RESEARCH PROBLEMS OF BAR MACHINES USED FOR THE DESTRUCTION OF FROZEN SOILS

O. D. Alimov

In recent years, for the preliminary loosening of frozen soil, so-called bar-type installations have begun to find wide application in the practice of construction organizations. Bar-type installations are created on the basis of various self-propelled machines, on which chain working members of cutting machines—bars—are mounted. Such installations have been created on S-80, S-100, TDT-60 tractors, on the basis of ETN-124, ETU-353 excavators, and others [1–4]. The installations differ in the dimensions and operating modes of their working members, the number of bars mounted on one machine, the devices for feeding the bar into the ground, the power of the drives, and the design of the intermediate transmissions. Bar machines are still being manufactured in the workshops of various organizations according to inventors’ proposals. In most cases, the basis for their improvement is only observations of the operation of individual designs and suggestions from rationalizers.

Earth-cutting machines operate and are tested under various conditions. Therefore, data on their productivity are in most cases not comparable. This does not make it possible to assess with sufficient objectivity the merits of one or another design solution, or to determine the most promising machine variants and directions for their improvement. All this determines the need to carry out special studies that would make it possible to evaluate the quality of existing machines and outline ways for their further improvement.

The quality of machines for cutting frozen soils should be assessed first of all by the factor of productivity in earthwork, in comparison with the most widespread methods (excavation of frozen soil with pneumatic hammers, wedges, excavators with preliminary warming of the soil, etc.).

Cutting frozen soils into blocks or to the point of complete crushing is an additional operation to the technological process used in summer. The need for such an additional operation is determined by the fact that earthmoving machines of the excavator type are designed for operation in summer and cannot excavate frozen soils without preliminary loosening.

Preliminary loosening of frozen soils in most cases leads to additional expenditures of money and labor. But in some cases the productivity of work performed in winter, in comparison with summer work, may even increase. This may

will occur in those cases where the use of new mechanisms makes it possible to significantly increase the productivity of operations in existing technological processes, to shorten a number of operations altogether, or to create a new, more progressive technology. Thus, for example, it is known that the use of bar installations for cutting slots in the ground when driving piles for building foundations makes it possible to increase the productivity of these works [5]. The use of bar machines makes it possible to carry out winter transplanting of large trees, which substantially increases the effectiveness of urban landscaping in comparison with summer plantings [6]. Other cases are also possible. Therefore, when conducting research on earth-cutting machines, attention should also be paid to seeking possibilities for their rational application in various branches of the national economy.

In improving existing machines, creating new machines for cutting frozen soil, and developing methods for their application, it is necessary, in addition to the productivity of the work, to take into account their cost, as well as the labor productivity of the workers and the degree to which their labor is facilitated.

To solve the problem, it is necessary to carry out a comprehensive study that would include:

1. The search for the most expedient technological processes for carrying out earthworks with the aid of bar machines.

2. The study of operating regimes of the bar working members of earth-cutting machines.

3. The study of various designs of bar installations.

Let us dwell on the principal tasks and on certain questions of the methodology for carrying out such a comprehensive study.

1. The search for the most expedient technological processes for carrying out earthworks with the aid of bar machines

The first task of these investigations should be to determine the area of possible application of bar earth-cutting machines.

Research in this direction should begin with identifying categories of construction and other work where preliminary loosening of the soil (dividing it into blocks, preliminary cutting of slots, etc.) can increase labor productivity, ease the labor of workers, and reduce the expenditure of funds for carrying out the work. In addition to describing the technology for carrying out these works, it is necessary to collect data on their actual labor input and cost, as well as on the volume of these works in the national economy (trusts, sovnarkhozes, republics, the country).

The identified types of work should be divided into groups. The technology of application of earth-cutting machines may serve as the basis of the classification.

Proceeding from the specific features of each group of works, it is necessary to formulate the tasks of further research. Obviously, in these studies attention will have to be paid to resolving the following questions:

a) to identify the possibilities of breaking away from the mass blocks of various size and shape, the forces required for this, and the expedient methods of applying them;

b) on the basis of economic calculations, to substantiate the methods of applying earth-cutting machines, the parameters of their working members, and the required productivity;

c) to substantiate the parameters of other machines working in combination with earth-cutting machines. To solve the tasks set, a research methodology is being developed for this direction, taking into account the nature of the tasks and the possibilities for solving them. The methodology, apparently, should include

theoretical and experimental studies of methods for separating blocks from the mass, as well as economic calculations of the productivity of machines and the cost of carrying out work under various alternatives. In doing so, it is necessary to take into account the productivity not only of earth-cutting machines, but of the entire complex of mechanisms.

The methodology for studying the separation of blocks from a soil mass should provide for the following.

1. The study of the principal physical and mechanical properties of frozen soils that influence their resistance to separation. In this connection, it is necessary to identify relationships that can be used to calculate the magnitude of the forces required for separation and to substantiate appropriate methods of applying them. For this purpose it is useful to generalize the literature data on the destruction of soils and rocks. In our opinion, for determining the forces involved in separating blocks it is possible to use the strength coefficient according to the scale of Prof. M. M. Protodyakonov and the known relationships of this coefficient with other characteristics of rocks [7]. To determine the strength coefficient of soil, one should first of all use the so-called DorNII impact devices. N. A. Zelenin has established [8] the relationship between the characteristics determined by DorNII methods and by the Protodyakonov method. It would also be desirable to find a simpler “express method.”

On the basis of the relationships revealed, it is necessary to attempt to predict what sizes of blocks should be separated, how best to separate them, and what forces will have to be applied in doing so. These predictions should be checked and refined by experimental investigations.

1. The substantiation of the necessary parameters and designs of an experimental installation.

To substantiate the parameters and the operating principle of the experimental installation, one should take into account the requirements and wishes arising from the tasks of improving the technology of earthworks in winter, and the conditions necessary for verifying predictions.

In our opinion, the main experiments should be carried out under production conditions. As experimental installations, tractors and hoisting cranes may be used; they must be equipped with appropriate dynamometers for determining the forces of block separation. Skidding tractors of the TDT-75 or TDT-40 type may also be suitable for these purposes. For cutting blocks, any bar-type installation may be used; however, it is desirable to use the same installation on which cutting regimes will be investigated. This will allow both studies to be conducted simultaneously and, as a result, will provide comparable data. The number of experiments must be substantiated with allowance for the accuracy of the measuring equipment and for deviations of the experimental data from mean values caused by soil nonuniformity and other factors. The experiments should be carried out in the most representative soils.

1. In processing the results of experiments, the principal observations of the process of block separation should be described, the behavior of the machines during this process should be recorded, and the principal quantitative characteristics of these processes should be presented. The results of the experiments should be compiled in tables, usually placed in appendices. To reveal the relationships among the principal parameters of separation, it is advisable to construct graphs, which in many respects facilitate the formulation and explanation of conclusions.

On the basis of the research results, proposals should be made as to which schemes for cutting blocks and which methods of separating them should be used for various conditions and types of work.

1. The technical-and-economic evaluation of the use of the set of mechanisms.

The proposals made in the preceding section should be verified by, for example, calculations of labor productivity and the cost of performing the work. The best confirmation of the correctness of the recommendations set forth may be the results obtained during testing and introduction of these proposals into practice.

The economic effect must be calculated with allowance for the entire set of machines used for the given type of work. Calculations of economic indicators should be carried out according to the methodology developed by the Academy of Sciences of the USSR for evaluating the effectiveness of new equipment. On the basis of these calculations, the proposals made earlier are corrected, the possible economic effect from their introduction into the practice of the national economy is determined, and ways are also outlined for further improvement of the mechanisms and of the organization of work.

2. Investigation of the operating conditions of bar-type working members of earth-cutting machines

The need to investigate the operating conditions of the working members of bar machines is determined by the following circumstance. In modern technical literature a considerable amount of material has been accumulated on the results of investigations of the operating conditions of bar-type working members of coal-cutting machines in undercutting coal. Recently works have appeared [9, 10] whose authors attempt to generalize the available data on the operating conditions of coal-cutting machines, develop a theory for selecting optimal operating conditions, and calculate the loads on the working members of coal-cutting machines. The data of these works may also be used in part in calculations of bar machines employed for cutting frozen soils. However, cutting frozen soils also has a number of specific features that must be taken into account. Specific to this case are the physical properties of frozen soil and their change during the cutting process (as a result of heating), the high abrasiveness of soils, the vertical arrangement of the bar, which affects the process of removing the cuttings, and so forth. The investigation of these specific features was initiated by works carried out at the WESF of the USSR Academy of Sciences under the direction of Professor G. V. Rodionov [11], and by other studies [12, 13]. However, the results of these investigations do not make it possible to answer sufficiently fully all questions connected with the selection of operating conditions for the working members of earth-cutting installations. This restrains the improvement of earth-cutting machines. Thus, for example, most machines for cutting frozen soils operate at cutting-chain speeds of about 1 m/sec. These speeds are considerably lower than the chain speed of a coal-cutting machine in undercutting coal and substantially limit the possible productivity of earth-cutting machines. The only argument advanced by some specialists to justify such low cutting speeds is that, at these speeds, the least wear of the cutters is observed. Sufficient data to confirm this opinion are not presented.

Designers likewise have no data on expedient combinations of the travel speed of an earth-cutting machine and the speed of motion of the cutting chain as a function of the physicomechanical properties of frozen soils, the installed power of the machine, the type of working member, and its dimensions.

To solve all these questions it is necessary to generalize the data

scientific and technical literature on the physico-mechanical properties of frozen soils, on cutting conditions for soil and rock with cutters, on cutter wear, and on methods for removing cuttings from the slot and their calculation. On the basis of all this, preliminary recommendations can be made.

Experimental investigations of soil-cutting conditions must be carried out with allowance for the principal specific features of this method, in order to identify possibilities for improving operating conditions.

Based on experience in the design and operation of slot-cutting machines, and taking into account the capacities of modern tractors—prime movers that can be used to create bar machines—the investigation of the operating conditions of earth-cutting machines must be conducted while varying their basic parameters within the following limits:

Cutting speed from 0.2 to 3.0—6.0 m/sec;
Feed speed from 0.2 to 3.0—4.0 m/min;
Feed force from 200—300 to 5000—10000 kg;
Depth of the slot from 0.4 to 2.0 m;
Angle of inclination of the bar to the horizon from 20 to 90 degrees;
Width of the slot being cut from 0.12 to 0.6 m.

For such investigations, a special installation may be built, or one of the existing earth-cutting machines may be adapted. The latter option makes it possible to avoid considerable expenditures. As such installations, the URMG-60 or the installation developed by the Department of Mining Machines of TPI on the basis of the ETV-353 excavator may be used. These installations have a range of feed speeds and cutting-chain travel speeds that satisfies the requirements, as well as hydraulic mechanisms for setting the bar. In addition, they must be equipped with instruments for recording the principal operating indicators. The feed forces of the machines can be measured by recording, with pressure gauges, the fluid pressures in the cavities of the hydraulic jack for setting the bar, or by means of a dynamometer placed between the bar and the tractor chassis.

To measure the force and speed of pulling the cutting chain, a device should be installed for recording the torque and rotational speed of the transmission shaft that transmits power to the cutting chain. The most suitable device for this purpose, in our opinion, is a reduction-type balancing dynamometer. Such a dynamometer can be built on the basis of an automobile gearbox, which also makes it possible additionally to vary the speed of motion of the cutting part of the machine within the required ranges. For this purpose, it is desirable that the gearbox have, in addition to reduction gears, also overdrive gears. To measure torque, the gearbox is suspended on rolling bearings so that it can rotate about an axis coinciding with the axes of the primary and secondary shafts. The gearbox is restrained from rotation by a force-measuring element, from whose readings the magnitude of the torque is determined. The force-measuring elements may be spring, hydraulic, strain-gauge, and the like.

Automobile gearboxes have devices for driving the speedometer shaft. This device can be used to drive an instrument recording the speed of motion of the cutting chain.

In developing the apparatus for recording torque, chain travel speed, tractor travel speed, and its tractive effort, it is expedient to use the experience of creating such instruments for monitoring the operation and for testing automobiles and other transport machines. It is necessary that the instruments provide reliable readings at various temperatures, including severe frosts.

When conducting experiments on cutting slots in frozen soils, it is necessary to observe a definite sequence. In each of the most characteristic soils, slots are cut with a vertically positioned bar, under different cutting regimes and with different degrees of blunting of the tool. The latter, apparently, can be taken into account by carrying out the experiments continuously, beginning with sharp teeth and ending with their maximum blunting. Between individual experiments, the wear of the teeth of the various cutting lines should be measured and photographed. The feed speed and force, torque, cutting speed, and other data are measured during the cutting process. For some soils, experiments must also be carried out at different angles of inclination of the bar in order to reveal the influence of various combinations of cutting and feed speeds, as well as the influence of different conditions for the removal of cuttings.

For a more detailed study of the processes of removing cuttings from the slot being cut, special experiments should be conducted. For this purpose, a previously cut slot can be filled with cuttings and then passed through again at different inclinations of the bar and at different feed and cutting speeds. The experiments should be accompanied by measurements of power and forces. It is possible to carry out some of these investigations on models as well.

Ordinary and high-speed motion-picture filming of the principal processes can be of considerable assistance in analyzing the results of the investigations.

In our opinion, the study of the operation of setting the bar should include: a) the study of changes in the force during cutting-in (deepening) of the bar into the soil; b) determination of the duration of this operation as a function of the moment applied to the bar; c) identification of the most appropriate method of removing cuttings; d) investigation of the stability of the bar unit when setting the bar.

As a result of investigations of the operating regimes of bar-type working members, the principal characteristics of bar units for cutting frozen soils should be obtained:

a) the process of cutting frozen rocks (a description of the physics of the phenomenon);

b) the resistance forces of the cutting chain when running idle;

c) the resistance forces of the chain at different feed and cutting speeds;

d) the feed forces at different feed speeds and speeds of motion of the cutting chain;

e) the power expenditures for driving the cutting part of the bar unit and for moving the unit;

f) tooth wear and its influence on the feed forces, chain resistance, and power expenditures;

g) the process of removing cuttings from the slot being cut. Power expenditures for removing cuttings under different operating regimes of the chain-type working member;

h) the process of setting the bar (a description of the process with the characteristic features of soil cutting, removal of cuttings, distribution of forces in the system during deepening of the bar, and stability of the unit).

3. Investigation of the Designs of Machines for Cutting Frozen Soils

The data obtained in investigating the operating regimes of bar-type working members constitute the basis for investigating various designs of machines for cutting frozen soils, with the aim of improving them.

The study of a design, as a rule, begins with a generalization of experience—

of various organizations in the country in the creation and operation of bar-type earth-cutting machines. Such a generalization should include a description of machine designs, the main units and their reliability, the technical characteristics of the machines, the methods and features of their operation, and data on productivity and workers’ working conditions. All machines in use should be classified according to their principal characteristic features. This will make it possible to shorten the description of the designs and will facilitate subsequent analysis of their elements.

The main characteristic elements of the design of earth-cutting machines are:

1. The bar-type working member and the system by which it is suspended on the machine chassis.
2. The transmission mechanism for driving the bar.
3. The mechanism for setting and fixing the bar.
4. The machine feed mechanism.
5. The power unit drive (engine and hydraulic system).

In studying the design of the indicated units it is necessary to determine to what extent these mechanisms make it possible to provide the required parameters and the reliability of operation of earth-cutting machines.

In studying bar-type working members it is necessary to identify expedient designs of cutting chains, the arrangements of their assembly, methods of fixing them in the bar guides, their service life, and the possibility of restoration. It is necessary to find the simplest methods of suspending and fixing bars on machines and to develop methods for calculating the principal elements of the working members.

In modern machines, power is transmitted from the engine to the bars by gear, chain, and cardan transmissions. Methods should be developed for selecting the basic parameters of these transmissions and methods of calculation that take into account the specific features of the drive of chain bars.

Mechanical and hydraulic transmissions are used for setting the bar of undercutting machines. The arrangement and parameters of these mechanisms have a substantial influence on the overall dimensions and strength of the bar-suspension units, as well as on the labor requirement of all manipulations with the bar. Therefore it is necessary to seek the most expedient layouts of these mechanisms and their parameters, and to develop methods for calculating the principal elements.

The most laborious, apparently, will be investigations of machine feed mechanisms. As we noted in [4], in order to ensure high productivity, earth-cutting machines must have high maneuvering speeds and a good combination of operating feed speeds with the speeds of motion of the cutting chain and with the drive power. To ensure this, additional gearboxes and reduction gears are installed on earth-cutting machines. Various designs of gear reduction drives are known [4, 14]; thus, in the URMG-60 unit a ratchet-type reduction gear is used, while in the ETN-124 excavators a gear-worm reduction gear with hydraulic drive is used. The literature contains no data for calculating these reduction gears; therefore it is necessary to investigate reduction gears of various types, determine their prospects and field of application, and develop methods of calculation. The criteria for evaluating the quality of reduction gears are the possibility of changing operating speeds within the required ranges, compactness, and reliability of operation in winter.

Feed mechanisms must be evaluated according to the feed forces that they can provide during operation of bar-type working mechanisms.

When considering the power and the mechanical characteristic of the drive, it is necessary to determine how many bars and what their dimensions

it is possible to establish, for a given engine power, what the characteristics of the transmissions should be and what productivity the given installation will provide. It would be of interest to determine what drive powers are limiting (minimum and maximum) for installations with one, two, and three bars, taking into account, of course, the possible operating regimes of bar mechanisms as a function of the weight of the installation and the type of running gear.

In creating new machines for cutting frozen soils, attention should be paid to the choice of a base for such installations. Cutting frozen soils in most regions of our country is seasonal work. Therefore, it is hardly expedient to create special machines that can be used only for cutting frozen soils. In developing machine designs, primary attention should be given to those variants that make it possible to use the machine base year-round. Machines that in winter can serve as a base for earth-cutting installations include standard tractors and automobiles, multi-bucket excavators, and some other special machines.

To determine the possibility of using one or another machine as the base for an earth-cutting installation, it is necessary to consider the following circumstances:

1. The presence in the machine design of power take-off devices for driving the bar working member, and determination of the required characteristics of additional transmissions (power, rotational speeds, torques, gear ratios of additional reducers).

2. The presence of the necessary working feed speeds, or the possibility of installing additional speed reducers. What characteristics the speed reducers must have in order to provide the working and maneuvering speeds of these machines.

3. The presence of hydraulic or another type of drive for mechanizing the setting of the bar. If such drives are absent on the base machine, the simplest methods of installing them should be sought.

4. The presence of devices to protect the machine transmissions against overload.

The solution of some of the questions posed above will require exploratory design and experimental work. The most expedient, from the technical point of view, variants for creating machines for cutting frozen soils should be compared according to economic indicators, and the best ones should be identified for the various branches of the national economy.

LITERATURE

1. Zelenin A. N., “The State and Prospects for the Development of Machines for Excavating Frozen Soils.” Construction and Road-Building Machines, No. 10, 1961.

2. Smorodinov M. I., Zhmaev M. I., Fedorov A. N., “Certain Questions in the Design of Machines for Cutting Frozen Soil and Research Tasks.” Construction and Road-Building Machines, No. 4, 1962.

3. Fedorin L. A., Excavation of Frozen Soils by Cutting Machines. Gosstroiizdat, Moscow, 1961.

4. Alimov O. D., Basov I. G., Pratusevich Z. M., Cutting Frozen Soil with the URMG-60 Installation. TsBTI of the Ministry of Construction Industry, Tomsk, 1962.

5. Kosarev S., “Simpler and Faster.” Construction Gazette, No. 135, 1962.

6. Alimov O. D., “Mechanization of Tree Transplanting in Winter.” Forestry, No. 12, 1962.

7. Protodyakonov M. M., “The Coefficient of Strength of Rocks according to Professor M. M. Protodyakonov.” In: Problems of the Destruction and Crushing of Rocks. Ugletekhizdat, 1955.

1. Zelenin A. N., Physical Foundations of the Theory of Soil Cutting. Publishing House of the Academy of Sciences of the USSR, 1950.

2. Beron A. I., Kazanskii A. S., Leibov B. M., Pozin E. Z., Coal Cutting. Gosgortekhizdat, 1962.

3. Fomichev V. P., Calculation of Loads on Undercutting Machines. Gosgortekhizdat, 1961.

4. Fedulov A. I., On the question of choosing a method for excavating frozen soils, Proceedings of the ZSFAN USSR, No. 16, 1956.

5. Zelenin A. N., Gal’perin M. I., Abezgauz V. D., Excavation of frozen soil by mechanical methods. Academy of Sciences of the USSR, ITEI, No. 32, Moscow, 1955.

6. Zelenin A. N., Veselov G. M., Research on the cutting of frozen soil. Proceedings of the IGD of the Academy of Sciences of the USSR, Vol. 4, 1957.

7. Zolotnik M. I., A creeper gear for reducing the speeds of a 6-ton-class tractor. Construction and Road-Building Machines, No. 7, 1962.