PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR
POLYTECHNIC INSTITUTE named after S. M. KIROV

Vol. 108  INVESTIGATION OF DRILLING MACHINES  1959

ENERGY INDICATORS OF ROTARY-PERCUSSIVE DRILLING OF BLAST HOLES

Ya. A. Serov

For the operation of a rotary-percussive machine in one regime or another, it is necessary to expend a certain amount of power on the operation of the drill rotator, the percussion unit, and the feed mechanism. In the literature we have reviewed, foreign researchers have not clarified the dependence of rotator power on feed force. Therefore it is impossible to judge the advisability of the choice of rotator power in rotary-percussive machines produced by various firms. Investigations have shown that the power expended on drill rotation in rotary-percussive and rotary methods of drilling increases continuously with an increase in the feed force and the rotational speed of the drill (Fig. 1). It should be noted that the paper gives the values of the powers of the rotator, hammer, and feeder transmitted to the drill, allowing for all losses [1]. At the highest speeds of rotary-percussive drilling of sandstones \((n_b = 408\ \text{rpm})\), the rotator power reaches 7 kW, while in drilling diabase and hornfels it is 2.5 kW. With an increase in the air pressure supplied to the hammer from 4 to 6 atm, the rotator power changes only slightly. Under identical conditions, rotary-percussive drilling requires somewhat greater power than rotary drilling. Increasing the number of blows (using the RH-754 hammer as the percussion unit instead of the OM-506) leads to an increase in the power consumed by the rotator when drilling sandstone by approximately 10–40%. The greatest increase in power in this case occurs at lower drill rotational speeds \((196\ \text{rpm})\). The magnitude of the power consumed by the rotator is influenced by the geometry of the tool used (Fig. 1).

The power transmitted to the drill by the percussion unit increases when more powerful hammers are used (including high-

(frequency) and when the pressure of the air supplied to the drilling hammer is increased. At air pressures of 4 and 6 atm, the power transmitted to the drill by the OM-506 hammer was 900 and 1100 W, while by the RH-754 hammer it was 1700 and 2600 W. The power expenditure for feed increases in proportion to the feed force.

The total summed power transmitted to the drill by the rotator, impact unit, and feeder (Fig. 2) increases with increasing feed force, drill rotation speed, frequency and energy of impacts, and depends little on the geometry of the tool. When operating in modes that provide the highest drilling rates in sandstones, the total power expenditures amounted to 6–9 kW, while when drilling

Fig. 1. Power required for drill rotation under various drilling modes:

rock—diabase, $f = 14 \div 16$;
$a$—rotary drilling with bit No. 4;
$b$—rotary-percussive drilling with bits No. 1 (I) and No. 4 (II);
air pressure in the hammer: 4 atm (1) and 6 atm (2);
drill rotation speed: —— 95 rpm, – – – 152 rpm.

diabase and hornfels, 3–4.5 kW. To increase the rate of rotary-percussive drilling of hard rocks, it is necessary to apply greater power to the drilling tool through three units—the rotator, hammer, and feeder. To solve this question, it is necessary to obtain data on the rational distribution of power among the individual units.

Some foreign authors [3] give in their works general considerations on the quantitative distribution of the power consumed by the individual units of the machine when drilling rocks of different hardness. These considerations, however, are not confirmed by experimental data. Nevertheless, for the design of rotary-percussive drilling machines, the ratio of the powers of the individual units is of great importance, since it approximately characterizes the distribution of the energy supplied

to the destruction of the bottom of the blasthole between the rotary and impact units.

The dependence of the relative power consumption by the individual units on the drilling regimes is shown in Figs. 3 and 4. In constructing the dependences shown in Figs. 3 and 4, the total power consumption was taken as 100%, while the powers of the individual units constituted a definite part of it.

From Figs. 3 and 4 it is evident that, under all drilling regimes, with an increase in the feed force and the rotation speed of the bit, the power of the rotator increases (the share of rotary destruction of the rock increases). On the other hand, because of this the relative power of the hammer decreases. Raising the air pressure in the hammer of the impact unit from 4 to 6 atm leads to an increase in the relative power of the hammer and to a decrease in the relative power of the rotator (Figs. 3 and 4).

Fig. 2. Dependence of the total power of the drilling installation on the regimes of rotary-percussive drilling:

1 — bit No. 1; 2 — bit No. 2; air pressure in the hammer: a — 4 atm; b — 6 atm; bit rotation speed: I — 51 rpm, II — 95 rpm, III — 152 rpm.

An increase in the number of blows (using hammer RH-754 as the impact unit instead of hammer OM-506) leads in all cases (Fig. 3) to an increase in the relative power of the hammer and to a decrease in the power of the rotator.

Under all regimes of rotary-percussive drilling, the relative power of the feeder remains almost unchanged.

The relative power consumption by the individual units shows that the process of destruction of rock of medium hardness occurs mainly due to the rotary motion of the drilling tool (Fig. 3), while in drilling hard rocks it occurs through penetration of the bits under the action of impacts (Fig. 4). Therefore, the share of the rotary unit in the first case accounts on average for 70% of the total power expenditure, and the share of the impact unit for 20%; in the second case, respectively, 40 and 50%. Moreover, the power of the rotary unit when drilling rocks of medium hardness reaches 7 kW, whereas when drilling hard rocks it is 2.5 kW.

Fig. 3. Relative power consumption by the rotator (1), hammer (2), and feed mechanism (3) under various rotary-percussive drilling conditions:

rock—sandstone, \(f = 8 \div 12\), drill rotation speed 408 rpm;
\(a\)—bit No. 2, \(p = 4\) atm; \(a_1\)—bit No. 2, \(p = 6\) atm; \(b\)—bit No. 4, \(p = 4\) atm; \(b_1\)—bit No. 4, \(p = 6\) atm;
—— hammer OM-506; — — hammer RH-754.

The geometry of the tool practically does not change the relative distribution of power among the individual units.

The energy intensity of rock destruction under all modes of rotary and rotary-percussive drilling decreases with

with increasing feed force, and then remains practically constant (Fig. 5).

The gradual decrease in the energy intensity of drilling is explained by the fact that the process of destruction at small feed forces occurs

Fig. 4. Relative power consumption by the rotator (1), hammer (2), and feed mechanism (3) under various modes of rotary-percussive drilling; rock:

— hornfels, – – – diabase; bit No. 4; hammer RH-754;
$a n_{\mathrm{b}} = 95$ rpm, $p = 4$ atm; $a_1 — n_{\mathrm{b}} = 95$ rpm, $p = 6$ atm;
$b — n_{\mathrm{b}} = 51$ rpm, $p = 4$ atm;
$v — n_{\mathrm{b}} = 152$ rpm, $p = 4$ atm.

not in the region of volumetric destruction, but in the region of elastic deformations and surface wear. During this period, before the onset of volumetric destruction, the power expenditures for the process of destroying the rock are large, while drilling rates are relatively low.

… rock. Therefore, the energy intensity of drilling is high, since it is directly proportional to the power expenditure and inversely proportional to the drilling speed.

The energy intensity of rotary-percussive drilling, as well as of rotary drilling, depends to a considerable extent on the geometry of the drilling tool. The volumetric work of destruction is smaller for bits that provide higher drilling speeds. The minimum energy—

Fig. 5. Energy intensity of the destruction process under different drilling regimes:
rock—hornfels; — · — \(n_b = 51\) rpm;
—— \(n_b = 95\) rpm; — — — \(n_b = 152\) rpm;
air pressure in the hammer: \(a\)—4 atm; \(b\)—6 atm; \(1\)—bit No. 1; \(2\)—bit No. 4.

energy intensity of drilling sandstone, \(6\text{–}9\ \mathrm{kgm/cm^3}\), was obtained when using bits Nos. 2 and 3 (with front angle \(\gamma = 0 \div -10^\circ\)) [2] and feed forces of \(500\text{–}600\ \mathrm{kg}\). Under these same drilling regimes, but when using single-chisel bits No. 1 (\(\gamma = -55^\circ\)), the energy intensity of drilling increased by a factor of 2–3 and reached \(16\text{–}22\ \mathrm{kgm/cm^3}\). A characteristic feature is that the minimum energy intensity, as a rule, corresponds to feed forces at which the increment in the speed of rotary-percussive drilling relative to rotary drilling reaches a maximum [1]. In drilling diabase and hornfels the energy intensity is \(33\text{–}39\ \mathrm{kgm/cm^3}\)

was obtained when using bits No. 4 (with \(\gamma = -25^\circ\)) and feed forces of 900–1200 kg. Under analogous conditions, the energy intensity of drilling with single-chisel bits No. 1 increased by a factor of 1.5–1.7.

With an increase in the rotational speed of the drill (from 95 to 152 rpm), the energy intensity of rotary-percussive drilling remains practically constant. However, in the case of drilling hornfels, increasing the number of drill revolutions from 51 to 95 rpm reduced the volumetric work on average by 60% (Fig. 5). This is explained by the high value of the drilling energy intensity at \(n_b = 51\) rpm, when considerable crushing of the rock was observed (50–70 blows occurred per one revolution of the drill), while the drilling speeds were low.

The energy intensity of rotary-percussive drilling of sandstone only slightly exceeds the energy intensity of the rotary method.

When drilling diabase, the energy intensity of destruction by the rotary method in the range of feed forces 300–1500 kg exceeds the energy intensity of rotary-percussive drilling by a factor of 20–2. The large value of the energy intensity of rotary drilling at small feed forces is explained by the low drilling speed, since at small feed forces the pressure at the contact point between the tool and the rock is insufficient for volumetric destruction of the latter. Under analogous conditions, in rotary-percussive drilling the blows on the drill ensure penetration of the cutter into the rock. Therefore the speeds of rotary-percussive drilling are higher and, consequently, the energy intensity is lower in comparison with the rotary method.

On the basis of the investigations carried out, it is possible to recommend parameters for individual units of a rotary-percussive machine.

When selecting the parameters of a machine intended for drilling blastholes during the driving of preparatory workings in rocks of medium strength (\(f = 8 \div 10\)), we proceeded from the condition of attaining high drilling speeds with a rational distribution of power among the individual units of the machine. Analysis of the power consumption by the individual units showed that, when high drilling speeds are attained in rocks of medium strength, the relative power expenditures by the rotator amount to 70%, and by the hammer to 20%; that is, there is reason to suppose that the main destruction of the rock occurs due to the rotational motion of the tool. Therefore, increasing the number of blows above 3500 per minute and raising the power of the hammer appears inadvisable. On the basis of these considerations, one may recommend a number of blows of 3000–3500 per minute with an impact energy of 3–5 kgm, and a rotator motor power of 4 kW at an optimum feed force of 1000–1200 kg [2].

When selecting the parameters of rotary-percussive drilling machines for rocks of high strength, we set ourselves...

The task is to increase the drilling rate without reducing the wear resistance of the bits. To increase the drilling rate, greater power must be applied to the drilling tool through three units (the feed mechanism, the rotator, and the impact unit). The relative distribution of power among the separate units shows that the power of the feed mechanism amounts to no more than 4% of the total power expenditure and is determined mainly by the drilling rate. The power of the rotator depends on the feed force, the rotational speed of the drill, and the strength of the rock (it increases with an increase in the rotational speed of the drill and the feed force, and with a decrease in the strength of the rock).

On the basis of investigations of operating regimes and tool wear resistance, it was established that the feed forces in rotary-percussive drilling should be taken within the range of 1000–1200 kg, and the number of drill revolutions as 90–100 per minute [1, 2]. It follows from this that increasing the power of the rotator above 2 kW is not possible. The only remaining way to increase the power applied to the drilling tool is by increasing the power of the hammer of the impact unit. The power of the hammer can be increased by increasing the number or the energy of the blows. Investigations established that the blow energy of the hammer cannot be increased above 4–5 kgm because of the insufficient strength of the hard-alloy plates of the drill bits [2]. Consequently, it is necessary to increase the power of the impact unit by increasing the number of blows from 3500 to 5000–6000 per minute, with the energy of a single blow not exceeding 4–5 kgm. It is obvious that an increase in the number of blows must be combined with an increase in the rotational speed of the drill (from 100 to 200 rpm). In accordance with the foregoing, one may recommend a number of blows of 3500–6000 per minute, a blow energy of 4–5 kgm, and a rotator power of 3 kW.

On the basis of the foregoing, it may be concluded that the parameters of the separate units of a rotary-percussive machine will differ for drilling conditions in rocks of medium and high strength.

REFERENCES

1. O. D. Alimov, I. G. Lapichev, Ya. A. Serov. Investigation of rotary-percussive drilling. Izvestiya TPI, vol. 106, Metallurgizdat, 1958.

2. Ya. A. Serov. Investigation of a drilling tool for rotary-percussive drilling of blast holes. Article in the present collection.

3. B. G. Fish. Percussive–Rotary Drilling. The Mining Magazine, 1956, March, vol. 94, No. 3, pp. 133–142.