Laboratory Studies of Lightweight Long-Stroke Electric Drills of the EDP-20 Type

N. S. Kolodyazhny, L. T. Dvornikov

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

Laboratory and industrial tests of prototypes of lightweight long-stroke electric drills and of the LDS-2 electric drill [1] showed that a more powerful rotator can be mounted on the feed frame of these electric drills, and that the feed force can be brought up to 500–600 kg, while the weight of the drill will change only by the amount of the increase in the weight of the electric motor and the rotator reducer.

On this basis, the Department of Mining Machines and Mine Transport of Tomsk Polytechnic Institute, in cooperation with the Special Design Bureau of the Tomsk Electromechanical Plant, drew up technical specifications for the creation of an experimental batch of lightweight long-stroke electric drills with motor power increased to 2 kW.

In accordance with the assignment, the Tomsk Electromechanical Plant developed a design and manufactured an experimental batch (5 units) of EDP-20 type electric drills. The technical characteristics and general view are given in Table 1 and in Fig. 1.

Table 1

The EDP-20 electric drills are made according to the schematic arrangement of the EDP-14 drills [10], using their feeders.

Laboratory studies of the EDP-20 electric drills were carried out on a universal test stand for studying rotary-action machines [2].

Fig. 1. General view of the EDP-20 drill.

The tests were carried out with the following aims:

1. To determine the serviceability of the following assemblies of the drill:
   a) the speed-switching device;
   b) the feed mechanism and friction clutch;
   c) the bracing device;
   d) the swivel for mounting the drill on the manipulator.

2. To determine the actual parameters of the drill (feed force, torque, power, efficiency, etc.) and to establish the following relationships:
   a) the power consumed by the motor as a function of the drill feed force and the torque on the auger;
   b) the efficiency of the drill as a function of the torque on the auger and the feed force.

1. Determination of the serviceability of individual drill assemblies

a) Speed-switching device

The speed-switching device consists (Fig. 2) of jaw clutch 8, gears 5 and 7, and a shifting fork with handle 9.

Clutch 8 can be fixed in three positions: speed I—when connected with gear 5, speed II—when connected with gear 7, and the neutral position.

Testing of the speed-switching device was carried out by repeatedly engaging and disengaging speeds I and II.

To test the clutch under load, various torques were created on the drill auger, up to “overturning” of the electric motor. The experiments were conducted at both speed I and speed II.

After 100–150 engagements, the operation of the switching mechanism deteriorated sharply. Upon disassembling the drill it was found that jamming of the clutch occurred because of deformation of the edge of the keyway of the spindle and of the jaw clutch, since they had not been heat-treated and their contact area with the key was insufficient for transmitting the torque arising during operation of the drill. This deficiency can be eliminated by hardening the jaw clutches and spindles, as well as by increasing the contact area between them.

The contact area can be increased by a splined connection of the jaw clutch with the drill spindle.

The handles of the speed-switching mechanisms, made of plastic, have insufficient strength and must be replaced with metal ones.

Fig. 2. Kinematic diagram of the EDP-20 drill rotator.

b) Feed mechanism

The mechanism for feeding the tool to the face—a cable winch driven by the drill electric motor (Fig. 2)—consists of drum 14, cable 16, and friction clutch 15.

The purpose of testing the feed mechanism was to determine the operability of individual elements when various feed forces were produced. To this end, with the aid of the friction clutch, different feed forces were set; and, when these reached their limiting value, observations were made of the nature of slipping of the disks. During the tests, the feed forces were determined from the readings of pressure gauges in the hydraulic-cylinder circuit of the test installation, and, for checking, by a dynamometer connected into the gap of the feeding cable.

The power used to produce these feed forces was recorded by a self-recording wattmeter of type N-379.

Tests of the feed mechanism at various feed forces and feed speeds showed that slipping of the disks of the friction clutch at feed forces of 500 kg and more occurs in jumps, with considerable fluctuation of the feed force (200–250 kg) and of the consumed power (Fig. 3, a). This is caused by poor-quality machining of the surfaces, considerable variation in thickness, and warping of the friction disks.

If it is taken into account that, in the drilling process, a change in feed force is inevitably accompanied by a change in cutting torque, it becomes clear that the fluctuations in consumed power will be still more significant.

When well-manufactured disks are selected, slipping occurs more uniformly, with smaller variations in feed force and consumed power.

Figs. 3 and 6 show recording diagrams of the power consumed when drilling limestone with a hardness coefficient \(f = 4\), with different feed forces and different drill-bit rotation speeds. It is apparent from the diagrams that even with small feed forces, the power fluctuations when the disks slip reach up to 1 kW. Such operation of the friction clutch does not meet the technical requirements.

Fig. 3a. Diagram of the change in consumed power during operation with disk slippage without torque on the drill bit.

Tests of the friction clutch with disks having polished friction surfaces showed that the fluctuations of the feed force are considerably reduced and, consequently, the power fluctuations are also reduced. At feed forces up to 400 kg, the change in feed force during disk slippage does not exceed 50 kg.

With polished disks, the stiffness of the spring compressing the disks must be increased, since the coefficient of friction of the disks is significantly reduced. An excessive increase in the number of disks in the clutch leads to a disproportionate increase in the transmitted torque and, consequently, in the feed force. The utilization coefficient of the disks decreases, control of the friction clutch is significantly worsened, and maintenance of the drill is made more difficult—the reverse withdrawal after completion of drilling. Therefore, lightweight long-stroke electric drills with manual return of the rotator backward must have friction clutches with a number of disks not exceeding 16 pcs. [8, 9].

Fig. 3b. Diagram of the change in consumed power during operation with disk slippage when drilling limestone.

c) Drill switch

During the tests the drill switch operated without failure. The plastic handle of the switch has insufficient strength and should be replaced by a metal one with a rubberized surface.

d) Spreading device

Experimental drilling in the laboratory, as well as the results of mine tests of the EDP-14 drills, showed that the spreading device of the feed units of the EDP-20 and EDP-14 drills has a number of advantages, among which should be included the possibility of creating additional spreading of the feed unit as the force on the feed rope increases, and the removal of spreading when the feed rope is freed from feed forces.

At the same time, the drill feed unit has shortcomings, the principal one being the considerable distance from the axis of the pick to the axis of the drill. This causes a large torque around the pick, especially at the moment of collaring, and when drilling the lower blastholes of the face it requires considerable cleaning up of the rock. Therefore it is necessary, as far as possible, to bring the spreading pick closer to the drill bit.

e) Drill swivel

For mounting the drill on the manipulator of the loading machine, a special swivel is used, manufactured together with the feed unit of the EDP-14 and EDP-20 drills. The main shortcoming of this swivel is the absence of a mechanism for fixing the position of the drill in the vertical plane. This considerably complicates the spreading of the feed unit, especially when drilling upper blastholes, and leads to an increase in the time of auxiliary operations.

2. Determination of the actual parameters of the drills

To determine the actual parameters of the electric drills, it is necessary to know the technical characteristics of their electric motors. Tests of the electric motors of drills Nos. 1 and 5 were carried out in the laboratory of the Sibelektromotor plant in Tomsk.

Studies of the electric drills, in order to determine their actual parameters, were conducted according to the unified method for rotary-action machines [2].

The results of the studies of the rotation mechanism are presented in Fig. 4.

From these data it follows that the EDP-20 drills, at the rated power of the electric motor, develop a torque at the drill bit of 4.2–4.6 kgm when operating at speed I and 1.5–1.8 kgm when operating at speed II.

The maximum value of the efficiency of the rotation mechanism reaches 0.6–0.62, as compared with a calculated value of 0.7; i.e., the drills have an efficiency 8–10% lower than the calculated value.

The results of the study of the feed mechanism, presented in Fig. 5, show that, to create the rated value of the feed force, a power consumption of 0.66–0.73 kW is required when operating at speed I, which corresponds to a motor-shaft power of 0.47–0.5 kW; and when operating at speed II, respectively, 0.92–0.96 and 0.68–0.7. The maximum value of the efficiency of the feed mechanism is 10–11%.

From the data of Figs. 4a and 5a it follows that, at the rated feed force,

with a feed force of 500 kg and at rated power, the drills can develop torques of 2.4–3 kgm at speed I and 1.0–1.2 kgm at speed II.

Fig. 4. Dependence of the consumed power (a) and efficiency (b) on the torque on the drill bit:
×—drill No. 1; ⊙—drill No. 2; 1—\(n_b = 300\) rpm; 2—\(n_b = 600\) rpm.

If it is taken into account that the rated power of the electric drill was determined for one-hour operation, while the period of drilling a blasthole is 1.5–4 minutes, operation of the electric motor with an overload of 60–80% may be considered entirely permissible. With a motor overload of 60%, the drill, at the rated value of the feed force, will develop at ...

Fig. 5. Dependence of power consumption (a) and efficiency (b) on the feed force on the feed cable:
×—drill No. 1; ⊙—drill No. 2; 1—feed speed 600 mm/min; 2—feed speed 1200 mm/min.

a)

Vertical axis: Drilling speed, mm/min, \(V\)

Horizontal axis: Feed force, kg, \(F_p\)

b)

Vertical axis: Power, kW, \(N_b\)

Horizontal axis: Feed force, kg, \(F\)

Fig. 6. Dependence of drilling speed (a) and consumed power (b) on the feed force when drilling limestone \((f=4)\):
\(\circ\) — \(n_b = 300\) rpm;
\(\times\) — \(n_b = 600\) rpm;
1 — \(N_{\text{total}} = f_1(F_p)\), \(N_{\text{total}}\) is the total power at the motor shaft;
2 — \(N_{\text{rot}} = f_2(F_p)\), \(N_{\text{rot}}\) is the power for rotating the drill;
3 — \(N_p = f_3(F_p)\), \(N_p\) is the power for feed.

the torque on the bit is 6–7 kgm at speed I and 2.3–2.8 kgm at speed II.

Taking into account the drilling-regime recommendations of a number of researchers [3, 4, 5, 6, 7], it may be concluded that the parameters of the EDP-20 drills, when operating with a 50–60% overload of the electric motor, fully provide the specified drilling rates in the rocks stipulated by the technical design assignment.

The results of experimental drilling of limestone ($f = 4$) at different spindle rotation speeds and different feed forces are shown in Fig. 6.

Conclusions

1. On the basis of the investigations carried out, it may be assumed that, when drilling rocks with a strength coefficient $f = 4$–5, EDP-20 electric drills will provide a drilling rate of 1200 mm/min; and with a strength coefficient $f = 6$–8, 600 mm/min.

2. The feeders of the EDP-14 drills ensure normal operation in combination with the EDP-20 rotary unit at feed forces greater than 600 kg.

3. The new design of switches for remote control, used in the EDP-20 drills, is fully serviceable and reliable in operation.

4. The laboratory tests carried out revealed a number of design shortcomings in the drills. This enabled the plant to eliminate them before conducting industrial tests under mine conditions.

References

1. Basov I. G., Kolodyazhnyi N. S., Pogorelov V. I., Some results of production tests of lightweight long-stroke electric drills. Izvestiya TPI, vol. 108, Sverdlovsk, 1959.

2. Alimov O. D., Dvornikov L. T., Kolodyazhnyi N. S., Universal installation for investigating rotary drilling machines. Izvestiya vuzov, Gornyi zhurnal, No. 8, Sverdlovsk, 1962.

3. Alimov O. D., Investigation of the processes of rock destruction during blasthole drilling. Tomsk University Press, 1960.

4. Buchnev V. K., Theory of blasthole drilling. Encyclopedic reference book, Mining, vol. 5, Ugletekhizdat, 1958.

5. Imas A. D., Azarkh V. L., Determination of drilling regimes for rocks. TsITI. Ugletekhizdat, 1952.

6. Mikhailov V. G., Drilling of blastholes. Metallurgizdat, 1957.

7. Pokrovskii G. N., Selection of the optimum regime in rotary drilling of blastholes by electric drills with hydraulic tool feed. Transactions of the ZSF, Academy of Sciences of the USSR, issue 19, 1957.

8. Chernavskii S. A., Ishkovich G. M., Kiselev V. A., et al., Design of mechanical transmissions. Mashgiz, 1959.

9. Telenkichev V. K., Limit devices against overloading of machine tools. Mashgiz, Kiev, 1957.

10. Shokhor N. I., Improvement of drilling equipment and local-ventilation fans. Mining Machines and Automation, TsITI Uglya, No. 5–6, 1961.