EVALUATION OF MEANS AND METHODS OF BLAST-HOLE DRILLING USED IN KUZBASS

V. Z. DOZMAROV, V. F. GORBUNOV

(Presented by the Department of Mining Machines and Mine Transport)

In driving development workings in Kuzbass, drilling mechanisms are used that differ both in the method of rock destruction and, even with one and the same method of destruction, in their structural design (the basic layout of the mechanism, mounting devices, etc.). For example, in the Prokopyevsk coal district, drilling of blast holes in rocks with \(f = 4—10\) is carried out by:

1. rotary-action drilling machines—hand-held electric drills ER-16 and column-mounted EBK-2M;

2. percussion-rotary drilling machines—hand-held hammers OM-506 and hammers with pneumatic supports PR-30l, PR-30lb, PR-18l.

3. rotary-percussion drilling machines mounted on drilling carriages (BU-1).

In addition, in 1959—1961, industrial tests were carried out on a number of new rotary-action drilling machines designed by Tomsk Polytechnic Institute, intended for drilling from removable manipulators of loading machines: the long-stroke pneumatic drill with screw feed SPV-2D, the long-stroke electric drill with rack feed EBR-1, with hydraulic feed ESDGP, the light drill with cable feed EDP-14, and the drill with hydraulic feed SD-1 (designed by KUZNIUI), intended for drilling from drilling carriages.

This paper presents the results of time-and-motion observations of the operation of various drilling mechanisms, evaluates their quality, and gives recommendations on the use of the most rational scheme of drilling mechanism and drilling method for Kuzbass conditions.

Table 1 summarizes the results of time-and-motion observations of the operation of various drilling mechanisms.

In analyzing the operation of drilling machines, we shall conventionally divide them into five characteristic groups that differ from one another in the technology of producing blast holes:

1. Hand-held drills.

2. Drilling hammers with pneumatic supports.

3. Column-mounted electric drills installed on removable manipulators of loading machines.

1. Long-travel drilling machines installed on removable manipulators of loading machines.

Table 1

1. Long-travel drilling machines mounted on drilling carriages.

Drilling blastholes with hand drills is characterized by considerable expenditure of the worker’s effort to hold the drill and create the required feed force, by a low drilling speed, and by a comparatively narrow field of application—in weak rocks. The time for preparatory-concluding and auxiliary operations during drilling is small. Considerable time is spent on rest. Drilling blastholes is associated with the following operations:

a) delivering the drills to the face;

b) collaring and drilling “by hand,” with periodic stopping for rest;

c) extracting the drill steel from the blasthole;

d) after drilling is completed, removing the drills from the face.

The second group of mechanisms—drilling hammers—is characterized by the following technology (sequence of operations) for producing blastholes:

a) manually carrying the drilling hammers, pneumatic supports, and air and water hoses to the face front (distance 15–20 m). Connecting the hoses to the hammers;

b) setting up the pneumatic support for drilling blastholes and the collaring process, which is carried out with the participation of two workers (the second worker holds the drill during collaring);

c) drilling the blasthole. The process requires considerable effort from the worker. At a blasthole depth of 2 m, there are 2–4 stoppages of the drilling process to reposition the support;

d) manual extraction of the drill steel from the blasthole and relocation of the drilling hammer with the pneumatic support to drill the next blasthole;

e) after drilling is completed, disconnecting the hoses from the drilling unit and removing the hammers with pneumatic supports from the face to a distance of 15–20 m.

The third and fourth groups of mechanisms—column-mounted and long-travel drills mounted on removable manipulators of loading machines—are characterized by the following identical operations:

a) installing the manipulator and drill on the loading machine, connecting the power sources and flushing hoses, and moving the loading machine up to the face;

b) setting the drill for drilling a blasthole. The process involves expenditure of workers’ effort (moving the manipulator boom, moving the drill relative to the boom, etc.);

c) drilling the blasthole. The process is mechanized;

d) mechanized extraction of the drill steel from the blasthole and setting the drill for drilling the next blasthole;

e) after drilling is completed, moving the loading machine away from the face front, removing the drill and manipulator, and disconnecting the hoses and cables.

The most labor-intensive operations in installations of this kind are their mounting on and removal from the loading machine.

When auger drills are used, the work is complicated by the repeated replacement of the drilling tool during the drilling of a single hole. The process of collaring is difficult and takes a comparatively long time, since there are no devices for supporting the drill during collaring.

For the fifth group of mechanisms—drilling machines mounted on drilling carriages—the characteristic features are fully mechanized processes of setting up and drilling a hole, extraction of the drill from the hole, and the absence of manual operations for mounting and dismantling the drilling machine before the start and after the completion of drilling. A substantial disadvantage in the use of such mechanisms is the need to exchange them at the face with loading machines, and the difficulty or impossibility of using them in long single-track workings.

As can be seen from Table 1, percussion-rotary drilling is characterized by relatively low drilling speeds, rather large expenditures of time on auxiliary operations during drilling, and small expenditures of time on preparatory and concluding operations. The cycle for drilling a face with a drilling hammer (40 holes to a depth of 1.9 m) lasts 470–660 min. With four drilling hammers operating at the face, it is 2.7–2.0 hours. The process of drilling with hammers involves considerable expenditures of physical labor. In addition, the strong vibration of the machines and their noise affect the health of the workers.

The positive aspects of percussion-rotary drilling are the small wear of the drilling tool, reliability in operation, and rapid interchangeability of drilling machines.

As studies by a number of authors [1] and the practice of conducting drilling operations have shown, the most appropriate field of application for machines of percussion-rotary action is rock with hardness \(f > 14\). The use in these rocks of the rotary or rotary-percussion method is inadvisable because of the great wear of the drilling tool and the high energy consumption of drilling operations. Large feed forces are required (up to 2000 kg), which leads to an increase in the power and weight of drilling machines.

In the Kuzbass, the hardness of rocks rarely exceeds \(f = 10\). Obviously, under these conditions the use of the percussion-rotary method is inadvisable.

At present, drilling machines of rotary action are gaining ever broader recognition for drilling holes in rocks of medium hardness.

We compare the operation of various rotary-action drilling machines used in the Kuzbass by their productivity. The productivity of drilling machines is evaluated by the time spent on the cycle of drilling the face [2].

\[ T = t_1 + t_2 + T_{\text{п з}}, \]

where

\[ \begin{aligned} T &\text{ — time spent on the cycle of drilling the face, min;}\\ t_1 &\text{ — time spent on the actual drilling of holes (machine drilling time), min;}\\ t_2 &\text{ — time spent on auxiliary operations during drilling of holes, min.} \end{aligned} \]

\[ t_2 = t_3 + t_4 + t_5 + t_6, \]

where

\[ t_3 \text{ — time for setting up the drilling machine for drilling a hole, min.;} \]

\(t_4\) — time for extracting the drilling tool from the blasthole, min;

\(t_5\) — time for changing the drilling tool, min;

\(t_6\) — other operations, min;

\(T_{\text{p.z}}\) — time for preparatory and concluding operations, min.

The smaller the time \(T\), the higher the productivity of the drilling machine.

For a drilling unit consisting of an EBK-2M drill and an MBI-5U manipulator mounted on a PPM-4 loading machine, the time \(T\) is equal to (see Table 1, column 6)

\[ T = t_1 + (t_3 + t_4 + t_5 + t_6) + T_{\text{p.z}} = 306 + (34.0 + 26.0 + 40.0 + \]
\[ +\,0.0) + 25 = 431 \text{ min.}, \tag{2} \]

for the cycle of drilling a face—40 blastholes.

For a drilling unit consisting of the long-stroke SPV-2D drill, mounted on an MBM-2 manipulator equipped with a drive for lifting the manipulator boom,

\[ T = t_1 + (t_3 + t_4 + t_5 + t_6) + T_{\text{p.z}} = \]
\[ = 80 + (52.0 + 10 + 0.0 + 8.0) + 35 = 185 \text{ min.} \tag{3} \]

Comparing (2) and (3), we arrive at the following conclusions:

a) The machine drilling rate of the SPV-2D drill in rocks with \(f = 6\)—9 is 3.8 times higher than the drilling rate of the EBK-2M drill in rocks with \(f = 4\)—7. This is explained, first, by the fact that the EBK-2M drills had not been adjusted to the most optimal operating conditions. The latter is achieved by changing the gear wheels in the drill reducer when the rock hardness changes and by changing the clamping force of the drill friction clutch.

The second reason for the large expenditure of time on drilling when using EBK-2M drills is the difficulty of the collaring process (in the chronometric observations cited, the collaring time is included in \(t_1\)). This occurs as a result of the absence of supporting devices for the drill, i.e., it is a consequence of the imperfection of the drill’s structural arrangement.

b) The time required to set up the SPV-2D drill in combination with the MBM-2 manipulator for drilling a blasthole is 1.7 times greater than the setup time for drilling a blasthole with a unit consisting of an EBK-2M drill and an MBI-5U manipulator. The increase occurs due to the fixing both of the position of the manipulator boom relative to its vertical post in the horizontal plane (by means of a toothed clutch) and of the manipulator swivel relative to the boom. When EBK-2M drills are used with MBI-5U manipulators, the manipulator is fixed by a prop post between the side of the working and the boom.

Investigations carried out in the laboratory of the Department of Mining Machines and Mine Transport of Tomsk Polytechnic Institute showed that the EBK-2M drill can develop feed forces of up to 1000 kg at considerable feed rates (up to 600—800 mm). If it is adjusted to such operating conditions, the drilling rate increases (the first component of formula (2) decreases). In this case, however, it will be impossible to drill with the EBK-2M drill from the MBI-5U manipulator because of the large bending moments acting on the manipulator and the absence of a mechanism for fixing the various positions of the boom. If, however, the EBK-2M drill is mounted on an MBM-2 manipulator, the time required to set up the machine for drilling will be approximately the same as in the unit with the long-stroke drill.

c) The time spent on extracting the drilling tool from the blasthole when SPV-2D drills are used is 2.5 times less than for EBK-2M drills, owing to the increased reverse-travel speed of the rotator, up to 10 m/min.

c) A substantial saving in time when using long-stroke drills is observed because there is no operation of changing the drilling tool—40 minutes per drilling cycle. When drilling with the EBK-2M drill to a depth of 1.9 m, three tool changes must be made.

d) The time for preparatory and finishing operations when using long-stroke drills with MBM-2M manipulators is somewhat greater (by a factor of 1.4) than with a drilling unit consisting of EBK-2M drills and MBI-5U manipulators, since in the former case the unit is heavier and more cumbersome.

As a result, for all cost elements, when using a drilling unit consisting of an EBK-2M drill and an MBI-5U manipulator, 439 min are spent on the cycle of drilling a face of 40 blast-holes, as against 185 min when drilling with an SPV-2D drill from an MBM-2 manipulator. If two drilling units operate in the face, then in the first case the drilling cycle will be 215 min, or 3 h 35 min; in the second, 92.5 min, or 1 h 32 min, i.e., 2.3 times faster.

When the EBK-2M drill is adjusted to the most rational conditions, the time for drilling blast-holes in both cases will be the same. In this case the EBK-2M drill must be operated from an MBM-2 manipulator. Then, in formulas (2) and (3), the time for preparatory and finishing operations \(T_{\text{p.z}}\) and the time for setting the drilling machines for drilling a blast-hole will be approximately the same and equal, respectively, to 35 and 52 min. The time saving per drilling cycle when using long-stroke drills will amount to about 50 min due to the reduction in the time spent on extracting the bit from the blast-hole and changing drilling rods, and, in addition, the time spent on the drilling process when using the EBK-2M drill (in the cited data it is included in \(t_1\)).

It should be noted that, when EBK-2M drills are used for drilling, the working conditions of the drivage workers are more difficult. It is very inconvenient to change the drill rod three times when drilling the upper blast-holes. In this case it is necessary to make a special platform for carrying out this operation. In addition, the worker changing the rods is constantly drenched with water, since even with the pipeline completely shut off, part of the water remains in the bits.

As time-study observations have shown, when drilling blast-holes with an EBK-2M drill in rocks with \(f = 6\text{–}8\), the RP-2 cutters had to be changed every 1.7–1.8 m, i.e., after each blast-hole. The wear resistance of RP-2 crowns when drilling these rocks with the SPV-2D drill was 6–8 blast-hole meters, i.e., 3.8–4.4 times higher. The SPV-2D drill is automatically adjusted to the most rational drilling conditions depending on the hardness of the rock, since a volumetric pneumatic motor with a soft characteristic \(F = f(n)\) is used as its feed drive. The force and feed rate of the motor vary depending on the hardness of the rock.

In the EBK-2M drills there are several strictly fixed settings for feed rates and spindle speeds, which remain unchanged when the hardness of the rock changes. Therefore drills with such rigid characteristics often operate under drilling conditions that differ greatly from the optimum for the given rock hardness.

It follows from the foregoing that, both in terms of the productivity of drilling operations and in terms of the wear resistance of the drilling tool, preference should be given to long-stroke drills.

Table 1 gives data on the operation of the SPV-2D long-stroke drill. In addition, the Tomsk Polytechnic Institute also tested long-stroke electric drills with rack feed, EBR-1, and with hydraulic feed, ESDGP-4. The time spent on prepara-

final and auxiliary operations in drilling with these drills is approximately the same as in drilling with the SPV-2D drill.

We also observed the operation of BU-1 drilling carriages with long-stroke rotary-percussive machines. Formula (1) for the time expenditure per cycle of drilling a two-track heading (40 blast holes) has the following form (see Table 1):

\[ T=t_1+(t_3+t_4+t_5+t_6)+T_p=130+(24+13+0+3)+105=275\ \text{min}. \tag{4} \]

The machine drilling time for 40 holes 1.9 m deep with the BU-1 unit \((t_1=130\ \text{min})\) is 1.6 times greater than the time required to drill the same number of holes with the SPV-2D drill \((t_1=80\ \text{min})\). This is explained by the lower feed forces of the BU-1 unit (900–1000 kg, as against 1200–1300 kg for the SPV-2D) and by the difference in the cutter designs used. In rotary drilling with the SPV-2D drill, RP-2 bits were used, with a cutter-blade sharpening angle of \(\beta=65^\circ\). For the rotary-percussive drilling method, bits are used whose tool geometry is intermediate between the geometry of cutters for rotary and percussion-rotary methods. For the latter, sharpening angles of drill bits of \(\beta=100\text{–}110^\circ\) are characteristic.

A bit with such a sharpening angle is stronger under impact loading and more wear-resistant; however, the drilling speed with such bits is lower than the drilling speed with RP-2 type bits at equal feed forces.

In addition to these reasons, a significant factor increasing the machine drilling time with the BU-1 unit was that, during drilling, the cutters were changed after 12–13 holes, i.e., after 23–25 drilled hole-meters. The nature of the change in drilling speed as a function of bit wear when drilling with the BU-1 unit is shown in Fig. 1. As can be seen from Fig. 1, the first 6–8 holes (11–13 m) are drilled at a higher speed—up to 1 m/min; but subsequently, as the bit wears, the drilling speed falls by almost half. As a result, the average machine drilling speed for one hole with the BU-1 unit is 0.5–0.6 m/min. Consequently, if the bits were changed more often—not after 11–13 holes, but after 6–8—then the first component of formula (4) would be comparatively smaller.

As noted above, in rotary drilling with the SPV-2D drill in the same rocks, the wear resistance of RP-2 type cutters was 6–8 hole-meters. When drilling in softer rocks, with an increase in both cases in the volume of drilled hole-meters per bit, the difference in bit wear resistance between the rotary and rotary-percussive methods decreased. In rocks with \(f=4\text{–}7\), the wear resistance of bits for both drilling methods is 25–35 m.

With an increase in rock hardness, bit wear resistance in rotary drilling falls faster than in rotary-percussive drilling. On the basis of our observations of cutter wear resistance, the rotary method of drilling can be recommended for drilling in rocks up to \(f=10\). In stronger rocks, it is better to use the rotary-percussive method. The advisability of using the universal rotary-percussive method in rocks of medium hardness \((f<10)\) must be considered from the standpoint of the economy of such units as compared with rotary drilling units.

Setting up the drilling machine mounted on the BU-1 drilling carriage for drilling a hole is fully mechanized and takes comparatively little time—on average 21 min per cycle of drilling a face. The time required to extract the drill from the hole, at a reverse rotation speed of 6 m/min, is 13 min for 40 holes. There are no time expenditures—

In-figure labels:
- \(t\), min
- Time for drilling one hole, min
- Change of bit
- Drilling out one hole during a face-equipment shift

Fig. 1. Time for drilling blast-holes in the face-equipment cycle at the Krasnyi Ugol’kop mine, double-track crosscut, \(S = 18.6\ \text{m}^2\), \(f = 9\text{–}11\). Hole depth \(l = 1.9\ \text{m}\); compressed-air pressure in the line \(p = 5.5\text{–}6.5\ \text{ati}\).

Fig. 2. Track layout in the crosscut.

for changing the drilling tool. In general, the time spent on auxiliary operations when drilling with the BU-1 unit is about 40 min per face-drilling cycle, or 1.7 times less than with long-travel drilling machines mounted on removable manipulators of loading machines. This is an incomparably great advantage of drilling carriages. However, drilling carriages also have another negative aspect—large time expenditures on preparatory and finishing operations—up to 1.5 hours per face-drilling cycle. Let us explain this with a specific example.

At the Krasnyi Uglekop mine, blast-hole drilling by a rotary-percussive drilling machine mounted on a drilling carriage is carried out in a double-track crosscut. One BU-1 drilling unit operates at the face. The track layout in the crosscut is shown in Fig. 2. Here 1 is the drilling carriage, 4 and 5 are loading machines, 2 is the platform for rolling mine cars from one track to the other, and 3 is the switch. In order to begin the drilling process, both loading machines must be removed from the face and moved onto one track, since along the other track (for example, the right-hand one) the carriage is rolled into the face. The face is drilled in two stages: first, one half of the face is drilled from the right-hand track; then the unit is rolled across platform 2 onto the left-hand track and the other half of the face is drilled. After drilling is completed, the mechanisms in the face are changed: the drilling carriage is removed and the loading machines are brought in. By the end of drilling, the mechanisms in the crosscut occupy the position shown in Fig. 2. Loading machine 4 is brought into the face along the right-hand track via switch 3, located no closer than 50 m from the face. Then an empty train of mine cars and the drilling carriage are placed behind it, and the end of the empty-car train is moved via switch 3. Loading machine 5 is brought up to the face along the left-hand track. The process of loading the rock begins. After loading is completed, the mechanisms are exchanged again.

Experience in operating BU-1 units has shown that they cannot be used in single-track workings. Even with a working length of 100–150 m, too much time is spent exchanging the drilling carriage for the loading machine. In addition, the cable of the loading machine, along its entire movement to the double-track working, has to be removed from the side of the working and then laid in a coil. A mechanism removed from a single-track working to the main double-track working interferes there with the normal operation of transport. Moreover, the BU-1 unit is not self-propelled, and physical effort by workers is required to move it 100–150 m.

A comparison of the time expenditures for a face-drilling cycle by drilling machines mounted on the manipulators of loading machines and on the manipulators of drilling carriages leads to the following conclusions: the overall time balance of the cycle speaks in favor of units of the first type. This is due mainly to the small time expenditures (in this case) on preparatory and finishing operations.

The machine drilling time of BU-1 units can be reduced somewhat if the bits are changed twice as often. The drilling process itself is simpler when BU-1 carriages are used.

Assessing the positive and negative aspects of drilling units, both types may be recommended for use in double-track workings. Single-track workings should preferably be driven using drilling machines mounted on removable manipulators of loading machines.

The number of long-travel drilling machines simultaneously operating at the face

drilling machines mounted on the removable manipulators of loading machines, in our opinion, should not exceed two. Otherwise the installation becomes very bulky; there are many supply hoses; the pressure drop of the compressed air in the network is large; the time for preparatory and concluding operations increases; the number of workers at the face increases; and the mutual maneuvering of the drilling machines becomes more complicated.

Two SPV-2D drills drill a two-track working (40 blast holes) in
$T = (t_1 + t_2) + T_{\text{p.z}} = 75 + 35$ min.

Suppose that four machines will operate at the face. Then the time $t_1 + t_2$ will decrease by approximately half and will be equal to 40 min. The time for preparatory and concluding operations will also increase approximately twofold and will be $T_{\text{p.z}} = 35 \times 2 = 70$ min. The total cycle time
$T = (t_1 + t_2) + T_{\text{p.z}} = 40 + 70$ min will not change, although the number of workers at the face will increase from 3 to 5.

REFERENCES

1. Alimov O. D., Basov I. G., Gorbunov V. F., Maikov D. N., Drilling Machines. Gosgortekhizdat, 1960.

2. Alimov O. D., On the evaluation of the quality of drilling machines. Izvestiya TPI, vol. 108, Metallurgizdat, 1959.