Some Results of Production Tests of Light Long-Stroke Electric Drills

I. G. Basov, N. S. Kolodyazhnyi, V. I. Pogorelov

Studies of the regimes of rotary drilling of shot holes in hard coal and in rocks of low strength \((f = 2 \div 4\) on Prof. M. M. Protodyakonov’s scale) show that the maximum productivity of modern hand-held electric drills and the fullest utilization of their power, \(1.0\text{–}1.2\ \mathrm{kW}\), can be ensured at feed forces of \(200\text{–}250\ \mathrm{kg}\) [1]. A worker, however, feeding the drill manually, can provide the drilling of horizontal shot holes with a force of \(18\text{–}30\ \mathrm{kg}\); i.e., the operation of hand-held drills in drilling hard coals and weak rocks is carried out under low-efficiency regimes.

In this connection, some plants are now producing the hand-held electric drills ERP-20 and SRP-1, which have forced feed. According to their technical characteristics, these drills can ensure the drilling of hard coals and weak rocks under the most expedient regimes, i.e., with a force of \(200\text{–}250\ \mathrm{kg}\) and a feed rate of \(0.5\text{–}0.9\ \mathrm{m/min}\). In practice, however, miners and drivage workers use ERP-20 drills less readily than ER-5 drills. The reason for this, in our opinion, is that the device for forced feed of the drill mechanizes only part of the labor-intensive work of the driller—it creates the required feed force. Holding the drill in the required position is still done manually, just as when ordinary ER-5 hand-held drills are used. If one takes into account that the weight of the ERP-20 and SRP-1 drills has been increased in comparison with the weight of ER-5 drills by \(4\text{–}7\ \mathrm{kg}\) and amounts to \(27\text{–}30\ \mathrm{kg}\) together with the bit and cable, it becomes clear that they cannot substantially ease the driller’s labor.

Because the ERP-20 and SRP-1 drills lack special devices for guiding the bit during collaring and drilling-

this operation, when there is a long rod and forced feed, is very labor-intensive and dangerous. All this devalues drills with forced feed.

A number of foreign firms equip hand-held electric drills with special feed devices mounted on jack columns. The feed devices have lunettes for guiding the drill bit when starting the hole. The drive of these feed devices, as a rule, is manual. Similar attachments for hand-held drills have also been manufactured in recent years by the Konotop Plant. These attachments carry the weight of the drill and drilling tool throughout the entire drilling process and, thus, free the worker from performing the most labor-intensive operation. However, because such feed devices are manually driven, the worker is still compelled to expend considerable effort on feeding the drill. In addition, their use, which involves installation on a jack column, leads to large expenditures of time on auxiliary operations.

In order to reduce the labor intensity of work with hand-held electric drills and increase their productivity, Associate Professor O. D. Alimov of the Tomsk Polytechnic Institute proposed creating for them a special supporting-and-feeding attachment, which the plant should supply together with the drills being manufactured.

For the most effective use of such an attachment in mining practice, it must satisfy the following conditions:

1) permit drilling a blasthole to its full depth (1.8–2.0 m) without changing drill rods;

2) have a device for guiding the bit when starting the blasthole;

3) free the driller from supporting and feeding the drill during the drilling process, leaving to him the functions of controlling the machine: switching the motor and feed mechanism on and off, setting it up before drilling, and changing the tool;

4) the supporting attachment must be mounted on a jack column or on existing manipulators, be simple in design, and sufficiently compact and light.

On this basis, a design was developed for a light long-stroke electric drill, which was manufactured partly at the Tomsk Electromechanical Plant and partly in the institute workshop. It is a modernized ERG-20 electric drill with forced feed, mounted on a long, light guide frame that permits drilling blastholes to the required depth without changing the drill rod (Fig. 1).

During drilling the drill moves along the guide frame by means of its feed mechanism, which is a winch whose drive is effected from the motor.

electric drill through a worm reducer. The electric drill is fed to the face by winding a steel cable 1 (Fig. 1) onto the drum of the winch; one end of the cable is fastened to the bracket of the guide frame. The feed mechanism has a friction clutch consisting of inner 2 and outer 3 conical disks, the first of which is connected to the shaft of the worm wheel of the reducer, and the second to the drum. By means of the clamping nut 4 it is possible to vary the compressive force of the clutch disks and thereby vary the force with which the drill is fed to the face. The housing of the drill reducer is made with a special lug 5 (Fig. 1), which serves for fastening the machine in the slots of carriage 1 (Fig. 2), movably secured to guide frame 2 of the feeding device.

Fig. 1. General view of a heavy long-stroke electric drill.

When drilling the face with long-stroke drills mounted on the manipulator, with the boom of the latter deflected to either side from the axis of the working, part of the useful stroke of the feeding device is lost. Therefore it must have a stroke compensator so that the entire set of holes can be drilled to the same depth. The light long-stroke drill has such a compensator with a ratchet locking mechanism. It consists of toothed notches 3 (Fig. 2) in the lower rib of the guide frame and a pawl 4, fastened to the bed 5 with a disk-shaped [[unclear: word cut off at page bottom, begins “pya-”]]

6 for fastening the entire installation to the manipulator. The guide frame enters the grooves of the bed with the ribs of angles 7 and, during operation of the drill, is fixed against backward displacement by a pawl entering the toothed notch of the guide rib.

To guide the drilling tool at the moment the blast-holes are collared, a lunette 8 is secured to the front part of the guide frame; it consists of a body with a hinged cover, a split cast-iron bushing, and the nut of the expanding pick 9. The rear rib of the lunette has a hole for hooking on the steel cable that feeds the drill mechanism.

Production tests of light long-stroke electric drills were first carried out at a stone quarry near the city of Tomsk, and then at mine 5–6 of the Prokopyevskugol trust, in the working face of a field drift with a mine opening cross section of 9.2 m² in the clear, when installing them with the aid of MBI-5u manipulators on a UMP-1 rock-loading machine.

Fig. 2. Diagram of the feed device of a light long-stroke electric drill

At the quarry, because of the absence of rocks of low hardness, experimental drilling was carried out in an area with homogeneous sandstone with a hardness coefficient \(f = 6\).

During the mine tests, drilling had to be carried out at the face with various rocks and, in particular, through carbonaceous and clay shales with inclusions of pyrite and quartz, gray siltstone and sandstone, whose hardness varied within the range \(f = 3 \div 6\).

Hexagonal drill steel with an inscribed-circle diameter of 25 mm was used as the drills.

Removal of the drilling fines of the broken rock from the blast-hole during drilling was accomplished by water supplied under a pressure of 1.2–1.5 ati through a sealing coupling into the axial channel of the rod. In view of the absence of crowns for rotary drilling with flushing, cutters 42 mm in diameter were used: for soft rocks, type RM (BI-501), and for rocks of medium hardness, RP-2 (BI-706); by means of a special adapter device designed by KuzNIIUI, these were fastened to the rod cone.

To evaluate the drilling regimes of light long-stroke electric drills during their testing, the power consumed was recorded by a self-recording wattmeter. The feed force was measured with a dynamometer inserted into the slot of the feed rope.

The experiments were carried out at a spindle rotation speed of 370 rpm.

The data from the study of sandstone drilling regimes with hardness \(f=6\) using long-stroke electric drills are summarized in the graph (Fig. 3), from which it is evident that, with an increase in feed force and consumed power, the drilling speed increases. Its increase is especially noticeable at feed forces from 250 to 280 kg and power consumption of 1.4–1.8 kW. But under such conditions, i.e., in the case

Fig. 3. Dependence of drilling speed on feed force (1) and consumed power (2).

of exceeding the rated power (1 kW), the motor of the ERP-20 drill operates unstably and often “tips over.”

It should be noted that, at feed forces below the maximum values provided by slipping of the clutch disks, drilling also proceeds with significant peaks and drops in consumed power (Fig. 4). This is explained by the imperfection of the design of the conical friction clutch of the drill feed mechanism, which does not allow the feed force to be regulated smoothly and maintained steadily at the required level by means of disk slipping. They often jam, as a result of which the correspondence between drilling and feed speeds is disturbed, leading to excessive loading of the motor.

To determine the possibility of drilling blast holes with drills having a somewhat greater motor power in these rocks, the joint operation of two ERP-20 machines was investigated, pri-

with one of them operating the drill rotation and the other the feed. This experiment showed that even a slight increase in the power going to drilling ensures stable operation of the drill electric motor at feed forces of 300 kg (instead of 250 kg), which makes it possible to increase the drilling speed by a factor of 1.5.

Tests of long-stroke drills both in the quarry and in the mine showed that the power of the ERP-20 electric motor is insufficient to provide the most effective drilling regimes, especially if it is taken into account that the hardness of the rocks in one and the same face, as it advances, may change substantially.

Fig. 4. Diagram of the power consumed by the electric motor of a long-stroke drill when drilling sandstone of \(f=6\) at a spindle rotation speed of 375 rpm and feed forces:

\(1\)—125–220 kg; \(2\)—90–120 kg; \(3\)—225–250 kg; \(4\)—275 kg.

change. For drilling rocks with hardness \(f=6\), the power of the electric motor of the long-stroke drill must be increased somewhat. This will make it possible to raise the productivity of such drills in comparison with the ERP-20 electric drill mounted on long guides, and to use them for drilling rocks with a hardness coefficient varying within the limits \(f=3\div6\).

In order to determine the effectiveness of introducing light long-stroke electric drills, they were tested in comparison with ER-5 hand drills, the most widespread in the mines of the Kuzbass.

Under the existing organization of labor in the mines of the Prokopyevskugol Trust, it is stipulated that, when carrying out main workings, three drivage workers work in the face per shift. Drilling of blastholes in rocks with \(f<5\) is usually carried out with ER-5 hand electric drills. In this case all three drivage workers participate in the dr—

...: one switches on and holds the drill in the required position, while the other two create the feed force on the face.

The production tests conducted on lightweight long-stroke electric drills confirmed the expediency of their development, above all because they considerably ease the labor of the drillers.

In the process of drilling with a long-stroke drill mounted on a manipulator, one person takes part; his functions are reduced to switching the machine on and off, as well as returning it to its initial position after drilling of the blasthole has been completed. Only during the transition from one blasthole to another does a second drifter assist in setting the feed beam between the face and the boom of the manipulator mounted on the loading machine, and also in fixing the position of the manipulator boom.

Time-and-motion observations of the operation of hand-held and long-stroke electric drills in one face revealed significant advantages of the latter in the mechanical drilling rate (see table). However, the overall drilling rate, taking into account auxiliary operations, is somewhat lower for the long-stroke drill. This is explained by the large expenditure of time on auxiliary operations in the drilling cycle with a long-stroke drill when it is mounted on an MBI-5u type manipulator. Observations showed that 60% of all auxiliary time is spent on extending the boom of the MBI-5u manipulator when moving from one blasthole to another, since there is no quick and reliable means of fixing it in one or another required position.

But the use of lightweight long-stroke electric drills, even when they are mounted on such imperfect manipulators, permits a crew of three drifters to work simultaneously on two machines. Thanks to this, the drilling rate of machines serviced by three drifters can be increased by more than 1.5 times (see table), and, with the proper organization of work in the face, even by 2 times.

Observations have established that when blastholes are drilled without flushing, using twisted-steel bits to depths greater than 1.2–1.3 m, the discharge of drill cuttings becomes difficult and the drilling speed drops sharply. Therefore, with hand drills, blastholes are usually drilled to a depth of no more than 1.2–1.3 m. The blasthole depth required by the drill-and-blast work plan (1.8 m) is not maintained, and the advance of the face per round is usually 0.9–1.0 m with a rock output of 8–10 mine cars.

Testing of light long-stroke electric drills showed that, with flushing of the blasthole, the drilling speed and the efficiency of removing cuttings of the broken rock, provided there is sufficient water pressure, do not depend on changes in blasthole depth up to 2 m. The drilling depth of blastholes with light long-stroke drills is 1.9–2 m, with an advance per round of 1.6–1.8 m and a rock output amounting to 15–16 two-ton mine cars; i.e., the drill-and-blast work plan is fulfilled. In addition, flushing the blasthole with water creates favorable working conditions for the drilling tool, as a result of which the service life of the bits doubles and the sanitary working conditions of the miners are improved.

A significant increase in the mechanical drilling speed and a reduction in the duration of auxiliary time can be achieved by eliminating the following design shortcomings revealed during the testing of prototype long-stroke drills.

1. The power of the motor of the ERP-20 drill does not provide effective drilling regimes for rocks with hard inclusions (pyrite, quartz veins, etc.). It must be increased to 1.6–1.8 kW.

2. The design of the friction clutch does not provide smooth regulation of the feed force and stable maintenance of the required value for the given drill power. In this connection, it is necessary to provide a limiting clutch that permits specified feed forces to be set for a given drill operating regime.

3. Because there is only one spindle rotation speed, it is impossible to select the required drilling regime for rocks of different hardness. Provision must be made for two or three spindle rotation speeds, with switching without disassembling the drill.

4. The presence of a separate coupling for flushing complicates the working conditions with the drill during drilling. Therefore, it is necessary to provide a spindle design that permits blastholes to be drilled with flushing without a special coupling for this purpose.

5. The design of the switch of the ERP-20 drill requires constant pressure on it to start the machine, which makes drilling difficult, especially for the upper blastholes. It is necessary to provide

the locking device for the on-position of the electric motor of the long-stroke drill.

It should also be noted, as a drawback of the design of the mounting devices, that they generally have wrench-type nut clamps. As a result, much time is spent on auxiliary operations. Therefore, the mounting devices should be manufactured with nut clamps having a freely moving lever.

The introduction of lightweight long-stroke electric drills, created with allowance for the shortcomings of the first designs, will make it possible, when drilling rocks with a hardness of \(f = 3 \div 6\), to increase drillers’ labor productivity by 1.5–2 times in comparison with the use of hand-held electric drills.

REFERENCES

1. V. L. Azarkh, A. D. Imas, O. P. Shumovskii. Determination of drilling conditions with hand-held electric drills. BTI, Ugletekhizdat, 1952.