SOME RESULTS OF TESTING PROTOTYPES OF LONG-STROKE FEEDERS

O. D. Alimov, P. A. Samoilov

The studies we have carried out on high-frequency drilling hammers [1] have shown that it is impossible to introduce into production pneumatic drilling hammers more powerful than the existing ones without creating special feed-and-support devices. Such devices must provide the necessary feed forces of the drilling hammers against the face and reduce auxiliary operations during drilling to a minimum.

One means of accomplishing this may be long-stroke feeders, which make it possible to drill blast holes to their full depth without changing the tool and which are equipped with devices to facilitate the process of starting the blast hole.

By assignment of the Mining Administration of the Kuznetsk Metallurgical Combine, we, with the participation of personnel from the Special Design Bureau of the Tomsk Electromechanical Plant, developed in 1957 and, at the beginning of 1958, manufactured prototypes of the following long-stroke feeders: 1) a screw type; 2) a piston type with a chain stroke multiplier; and 3) a piston type with a cable stroke multiplier. The principal technical data of these feeders are given in Table 1.

Below, certain questions concerning the creation of prototypes of long-stroke feeders and the results of their testing are considered.

The screw-type long-stroke feeder (Fig. 1, a) is, in its operating principle, analogous to the screw feeder KTsM-4 produced serially by domestic industry, but its design incorporates a number of new solutions. These solutions are due both to the greater feed length (1.8 m) and to the desire to eliminate shortcomings revealed during the testing of drilling hammers with KTsM-4 feeders.

Table 1

* In the numerator are given the values of the indicators for the feeder with a solid rod, and in the denominator—for that with a cable stroke doubler.

Among the disadvantages of operation with the KTsM-4 screw feeder should be included lower drilling speeds than with the piston feeder [2] and the considerable difficulty of drilling blastholes. Moreover, the latter increases with increasing drill length.

The lower drilling speeds with the KTsM-4 screw feeder can be explained by the presence in it of a feeding system more rigid than that of the piston feeder. During drilling, because of the small helix angle of the lead-screw thread \((\alpha = 17^\circ 40')\), considerable resistance arises to oscillation of the drilling-hammer body and to its withdrawal from the limiting collar of the drill. This leads to an increase in the moment of resistance to rotation of the drill in

in the borehole, deterioration of the working process of the hammer and, as a consequence, a reduction in drilling speed.

Taking the above into account, in the screw-type long-stroke feeder the lead angle of the thread of the lead screw was increased to 22°20′. To improve the strength and reliability of operation of the lead screw, its diameter was increased from 24.4 mm (in the KTsM-4 feeder) to 36 mm. For the same purpose, the thrust bearing of the lead screw was moved to the front part of the feeder frame, which ensures that the screw works in tension when feeding the drilling hammer to the face.

Fig. 1. Schematic diagrams of prototype long-stroke feeders of screw type (a) and piston type with cable doubling of the stroke (b):
1—drilling hammer; 2—pneumatic engine; 3—drilling-hammer carriage; 4—lead screw; 5—manipulator boom; 6—guide carriage; 7 and 8—rod and cylinder of the recoil compensator; 9—feeder frame; 10—bit; 11—steady rest; 12—feed pneumatic cylinder; 13—cables (chains); 14 and 15—working springs.

To facilitate collaring a borehole with a long drill, the screw-type long-stroke feeder is provided with a special guiding device—the steady rest 11 (Fig. 1, a), installed at the front end of its frame. However, as observations of the operation of this feeder when mounted on MBM-2 manipulators and the TB-3 drilling carriage showed, in addition to the steady rest the feeder must be equipped with a device for fixing it relative to the face. The need for this device is due to the fact that a long-stroke feeder, even when mounted on such a powerful manipulator as the MBM-2, vibrates strongly during drilling and deviates from the prescribed direction. The latter leads to fairly frequent disturbances in the operation of the drilling hammer and breakage of the drill.

Observing the operation of the TB-3 drilling carriage at the face, one can note that, when moving from one borehole to another, the front end of the feeder moves a considerable distance away from the face (Fig. 2). In order to preserve the useful stroke length of the feeder, the driller is forced to work with longer drills, each time adjusting their length in accordance with the offset obtained during alignment to the new borehole. Such work is not only laborious, but also requires considerable auxiliary time expenditures.

Fig. 2. Diagram for determining the stroke of the rod of the feeder-offset compensator:
1 — initial position of the feeder; 2 — position of the feeder after it has been moved by the manipulator boom in the vertical plane to the maximum rotation angle \(\alpha_{\max}\); 3 — the same, in the horizontal plane to the maximum rotation angle \(\beta_{\max}\).

In the screw-type long-stroke feeder this drawback is absent owing to the use of a special device by means of which the feeder can be moved toward the face by the amount of its offset. We have called this device an offset compensator.

The feeder offset compensator (Fig. 1, a) is a pneumatic jack, the rod 7 of which is rigidly connected with the guide

with carriage 6, fixed on the boom of manipulator 5, and cylinder 8—with the feeder frame 9, which is able to move relative to the carriage guide.

The stroke of the rod of the recoil compensator must be equal to or greater than the maximum possible recoil of the feeder from the face. As can be seen from Fig. 2, the latter is equal to the sum of the feeder recoils when the manipulator boom is deflected in the vertical and horizontal planes

\[ l_k = l_1 + l_2 \text{ mm}, \tag{1} \]

where \(l_k\) is the stroke of the rod of the recoil compensator, mm;
\(l_1\) is the magnitude of the feeder recoil from the face at the maximum angle of rotation \((\alpha_{\max})\) of the manipulator boom in the vertical plane, mm;
\(l_2\) is the same at the maximum angle of rotation \((\beta_{\max})\) of the manipulator boom in the horizontal plane, mm.

Expressing \(l_1\) and \(l_2\) in terms of the length of the manipulator boom \(L_c\) and the maximum angles of rotation of this boom in the horizontal and vertical planes, we obtain

\[ l_k = 2L_c\left(\sin^2 \frac{\alpha_{\max}}{2} + \sin^2 \frac{\beta_{\max}}{2}\right)\text{ mm}. \tag{2} \]

In the experimental prototypes of long-stroke feeders, \(l_k = 70\) mm was adopted; for drilling carriages with manipulator booms of length \(L_c = 2400\) mm this provides compensation for feeder recoil when drilling any blasthole in an opening with a cross section of up to \(9 \text{ m}^2\).

When drilling carriages with manipulator booms of a different length are designed, the required stroke of the compensator rod can be determined from formula (2).

The presence of a recoil compensator on the feeder makes it possible not only to eliminate losses of its useful length easily, but also to fasten the feeder more reliably relative to the working face and the manipulator boom. In this case, the feeder is fixed at the blasthole collar by spike 10 (Fig. 1, a).

To prevent the feeder from recoiling from the face during drilling, the force pressing it against the face must be taken somewhat greater than the force required to feed the drill hammer to the face at the maximum drilling speed.

Piston-type long-stroke feeders with chain and rope stroke doublers have the same operating principle (Fig. 1, b). Drill hammer 1 moves along guide frame 9 to the face and back by means of piston pneumatic jack 12 with a stroke doubler. The stroke doubler is a block-and-tackle system whose flexible links are chains or ropes 13. In order to reduce dynamic loads and thereby eliminate breakage of chains (ropes) during operation of the drill—

Fig. 3. General view of the long-stroke feeder with a chain drive.

of the drill hammer; their attachment to the guide frame of the feeder is effected by means of spiral springs 14 and 15.

Like screw feeders, piston feeders are equipped with a cradle, a recoil compensator, and a pick. Fig. 3 shows the general view of a piston long-stroke feeder with a chain stroke doubler when it is mounted on the boom of the manipulator of the TB-3 drilling carriage.

Experimental models of long-stroke feeders were tested under mine conditions at the Tashtagol mine.

The purpose of the tests was:

1) to give a preliminary assessment of the serviceability of the basic schemes and individual components of each feeder;

2) to compare the operation of high-frequency drill hammers and hammers with a normal number of blows when drilling with long-stroke feeders in hard rocks;

3) to determine the most expedient feed forces when drilling with various types of drill hammers mounted on long-stroke feeders, in order to correct the main parameters of the feeder drives.

Each feeder was tested with a high-frequency drill hammer of the PR-25 type and an ordinary column hammer of the KTsM-4 type. Drilling was carried out into the side of a drift through ore with a strength coefficient \(f = 12 \div 14\) on the scale of Prof. M. M. Protodyakonov. Removal of drill cuttings from the blasthole was effected by flushing. Moreover, when working with the PR-25 drill hammer, side flushing was used (through a hydraulic coupling), while with the KTsM-4, axial flushing was used (through the hammer). In testing the feeders, drill steels 2050–2850 mm long were used, with removable single-chisel bits \(d = 43\) mm, tipped with VK-15 hard alloy. The blastholes were drilled to a depth of up to 1.8–2.3 m.

The tests were conducted according to a procedure developed by the research staff of the Department of Mining Machines and Mine Transport of the Tomsk Polytechnic Institute [3].

The schematic diagram of the experimental installation is shown in Fig. 4.

The experiments were carried out at air pressures supplied to the hammer of 4, 5, and 5.5 atm and at a specified air pressure at the motor (feed pneumatic cylinder) of the feeder. As the experiments were conducted, the air pressure supplied to the motor (feed pneumatic cylinder) of the feeder was increased in increments of 0.25 atm up to a value at which the hammer ceased to operate (“stall”).

From the value of the air pressure supplied to the motor (feed pneumatic cylinder) of the feeder, the feed force of the drill hammer on the face was calculated. In this case, the feed force developed by piston feeders was determined as the product of the air pressure and the piston area of the feed pneumatic cylinder. The feed force of the screw feeder, however, was estimated conditionally by the air pressure supplied to the pneumatic motor of the fe—

sensor. For each feed force, up to 10–12 experiments were carried out.

The pressure of the flushing water in all experiments was kept constant and was equal to: for side flushing, 1–1.5 atm, and for central flushing, 2.5–3 atm. The supply of water at the indicated pressure ensured complete cleaning of the borehole from drill cuttings and stable operation of the drilling hammer.

Fig. 4. Layout of the installation for testing long-stroke feeders:
1—drilling hammer; 2—air distributor; 3—sliding compensator; 4—trigger valve of the stroke compensator; 5—mechanism for limiting free vibrations; 6 and 7—device of the scale for measuring and indicating the depth of the drilled hole; 8—screw jack; 9, 11, and 13—pressure gauges; 10, 15, and 16—control valves; 12—valve for starting water for flushing; 14—automatic lubricator.

Together with the newly created prototypes of long-stroke feeders, a standard screw feeder with the KTsM-4 drilling hammer was tested, which made it possible to compare their operating characteristics.

The tests carried out showed the following:

1. The nature of the change in drilling speed as a function of the feed force at the face is the same for the tested hammers with all types of feeders. As the feed force increases, the drilling speed first rises to a maximum and then decreases (Figs. 5, 6). The maximum drilling speeds for each type of drilling hammer and feeder correspond to quite definite feed forces, the values of which are given in Table 2.

The feed forces of the PR-25 high-frequency drilling hammer required to obtain maximum drilling speeds on all types

Table 2

Drilling rates with KTsM-4 and PR-25 hammers on long-stroke and standard screw feeders at optimal feed forces

the feeders must be 5–23 kg greater than the feed forces when drilling with the KTsM-4 hammer. However, the drilling rates at the optimal feed forces, despite its greater impact power, are 10–14% lower than those of the KTsM-4 hammer (Table 2).

Similar results were obtained by us earlier in comparative tests of the KTsM-4 hammer and the high-frequency RH-754 hammer [1], which were also carried out in drilling hard rocks. Tests of these same hammers in drilling rocks of medium hardness ($f = 6 \div 8$) gave opposite results [2]. In the latter case, the KTsM-4 hammer at optimal

at equal feed forces, had a drilling speed 28–55% lower than the drilling speeds of the high-frequency hammers PR-25 and RN-754.

These results can be explained by the fact that, for effective destruction of rocks of medium hardness, an impact energy of 3.5–4.0 kgm is sufficient, and this is provided by modern high-frequency hammers. When drilling harder and more viscous rocks (\(f = 12 \div 14\) and higher), which are most typical of the mines of Gornaya Shoriya, effective destruction is ensured at higher impact energies (5–6 kgm and more).

This circumstance once again confirms our opinion [1] that, for drilling blastholes in rocks of high hardness, it is necessary to create special high-frequency drifter drills with an impact energy of more than 5–6 kgm.

Fig. 5. Dependence of drilling speed on feed force; air pressure at the hammer 5 atm:
1—piston long-stroke feeder with cable stroke doubler and KTsM-4 hammer; 2—the same, PR-25 hammer;
3—piston long-stroke feeder with chain stroke doubler and KTsM-4 hammer; 4—the same, PR-25 hammer; 5—unstable operation of the drilling hammer.

1. Each drilling hammer, when operating on piston feeders with both cable and chain stroke doublers, had approximately the same (\(\pm 2\)–6%) drilling speeds (Table 2 and Fig. 7). When operating on the screw long-stroke feeder, the PR-25 drilling hammer showed a drilling speed 11–24% lower, and the KTsM-4 hammer 5–24% lower, than on the piston long-stroke feeder. Still lower drilling speeds (by 34–43%) were obtained when operating the KTsM-4 drilling hammer with the standard screw feeder.

The higher performance indicators of drilling hammers on the screw long-stroke feeder in comparison with the standard

Fig. 6. Dependence of drilling speed on the air pressure supplied to the feeder motor; air pressure at the hammer, 5 atm:

1 — long-stroke screw feeder with a KTsM-4 hammer;
2 — same, with a PR-25 hammer;
3 — standard screw feeder with a KTsM-4 hammer;
4 — unstable operation of the drilling hammer.

Fig. 7. Maximum drilling speeds with PR-25 and KTsM-4 hammers with different types of feeders:

1 — piston long-stroke feeder with cable stroke doubler;
2 — piston long-stroke feeder with chain stroke doubler;
3 — screw long-stroke feeder;
4 — standard screw feeder.

can be explained by the improvements introduced into the design of the newly created screw feeder. The thread lead angle of the running screw, increased to \(22^\circ 20'\), and the presence in the feeder of an additional elastic element in the form of a pneumatic jack—an offset compensator—which reduced the rigidity of the feeder’s feeding system, contributed to the most effective operation of the drilling hammers under optimal conditions.

1. For all types of long-stroke feeders, the wear of drill bits when drilling with the high-frequency PR-25 hammer is 32–35% less than when drilling with the KTsM-4 hammer (Table 3).

Table 3

Results of observations of bit wear

The high wear resistance of drill bits when drilling with high-frequency hammers makes it possible, when working with long-stroke feeders, to change the drill not at every borehole, but after drilling two or three boreholes. This will additionally make it possible to reduce the time spent on auxiliary operations.

From the data given in Table 3 it is also evident that the wear resistance of drill bits for both types of hammers with the screw long-stroke feeder is lower than with the piston feeders. This can be explained by the fact that, despite the measures taken (increase of \(\alpha\), presence of an additional elastic element), the newly created screw feeder still has a rather rigid feeding system.

1. All the tested feeder designs are entirely serviceable, ensuring stable operation of the hammers; however, as can be seen from the data in Table 1, the screw long-stroke feeder has smaller overall dimensions, lower weight, and a somewhat greater relative feed length (0.67) than the piston feeders (0.65). Through better selection of parameters, the newly designed long-stroke screw feeders provide a drilling speed greater than that of the standard screw feeders supplied by factories with KTsM-4 hammers (Fig. 7).

However, the piston long-stroke feeders, especially with a rope stroke doubler (owing to their lower weight and cost, ...

and the greater convenience in operation of a rope than of a chain), for operation with more advanced drill carriages they are no less promising than screw feeders, since they are simpler to manufacture, provide the highest drilling speeds and less wear of the drilling tool. In addition, by making a slight change in the fastening of the front block to the guide frame and of the traction rope to the carriage of the drilling hammer, the relative feed length of the piston feeder can be increased to 0.70–0.72.

Thus, on the basis of design developments, using the authors’ previous investigations, designs of long-stroke feeders have been created that provide higher drilling speeds and lower time expenditures for auxiliary operations than commercially produced feeders. The new feeders may be recommended for newly designed drill carriages.

Taking into account the comparatively large weight of long-stroke feeders together with the drilling hammer, drilling tool, and hoses (170–230 kg), the manipulators of drill carriages for such feeders must have a special drive for the lifting mechanism.

REFERENCES

1. O. D. Alimov, I. G. Basov, P. A. Samoilov. On the advisability of using high-frequency pneumatic drilling hammers. Kolyma, No. 9, 1957.

2. O. D. Alimov, I. G. Basov, P. A. Samoilov. Some results of investigating the operating conditions of pneumatic drilling hammers. Izvestiya TPI, vol. 106. Drilling Machines, Metallurgizdat, 1958.

3. O. D. Alimov, I. G. Basov, V. F. Gorbunov. A methodology for laboratory investigation of the influence of feed force on the drilling speed of pneumatic drilling hammers. Izvestiya TPI, vol. 88, 1956.

NOTED MISPRINTS