O. D. ALIMOV, I. G. BASOV, F. F. ZELINGER

SOME RESULTS OF STUDYING CUTTING MODES FOR FROZEN SOILS USING THE “MOROZ” BAR-TYPE EARTH-CUTTING MACHINE

The operating modes of bar-type earth-cutting machines are characterized by the cutting and feed speeds, the geometry of the cutters and their arrangement in the chain, the dimensions of the slot being cut, and the intensity of removal of the cuttings. With a rational combination of these parameters, it is possible to obtain the highest productivity of the machine. Thus, the rational or optimal operating mode of a bar-type earth-cutting machine should be understood as such a combination of the above-mentioned parameters that makes it possible to obtain the greatest productivity in cutting slots at a given drive power of the machine.

In recent years much work has been done to improve bar-type earth-cutting machines [1–6], but many questions connected with the selection of optimal operating modes still remain unresolved. In the technical literature one cannot, for example, find an answer to the question of what the magnitude of the cutting-chain speeds and feeds should be, and in what ratio they must be taken when combining the cutting process with movement of the machine. Most existing earth-cutting machines operate at cutting speeds only slightly exceeding 1 m/sec. These speeds are considerably lower than the speeds for cutting coal with similar working members and, in the opinion of the authors of the present work, substantially limit the possibilities of increasing the productivity of earth-cutting machines. The only argument given to justify such low cutting speeds is that, allegedly, less wear of the cutting teeth is observed in this case. However, sufficiently convincing data in support of this opinion are not given [3, 4, 5].

To resolve the questions raised above, experimental work was carried out to study soil-cutting modes with bar-type working members, using the experimental “Moroz” installation.

The present work gives some results of these experimental investigations.

The experiments were conducted under field conditions in the winter of 1963–1964 in a riverside district of the city of Tomsk, on soils of undisturbed structure, not containing inclusions of rock (Table 1). Level sites measuring 300×1200 m each were selected for the investigations. The snow cover was 0.1–0.35 m. The air temperature during the period of conduct—

...during the experiments ranged from \(-8^\circ\) to \(-26^\circ\)C at wind speeds of up to 14 m/s.

During the tests, the cutting chain of the bar was arranged in a “herringbone” pattern with nine cutting lines. KMZ-1 bits with a normal holder were used for cutting.

Table 1

On the basis of processing the experimental data, graphs were constructed illustrating the relationships under investigation.

The productivity of bar-type earth-cutting machines, like that of bar-type coal-cutting machines used for undercutting coal, depends to a considerable extent on the average feed rate of the machine. The higher the average feed rate that can be achieved, the greater the productivity of the machine. The maximum possible feed rates of cutting machines with a chain working member are limited by the depth of chip that can be removed by each cutter, as well as by the speed of motion of the chain and the distance between cutters in each cutting line.

The maximum chip depth may be equal to the length of the part of the bit protruding from the holder of the cutting chain. Usually the bits are secured so that they protrude from the chain holders by 40–45 mm. However, when coal is undercut by cutting machines, the chip depth removed by each cutter does not exceed 14 mm. Taking this into account, bits are also designed whose front face is reinforced with a hard-alloy insert up to 18 mm long, measured from the cutting edge. Such values of the chips removed, in combination with chain speeds on the order of 2 m/s used in most cutting machines and a distance of 1710 mm between bits, limit the maximum feed rates of cutting machines, which at present are 0.5–2 m/min.

In studying the cutting modes of frozen soils with the “Moroz” installation, it was possible to vary the cutting and feed speeds over a considerably wider range than in the known tests of chain cutting machines. Thus, the speeds of chain motion when cutting frozen soil were brought up to 5.5 m/s, and the feed per bit—to a value exceeding the protrusion of the bit from the chain holder.

With the same arrangement of the cutting chain set, the depth of the chip removed by each tooth depends on the combination of cutting and feed speeds. At feed speeds of up to 33 m/h, the chip depth decreases substantially as the cutting speed increases only up to 1.0–1.5 m/s (Fig. 1). This combination of cutting and feed speeds provides a chip 8–10 mm deep. A further increase in cutting speeds at such feed speeds does not lead to any substantial change in chip depth and is inexpedient, since it will result only in greater tool wear and greater power consumption to overcome the friction forces of the cutters.

Fig. 1. Dependence of chip depth on cutting speed at feed speeds: □ — 18.8 m/h; △ — 38 m/h; × — 95 m/h; ● — 180 m/h.

For successful operation of standard cutting chains of slotting machines when cutting frozen soil, if not only cutting but also removal of the cuttings from the chain is taken into account, the chip size per tooth can evidently be 20–30 mm.

Most earth-cutting machines built on the basis of tractors of the S-80 and S-100 types are designed for feed speeds of 50–60 m/h. It is clear from Fig. 2 that, at such feed speeds, in order to achieve a chip depth of 20 mm, cutting speeds of not less than 1.0 m/s are required. As will be shown below, a chip depth of 20 mm is the most advisable when cutting frozen soils with chains of standard coal-cutting machines.

With an increase in the feed speed of earth-cutting machines above 60 m/h, it is necessary to increase the cutting speeds; otherwise the depth of the chips removed will exceed the tooth overhang, and the machine will be forced to destroy the soil with the chain lugs. The latter will lead to undesirable power expenditures for friction of the chain against the soil and the guide frame, and to greater wear of the chain.

Thus, at machine feed speeds of 90–95 m/h, the cutting speeds should be as high as 1.5–2.0 m/s (Fig. 1). If it is necessary to ensure a slot-cutting speed of up to 180 m/h, then in this case the chain speeds should be above 2.0 m/s in order to avoid friction of the chain lugs against the virgin soil.

Figs. 2 and 3 show the dependences of the averaged pulling force of one tooth of the cutting chain on chip depth at various cutting speeds in frozen soil. The averaged pulling force of one tooth of the cutting chain was determined by dividing the magnitude of the force required to pull the chain by the number of teeth in contact with the soil. Thus, it takes into account the force of cutting the soil, the friction of the lug against the guide frame, and the resistance of the cuttings being carried away. By the term “averaged force” of pulling a tooth, we also wished to emphasize the circumstance that the cutting force of the soil is not constant along the length of the face of the slot being cut. It is known that the temperature of frozen soil in the mass changes with distance from the surface being frozen. In connection with this, the strength of the soil also changes [4]. In what follows, for simplicity of exposition, the averaged pulling force of one tooth will be called the mean pulling force of one cutter. From Figs. 2 and 3 it is clear that, as the chip depth increases, the pulling force of the tooth increases. Moreover, with an increase in chip depth from 5 mm to 40 mm, that is, to a value almost equal to the cutter overhang, the cutter pulling force increases in proportion to the chip depth (Fig. 2).

The mean value of the pulling force of one cutter in the chip-depth range of 4–42 mm varies within the following limits: at a cutting speed of 0.43 m/s—from 15.6 to 119 kg; at a cutting speed of 0.78 m/s—from 11 to 105 kg; at a cutting speed of 1.31 m/s—from 13 to 96 kg. At a chip depth of more than 20 mm, increasing the cutting speed from 0.43 to 1.31 m/s (Fig. 2) somewhat reduces the cutting force.

With an increase in cutting speed above 2.0 m/s, already at a chip thickness of 5 to 15 mm the mean pulling force of the cutter decreases substantially (Fig. 3). It may be assumed that the decrease in cutter pulling force with increasing cutting speed occurs because, as the chain speed increases, the resistances to chain motion along the carrier and return runs of the bar are reduced, and the plastic deformations of the soil during its destruction also decrease; a greater share of the frozen soil is destroyed in a brittle manner.

At cutting speeds of 0.43 m/s, a chip depth three times greater than the cutter overhang was achieved. It was recorded that, under such cutting regimes, the increase in the mean pulling force of the cutter with increasing chip depth occurs less intensively.

(Fig. 2). Unfortunately, the power of the drive of the “Moroz” installation was insufficient for cutting soil with a chip of such depth at other cutting speeds. But if the noted phenomenon is confirmed, it will make it possible to assume that the reduction in the pulling force on the chain cutter at chip depths exceeding the height of the cutter occurs under the influence of a scale factor. It will then be possible to recommend, for the destruction of frozen soils, chains with the greatest possible cutter width and a smaller number of cutting lines. In order to obtain a definitive answer to

Fig. 2. Dependence of the pulling force of one chain cutter on chip depth at cutting speeds: ○ — 0.43 m/s; × — 0.78 m/s; △ — 1.31 m/s.

these questions, it is necessary to carry out broader investigations of the cutting modes of frozen soils and of the load on the cutting chain.

With an increase in the machine feed speed, the average pulling force of one cutter at various cutting speeds changes nonuniformly (Fig. 4). At cutting speeds of 0.43 m/s and 0.78 m/s, a rapid increase in the cutter pulling force is observed up to a feed speed of 100 m/h. A further increase in feed is accompanied by a less intensive growth of the average cutter pulling force.

These same dependences at cutting speeds of 1.31; 2.3; 3.4 and 5.4 m/s have a somewhat different character.

Knowing the magnitude of the force required to pull one cutter, one can determine the pulling force of the entire chain and the torque on the drive sprocket of the bar. Their magnitudes will depend on the dimensions of the bar and on the number of teeth simultaneously in contact with the soil.

Figure 5 shows the dependence of the average torque on the bar sprocket on the cutting speed for the “Moroz” unit, with a slot depth cut in the soil of 1.6 m and an average number of cutters in contact with the soil of 13.

Fig. 3. Dependence of the pulling force of one chain cutter on chip depth at cutting speeds: ○ — 2.3 m/sec; × — 3.4 m/sec; △ — 5.4 m/sec.

The torque on the shaft of the drive sprocket decreases with increasing cutting speed at the same feed speed. This occurs because of the decrease in the depth of the chip cut by the cutter. At a cutting speed of 0.43 m/sec and a machine feed of 180 m/h, the largest torque values were recorded, reaching 500–600 kgm. Cutting speeds of 1.0–1.3 m/sec, most often used in bar-type machines, correspond to torques of 200–450 kgm.

The most noticeable change in the magnitude of the torque is observed as the cutting speed increases to 3 m/s. A further increase in the cutting speed has no substantial effect on the magnitude of the torque.

Fig. 4. Dependence of the average pulling force of one chain cutter on feed speed at cutting speeds: ○ — 0.43 m/s; × — 0.78 m/s; △ — 1.31 m/s; ▼ — 2.3 m/s; □ — 3.4 m/s; ● — 5.4 m/s.

It should be noted that, with an increase in cutting speed above 2.3 m/s, the values of the torques at feed speeds of 18.8 m/h, 33 m/h, and 95 m/h differ only slightly (Fig. 5).

The cutting speed also affects the power required for destroying frozen soil and transporting the cuttings (Fig. 6).

At feed speeds of the earth-cutting machine of 18.8 m/h and 33.0 m/h, and with an increase in cutting speed from 0.43 m/sec to 2.4 m/sec, the power consumed for cutting and transporting the soil increases by approximately a factor of 2. A further increase in cutting speed to 5.4 m/sec does not lead to a substantial change in the power consumed by the cutting member. At a feed speed of 95 m/h, no significant changes are observed in power consumption when the cutting speed is increased from 0.43 to 5.4 m/sec.

Fig. 5. Dependence of the magnitude of torque on cutting speed at feed speeds: ○ — 18.8 m/h; × — 33 m/h; △ — 95 m/h; □ — 180 m/h.

For a machine feed of 180 m/h, a different pattern is characteristic for the change in power consumption for cutting and transporting frozen soil as a function of cutting speed. Increasing the cutting speed from 0.43 to 1.3 m/sec leads to a sharp increase in power (approximately by a factor of 2). This portion of the curve corresponds to chips whose depth is greater than the projection of the tooth from the chain cam. A further increase

an increase in the cutting speed to 3.4 m/sec reduces the power expended on cutting also by approximately a factor of 2, while at a cutting speed of 5.4 m/sec the power again increases somewhat, but not significantly.

Increasing the cutting speed above 1.3 m/sec at a feed speed of 180 m/h made it possible to reduce power consumption. This occurs because, at a cutting speed greater than 1.3 m/sec, the chip removed by each

Fig. 6. Dependence of the power expended on the destruction and transportation of soil on cutting speed at feed speeds: ○—18.8 m/h; ×—33 m/h; △—95 m/h; □—180 m/h.

cutter is, in depth, approximately equal to the part of the cutter protruding from the holder (Fig. 1).

With an increase in feed speed, in all cases the power required to drive the cutting member increases (Fig. 7). At a machine feed speed of 60 m/h, the power consumption for driving the bar-type.tagext

the working member amounts to as much as 22 hp. By selecting more appropriate cutting speeds, the required power can be reduced to 13–15 hp, that is, by 30–40%. With a drive power for the cutting part of 25–35 hp, it is possible to cut slots in frozen soil to a depth of 1.6 m with a machine feed speed of up to 180 m/h. This is expediently carried out at cutting speeds on the order of 3–3.5 m/s.

Fig. 7. Dependence of the power expended on destruction and transport of the comminuted soil on the feed speed at cutting speeds:
○ — 0.43 m/s; × — 0.78 m/s; △ — 1.31 m/s; ● — 2.3 m/s;
□ — 3.4 m/s; ▼ — 5.4 m/s.

Figure 8 shows the dependence of the resistance to movement of the bar-type working member, conventionally called the feed force of the unit, on the cutting speed. The feed force varies significantly depending on the cutting speed and the feed speed. The most significant feed forces are required at cutting speeds up to 2.0 m/s. With an increase in cutting speeds above 2.0 m/s, substantially smaller feed forces are required to achieve the necessary productivity in cutting slots in frozen soil. In this case, even for such high feed speeds as 180 m/h, the required forces—

the feed forces do not exceed 800 kg. This circumstance is of considerable interest. It indicates that the chassis of ordinary automobiles and wheeled tractors can be widely used for creating bar-type earth-cutting machines.

Vertical axis: installation feed force, kg
Horizontal axis: cutting speed, m/sec

Fig. 8. Dependence of the installation feed force on cutting speed at feed speeds: ○—18.8 m/h; ×—33 m/h; △—95 m/h; □—180 m/h.

It should be noted that the above dependences were constructed from averaged data obtained when the soil was frozen to a depth of 0.7 to 1.5 m, at air temperatures from −8 to −26°. In this case, the density of the frozen soil, characterized by the number of blows required for penetration of the DorNII impactor, ranged from 10 to 660. Therefore, the conclusions drawn may to some extent serve as a basis for recommendations on improving and creating new bar-type machines for cutting frozen soils.

In particular, it may be concluded that most of the bar-type earth-cutting machines created up to the present time operate under irrational conditions. This does not allow their power to be used effectively in order to achieve high productivity. Under rational operating conditions, to achieve cutting speeds of the cutting chain

…chain speeds of up to 180 m/h, the required power of the drive of the cutting part does not exceed 35 hp. If one takes into account that under such operating conditions an additional 4–5 hp must be expended on machine feed, then high-productivity single-bar machines can be created on the basis of tractors, trench excavators, and motor vehicles with a drive power of 50–55 hp. Their productivity may exceed by a factor of 2–3 the productivity of existing earth-cutting machines, even those built on the basis of such powerful tractors as the S-80 and S-100. The main reason for the low productivity of bar-type earth-cutting machines built on the basis of S-100-type tractors—even those having reduction gears and hydraulic mechanisms for setting the bar—is the presence of low cutting speeds, which does not permit useful utilization of the machine drive power. For the most expedient use of the drive power of such machines, the speeds of motion of the cutting chains should be increased to 2.5–3.5 m/s. Final recommendations on this question should be given after studying the loads on the chain at various cutting speeds, taking dynamic components into account.

Single-bar machines can be successfully created on the basis of crawler and wheeled tractors of low power (20 hp). Such machines will find application where the volumes of work are small. The speeds of motion of the cutting chains of such machines should be on the order of 2–3 m/s.

In seeking the possibility of further increasing the productivity of bar-type earth-cutting machines, exploratory work should be carried out to increase machine feed speeds by changing the design of the cutters and their arrangement on the cutting chain. In particular, five- and three-line chains with wide cutters should be tried in operation, as well as cutting chains with scrapers arranged successively one after another and alternately with cutters. Apparently it will be expedient to use, for example, chains in which the first cam carries a central cutter, the second cam two side cutters, and the third cam a scraper. The height of the scraper may be somewhat less than the height of the cutters. It is possible that the scraper should be made conical or provided with one or several cutters.

Experience with various chains should be obtained in cutting both frozen soil and thawed soil, hard clays, limestone, and coal.

REFERENCES

1. O. D. Alimov, I. G. Basov. Earth-cutting installations on the basis of ETU-353 excavators. Construction Mechanization, No. 9, 1963.

2. O. D. Alimov, I. G. Basov, Z. M. Pratusevich. Cutting frozen soil with the URMG-60 installation. TsBTI and NTO Stroiindustriya, Tomsk, 1962.

3. A. N. Zelenin. Destruction of frozen soils by cutting, impact, and vibration. TsINTI NAM, series IV, Moscow, 1962.

4. V. D. Abezgauz, M. I. Galperin. Excavation of frozen soils in mechanized trench digging. Gostoptekhizdat, Moscow, 1962.

5. T. V. Miklashevskaya. Basic trends in the technology of excavating frozen soils. VINITI, Moscow, 1960.

6. V. A. Shtobbe, Yu. V. Troyanovskii. Application of the two-bar RMGU-2 machine for loosening frozen soil.

7. O. D. Alimov, I. G. Basov, F. F. Zelinger, V. G. Yudin. Methodology for studying modes of cutting frozen soils. Article in the present collection.