Feed Mechanisms of Drilling Hammers

O. D. Alimov, I. G. Basov, V. F. Gorbunov

(Presented by Prof. P. M. Alabuzhev, Doctor of Technical Sciences)

On the basis of investigations carried out on drilling hammers of types OM-506, PM-508, RP-17 [1–4], it has been established that the feed mechanisms of drilling hammers, in order to ensure a high drilling rate and stable operation of hammers of this type, must provide such a feed characteristic as would make it possible, during drilling, to have a certain withdrawal of the drilling-hammer body from the limiting collar of the drill, in order to reduce the resistance to rotation of the drill and the wear of the bit blade. The feed mechanisms must have reliable and simple control and must make it possible for one driller to service several machines. Automatic variation of the feed rate and feed force is most expediently carried out as a function of the change in the moment of resistance to rotation of the drill. In addition, the supporting devices of feeders—columns, tripods, brackets, etc.—must ensure rapid installation of the drilling hammer at the working place. The design and dimensions of the installation must make it possible to drill the face of development workings of any cross section with a minimum number of equipment rearrangements.

In the present work, certain types of feed mechanisms are considered, proceeding from the above-mentioned requirements.

The feed mechanisms of drilling hammers existing in mining-industry practice may be subdivided into pneumatic supports, piston, screw, chain, rack-and-pinion, and other types of feeders.

Pneumatic Supports

In mines and pits in the USSR and abroad, in the postwar years, drilling with hand-held drilling hammers from various kinds of pneumatic supports has become widespread.

The designs of pneumatic supports are described in sufficient detail in contemporary technical literature [5–9]. The technical characteristics of the pneumatic supports most widely used in the mines and pits of the USSR are given in Table 1.

The use of pneumatic supports has facilitated the labor of drillers, reduced the effect of recoil, and increased labor productivity. Pneumatic supports are very simple in design, reliable in operation, and considerably reduce the time of auxiliary operations connected with installing the drilling hammer in the face before drilling holes. The elimination of the need to support the weight of the hammer by the muscular strength of the driller made it possible to increase the power of hand-held hammers. The hand-held drilling hammers PR-35 and PR-30, recently produced, are close in developed power to column-type drilling hammers. In a number of cases, when drilling holes in especially hard rocks and when driving development workings of small cross section, workers prefer to use hand-held drilling…

hammers mounted on pneumatic supports than with more cumbersome column-type drilling hammers mounted on expansion columns.

Table 1

However, as even a simplified analysis [2] shows, the existing pneumatic supports do not ensure drilling under optimal conditions. It is impossible to ensure drilling with hand-held drilling hammers from pneumatic supports under optimal conditions because skewing of the drill in the blast hole, owing to the application of the feed force not along the axis of the hammer, creates considerable resistance to rotation of the drill; this leads to unstable operation of the drilling hammer long before optimal conditions are reached. Therefore, in most cases drilling with hand-held hammers from pneumatic supports is carried out with feed forces that are knowingly smaller than the forces providing the maximum drilling rate, and consequently under less productive conditions. In view of the fact that, when drilling from a pneumatic support, the driller has to apply an additional feed force, pneumatic supports do not completely eliminate the harmful effect of vibration on the worker’s health. At the “Novaya” mine of the “Leninruda” trust of the Krivoi Rog iron-ore basin, in order to eliminate the above-mentioned shortcomings, engineers I. I. Mineev, S. S. Samoilov, and G. G. Petrenko proposed an improved UPP-1 pneumatic support (Fig. 1). It is a PPK-17 pneumatic support with an added cylinder for adjusting the position of the drilling hammer and the drill relative to the axis of the blast hole.

Fig. 1. Improved UPP-1 pneumatic support.

For the same purpose, at the “Bolshevik” mine of the “Leninruda” trust, innovating drillers P. I. Chaikovskii, G. S. Goloborodko, and P. P. Sidorenko proposed using, in addition to the pneumatic support, a light expansion column for fixing on it the guide shank (pipe) attached to the handle of the drilling hammer (Fig. 2). Drillers Chaikov-

[[unclear: beginning of paragraph]] P. I., Goloborodko G. S., and Sidorenko P. P., using the above-mentioned devices, were able to work simultaneously on 2 and 3 drilling hammers, fulfilling the shift production norm by 277%. Subsequently, at the suggestion of driller Feshchenko A. I., the strut column supporting—

Fig. 2. Pneumatic support with a light strut column.

—supporting the guide shank of the drilling hammer was replaced by supporting brackets (Fig. 3), which are installed 2.2 m from the face line. To fasten them in the walls of the working, short blast-holes—250–300 mm—are drilled; one end of the bracket (wedge) is fastened in the blast-hole by means of a small wedge. The breaking down of the entire face area is ensured by moving the supporting bushing along the bracket tube and rotating it about its axis.

According to data from the Dzerzhinskruda trust, with one installation of two brackets the entire face is broken down with the simultaneous operation of two PA-23 drilling hammers with PPK-18 pneumatic-support columns. The time of pure drilling and labor productivity increase by 80% in comparison with drilling by a single drilling hammer.

From the above consideration it is evident that the proposed additional devices, when drilling from existing pneumatic supports, make it possible to increase the driller’s labor productivity by—

Fig. 3. Pneumatic support with brackets.

to make it possible for one driller to service two, and sometimes three, operating hammers. But the above-mentioned devices for pneumatic supports do not fully automate the feed of drilling hammers to the face. The simultaneous servicing of 2–3 drilling hammers mounted on pneumatic supports requires considerable physical effort from the worker. In addition, the devices considered above do not eliminate—and in a number of cases aggravate—the following shortcoming of pneumatic supports: the difference between the vertical component of the spreading force of the pneumatic support \((Q)\), Fig. 4, and the weight of the hammer \(G_m\), reduced to the axis of the hinge, can most expediently be compensated during drilling only by applying to the hammer an additional external force along the same axis of the hinge and directed perpendicular to the axis of the blasthole.

Fig. 4. Distribution of forces during drilling with a pneumatic support.

When this force is replaced by the force \(N_1\), applied at a certain distance from the axis of hinge \(O\), as is the case when an additional cylinder is used (Fig. 1), or a guiding shank (Fig. 2), there arises a moment \(M_1 = Nl = N_1l_1\), overturning the hammer about hinge \(O_1\) (Fig. 4) counterclockwise, and a moment \(M_2 = N_2l_2\), acting in the opposite direction.

In order for the axis of the hammer to coincide with the axis of the blasthole, it is necessary that \(M_1 = M_2\), \(Nl_1 = N_2l_2\), and \(N_1 + N_2 = Q - G_m\). The additional force of interaction of the lateral surface of the drill bit with the surface of the blasthole arising in this case,

\[ N_2 = \frac{Q - G_m}{1 + Q_2/l_1} \]

creates additional resistance to the rotation of the drill in the blasthole, distorts the direction of the blasthole, and bends the drill. The transverse bending of the drill, in combination with longitudinal impacts, adversely affects the strength of the drill. Thus, the use of pneumatic supports somewhat reduces the labor intensity of drilling operations, but does not automate the process of feeding the hammer to the face. As a result, it is necessary to carry out further work on improving pneumatic supports.

On the basis of data from the technical literature and observations we have made of drilling with pneumatic drilling hammers mounted on pneumatic supports, the following additional requirements for pneumatic supports may be formulated.

1. The fastening of the hammer to the pneumatic support must be a convenient, quick-acting connecting device, providing the possibility of turning the drilling hammer about the axis of the hammer through an angle of \(\pm 15\text{–}20^\circ\). This makes it easier to turn the drilling hammer together with the drill by hand in cases where the hammer stalls as a result of jamming of the drill.

2. Regulation of the spreading force of the pneumatic support must be rapid and reliable. It can be carried out by means of a simple valve installed in a cut in the hose supplying air to the pneumatic support. In this case, for smooth regulation of the expanding force in the cylinder

a throttling orifice of \(d = 1\) mm should be provided in the pneumatic support.

1. The pneumatic support should be reversible, i.e., all designs should include devices ensuring wedging and return travel by means of compressed air. This will reduce labor input and increase productivity by reducing the time required to reset the pneumatic support during the drilling of a single blast-hole.

2. By design, pneumatic supports may be:

a) with a cylinder fastened to the hammer and an extending supporting rod (Fig. 2);

b) with a rod fastened to the hammer and an extending supporting cylinder (Fig. 5).

Plants of the Soviet Union manufacture pneumatic supports of the first type. The advantage of this design is that the reduced weight of the hammer, \(G_m\), is somewhat increased for the same weight of the pneumatic support, and as a result the horizontal component of the wedging force of the pneumatic support can be somewhat increased without additional effort by the driller. This arrangement is safer in operation with a reversible pneumatic support. The second type of pneumatic support is manufactured by a number of foreign firms. The merits of this type of design are the convenience of freeing the support part from the ground by hand (for this purpose the thrust cylinder of the support is provided with a special handle), and the lower total weight of the drilling hammer, which facilitates collaring. For a reversible support such an arrangement is not applicable, since rapid upward movement of the feeder cylinder along the rod as far as the stop may injure the worker. Some foreign firms (“Meudon,” France) manufacture pneumatic supports that can be attached to the hammer by either end, which makes them more universal.

Fig. 5. Pneumatic support with supporting cylinder

1. For reliable bearing of the support against the rock, the end of the rod should be equipped with a two- or three-pronged fork (Fig. 5).

2. Pneumatic supports for drilling blast-holes in development workings should have the following parameters:

a) length of the pneumatic support in the collapsed state: 1000–1200 mm,

b) piston stroke: 650–700 mm,

c) weight not more than 19 kg,

d) extending force at an air pressure of 5 atm:

for OM-506 — 120–125 kg

for RP-17 — 80–90 kg.

Piston Feeders

Pneumatic piston feeders have become widespread both in the ore-mining and in the coal industry. Owing to the absence of centralized manufacture, many mines and pits make piston pneumatic feeders of their own design.

Of the piston-type feed mechanisms known to us, the most acceptable for hammers of the OM-506 and PM-508 types are feed mechanisms of the PK-1 and VPK types from the Kyshtym Mechanical Plant; the AP-1 feed mechanism, designed and manufactured by the Tomsk Electromechanical Plant but not yet introduced into production; and also feed mechanisms with the feed cylinder arranged along the axis of the hammer, similar to the TP-4 telescopic drilling hammers. In the AP-1 feed mechanism, as in the PK-1 feed mechanism, the hammer is mounted on a movable cylinder (Fig. 6). A certain difference between the AP-1 feed mechanism and the PK-1 is that, in the design of the AP-1 feed mechanism, the body of the feed mechanism is lightened, and the rubber hose connecting the three-way valve of the feed mechanism with the front chamber of the cylinder is replaced by a metal tube.

Fig. 6. Piston feed mechanism AP-1.

Feed mechanisms of the PK-1 and AP-1 types, with the correct choice of cylinder diameter and piston stroke, can ensure sufficiently stable operation of the hammer. Regulation of the feed force in these feed mechanisms can be carried out by means of a valve installed at the air inlet to the feed-mechanism cylinder, and of a throttling orifice connecting the feed-mechanism cylinder with the atmosphere. The longitudinal oscillations of the hammer that arise during drilling are, to a considerable extent, damped by the air buffer of the feed mechanism and, as a result, the vibration forces acting on the supporting elements of the installation are reduced. This makes it possible to use less strong, but lighter and more convenient-to-operate, expansion columns and manipulators.

Unlike the PK-1 and AP-1 feeders, the VPK-1 feeder is equipped with a telescopic feed cylinder (Fig. 7). Instead of a column, the VPK-1 feeder is fastened by a pin inserted into the blasthole to a depth of 150–200 mm, which considerably facilitates and simplifies its installation. The pin length is 270 mm, diameter 33–34 mm. The VPK-1 pneumatic feeder is used when drilling blastholes with hand-held drilling hammers in rock with a strength coefficient of not less than 10 on Prof. Protodyakonov’s scale.

The VPK-1 feeder and feeders similar to it in their installation at the face (the Guchin and Eremin feeders) are distinguished by simplicity of design and are inexpensive to manufacture. Their installation at the face takes 2–3 minutes. The telescopic arrangement of the feed cylinder makes it possible to reduce substantially the dimensions

Fig. 7. VPK-1 piston feeder.

of the piston feeder for one and the same stroke length. In view of this, piston feeders with a telescopic cylinder can be successfully used for drilling cut blastholes when driving development workings of small cross-section in hard rocks, using a wedge cut. The disadvantage of the VPK-1 telescopic feeder is that it is impossible to carry out the reverse motion of the feeder by means of compressed air; therefore the drilling hammer is withdrawn from the face manually.

Piston feeders of the PK-1, AP-1, and VPK-1 types, in the structural form in which they are manufactured, can ensure constancy of the feed force when drilling various rocks at different speeds. This does not eliminate the necessity for the driller to intervene in controlling the operation of the feeder during drilling. For full automation of the feed, as we established in previous investigations, it is necessary that the feeder change the feed force and feed speed depending on the resistance to rotation of the drill in the blasthole. We consider that such an automatic feeder can be created on the basis of a piston feeder with the feed cylinder arranged along the axis of the tool and the hammer. Feeders of this type became widespread in the mines of the Urals during the Patriotic War [13], and at present are being successfully used at a number of mines in Siberia when drilling with OM-506 and PM-508 hammers (Fig. 8), and in some cases also with KTsM-4.

In this feeder the axes of the feeder cylinder, the drilling hammer, and the blasthole coincide. Therefore the design scheme permits rotation of the drilling hammer about its longitudinal axis without misalignment of the drill in the blasthole. The mean torque developed by the drilling hammer on the drill is, on the one hand, equal to the moment of resistance to rotation of the drill, and on the other—to the reaction moment tending to turn the body of the drilling hammer in the direction opposite to the rotation of the drill. This can be used for automatically changing the feed force as a function of the moment of resistance to rotation of the drill.

If the drilling hammer is held against rotation relative to the feeder cylinder by a special elastic element installed between

with the body of the hammer and the fixed part of the feed mechanism, then, with different resistance to rotation of the drill in the borehole, the elastic element will be deformed by different amounts and the body of the hammer will turn through different angles relative to the fixed cylinder. If the hammer body is connected with a special slide valve installed in the fixed part of the feed mechanism, then, as the hammer body turns, it is possible to change the amount of air entering the cylinder. If there is a small opening in the cylinder of the feed mechanism connecting its cavity with the atmosphere, a change

Fig. 8. Feeding mechanism of the Artemovsk hand drill.

in the amount of air entering the cylinder will lead to a change in its pressure and, consequently, in the feed force. As a result, when the moment of resistance to rotation of the drill changes, the feed force will change automatically, which is what is required for successful multi-hammer drilling.

The basic diagram of such an automatic device may be presented as follows (Fig. 9). During drilling, the hammer is fastened to the head of the feed-rod 1 (Fig. 9) and is secured against rotation in the direction opposite to the rotation of the drill by means of bracket 2. The force from the bracket is transmitted to the feed cylinder body 3 through pusher 4, spring 5, stop 6 mounted on feed rod 7, and key 8. When the torque developed by the drilling hammer on the drill changes, the reactive moment changes, and as a result the magnitude of the deformation of spring 5 changes; this deformation limits the rotation of feed head 1 relative to rod 7. In this case, valve 10, connected with the feed head by shaft 9, turns in its seat, installed in the feed rod, and changes the admission of air into the rear cavity of the feed cylinder. At the maximum torque, corresponding to the case when the hammer stalls, spring 5 is deformed by such an amount that valve 10, having turned completely, closes opening 11; the feed force is thereby reduced.

Fig. 9. Basic diagram of the automatic device of a piston feed mechanism.

Additional regulation of the air pressure in the feeder may be carried out manually by means of cock 13. For reverse feed of the hammer away from the face, the hammer is turned in the direction of drill rotation (counterclockwise); valve 10 is set to a position that ensures the admission of compressed air into the front cavity of the cylinder through opening 14.

In our opinion, stable operation of such an automatic feeder can be ensured by the appropriate selection of the cross section of opening 12, which throttles the air from the rear cavity of the cylinder, and by the selection of the characteristic of spring 5. Stable operation of this system under a sharp change in the magnitude of the torque over one impact cycle is aided by the considerable mass of the hammer body. As a result, the automatic feeder will change the feed force not as a function of the fluctuation of the moment over one impact cycle, but as a function of a certain averaged moment developed by the drilling hammer over several blows. In this case the hammer body plays the role of a flywheel, equalizing the load on the elas—

element—the spring 5; we believe that, on the positive side, this arrangement differs from the similar arrangement of an automatic feeder proposed by G. F. Trofimov [10].

Screw Feeders

For feeding drilling hammers weighing 37 kg and more, screw feeders have become widely used.

By type of drive, screw feeders may be subdivided into:

1) screw feeders with manual drive;
2) screw feeders with a special drive from a pneumatic motor;
3) screw feeders driven by the impact-rotary mechanism of the drilling hammer;
4) screw feeders having a common drive for feeding and rotating the drill steel.

Screw feeders with manual drive have not become widely used in the practice of mining enterprises of the Soviet Union, since they do not provide a substantial reduction in labor intensity or an increase in labor productivity. The most widespread in the practice of the mining industry of the USSR and abroad have been screw feeders with a special drive from a pneumatic motor. The best-proven models of feeders of this type are the Ingersoll-Rand and KTsM-4 feeders.

According to factory data, the KTsM-4 drilling-hammer feeder has the following technical characteristics:

1) overall length of the feeder—1560 mm;
2) feed length—900 mm;
3) tractive force developed by the feeder at \(P = 6\) atm—100 kg;
4) air consumption for the forward stroke—0.1–1.19 m³/min; for the return stroke—0.2–0.32 m³/min;
5) total weight of the feeder—38 kg.

The Ingersoll-Rand and KTsM-4 feeders have proved themselves well in the practice of drilling with column-mounted drilling hammers. They are relatively simple in design, have a compact drive, a relatively long feed stroke, and can provide large feed forces. Regulation of the feed rate makes it possible for one worker to control two drilling hammers during drilling.

It is natural, therefore, that a number of plants (the Pneumatika Plant, the Tomsk Electromechanical Plant, and the Kommunist Plant) created similar PP-1 and PP-3 feeders for other drilling hammers and, in particular, for feeding OM-506 hammers. However, production tests of these feeders did not yield positive results. In our opinion, the reason for the failures is that feeders of the KTsM-4 type, without changing their parameters, can be successfully used only for hammers that develop a considerable torque on the drill steel. Drilling hammers of the OM-506 type do not possess such features, and the feed force developed by the feeder is excessive for them. Thus, the results of measuring the feed force developed by a feeder of the KTsM type, carried out by engineer P. A. Samoilov in the laboratory of the Department of Mining Machines and Mine Transport of TPI (Fig. 10), show that at drilling speeds of 150–200 mm/min, which are practically achieved when drilling blast-holes with an OM-506 hammer in rocks of high hardness, the KTsM-4 feeder at a compressed-air pressure of 4–5 atm develops a feed force of 90–120 kg. This considerably exceeds the feed forces at which OM-506 hammers operate stably.

The investigations we have carried out show that screw feeders of the KTsM-4 type can provide some oscillation of the hammer body along

the feeder during drilling and its withdrawal from the limiting collar of the drill steel. This can be achieved in a KTsM-4-type feeder only when the screw pair and the planetary reducer are made as non-self-locking mechanisms.

Fig. 10. Dependence of feed rate on feed force for a KTsM-4-type pneumatic screw feeder.

Axis labels in the figure: feed rate, mm/min; feed force, kg.

For this purpose, for example, the lead screw of KTsM feeders is made four-start with a thread pitch of 25.4 mm, which, at the mean diameter ...

a thread of 24.4 gives a thread lead angle of \(17^\circ 40'\). In this case the longitudinal oscillations of the hammer are transformed into rotary-oscillatory motions of the lead screw, the planet-carrier of the planetary mechanism, and the rotor of the pneumatic motor. Compressed air, supplied to the pneumatic motor of the feed mechanism, serves here as the elastic damping element. But in order to move backward, the hammer body, mounted on a feed mechanism of the KTsM type, must overcome considerable resistances; thus, for the backward motion of the hammer body with the feed-mechanism motor disconnected from the air line, an additional longitudinal force of the order of 35–45 kg must be applied to the body of a working hammer, and 100–120 kg to a nonworking hammer. As a result of these resistances, feed mechanisms of the KTsM type provide a more “rigid” feed of the hammer than piston mechanisms. This adversely affects the stability of hammer operation during drilling and leads to considerable dynamic loads on the mounting devices. In particular, as a result, the feed devices and manipulators on which feed mechanisms of the KTsM type are installed must be stronger and more rigid than for the installation of piston feed mechanisms.

We believe that screw feed mechanisms with a pneumatic motor can be successfully used both for heavier and for lighter hammers than the KTsM-4, only if their parameters are specially calculated for the given type of hammer. The initial data for calculating such feed mechanisms for the PM-508, OM-506, and RP-17 hammers may be obtained from experimental investigations carried out according to the method proposed above [4].

In recent years a number of foreign firms have widely advertised screw feed mechanisms with a fixed screw and a movable lead nut, installed in the body of the drilling hammer and driven by the reversing mechanism of the hammer or by a special motor, which simultaneously rotates the drill bit. Such a design solution simplifies the feed mechanism and somewhat complicates the construction of the hammer. We have not encountered sufficiently detailed descriptions of these feed mechanisms or of experience in their operation.

Screw feed mechanisms of the KTsM type are often called automatic feed mechanisms. This name is apparently justified by the fact that these feed mechanisms can automatically provide a feed rate of the drilling hammer into the hole equal to the drilling rate. As for automation of feed in the full sense of the word, that is, when the feed mechanism automatically ensures stable hammer operation at optimum conditions and does not require minute-by-minute intervention by the driller, screw feed mechanisms of the design known to us do not provide this. Nor can the automatic differential-screw feed mechanisms proposed by Sidorenko [12] provide it, since the principle of automation implemented by them consists in automatically maintaining a feed rate equal to the drilling rate and a constant feed force.

Proceeding from the previously formulated requirements for automation of the feed of drilling hammers, in 1953 P. M. Alabuzhev and O. D. Alimov, together with employees of TEMZ, developed the design of a two-differential automatic feed mechanism, which can be recommended for column-mounted pneumatic and electro-pneumatic drilling hammers having continuous rotation of the drill bit. The design of the automatic feed mechanism provides automatic variation of the feed rate and feed force depending on the rate of advance of the blasthole and on the resistance to rotation of the drill bit in the blasthole.

Automatic variation of the feed rate and feed force depending on the above-mentioned factors is accomplished by means of two kinematically

connected differentials—a screw differential and a gear differential. The basic diagram of the automatic feed device is shown in Fig. 11. The mechanisms for rotating the drill and for feeding the drilling hammer are driven by a common electric motor. The two mechanisms are kinematically connected with one another and are located in the front part of the drilling-hammer housing.

Rotation from electric motor 1 (Fig. 11) is transmitted through gear train 2, 3, 4 to gear wheel 5, which is the driver of the satellites 6 of the unbalanced cylindrical differential, which distributes the motion between rotation of the drill (gear wheels 7 and drill 15) and feed of the drilling hammer to the face (gear wheels 7, 12 and lead screw 13).

Fig. 11. Basic diagram of a two-differential automatic feed device.

The two driven gear wheels 7 and 8 of the differential can rotate at a speed equal to the rotational speed of driver wheel 5 only under a definite ratio of the moments overcome by the differential half-axes—the moment of resistance to rotation of the drill and the moment of resistance to rotation of the lead screw. Gear wheel 7, by means of a hexagonal hub-sleeve, transmits rotation to drill 15 and, at the same time, by means of an external gear rim—to gear wheel 12. Gear wheel 12 has a hub made in the form of a nut, which, during rotation, can screw onto lead screw 13 or unscrew from it. Gear wheel 12 can move along the screw only simultaneously with the housing of the drilling hammer; therefore, when the nut of wheel 12 screws onto screw 13, the drilling hammer is fed to the right—toward the face; when it unscrews, the drilling hammer is retracted to the left—away from the face.

Lead screw 13, fixed in two supports of the trough-shaped housing of feeder 11, is in turn also set into rotation by means of gear wheels 6, 8, 9, and 10. The latter rotates lead screw 13 by means of a hub with two internal key projections entering the longitudinal grooves of lead screw 13; since the key grooves are cut along the entire length of screw 13, gear wheel 10, while rotating screw 13, can at the same time move together with the drilling-hammer housing along the feeder housing. The gear ratios of gear trains 7, 12 and 9, 10 are selected in such a way that, with the same number of revolutions of gear wheels 7 and 9, equal to the number of revolutions of driver gear wheel 5, gear wheel 12 makes \(\Delta n\) revolutions per minute more than gear wheel 10 and screw

1. If, in this case, the pitch of the screw thread is equal to \(h\), the feed rate of the drilling hammer at the face will be

\[ v=\Delta n\cdot h . \tag{1} \]

Feed at the rate calculated by formula (1) will occur only if the torque required for rotation of the drill and for feed, with which one axle shaft of the bevel cylindrical differential is loaded, corresponds to the moment of resistance to rotation of the lead screw, with which the second axle shaft of the differential is loaded. The moment of resistance to rotation of the lead screw is created artificially, by means of the friction multi-disc clutch 14. In the event that the drill bit jams in a crack in the rock, the blast hole becomes clogged, or the hardness of the rock increases, at the same feed rate there would inevitably have to be an increase in the moment of resistance to rotation of the corresponding axle shaft of the differential. And since it cannot be greater than the value determined by the moment on the second axle shaft and by the design of the differential (the ratio of the arms), the rotational speed of gear wheels 7, 12 will accordingly decrease, and the rotational speed of gear wheels 8–10 will increase. As a result, the feed rate will decrease. At \(n_{12}=n_{10}\) the feed rate will be zero; at \(n_{12}<n_{10}\) the drilling hammer will be withdrawn from the face until the moment of resistance to rotation of the drill decreases to the calculated value.

Conversely, when the feed resistance or the resistance to rotation of the drill decreases, the hammer feed will be carried out at a higher rate. The maximum feed rate of the hammer to the face will be equal to \(v_{\max}=n_{12,\max}\cdot h\), when \(n_{13}=0\), that is, when the drill experiences no resistance, for example when feeding the hammer to the face after changing the tool. The required operating mode of the drilling hammer, the magnitude of the feed force, and the torque are set by the corresponding tightening of the spring compressing the discs of the brake clutch. Rapid withdrawal of the drilling hammer from the face can be carried out by reversing the motor with the same tightening of the friction clutch. Testing of the indicated feeder under laboratory conditions confirmed the operability of the design. In further design development of the indicated feeder scheme for a specific machine, it is necessary to attempt to replace the multi-disc friction clutch with hydraulic loading devices permitting load regulation over wide ranges.

Chain and Other Types of Feeders

For feeding heavy drilling hammers of the KT-70 type, the Krivoi Rog “Kommunist” plant manufactured the PP-6 chain pneumatic feeder (Fig. 12), of the type of the Ingersoll-Rand chain feeder widely used in open-pit workings. The drilling hammer moves along guides. Sprockets are fastened at the front and rear ends of the guides. These sprockets serve to guide the drive roller-and-plate chain, the ends of which are fastened to the body of the drilling hammer. The chain is set in motion by a pneumatic piston engine, which is suspended from the lower part of the guides. For better centering of the drill during collaring, a special coupling (lunette) is fastened in the front part of the guides.

The feeder is mounted on a traverse between two screw prop columns. The external screw thread of the prop columns makes it possible, with the aid of special nuts, to move the traverse with the feeder vertically. At the same time, the design of the clamping collar of the traverse makes it possible

Fig. 12. Chain pneumatic feeder PP-6.

to set the feeder at a certain angle of inclination to the horizon and to the axis of the crossbeam.

Technical characteristics of the PP-6 feeder:

1. Feeder length — 2000 mm
2. Feeder weight — 160 kg
3. Feeder travel — 1000 mm
4. Axial feed force — 300 kg
5. Air consumption — 0.8 m³/min
6. Pneumatic motor power — 1.25 hp
7. Pneumatic motor type — MP-4
8. Working pressure of compressed air — 5–7 atm
9. Weight of columns with crossbeam — 118 kg

Operation of chain feeders for drilling hammers in the underground conditions of Krivorozhye has shown that installing a chain feeder on two jack columns is very labor-intensive, requires considerable physical effort from the workers and a relatively large amount of auxiliary time, even when drilling deep boreholes, where frequent rearrangement of the drilling hammer is not required. Because of the large dynamic loads, the drive chains often fail. Chain feeders are used with great success in open-pit workings. In these cases they are mounted on special three-wheeled carts. This makes it possible to reduce substantially the time spent on auxiliary operations. The simplicity of the feeding device when a chain is used makes it possible to manufacture feeders with a considerable feed travel (4 meters and more), which is especially important for drilling in open-pit workings.

Reliable operation of the chain under dynamic loads can be ensured by the appropriate quality of its manufacture and by providing suitable elastic elements in the chain-tensioning device.

In recent years, heavy machines have been created in West Germany for so-called percussion-rotary drilling, in which the machine is fed to the face with a force of up to 2 tons. These machines are equipped with rack feeders. The use of rack feeders is apparently explained by the fact that screw and chain feeders proved insufficiently strong for these conditions.

The greatest productivity in drilling blast holes and the greatest rate of drivage of workings are achieved by production innovators when drilling hammers are mounted on the manipulators of loading machines or on special drilling carts (Fig. 13).

In our opinion, under present-day conditions for carrying out preparatory workings (widespread use of two-track workings, drivage of single-track workings of enlarged cross section for two three-ton mine cars; use for loading primarily of intermittent-action machines), it is most advisable in two-track workings to install manipulators on special carts in such a way as to ensure the simultaneous operation of 5–8 drilling hammers. For single-track workings, with infrequent lay-bys, it is better to mount manipulators on loading machines or on small-size drilling carts. To mount pneumatic drilling hammers on drilling carts, it is necessary to use long-travel feeders with a travel somewhat greater than the length of the blast hole. This will make it possible to increase labor productivity by reducing the time for changing the tool and will reduce consumption of the tool itself. Thus, according to Paul Schulz [13], when drilling with four drilling hammers using supports, 60 m of blast holes in one face were drilled in 420 min, whereas when drilling with two drilling

with hammers mounted on long-stroke feed mechanisms of the Bohrtel system amounted to 189 min. Drilling was carried out in sandstones with pyritiferous inclusions. The number of drilled hole-meters during the comparative tests was 3680. During this time, when drilling with feed mechanisms there were only 9 breakages of drill rods, whereas when drilling by hand under equal conditions there were almost ten times as many breakages.

Fig. 13. Four-hammer drilling carriage.

Conclusions

1. The feeding devices for drilling hammers currently existing in practice do not provide full automation of the feeding of the drilling hammer to the face.

2. The most acceptable types of feed mechanisms for light drilling hammers of the RP-17, PM-508, and OM-506 types are piston feed mechanisms of the PK-1 and AP-1 types and screw feed mechanisms of the KTsM type, provided their principal characteristics are selected correctly. Automatic feed mechanisms for these types of hammers can be developed on the basis of piston feed mechanisms with the feed cylinder arranged along the axis of the hammer.

3. For heavy drilling hammers, screw, chain, and rack feed mechanisms are the most expedient. For further research and development on this basis of automatic feed mechanisms for heavy drilling hammers, screw feed mechanisms equipped with differential mechanisms are of considerable interest.

References

1. Alabuzhev P. M., Alimov O. D. The influence of feed force and the angle of rotation of the drill between blows on drilling speed. Izvestiya TPI, vol. 75, 1954.

2. Alimov O. D. The influence of feed force on drilling speed with pneumatic drilling hammers. Izvestiya TPI, vol. 75, 1954.

3. Alimov O. D., Basov I. G. Rational feed forces for the PM-508 drilling hammer when drilling rocks of various hardness. Izvestiya TPI, vol. 88, 1956.

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

1. Handbook of Mining Engineering. Vol. 1. Metallurgizdat, 1952.

2. Voroshilin I. R. Mechanization of Mining Operations. Metallurgizdat, 1952.

3. Totrov G. V. Mining Machines. Metallurgizdat, 1952.

4. Colliery Engineering, No. 1, 1954.—Airleg-mounted drill.

5. C. H. Vivian—New Speed Records in Advancing such a Bore are Claimed by Tonawanda Crews. Compressed Air Magazine, No. 2, 1955.

6. Trofimov P. F. Automatic feeders for rock drills. Geology and Mining. Proceedings of the M. I. Kalinin Institute of Non-Ferrous Metals and Gold, No. 16, 1947.

7. Sidorenko A. K. Automation of the feed of pneumatic drilling hammers. Mining Journal, No. 11, 1954.

8. Paul Schulz.—Bohrmaschine-Vorschubgerät Bohrteufel. Glückauf, No. 33/34, 1953.

9. Benuni A. Kh. High-speed methods of drifting. Metallurgizdat, 1946.