On a New Type of Percussion-Rotary Drilling Machine

V. N. Leont’ev

In the development of thick, steeply dipping seams of hard coal, coal chutes—or, as they are called in Kuzbass, “furnaces”—occupy a significant place in the overall complex of preparatory workings. The volume of this type of working is exceptionally large when seams are developed using movable shield support, where chutes are driven especially frequently—approximately every 5 m along the strike of the seam. In this case, for only a single extraction section, with its comparatively limited dimensions along the strike (25 m) and an accepted stage height of 100 m, there are 50 m of horizontal workings in the form of drifts on the main and ventilation horizons, and 500 m of chutes. It is obvious that only by forced driving of the chutes can the timely preparation of the front of stoping operations be ensured here.

In Kuzbass practice three methods of driving chutes have become established: by means of blasting, with pneumatic picks, and by using percussion-rotary drilling machines. Driving chutes by blasting is a low-productivity and unpromising method of drivage, a method that must undoubtedly be prohibited in mines dangerous in gas and dust [1].

Driving chutes with pneumatic picks requires highly qualified labor, makes the coal breaking operation very labor-intensive and low in productivity. The average productivity of a face worker with a pneumatic pick here amounts to only 2.5 m/shift. The effort to mechanize the work and thereby achieve a positive solution to the problem of forced driving of chutes led to the appearance of special percussion-rotary drilling machines, the purpose of which is to drill large-diameter boreholes (up to 0.5 m), with their subsequent enlargement to the required dimensions. Among such machines, the PSB-1, “Kuzbass,” SBM-1, and SBM-2 machines are currently used [2; 3; 4].

The design of the machines listed has a number of common features, as does the nature of their operation. Initially, from the main haulage drift, with the aid of a drill bit and a small reamer, a borehole up to 0.5 m in diameter is drilled through the entire height of the stage. Subsequently this borehole, with the aid of a larger reamer, is additionally drilled out from top to bottom to the dimensions of a normal chute. The drilling rig is usually mounted on a movable carriage and consists of an electric motor, a reducer, and a working shaft in the form of a spindle to which the drill rods are connected. Rotation of the drilling tool and the necessary thrust motion are transmitted by the machine spindle through the system of drill rods. During drilling, the string of drill rods is periodically lengthened by attaching (screwing on) short drill rods to it from below; during reaming of the borehole, on the contrary, these rods are gradually removed. Ultimately, when the borehole is of great depth, the drill-rod string becomes very long, easily bends, and therefore requires supporting “lanterns,” which are installed every 4–5 m of the string.

The most advanced of the machines mentioned should be considered the SBM-2 machine designed by Engineer A. A. Mogilevskii. The machine has the following technical characteristics: initial borehole diameter—390 mm; diameter of the reamed borehole—850 mm; borehole length—up to 150 m. Shift output: in drilling—45 m; in reaming—20 m; in lowering the tool—70 m.

Overall dimensions of the machine during transport: length—1873 mm; width—844–1164 mm; height with skid—1400 mm.

Weight of the machine with motor: 1850 kg. Motor of type MA-143—1/4 at 1500 rpm, with a power of 11.4 kW. The average monthly output of SBM-1 machines, allowing for reaming boreholes to a diameter of 750 mm, ranges from 300 to 500 m. Individual machines at the Comrade Stalin mine achieved an output of almost 1000 m per month. But, despite the serious successes achieved as a result of the use of percussion-drilling machines, it cannot be said that the task of creating a serviceable and highly productive percussion-drilling machine has already been completely solved, since the machines possess a number of serious design shortcomings. It is necessary persistently and steadily to continue work on improving the design of existing types of machines and, at the same time, to work on the creation of machines based on other principles.

We consider the principal shortcomings of modern percussion-drilling machines to be the following:

1. The long string of drill rods, assembled from separate, comparatively short rods, under the influence of the feed force is easily subject to longitudinal bending, i.e., it always has a tendency to curve. Additional devices are required in the form of so-called lanterns, which support the string and to a certain extent prevent its excessive curvature. The composite string of drill rods is certainly a weak point in the design of the machines, since even with lanterns present, bending of the rods and deviations of boreholes from the specified directions are still observed, and often very considerable ones. Thus, PSB-1 machines sometimes give deviations of up to 7 m.

2. In operation it is necessary to have a set of parts consisting of a large number of drill rods (more than 100 pcs.) and lanterns, which makes the entire drilling installation cumbersome and non-transportable. The need for a large number of drill rods often leads to interruptions in the timely supply of drilling machines with them and to machine downtime.

3. The bulky drilling installation blocks the drift (usually single-track) for several days, until the borehole has been drilled, making transport work along the drift impossible. As a result, the driving of the main drift is either suspended, or the drilling of boreholes is timed to coincide with the period when the drift has already been driven. All this increases the time required to prepare the section and leads to a reduction in the rate of drift driving. The normal procedure should be considered one in which the drilling of boreholes is carried out simultaneously with the driving of the main haulage drift, does not interfere with it, and, on the contrary, facilitates it by providing the drift with good ventilation through its timely connection with the ventilation horizon.

4. The machines are not adapted to receive and remove coal coming from the borehole during its drilling and reaming. Coal spills onto the machine, onto the workers, and is scattered haphazardly along the drift. Continuous cleaning of the drift is required, with manual loading of the coal.

In connection with the observations made, the design of a percussion-drilling machine today must meet the following requirements:

1. The machine must provide for drilling the borehole immediately to the dimensions of a normal chute. The practice of mining thick seams in the Kuzbass shows that the final diameter of the borehole must be no less than 1.0–1.2 m.

1. The design of the machine must reliably ensure that the raise advances in the specified direction.

2. The machine must not obstruct the main haulage drift, must not interfere with the operation of transport or with passage through the drift. A partial solution to this problem, under the conditions of thick, steeply dipping coal seams, will be to drive the main haulage drift with an auxiliary drift parallel to it, located at the same level. When paired workings are driven, the well-known conveniences are achieved in the operation of transport and in the ventilation of the faces, and independent and simultaneous driving of both the drifts and the raises is ensured.

3. When a raise is driven, up to 100 t of coal is extracted, chiefly fines. It is necessary to devise a method for catching it and automatically loading it into mine cars.

4. The percussion-drilling machine must be simple in design, simple to control and operate, and the entire installation must be portable and transportable. Below is given a brief description of the LL-1 percussion-drilling machine¹ (Fig. 1), whose design represents an attempt at a practical solution of the tasks set forth above.

Fig. 1

The machine has been designed for drilling boreholes 1.0 m in diameter and has the following characteristics: overall length of the machine—2.4 m, width—1.2 m, weight (approximately)—1000 kg. The machine has one electric motor with a power of 11.5 kW (approximately). The drilling rate of the borehole is 12 m per hour of the machine’s net operating time; per shift—50–60 m. Drilling depth is up to 100–150 m. The machine is serviced by two workers—a drilling foreman and his assistant.

The machine consists of the following main parts: the cutting drum (11), the central cutting member (1–3), the reducer (7), the electric motor (8), the feed drum (12), and the guide drum (10).

The cutting drum is made of boiler iron. On its upper end surface there are 15 cutting teeth, tipped with pobedit and arranged in three cutting lines. The drum is rotated by the electric motor and turns clockwise; rotational speed—25 rpm, cutting speed—1.3 m/sec. By means of a clamp ring fastened to the lower inner surface of the cutting drum, the latter is connected with an analogous clamp (5) located on the inner upper part of the feed drum (12). Both clamps are fastened together by an annular toothed rack into a strong annular lock, allowing the drums to rotate freely relative to one another. In the clamps of the lock and along its entire circumference there are balls, forming a ball support for the upper cutting drum. To disconnect the drums for the purpose of dismantling the machine, it is sufficient to detach the annular toothed rack. By means of three lugs (4), the cutting drum is fastened to an internally meshing gear, which is mounted freely on the reducer housing and receives rotation from it. In an analogous manner, the feed drum (12) is also mounted and receives rotation; it is likewise made of boiler-iron sheet and on the outside has a flat supporting surface (14) made of thick strip iron, welded on edge and along a helical line. The feed drum makes 1 revolution per minute, rotating counterclockwise. In this process the helical supporting surface (14) moves along the helical groove in the walls of the borehole. The cutting, feeding, and guiding drums, during their movement, fit comparatively tightly against the walls of the borehole. To form the helical groove in the borehole walls, a special cutter (6) is used, which is fastened to the feed drum and is rotated by the annular toothed rack; the number of revolutions of the cutter is up to 200 per minute, its length is 100 mm, and its mean diameter is 15 mm. The cutter (6) is a slightly conical steel rod, having a coarse trapezoidal screw thread and three longitudinal grooves for removing cuttings (of the tap type). The cutting edges of the cutter are tipped with pobedit. The cuttings produced by the cutter enter the feed drum through a special window in the wall of this drum. Thus, when the feed drum rotates, the helical supporting surface, sliding along the inclined plane of the groove present in the borehole walls, moves the drum forward, and with it the entire machine. In one revolution of the feed drum the machine advances by 200 mm, i.e., the pitch of the helical supporting surface is 200 mm. With a width of the helical supporting surface of 100 mm and with its total mean length of approximately 12 m, the area of the supporting surface is 12,000 sq. cm. Taking the weight of the machine as 1000 kg, the specific pressure from the weight of the machine on the coal pillars beneath the helical supporting surface is found to be very small—approximately 85 g per sq. cm.

The feed drum, by means of a clamp ring fastened to its lower inner surface, is connected with the clamp (9) of the guide drum. Similarly to the cutting drum, here too, by means of an annular toothed rack, rotation is transmitted to the cutters (15), by which longitudinal grooves are cut in the walls of the borehole.

The guide drum (10) does not rotate and consists of two drums (10 and 13), unequal in height, made of boiler-iron sheets. The upper, lower drum is fastened to the feed drum by the annular lock just mentioned. Two cutters (15) are fastened to its sides, milling longitudinal grooves in the walls of the borehole. The cutters (15) are the same as the cutter of the screw groove. For the discharge of cuttings, the guide drum has special windows. By means of three paws this drum is rigidly connected with the housing of the electric motor. The lower guide drum is fastened to the projecting ends of these paws and has two longitudinal bearing surfaces (16), sliding freely in the longitudinal grooves in the walls of the borehole. The bearing surfaces (16) keep the reducer housing and the electric motor from rotating.

The central cutting member (1—3) consists of a central drill with an enlarging spiral (1), two horizontal cutters (3), and a cone (к). The drill with the spiral makes 375 rpm, rotating clockwise. Receiving rotation from the motor reducer, it drills at the center of the face a borehole 160 mm in diameter. In this borehole the transmission (2) of the horizontal cutters is freely accommodated. The transmission consists of three bevel gears, which transmit rotation to the horizontal cutters (3) from the central shaft. The cutters (3) are fastened in brackets of a hollow bushing freely mounted on the central shaft. The bushing is rotated by the motor reducer counterclockwise at a speed of 0.76 rpm. Thus the cutters rotate about their own axes at a speed of 375 rpm and about the axis of the central shaft at a speed of 0.76 rpm, while at the same time moving forward together with the machine. Owing to this, the cutters (3) undercut the solid coal along a helical line, forming from the coal helical slabs 110 mm thick. These latter either fall off by themselves or are easily broken by the pressure of the cone (к). The length of the cutters (3) is variable and depends on the strength of the coal being undercut.

The reducer is placed between the cone (к) and the electric motor (8); the steel casing of the reducer is firmly fastened to the housing of the electric motor. Through windows in the walls of the reducer housing, motion is transmitted to the external gears, which are connected by paws with the cutting and feed drums (11) and (12). The motor is connected to the reducer by means of a friction clutch.

The flexible rubber cable (17) feeding the electric motor is freely wound off the motor and is protected from mechanical damage by a wire braid, and against rupture by longitudinal wires woven into this braid; these latter are fastened to the motor housing.

For transporting the machine along drifts and for starting holes, a carriage of special design is used. The carriage makes it possible to move the machine on rails either in a horizontal position (when the drift height is small) or in a vertical position. The carriage has an extendable frame in which inclined screw surfaces are fastened. The machine is inserted (screwed) into the carriage. When starting a hole, the carriage, and with it the machine, are set in a vertical position and are given an inclination corresponding to the dip angle of the coal seam; then, with the aid of screws, the extendable frame together with the machine is pressed up to the face until it bears against the coal. After this the motor is started, and the machine, cutting into the coal, crawls out of the carriage along the inclined screw surfaces. The coal undercut by the cutting drum of the machine and by the central cutting member falls off in the form of flat pieces (110 mm thick) and drops into the annular space between the reducer and the drums; the minimum width of the annular space is 280 mm. In the case of a steep dip of the coal seam, the broken coal goes by gravity through the machine and along the borehole. The direction of the borehole is initially set by the corresponding position of the carriage and the machine; subsequently this direction—

...the load is borne by the machine itself and by the fact that it fits comparatively tightly against the wall of the borehole. The machine is lowered by the usual reversal of the motor.

At the moment when the machine emerges from the borehole, a car is placed beneath it in the drift, and the machine enters the car by itself.

During the drilling of the borehole the car is moved aside and does not interfere with the operation of transport. Coal from the borehole flows by gravity into the drift directly into the mine cars.

Conclusions

The machine considered has the following advantages:

1. The machine is a kind of combine (drilling unit). It drills a borehole one meter in diameter and does not require either preliminary drilling or subsequent reaming of the borehole; that is, the raise working is obtained at once in finished form.

2. During operation the machine does not obstruct the drift, does not disrupt the normal operation of mine transport, and does not delay the driving of the drift.

3. The machine requires an insignificant number of auxiliary operations and a small staff of service workers. The productivity of the machine is high.

4. The machine is easily and conveniently transported through the workings, produces coal in large pieces, which noticeably reduces the specific consumption of electric power and the required motor power.

We believe that the design features of the present machine will serve as a good basis for creating an industrial model of a new type of high-productivity percussion-drilling machine.

Literature

1. Rodionov G. V.—On directions in the mechanization of the Kuzbass. Ugol’, Nos. 10–11, 1943.
2. New percussion-drilling machine SBM-1. Ugol’, Nos. 10–11, 1943.
3. Khryapkin N. T.—Mechanization of the driving of raise workings. Ugol’, Nos. 4–5, 1945.
4. Pokrovskii N. M.—Driving of mine workings. Gostoptekhizdat, 1945.

1. The design of the machine was proposed by engineers N. D. Lazarevich and V. N. Leont’ev. Priority No. 65283. ↩