ON THE DEVELOPMENT OF LONG-STROKE PNEUMATIC ROTARY DRILLING MACHINES

O. D. ALIMOV, V. Z. DOZMAROV

Theoretical and experimental studies of the processes of rock destruction [1, 2, 5] substantiate the possibility of creating rotary drilling machines capable of drilling blast holes in rocks with \(f = 6—10\) at speeds of up to \(2—3\ \text{m/min}\). To ensure such drilling speeds, quite definite parameters of drilling machines are required. In Fig. 1 \((a, б, в)\) the relationships are given between drilling speed, feed force, number of revolutions of the drill, and torque in rotary drilling. The drilling speed of blast holes \(40—46\ \text{mm}\) in diameter increases with feed force and, for all feed forces, has a maximum value at a drill rotational speed of \(300—450\ \text{rpm}\). As the feed force increases, the torque required to rotate the drill also increases.

According to research data [1, 2], in order to obtain drilling speeds of \(2—3\ \text{m/min}\) in rocks characteristic of Kuzbass mines, it is advisable to have drills with feed forces of \(600—1300\ \text{kg}\). However, as the practice of drilling operations has shown, the use of rotary drilling machines designed according to the schemes of EBK-2m column drills with increased parameters does not provide the expected increase in drilling productivity. The auxiliary operations characteristic of column drills (collaring, changing rods) nullify the speed qualities of such machines. In addition, the absence of guiding devices for the drills leads, at high feed forces, to even greater difficulty during collaring and to bending of the drilling tool. Therefore, for drilling machines being developed to operate with high forces and feed speeds, it is necessary to seek new structural schemes. The Department of Mining Machines and Mine Transport of the Tomsk Polytechnic Institute is engaged in developing new structural schemes for rotary drilling machines and creating new types of drilling machines. Here, various schemes and parameters of long-stroke drilling machines were substantiated, and on their basis a number of machines with electric and pneumatic drives, with mechanical and hydraulic feed, were created [2—4, 6].

In creating long-stroke pneumatic drills mounted on the manipulators of loading machines, the following requirements were used as a guide:

1. The drilling machine must have parameters ensuring drilling speeds of up to \(2—3\ \text{m/min}\) and a reverse speed of the drill of \(8—\)

10 m/min. Since in the process of drilling blastholes the hardness of the rocks changes very often (especially when crosscuts are being driven), the drill must have the ability to change the drilling conditions automatically,

Fig. 1. Interdependences between drilling parameters:
a) dependence of the drilling speed \(U\) on the load \(P\) on the bit (according to L. A. Schreiner’s data); b) dependence of the drilling speed \((U,\ \text{m/min})\) on the rotational speed of the cutter \((n,\ \text{rpm})\) (according to G. N. Pokrovskii); c) zones of variation of torque as a function of feed force in rotary drilling in sandstone \(f\ 8—12\).

adjusting itself to the most economical mode (within the limits of the motor power), which ensures the maximum possible drilling speeds. It is not advisable to create conditions that provide drilling speeds above 3 m/min. In this case the reduction in drilling time will constitute an insignificant percentage relative to the total cycle time for drilling a blasthole, taking auxiliary operations into account. When drilling a blasthole 2 m deep, increasing the machine speed from 3 to 4 m/min will reduce the blasthole drilling time by 10 sec, whereas the average time of auxiliary operations when drilling a blasthole is 2–3 min. Further increases in the productivity of drilling operations should expediently be achieved by reducing the time of auxiliary and preparatory-completion operations.

1. The drilling machine must have devices for supporting the drill during drilling and collaring, drill blastholes to full depth without changing rods, have devices that create the thrust of the drill during the drilling process between the face and the manipulator, and devices that compensate for the drill’s withdrawal from the face when the manipulator boom is turned [2]. The presence of the listed elements will make it possible to reduce the time of auxiliary operations during drilling and thereby increase the productivity of drilling operations.

2. The drilling machine must be simple in design and control, reliable in operation, inexpensive, and, if possible, light (150—

170 kg), be quickly and conveniently disassembled into separate parts during assembly and disassembly on the manipulator of the loading machine, and require a minimum amount of auxiliary equipment. These qualities make it possible to reduce the time of preparatory and concluding operations during drilling and to increase the economic efficiency of the new equipment.

Work on the creation of pneumatic drilling machines was carried out in the following directions:

1. Justification of the structural scheme of the drilling machine.
2. Investigation of various types of pneumatic drive for drilling machines, with the aim of ensuring the necessary drilling modes while using the most economical types of motors with minimum weight and dimensions.
3. Investigation of the created designs of drilling machines under laboratory and production conditions.

As a result of analyzing various possible schemes for long-stroke drilling machines, it was concluded that for pneumatic drills it is most expedient to have a scheme with separate drives for feed and rotation of the drill steel. The long-stroke electric drills with rack-and-pinion and rope feed developed at the Department of Mining Machines and Mine Transport of TPI—EBR-1, EBR-2, EDP-14, EDP-20 [1, 2, 6, 7], as well as the electric drill with hydraulic feed ESDGP [2]—have one common motor for feed and rotation of the drill steel.

The principal advantage of the two-drive design of drills, in comparison with the single-drive design, is, in our opinion, the simplicity of the drill design, since there is no complicated reducer dividing the motor power into two channels. The use in electric drills of one motor with the division of power between rotation and feed of the drill steel is justified by the fact that in this case fewer control devices are required (starters, leakage relays, transformers, clutches, etc.). In the case of using pneumatic energy, however, these additional links are absent.

To choose the type of feed for long-stroke pneumatic drills, an analysis was made of various feed mechanisms: rope, rack-and-pinion, chain, screw, and hydraulic. In terms of a number of factors (simplicity, reliability in operation, compactness, provision of the necessary drilling modes, etc.), preference was given to screw feed. On its basis a scheme of a two-screw feeder was developed, and several variants of long-stroke drills were created: SPV-1D, SPV-2D, SPV3 [3, 4].

With the same structural scheme, the drills differed from one another in the type of pneumatic drives for feed and rotation of the drill steel, and also in the design of the screw feed mechanisms. The SPV-1D drill has, as the motor of the rotator, a rotary motor from the experimental drilling machine VNIIOMShS. To reduce the number of revolutions of the drill steel and increase its torque, a planetary reducer with a gear ratio \(i = 5.3\) was built into the motor design.

Rotation of the drill steel of the SPV-2D drill was performed by a DR-5 piston pneumatic motor with a built-in reducer \((i = 2)\). As the drive of the rotator of the SPV3 drill, a gear-type pneumatic motor of special design was used. The rotator and feeder of the SPV3 drill are unified with the design of the BU-1 rotary-percussive drilling installation.

To determine the actual parameters, the drill rotators were tested on a brake stand. Figure 2 shows the variation of the torques of the rotator motors as a function of the number of revolutions of the drill steel. The rotator of the SPV-1D drill with a rotary motor, at an air pressure in the network of 5–6 atm and a drill-steel speed of \(n = 300\)–400 rpm, develops a torque on the drill steel of 8–10 kgm.

The overload capacity of the rotary drive used is small. It stops at an output-shaft rotational speed of 100 rpm and \(M_{\mathrm{cr}} = 10.0\text{--}12.5\ \mathrm{kgm}\) (air pressure 5 and 6 ati). The ratio

[Figure: torque characteristics. Vertical axis: “Torque, kgm”; horizontal axis: “Number of revolutions of the drill rotation, rpm.” Curves are marked by air pressures of 3, 4, 5, and 6 ati.]

Fig. 2. Torque of the drives of long-stroke pneumatic drills of the SPV type: \(\square\)—with a rotary motor, \(\bigcirc\)—with a piston motor, \(\triangle\)—with a gear-type motor for drill rotation.

\[ \frac{M_{\max}}{M_{\mathrm{p}}}=1.05\text{--}1.2 . \]

The effective power of the motor is low, while the specific air consumption per 1 effective hp is very high—\(2\ \mathrm{m^3/min/hp}\). A theoretical calculation of the power and air consumption of this motor shows that, for its rotor dimensions, the effective power should be higher and the air consumption lower. The high air consumption and low efficiency of the rotary motor for drill rotation are explained by a drawback common to this type of motor—air leakage between the rotor and the stator of the motor.

The SPV-2D and SPV3 drill drives with piston and gear motors, within the required range of drill rotation speeds—300–400 rpm—have approximately the same torque at a given air pressure in the supply line. At an air pressure of \(p=4\) ati, a change in rotational speed from 300 to 400 rpm corresponds to a change in torque of the gear drive from 12 to \(9\ \mathrm{kgm}\), and of the piston drive from 11 to \(5\ \mathrm{kgm}\). At an air pressure in the supply line of 5 ati, these limits for the gear and piston drives are, respectively, \(17\text{--}14\ \mathrm{kgm}\) and \(18.5\text{--}10\ \mathrm{kgm}\).

An advantage of the gear drive of the SPV3 drill is the stability of the torque when the number of drill revolutions changes. At \(p=6\) ati and when the drill rotational speed changes from 300 to 400 rpm, the torque changes by only \(3\ \mathrm{kgm}\). In this same range of speed variation, the piston drive of the SPV-2D drill at \(p=5\) ati changes its torque by \(8.5\ \mathrm{kgm}\).

A drawback of the gear drive is its low overload capacity. The motor stops at 120–130 rpm. The ratio

\[ \frac{M_{\max}}{M_{\mathrm{p}}}=1.05\text{--}1.25 . \]

When drilling rocks whose strength often varies...

... and inclusions of harder bodies are encountered. Therefore, frequent “slipping” of the drill rotator of the SPV3 with a gear motor should be expected, despite its large torque.

The piston drill rotator of the SPV-2D, despite the sharper change in \(M_{\mathrm{cr}}\) and its smaller value, will operate more steadily. It stops at 50 rpm of the drill. The overload capacity is

\[ \frac{M_{\max}}{M_{\mathrm{n}}}=1.9\text{--}2.3. \]

Another advantage of the piston rotator over the gear-type one is the lower specific air consumption per 1 effective hp \((1\ \mathrm{m^3/min/hp}\) versus \(1.3\ \mathrm{m^3/min/hp})\).

The design scheme of the feeders of the SPV-1D, SPV-2D, and SPV3 drills is the same. Table 1 gives data on the motors of the drill feeders and the characteristics of their feed mechanisms.

Table 1

The test results for the feeders of the SPV-1D, SPV-2D, and SPV3 drills are given in Figs. 3 and 4. At constant pressure of the compressed air in the network, an increase in the resistance to motion of the rotator leads to a decrease in the feed speed of the feeders. At a certain maximum value of the feed force, the motion of the rotators ceases.

The SPV-1D drill, which has a single-start screw feed mechanism, provides the feed speeds and feed forces required when drilling holes in rocks with \(f = 4\text{--}10\). A disadvantage of the SPV-1D drill feeders is the low return-stroke speed. With an air pressure in the network of 5 atm, the return-stroke speed is \(3\ \mathrm{m/min}\). This means that, for the operation of withdrawing the rotator after drilling, at a hole length of \(2\ \mathrm{m}\), 40 sec are spent per hole, or 27 minutes for 40 holes.

Another disadvantage of the single-start feed mechanism of the SPV-1D drill is its low efficiency.

The advantage of the four-start screw feed mechanism of the SPV-2D drill is the high speed of withdrawal of the rotator \((13\text{--}15\ \mathrm{m/min}\) at \(p = 4\text{--}5\ \mathrm{atm})\) and a higher efficiency compared with single- and two-start...

…feed mechanisms, and so forth. However, the feeder of this drill cannot ensure a stable drilling speed of less than 1.5 m/min, since, with a further reduction in the speed of the DR-2 feed motor, it stops.

Among the shortcomings of the four-screw feeder one should include the abrupt change in feed speed with a slight change in feed force. A reduction in the feed force from 1250 to 1100 kg \((p = 5\ \text{atm},\) Fig. 3) corresponds to an increase in feed speed from 2 to 4 m/min.

When drilling rock, in order to maintain a constant drilling speed and avoid frequent stoppages of the feed motor, it is necessary constantly to vary the air pressure supplied to the feeder motor.

Fig. 3. Relationship between the feed force and the feed speed of feeders: ○—single-screw feed mechanism of the SPV-1D drill, □—four-start screw feed mechanism of the SPV-2D drill.

The feeder of the SPVZ drill has a smoother change in speed when the feed force is varied. A change in the feed force from 750 to 1500 kg \((p = 4\ \text{atm},\) Fig. 4) corresponds to a change in feed speed from 3 to 0.9 m/min. At the same air pressure in the line, the feeder of the SPVZ drill develops greater feed forces than the feeders of the SPV-1D and SPV-2D drills. The return speed of its rotator is 5.5–7 m/min at \(p = 4\text{–}5\ \text{atm},\) which sufficiently meets the specified requirements.

As noted above (Fig. 1, b), a definite value of rotator torque must correspond to the feed force produced by the feeder. At a line pressure of 5 atm, the feeders of the SPV-1D and SPV-2D drills develop feed forces of up to 1300 kg. In order for the drilling process to be stable, the drill rotators must have a torque within the range of 20–25 kgm. This requirement is met by the rotators of the SPV-2D and SPVZ drills in the range of drill rotation speeds from 50 to 250 rpm, and is not at all met by the rotator of the SPV-1D drill, which has \(M_{\mathrm{cr\,max}} = 9\ \text{kgm}\).

Already at an air-line pressure of 5 atm, the feeder of the SPVZ drill develops a feed force of up to 1800 kg. Such a feed force must correspond…

correspond to a rotator torque on the order of \(35\ \text{kgm}\). The drill rotator itself, at \(p=6\ \text{atm}\), develops a maximum torque \(M_{\text{torque max}}=22\ \text{kgm}\). Consequently, when drilling rock it is necessary to regulate—

Fig. 4. Relationship between the force and the feed rate of the SPV3 drill feeder.

Vertical axis: feed force, kg.
Horizontal axis: number of revolutions of the feeder screw, rpm.
Curves: \(2\ \text{atm}\), \(3\ \text{atm}\), \(4\ \text{atm}\), \(5\ \text{atm}\), \(6\ \text{atm}\).

—the pressure of the air supplied to the feeder; otherwise the rotator will frequently overturn. It is advisable to use the SPV3 drill feeder with this type of rotator at an air pressure of \(3\ \text{atm}\). In this case it will develop a feed force of up to \(1000\text{–}1100\ \text{kg}\). The pressure of the air supplied to the rotator should be \(5\text{–}6\ \text{atm}\), in order to provide \(M_{\text{torque}}=20\text{–}22\ \text{kgm}\). To make full use of the capabilities of the SPV3 drill feeder, the rotator must have a considerably higher torque and overload capacity.

Industrial tests of the SPV-1D and SPV-2D drills at the Stepanov quarry in the city of Tomsk and in the mines of Kuzbass confirmed the working capacity of the SPV-2D drill and the shortcomings of the SPV-1D drill [4]. In rocks with hardness \(f=6\text{–}8\), the SPV-2D drill provided a machine drilling speed of up to \(1500\ \text{m/min}\) at an air pressure in the line of \(3.5\text{–}4.5\ \text{atm}\). The time required to drill off one face with an area of \(14.5\ \text{m}^2\) (38 blast holes) was \(3.5\text{–}3.8\) hours. With the same time for drilling off the face, the SPV-2D drill replaced four PR-30l6 drilling hammers, and labor productivity increased by more than a factor of 2. SPV3 drills are currently being prepared for industrial tests.

On the basis of the research and design work on the creation of long-stroke pneumatic drills, as well as their industrial tests, the following conclusions may be drawn:

1. The proposed path for developing long-stroke pneumatic drilling machines is correct, as was confirmed by industrial tests of drills. The design scheme of the drill feeders of the SPV type proved to be serviceable and reliable in operation. The time required for auxiliary operations in drilling blast holes was significantly reduced in comparison with column-type drilling machines and drilling hammers; the machine drilling rate increased and, as a result, the overall labor productivity in drilling the face increased.

2. The design of the screw feed mechanism must be improved in order to ensure the required drilling regimes and to increase its efficiency.

3. Further investigation of pneumatic feed drives of various types must be carried out in order to select the most economical type that provides the necessary drilling regimes.

4. Work on improving drill rotators should proceed in the direction of increasing their torques to 25–35 kgm at \(n = 300\text{–}450\) rpm of the drill, selecting the most economical types of pneumatic motors, and reducing their weight and overall dimensions.

5. The SPV-2D and SPV3 drills may serve as the basis for creating industrial batches of long-stroke pneumatic drills.

References

1. Alimov O. D., Investigation of the Processes of Rock Destruction in Blast-Hole Drilling. Tomsk University Publishing House, 1960.

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

3. Alimov O. D., Dozmarov V. Z., Gorbunov V. F., Zhulev Yu. A., Lisovskii E. I., A Feeder for Moving a Drilling Tool. Author’s Certificate No. 141462.

4. Alimov O. D., Dozmarov V. Z., Long-Stroke Pneumatic Drill SPV-2D. Kolyma Journal, No. 4, 1962.

5. Pokrovskii G. N., Basic Regularities in Rotary Drilling of Blast Holes with Constant Feed Force. Proceedings of the WSF, Academy of Sciences of the USSR, issue 19, 1957.

6. Kolodyazhnyi N. S., Dvornikov L. T., Results of Laboratory Investigations of EDP-20 Electric Drills. The article is included in the present collection.

7. Alimov O. D., Kolodyazhnyi N. S., On the Creation of Long-Stroke Electric Drills with Mechanical Feed. Izvestiya Vuzov, Mining Journal, No. 2, 1963.