TECHNICAL CHARACTERISTICS OF PNEUMATIC DRILLING HAMMERS

O. D. Alimov

In the postwar years, the factories of the Soviet Union have created many highly productive machines for the mechanization of heavy and labor-intensive processes in the mining, coal, and construction industries. Among them are new, more advanced and more productive pneumatic drilling hammers of the OM-506, KTsM-4, and other types, the use of which has made it possible to increase significantly the productivity of drilling-and-blasting operations.

The production by our industry of drilling hammers with various technical characteristics and various devices for facilitating their operation—hand-held, telescopic, and column-mounted drilling hammers—makes it possible to select and use them most appropriately for different conditions of mining work.

Thus, for drilling blast holes in hard rock during the driving of preparatory workings, column-mounted drilling hammers of the KTsM-4 type, mounted on automatic feeds, have been created. Column-mounted drilling hammers are also successfully used in drilling the face in ore mining.

Telescopic drilling hammers PT-30 and TP-4 made it possible to ease substantially the work of drillers in the most labor-intensive process of drilling blast holes directed vertically upward. This enabled Stakhanovite drillers to switch to simultaneous operation with two and even four drilling hammers.

The labor intensity has also been considerably reduced in drilling horizontal and inclined blast holes with hand-held drilling hammers through the use of pneumatic supports. When drilling with hand-held drilling hammers equipped with pneumatic supports, the force required to hold the hammer in the necessary position, and also partly the feed force, is provided by the telescopic pneumatic support. Owing to this, the role of the driller in the drilling process has changed significantly, being reduced mainly to regulating the operation of the drilling hammer and restraining the drilling hammer from lateral displacement. This has made it possible to reduce the effect of hammer recoil on the driller’s health, to increase the weight of the so-called hand-held drilling hammers to 30–35 kg and, as a consequence, to increase their power and productivity.

For drilling blast holes and deep large-diameter boreholes in rocks of high hardness, the Krivoi Rog “Kommunist” Plant has in recent years created powerful column-mounted drilling hammers weighing 50–70 kg.

However, the existing variety of designs of the drilling hammers produced creates a number of difficulties in their selection and operation. Thus, for example, at present there are up to 9 types of hand-held drilling hammers, several of which differ on the basis of minor (non-principal) design differences (OM-506l, OM-506m, PM-508).

The selection of a drilling hammer for particular working conditions, as a rule,

A correct assessment of its quality is made difficult by the absence in the literature of comparative technical characteristics of drilling hammers obtained under identical operating or testing conditions. Therefore, data from laboratory and industrial tests of pneumatic drilling hammers manufactured by plants of the Soviet Union, which were carried out in 1952–1953, are of considerable interest.

The laboratory tests were carried out by the Department of Mining Machines and Ore Transport at the Tomsk Electromechanical Plant. The industrial tests were carried out by an interdepartmental commission at the Sokolny mine of the Leninogorsk Polymetallic Combine.

The purpose of the tests was to establish the comparative technical characteristics of drilling hammers as a function of air pressure within the range of 4–7 atm.

All hammers manufactured by plants of the Soviet Union (with the exception of the heavy column-mounted drilling hammers KS-50, PK-60, and KT-70 of the Krivoi Rog “Kommunist” plant) were tested by a single method, on the same laboratory installations and under the same production conditions. The results obtained are given in Tables 1 and 2.

Data for the heavy column-mounted drilling hammers of types KS-50, PK-60, and KT-70, as well as for the hand hammer RT-38, are presented on the basis of laboratory tests by the Krivoi Rog “Kommunist” plant.

To make it possible to compare these and other data, Tables 1 and 2 give the characteristics of the hammers when operating at an air pressure of 5 atm. From Tables 1–2 it is evident that even hammers of the same type, when operating at the same air pressure, have different technical characteristics and a different final result—the drilling rate.

As is known [1–6], the principal parameters determining the rate of percussive-rotary drilling are the impact energy, the number of impacts, and the number of revolutions of the drill. On the basis of the test data it can be established that the numerical values of these parameters for pneumatic drilling hammers at an air pressure of 5 atm lie within the limits indicated in Table 3.

A simultaneous increase in the energy and number of impacts of modern drilling hammers without changing their design and dimensions is possible by increasing the compressed-air pressure. As can be seen from Figs. 1 and 2, increasing the compressed-air pressure from 4 to 7 atm increases the impact energy of the hammer by 70–80% and the number of impacts by 17–25%. This leads to a considerable increase in the drilling rate. The drilling rate with hand-held and telescopic drilling hammers, Figs. 3 and 4, when the air pressure is increased from 5 to 7 atm, increases during drilling in rock of hardness \(f = 8\text{–}10\) (according to Professor Protodyakonov’s scale) by 30–140%; during drilling in rock of hardness \(f = 14\text{–}15\), respectively, by 26–100%. The drilling rate with column-mounted drilling hammers of the KTsM-4 type increases respectively by 90–50%.

In addition, when the compressed-air pressure is increased to 7 atm, most hammers show an increase in the isothermal efficiency coefficient (Fig. 5), a decrease in the total consumption of electric power per linear meter of blasthole, and the operating regime of the hammer becomes more stable. A comparison of the main indicators of drilling hammers at pressures of 5 and 7 atm is given in Table 4.

The highest isothermal efficiency, and consequently the most expedient conversion of compressed-air energy into impact energy, is achieved in the drilling hammers OM-506, PA-23, and PR-35, where at an air pressure of 7 atm the isothermal efficiency reaches 25%. This gives grounds for concluding that in these drilling hammers the ratio of the principal parameters is better than in the others.

Fig. 1

Fig. 2

Air pressure, atm.

Fig. 3

Air pressure, atm.

Fig. 4

Air pressure, atm.

Fig. 5

Table 1

Continuation of Table 1

Table 2

Continuation of Table 2

*) Drilling speed determined when drilling with a bit of 85 mm diameter.

Table 3

Unfortunately, it is not yet possible to answer the question of how close this efficiency is to the theoretically possible and expedient value, and, consequently, how close the ratios of the main design parameters in modern drilling hammers are to the optimum, since at present there is still no sufficiently developed theory for this. There are also no data on the influence, on the operation of drilling hammers, of different structural designs of the air-distribution mechanisms, devices for rotating the drill steel, the presence of intermediate strikers (in the TP-4 and PT-30 hammers), the magnitude of clearances, and the quality of lubrication. The influence of these factors must be determined by special investigations.

Power expended in drilling by pneumatic drilling hammers

The power expended in drilling by pneumatic drilling hammers is used:

1) to create the necessary impact energy;
2) to overcome the resistance to rotation of the drill steel;
3) to feed the drilling hammer;
4) to carry out flushing and blowing of the blasthole.

Since determining the power expended separately on the impact and rotary assemblies in pneumatic drilling hammers presents considerable difficulty, tests usually determine the total power expended on the operation of the drilling hammer during drilling. The latter is expressed either by the consumption of compressed air in m³/min or by the power expended at the compressor, in kW. As can be seen from Tables 1–2, the power expended directly on operation of the drilling hammer at a pressure of 5 atm is, for hand-held hammers, 5.65–1.3 kW; for telescopic hammers, 7–12.4 kW; for column-mounted hammers, 11.8–15 kW.

If it is assumed that, when drilling holes up to 2 m deep and 42–45 mm in diameter, drilling hammers operate steadily at 100–200 revolutions of the drill steel per minute, which corresponds to an average torque on the drill steel of 75–25 kg/cm [3], then the power required for rotating the drill steel is $N = 0.076 \div 0.051$ kW. As shown by N. N. Esin [7], the efficiency of the rotary devices of modern drilling hammers is 14%. Then $N = 0.55 \div 0.36$ kW is expended on rotating the drill steel. The remaining part of the energy supplied to the hammer is expended by the impact assembly. To create the optimum feed force

Table 4

60–100 kg at a drilling speed of 100,500 mm/min requires a power expenditure of 0.001–0.01 kW. For flushing the hole, with a water consumption of 5 l/min and a pressure of 4.5–6 atm [9], no more than 0.010 kW is expended. Thus, the largest part of the power during drilling is spent on creating the required impact energy and on rotating the drill. The total power at the drill-turning device and piston in hand-held and telescopic drilling hammers is 0.80–1.8 kW. Then, at an operating air pressure of 5 ati and an air consumption of 2–3.8 m³/min, the isothermal efficiency of the hammer is 10.4–20%, and the overall efficiency of the installation is 4.7–8.9%, Tables 1–2.

At the same time, the total power expenditure per operating hand-held hammer is up to 20 kW, and for a column-mounted hammer, up to 34.2 kW.

Fig. 6

The energy balance in drilling with pneumatic drilling hammers is shown in Fig. 6. The extremely low efficiency of existing drilling hammers requires the search for ways to increase it both on the basis of a thorough study of the working process of pneumatic hammers and their possibilities, and on the basis of the creation of drilling hammers with other, more economical processes [2].

LITERATURE

1. Alabuzhev P. M., Alimov O. D. The influence of feed force and the angle of rotation of the drill between impacts on the rate of percussive-rotary drilling of holes. Izv. TPI, vol. 75, 1954.

2. Alabuzhev P. M. and Alimov O. D. On the question of designing electropneumatic impact machines. Izv. TPI, vol. 78, 1954.

3. Alimov O. D. Investigation of the mechanism of destruction of rocks in percussive-rotary drilling and of the initial parameters of drilling hammers. Author’s abstract. Tomsk, 1953.

4. Alimov O. D. The influence of feed force on the drilling speed of pneumatic drilling hammers. Izv. TPI, vol. 75, 1954.

5. Buchnev V. K. Drilling and Blasting Operations. Ugletekhizdat, Moscow, 1950.

6. Voroshilin I. R. Mechanization of Mining Operations. Metallurgizdat, Sverdlovsk–Moscow, 1952.

7. Esin N. N. Analysis of diagrams of the working process of light drilling hammers. TsSfAN, 1953.

8. Shreiner L. A. Physical Foundations of the Mechanics of Rocks. Gostoptekhizdat, Moscow, 1950.

9. Temporary Manual for Drilling Holes with Side Flushing. Ugletekhizdat, 1953.

Noted Misprints