In rocks of such hardness, the rotary method is not yet applicable, and the percussive-rotary method does not give high results. Therefore, the data obtained in testing the rotary-percussive drilling method are encouraging. They confirm the possibility of creating, on the basis of rotary-percussive machines, high-performance and universal installations for drilling blast-holes and boreholes at the Khaidarkan mines.

Conclusions

1. Drilling exploratory boreholes in the rocks of the Khaidarkan deposit with rotary-percussive machines has advantages over drilling with KTsM-4 core drills because of:
   a) a machine drilling rate 3–4 times higher,
   b) an increase in labor productivity by 60–70%,
   c) improved sanitary and hygienic working conditions for drillers.

2. In comparison with the EBG rotary-drilling machine, the installation based on the BU-1 machine makes it possible:
   a) to increase the average machine drilling rate for boreholes 42 mm in diameter by 30%,
   b) to reduce cutter consumption by up to 2.5 times.

To obtain complete data on the technical and economic effectiveness of using rotary-percussive drilling machines at the mines of the YuGMK named after Frunze, it is advisable to conduct broader tests, taking into account all improvements of the BU-1 machine identified in the present work.