Results of Laboratory Tests of the EBK-2m Core Electric Drill

L. T. Dvornikov, N. S. Kolodyazhnyi

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

The EBK-2m core electric drill (electric core drill, second model) is mass-produced in the Soviet Union by two plants: the V. V. Vakhrushev Tomsk Electromechanical Plant and the “Krasnyi Metallist” Konotop Electromechanical Plant.

The differential-screw feed mechanism adopted in the design of the EBK-2m drill was first used in the E-153 drills of the German firm Siemens-Schuckert, produced since 1928. In the Soviet Union, such a drill began to be mass-produced at the Tomsk Mechanical Plant in 1933 under the designation EK-2. Later this drill was modified somewhat and up to the present time has been produced under the designation EBK-2m.

The main reasons why the EBK-2m core electric drill, which has been mass-produced since 1933, continues to find the widest application in the coal industry of the USSR are, in our opinion, the following:

a) Work on the creation and introduction of new core drills is proceeding very slowly. For example, the ESGP-4 core drill, developed in 1955–1956, is still not being mass-produced.

b) The design of the EBK-2m core drill is simple and very convenient in operation; it makes it possible to provide all the necessary operations during drilling: working drilling speed, rapid retraction of the drilling tool, and rapid advance of the drilling tool to the bottom of the shot hole. It is obvious that, for the entire seven-year period up to 1965, the drilling-and-blasting method of driving mine workings will continue to have the widest application. It is also clear that until a reliable design of a drilling machine more productive than the EBK-2m is created, the latter will continue to be produced and used everywhere. Therefore, at present it is very important to identify reserves for increasing the productivity of drilling operations using EBK-2m drills.

In recent years, on the basis of scientific recommendations, the plants manufacturing EBK-2m drills have made a number of changes in the design, the chief of which are: the use of a multi-disk friction clutch and an increase in the feed force to 1000 kg.

The EBK-2m drill (Fig. 1) consists of an electric motor with a reducer that reduces the spindle speed, a spindle feed mechanism, and ...

and handles for controlling start-up, stopping, switching on and off the feed and the reverse motion of the spindle.

Fig. 1. Kinematic diagram of the EBK-2m drill.

Transmission of rotation from electric motor 3 to lead screw 1 is carried out by three pairs of gear wheels 4–9. With clutch 7 engaged, rotation is also transmitted to nut 14, and the spindle is fed forward (working feed speed).

With clutch 7 disengaged, rotation is transmitted only to the spindle, which, rotating in the fixed nut 14, moves backward (reverse travel).

Technical characteristics of the EBK-2m

The present work was carried out for the purpose of determining the quality of manufacture of production drills, determining the overall efficiency of the drill, and finding reserves for increasing drilling productivity. A comprehensive study was conducted of one drill from the batch produced in 1961, No. 1927. The set of investigations included:

a) recording the complete characteristic of the drill motor;

b) recording the load characteristics of the drill at various spindle speeds and various feed rates, and determining the effective torques and feed forces;

c) determining power losses in the motor and reducer;

d) checking the reliability of operation of the safety friction clutch.

Tests of the drill electric motor were carried out in the TEMZ laboratory according to the standard procedure in accordance with the TU rules. A no-load test, a short-circuit test, and the load characteristic were taken.

Figure 2 presents the dependences of the change in the motor speed, shaft power, and magnitude of the losses in the motor on the consumed power.

The no-load power of the motor, when the voltage is varied from 440 to 120 volts, changes from 310 to 119 W. At the nominal voltage of 380 volts, \(P_0 = 240\) W. The current consumed in this case is \(I_0 = 2.21\) A, \(\cos \varphi = 0.165\).

Fig. 2. Dependence of the speed \(n\), the magnitude of losses \(P_{\text{dv}}\), and the shaft power \(N_b\) of the EBK-2m drill motor on the magnitude of the power consumed.

From the short-circuit test, a change in voltage from 380 to 100 volts corresponds to a change in short-circuit power from 22,800 to 729 W, in power factor from 0.655 to 0.492, and in torque \(M_k\) from 4 to 0.195 kg·m. At the nominal voltage \(U = 380\) V, \(P_k = 22.8\) kW, \(\cos \varphi_k = 0.655\), \(M_k = 4\) kg·m, \(I_k = 53\) A.

The load characteristic was obtained as follows: at a voltage of 380 V, the load on the motor shaft was varied; in this process the consumed power changed from 1.575 kW to 11.750 kW, the motor current changed from 3.15 to 20 A, the speed from 2961 to 2490 rpm, and the slip \(S\) from 1.3 to 19.000.

At the nominal consumed power \(P_1 = 3125\) W, the values of the principal parameters were:

\[ i = 5.5\ \text{A}; \qquad S = 2.98; \qquad n_{\text{dv}} = 2910\ \text{rpm}. \]

On the basis of the load characteristic, the total losses in the motor were determined as a function of the power consumed by the motor.

It follows from Fig. 2 that the nominal power of 2.7 kW on the motor shaft corresponds to a consumed power of 3125 W; i.e., the total losses in the motor are 425 W.

Then the efficiency of the motor is

\[ \eta = \frac{2700}{3125} = 0.865, \]

and the power factor is \(\cos \varphi = 0.867\).

Table 1 presents the comparative test results of the drill electric motor in comparison with the requirements of the technical specifications.

Table 1

Comparative results of type tests of the motor
of EBK-2m drill No. 1927

The rated torque on the shaft of the drill motor is 0.905 kgm, the maximum torque is 3.29 kgm, and the starting torque is 4 kgm.

Comparing the test data for drill motor No. 1927 with the requirements of the technical specifications, the following conclusion may be drawn: the drill motor has been manufactured to a high standard; it has high values of efficiency and of the ratios

$$ \frac{M_{\max}}{M_{\mathrm{nom}}}, $$

$$ \frac{M_{\mathrm{start}}}{M_{\mathrm{nom}}}, $$

and the no-load losses are below the specified requirements.

The drill tests as a whole were carried out on a universal installation for investigating rotary drilling machines [1]. The drill was loaded with resisting torques of different magnitudes and with forces resisting motion. The consumed power was recorded by an H379 self-recording wattmeter. Load tests were carried out for various rotational speeds. In plotting the dependences $N_{\mathrm{p}} = f(F_{\mathrm{p}})$ for various torques, it was found that the increase in the power consumed by the motor with increasing feed force, at different torques, occurs by the same amounts.

On the basis of the investigations carried out on the drill under load, it was found that the drill reliably withstands a feed force of 1000 kg.

Figure 3 presents the dependence (based on Table 2) of the power consumed by the motor on the torque at the bit for various rotational speeds. It follows from the figure that this dependence is linear. At rated power the drill develops torques in accordance with Table 3.

In the course of testing the drill feed mechanism, the operation of the friction clutch was studied and the possible actual feed forces were determined.

Table 2

Values of torque \(M_{\mathrm{cr}}\), kg·m, force on the dynamometer \(T^*\), kg, and consumed power \(N_{\mathrm{p}}\), for different numbers of revolutions

\(^*\) \(T\) is the force on the dynamometer installed in the break in the rod that brakes the outer cage of the friction clutch of the test installation.

The tests carried out made it possible to draw the following conclusions:

1. The drill can develop feed forces, depending on the compression of the friction-clutch spring, of up to 1500 kg.

Fig. 3. Dependence of the magnitude of the power consumed on the torque on the drill spindle.

Table 3

Within the interval of the linear portion of the spring characteristic, the maximum feed force varies from 400 to 1200 kg.

1. After prolonged slipping of the disks of the friction clutch, an increase is observed both in the maximum feed force and in the power consumed (Fig. 4). In Fig. 4 the numerals 1, 2, 3, 4, 5 denote drops in feed force and, consequently, in consumed power. This was achieved in the following way: with maximum compression of the friction-clutch spring, the drill was switched on; the valve-throttle of the hydraulic system of the test installation was completely closed. The first actuation of the friction clutch was observed at a pressure in the stand hydraulic system of 6 atm, i.e., at \(F_{\text{p}} = 1200\) kg; this corresponded to a consumed power \(N_1 = 1\) kW. After repeated slipping of the clutch disks, an increase in feed force and consumed power was observed. The dropping of the feed force was carried out very rapidly. After the pipeline had been closed by the valve-throttle, an intensive increase in feed force was observed, and the first actuation of the clutch occurred at a feed force equal to the feed force that had been developed by the moment of the drop in oil pressure in the installation hydraulic system.

a)

[Graph axis label:] Power consumption, kW

Diagram of the increase in power consumption during slip-testing of the friction-clutch disks.

b)

[Graph axis label:] Power consumption, kW

Diagram of the change in power consumption during slip-testing of the friction-clutch disks.

Fig. 4.

This indicates that the coefficient of friction of the disks during slipping changes in the direction of increase. If the first actuation of the disks occurred at a feed force of 1200 kg, then after 2 minutes of clutch operation the maximum feed force reached 2000 kg. In Fig. 4b, jumps are shown in the shedding of the power consumed by the engine as a result of slipping of the clutch disks. This fluctuation amounted to 100–150 W. At the same time, the feed force fluctuated by 50–100 kg. The kinematics of the EBK-2m drill provides for the possibility of obtaining 18 different feed rates at six different spindle speeds.

For all 18 feed rates, curves were obtained for the variation of consumed power as a function of feed force. On the basis of the results of these experiments, the nomogram shown in Fig. 5 was constructed.

Fig. 5. Nomogram for determining the power consumed by the motors from the known feed rate, feed force, and spindle speed.

It is characteristic that, at one and the same feed rate and identical feed force, the power consumed by the motor differs for different spindle speeds. Moreover, a higher number of revolutions corresponds to greater consumed power.

This is due to the fact that at higher numbers of revolutions of the reducer, greater losses occur in it. Using the nomogram (Fig. 5), it is easy to find the power consumed by the motor, knowing the feed rate and feed force. The value of the consumed power is given without taking into account the efficiency of the motor.

In Fig. 6 a nomogram is presented, constructed for the formula

\[ N=\frac{F_{\text{п}}\cdot V_{\text{п}}}{60\cdot 102},\ \text{kW}. \]

By this formula the useful power required for feeding the drill bit at the rate \(V_{\text{п}}\) and force \(F_{\text{п}}\) is calculated.

Using the nomograms (Figs. 5 and 6), it is easy to determine the efficiency of the feed mechanism of the drill.

Figure 7 shows the change in the efficiency of the drill motor, the drill reducer, and the drill as a whole as a function of consumed power for different numbers of revolutions.

The maximum efficiency of the drill corresponds to 5 kW of consumed power for all speeds. It is characteristic that the maximum

Fig. 6. Nomogram for the formula
\[ N_{\text{pol}}=\frac{F_{\text{p}}\cdot V_{\text{p}}}{60\cdot 10^2},\ \text{kW}. \]

efficiency of the drill decreases with increasing spindle speed. At a rotation speed \(n=123\ \text{rev/min}\), \(\eta_{\max \text{ dr}}=0.725\); at a spindle rotation speed \(n=408\ \text{rev/min}\), \(\eta_{\max \text{ dr}}=0.58\), i.e., the maximum efficiency decreases by 20%. If one takes into account that the efficiency of the motor does not depend on the spindle speed, then it is clear that the change in drill efficiency occurs because of a change in the efficiency of the reducer. The spindle rotation speeds 196 and 169, 270 and 297 differ little from one another, and therefore are hardly expedient. The efficiency of the reducer varies, depending on the number of drill revolutions, within the range 0.86–0.685.

The efficiency of the drill varies within the range 0.725–0.58.

The most economical operating conditions are the lower speeds. It is advisable to have only the following spindle rotation speeds: 123, 169, 297, 408 rev/min, and, for these speeds, different feed rates. This circumstance can significantly simplify the work of readjusting the drill. The presence of a smaller number of change gears will undoubtedly make the work of readjusting the drill clearer.

Final conclusions on this question can be drawn only after studying the possibility of providing the required number of feed speeds at four different spindle rotation speeds.

The efficiency of the drill feed mechanism was determined for all eighteen feed speeds and for feed forces of 400, 600, 800, 1000, and 1200 kg for each speed, a total of 90 values.

Fig. 7. Dependence of the efficiency of the motor, the efficiency of the reducer, and the efficiency of the drill as a whole on the amount of power consumed for different cylinder speeds.

Losses in the drill motor were excluded from the value of the consumed power.

From analysis of the data on calculating the efficiency of the feed mechanism, it may be concluded that:

a) the efficiency of the feed mechanism of the EBK-2m drill is within the range of 4–12%;

b) lower feed speeds correspond to lower efficiencies for the same feed forces.

Conclusions

1. The electric motor of the EBK-2m drill is well made, has a high overload capacity; the motor efficiency is 86.5%.

2. The torques developed by the drill fully correspond-

are necessary for drilling blastholes in rocks with hardness up to \(f = 12\) on Prof. Protodyakonov’s scale.

1. The spindle rotation speeds \(n = 196\) rpm and \(n = 270\) rpm duplicate the rotation speeds \(n = 169\) rpm and 297 rpm; therefore they are hardly expedient, and merely introduce confusion when selecting the required number of drill revolutions for specific conditions.

2. The multi-disc friction clutch provides feed forces on the drill spindle of up to 1200 kg. Actuation of the clutch discs occurs with a reduction of the feed force by 50–100 kg. Prolonged slipping of the discs leads to an increase in the feed force to 2000 kg and more.

3. The efficiency of the drill reducer depends to a significant degree on the spindle speed. A higher spindle speed corresponds to a lower efficiency value. The efficiency of the reducer at \(n = 123\) rpm is 86% (at rated load), while at \(n = 408\) rpm it is 68.5%, i.e., 20% lower.

4. The efficiency of the feed mechanism varies, depending on the feed force and the spindle speed, from 4 to 12%.

5. The overall efficiency of the drill, without taking into account the efficiency of the feed mechanism, is 72.5–57.5%; with the efficiency of the feed mechanism taken into account, it barely reaches 40%.

6. The eighteen feed speeds of the drill only introduce considerable confusion when selecting the required speed. It is therefore advisable to eliminate some of the duplicate feed speeds. The number of pairs of change gears must be reduced to a minimum.

7. With careful study of the mining-engineering conditions and the selection of the required rotation and feed speeds, the EBK-2m drill can provide high drilling rates in rocks with hardness up to \(f = 12\). This is confirmed by data from experimental drilling carried out by KuzNIIUgol in 1957 in the mines of Kuzbass [2].

REFERENCES

1. Alimov O. D., Dvornikov L. T., Kolodyazhnyi N. S. A universal installation for laboratory testing of rotary-action drilling machines. Gornyi zhurnal, Izvestiya vuzov, No. 8, 1962.

2. Alikin Yu. K. Experimental operation of rock electric drills with hydraulic feed. Ugletekhizdat, 1957.