O. D. Alimov

Experience in Creating Bar-Type Earth-Cutting Machines Based on Trench Excavators

Bar-type earth-cutting installations are finding ever wider application in winter construction work. Practice has shown that the use of these machines in developing frozen soils that do not contain significant inclusions of gravel and other rock materials makes it possible to substantially increase the productivity of earthwork during winter construction.

Until now, bar-type earth-cutting machines have been manufactured as individual experimental installations or in small batches. In design these machines are diverse. They have been created on the basis of various tractors, excavators, and cutting units of coal-cutting machines. These machines differ in the designs of their individual assemblies, in their technical characteristics, and in the final result—the productivity of the machine, the productivity and working conditions of the operating workers.

At first, the creation of diverse machines for one and the same purpose was apparently justified. This made it possible to involve a large number of engineering and technical personnel and worker-innovators in the creation and introduction of new machines, to create a number of original variants of machines and assemblies, and to test their operability under different conditions. As a result, the expediency of the broad use of bar-type earth-cutting machines was practically proven. Now, however, when there is both the possibility and the necessity of widely using bar-type earth-cutting machines in practice, the questions of selecting the most expedient machine designs and of organizing their series production at one or several plants must be resolved. For this, it is necessary first of all to resolve the questions of the base machines for earth-cutting installations and the most expedient operating regimes for them.

The greatest number of earth-cutting machines has been created on the basis of tractors of the S-80, S-100, and TDT-60 types; a smaller number—on the basis of trench excavators. Meanwhile, the use of trench excavators as bar-type earth-cutting machines, in our opinion, is of primary importance.

The point is that the majority of trench excavators produced by our industry are intended for work only in the summer. In winter, even with slight freezing of the soil, operation of multi-bucket excavators without additional loosening of the soil is impossible. For this reason, trench excavators during the winter,

as a rule, stand idle. If it were possible, with a minor change in design, to use in wintertime a large part of the trench excavators as earth-cutting machines, this would yield a large economic effect.

There are significant prerequisites for a positive solution of this problem. First, trench excavators have chassis designs that provide them with travel operating speeds also needed for the continuous operation of bar-type earth-cutting machines, that is, within the range from 0.2 to 3.0 m/min. As a result of using these excavators as a base for earth-cutting machines, there is no need for additional speed reducers, without which productive operation of earth-cutting machines created on the basis of standard tractors is impossible.

Second, the design of trench excavators makes it possible to provide a drive for the cutting bars with only minor modifications to the machine and, consequently, with a small outlay of funds.

Practice has already accumulated some experience in converting trench excavators into bar-type earth-cutting machines.

The greatest number of attempts has been made to convert excavators of the ETU-353 type. ETU-353 excavators are widely used in practice and have travel operating speeds most suitable for bar-type earth-cutting machines. Several bar-type earth-cutting machines created on the basis of the ETU-353 were demonstrated at the USSR Exhibition of Achievements of the National Economy in 1962 [1]. The bucket working equipment was removed from the excavators and bars from coal-cutting machines were installed (Fig. 1). The drive

Fig. 1. Two-bar machine based on the ETU-353.

of the bars is provided from the excavator engine through the gearbox, chain transmissions, and the countershaft. The countershaft is fastened to the lower part of the excavator’s upper frame. The corresponding sprockets for driving the cutting chains of the bars are first installed on the countershaft. A bar or several bars are attached to an additional frame, which, by means of lugs, is in turn hinged to the supports of the countershaft and can rotate around it.

main. The speed of movement of the cutting chains during operation of the machine is 1.1 m/sec. For raising the bars, the winch used is the excavator boom-hoisting winch. Lowering the bars and sinking them into the ground is carried out under the action of the bars’ own weight.

As practice shows, penetration of the bar into frozen ground under its own weight is ineffective and does not make it possible to make full use of the machine’s power for breaking up frozen ground. The desire to make fuller use of the excavator engine power for the useful work of cutting slots apparently led the designers to equip such earth-cutting machines with two and three parallel-mounted bars. But in this case as well, combining soil cutting with movement of the machine proved difficult, since the bars are not held in the specified position and, even at low travel speeds of the machine, are forced out of the ground. These machines have no devices for forcibly holding the bars in the specified position. In addition, the installations have such a mounting of the bars that, even when they are turned downward to the maximum, they do not assume a vertical position. This does not allow the length of the bars to be used most fully to achieve the maximum depth of the slots being cut, and adversely affects the balance of the machine.

In connection with this, the productivity of earth-cutting machines in such a design is comparatively low.

Fig. 2. BETU bar-type earth-cutting machine.

The noted shortcomings have largely been eliminated in the designs of earth-cutting machines created on the basis of excavators at the Tomsk Polytechnic Institute (TPI).

In the BETU bar-type earth-cutting machine (B—bar-type, ETU—the base machine from the ETU-353 excavator, Fig. 2), the drive of the cutting part is carried out according to the same scheme as in the machines demonstrated at VDNKh, but the gear ratios were changed to increase the cutting speeds.

On the basis of experience in creating and operating installations of the URMG-60 type [2], it was established that cutting-chain travel speeds on the order of 1.0 m/sec, which are most often used in earth-cutting machines built on the basis of both ETU-353 excavators and S-80 and S-100 tractors, are insufficient. In the BETU machine, the cutting-chain travel speeds were brought up to 1.8 m/sec. This was achieved by reducing the gear ratio in the second stage of the chain transmission. For this purpose, on the turret shaft of the ETU-353 excavator, the gear wheel with 40 teeth was replaced by a smaller one with 17 teeth, with the same module and the former method of fastening to the safety friction clutch. As in previously created machines of this type, the cutting bars were fastened to a metal suspension, hinged on the supports of the turret shaft. But the design of this suspension was simplified. The suspension is a rectangular box 1 (Fig. 3), made of 30 mm sheet steel. For fastening the beams of the bars inside the box there are inserts 2, the ends of which project from the box by the length necessary to accommodate the six fastening bolts of the standard bar beam. In this case, the bar beam is placed between the outer ends of inserts 2 and is fastened to them with bolts. Depending on need, one, two, or three bars may be installed on one box.

Fastening the bar beam to the projecting ends of the inserts makes it possible to simplify the construction of the box, provides better access to the fastening bolts, and at the same time somewhat lengthens the working element. As a result, with the same bar length the BETU machine can cut deeper slots in the ground. This is also facilitated by a somewhat different fastening of the turret-shaft supports to the upper frame of the excavator. The turret-shaft supports are fastened to the guides of the upper frame of the excavator by means of triangular inserts. The dimensions of these inserts make it possible to ensure rotation of the frame for fastening the bars through such an angle that, in the lower extreme position, the bar occupies a vertical position. This also ensured better balance of the machine, better utilization of the weight and cutting force for achieving maximum feed forces.

To mechanize the operations of setting the bar in and holding it in the required position, a hydraulic system is additionally installed. The hydraulic system consists of the standard hydraulic pump of the DT-54 tractor, a hydraulic distributor, an oil reservoir, pipelines, and hydraulic jacks for setting the bar.

Installation of such a hydraulic system on the basis of the ETU-353 excavator presents no particular difficulties. The engine of this excavator is analogous to the engine of the DT-54 tractor, and its design provides a device for installing a hydraulic pump. As the jack for setting the bar of the BETU machine, a piston jack from the “Belarus” excavator is used. The cylinder eye of the jack is fastened to a crossmember installed on the upper part of the excavator frame, while the rod eye is fastened to the hinge of brackets 3 (Fig. 3), welded to the bar-mounting frame. When oil is forced into the upper cavity of the jack cylinder, the bar is lowered and penetrates into the ground. When oil is forced into the rod-side cavity of the jack, the bar is withdrawn from the ground and raised into the transport position.

The dimensions of the jack and brackets, and the placement of the crossmember on the upper frame, are selected in such a way that, when cutting the ground, the bar can occupy a vertically downward position, and in the transport position it is turned upward. The angle between the axis of the bar and the horizontal in the transport

View along A

Fig. 3. Suspension box for the bars of the BETU.

position is about 15°. The total angle of rotation of the bar is 105°.

The technical characteristics of the first experimental prototype of the BETU are given in the table.

Experience in operating the BETU at construction sites in the city of Tomsk confirmed its high operational qualities [3]. Its shift output, when the ground was frozen to 1 m, amounted to as much as 700 m of slots per shift and 350–400 m/shift when the ground was frozen to a depth of up to 1.5 m.

When loosening frozen ground for the laying of a sewer-collector trench, one BETU machine provided a working front for the simultaneous operation of three excavators digging a trench to a depth of 3.6–5.2 m—one ETU-353 multi-bucket excavator and two E-302 single-bucket excavators. At the same time, the shift output of the ETU-353 multi-bucket excavator reached 250 m³, and that of the E-302 excavators was 150–160 m³ per shift.

Thus, the conversion of one ETU-353 excavator into a bar-type earth-cutting machine not only made it possible to use this machine beneficially year-round, but also made it possible to “revive” and productively employ several more excavators under winter conditions. There is no need to speak further about the benefit of this for the national economy.

The technology of earthworks performed with the aid of the BETU did not require the installation of two or three bars on the machine. With a single bar, the BETU proved to be the most maneuverable and universal. The presence of a device for forced penetration and for holding the bar in the ground, together with a sufficiently wide range of feed speeds, ensured the most complete loading and rational use of the 54 hp engine with one bar. At the same time, it proved possible to ensure high specific forces and feed values for each tooth of the cutting chain of up to 37 mm. This, apparently, led to very high wear resistance of the teeth. Thus, when the BETU worked in frozen soils, where inclusions of rock were rarely encountered, the service life of one set of teeth was up to 2500 m² of slots in the ground. Failure of the teeth in this case occurred mainly as a result of wear of the tooth-head body near the hard-alloy plate. As a result, teeth with brazed plates seemed to sharpen themselves. When operating under such conditions, one set (bar, chain, and guide frame) is quite sufficient for operation of the machine throughout the entire winter season.

Under certain conditions of use of earth-cutting machines, it may be advisable to install two or three bars simultaneously. In these cases, on machines of the BETU type it is necessary to install in parallel two hydraulic jacks for forcing in the bar. The BETU design provides the capability for this.

The earth-cutting machine “Moroz” (Fig. 4), created at TPI also on the basis of the ETU-353 excavator, has a somewhat different design. The conversion of the ETU-353 excavator into the “Moroz” earth-cutting machine consists of the following. With the onset of frost, the upper frame is removed from the ETU-353 excavator together with the complete set of equipment mounted on it: the bucket working member, turret shaft, hopper, conveyor, etc. The equipment removed from the excavator chassis is repaired and then preserved for the entire winter period.

On the base of the excavator chassis, the cutting part of the cutting machine 1 is installed. For fastening the reducer of the cutting part and the hydro-

a hydraulic cylinder of the bar-advance mechanism is installed on the lower frame of the excavator with an additional welded frame 2.

The drive of the driving shaft of the reduction gear of the cutting unit is effected from the engine through the excavator gearbox and a cardan shaft. The front end of the cardan shaft is fastened to the shaft which, in the gearbox of the ETU-353 excavator, serves to drive the belt conveyor.

Fig. 4. “Moroz” earth-cutting machine.

To ensure a cutting-chain travel speed of the slot-cutting machine on the order of 2.0 m/sec, the engine of its drive must have a speed of about 1450 rpm. The crankshaft of the ETU-353 engine can have such speeds, but in the gearbox these speeds are reduced and, at the output shaft for driving the belt conveyor, the rotational speeds are only 260 or 456 rpm. To increase the rotational speeds of this shaft, the gear ratios of the gear transmission in the gearbox were reduced. For this purpose, the gears \(z = 15\) and \(z = 23\) of the last transmission stage of the power take-off shaft drive were replaced by gears with numbers of teeth \(z = 22\) and \(z = 21\), respectively. This made it possible to increase the rotational speed of the cardan shaft to 765 rpm.

As the primary shaft of the reduction gear of the cutting unit of the installation, a shaft was used which, in the reduction gear of the cutting unit of the slot-cutting machine, is an intermediate shaft. The cardan shaft is connected to it. This made it possible to reduce the gear ratio of the reduction gear of the cutting unit of the KMP by a factor of 1.75.

As a result of all these changes, the chain of the bar of the “Moroz” machine can have travel speeds of 0.98 and 1.94 m/sec.

A hydraulic system similar to the hydraulic system of the BETU is mounted on the “Moroz” machine. Unlike the BETU, the hydraulic cylinder on the “Moroz” machine is installed differently. The bar is advanced when the rod is drawn into the cylinder of the hydraulic cylinder, that is, when oil is supplied to the rod-side cavity of the hydraulic cylinder. With identical dimensions of the hydraulic cylinders and oil pressures, the maximum force for inserting the bar in this case will be somewhat less than can be provided with the hydraulic-cylinder arrangement used in the BETU. But, on the other hand, the conditions are improved

the operating conditions of the hydraulic jack are improved and the forces tearing the cutting part away from the machine chassis are reduced. In addition, the possibility of deformation of the hydraulic-jack rod as a result of longitudinal bending is eliminated, which was observed during operation of the BETU. The direction of the force developed by the hydraulic jack in the “Moroz” installation is toward the machine chassis, thereby partly relieving the fastening parts of the cutting unit, which absorb the force from the bar during machine feed.

As the hydraulic jack for deepening the bar, a hydraulic jack from the TDT-60 tractor was used; as the remaining elements of the hydraulic system, standard units of the DT-54 tractor hydraulic system were used.

“Moroz” is better balanced than the BETU, and the absence of an upper frame allows the operator to observe the work of the operating member and the movement of the machine more effectively. To improve the operator’s working conditions, an enclosed cab has been installed. The “Moroz” machine is intended for loosening frozen ground in various construction operations in winter, for winter transplanting of trees, etc. Of interest was the experience of using it also for cutting trenches under winter conditions in bogs for draining the latter. In this case, vertical slots were cut in the frozen bog. Linear charges of explosive were laid in the cut slots and then detonated. As a result, drainage ditches were obtained. Ditches were cut in the same way in dense soil on necks of land separating bogs from water-collection basins. Experience showed that the operating modes of the working member ensure successful operation of the bar earth-cutting machine both in dense soils and in viscous, highly waterlogged boggy soils, where roots and tree trunks are often encountered.

The “Moroz” machine found its principal use as an experimental installation for studying soil-cutting modes. In this case, gearboxes with the corresponding apparatus for measuring the torques required to drive the chain member, at various modes of its operation; the speeds of motion of the chain working member and machine feed; the forces acting on the bar, etc., were additionally installed between the gearbox and the cutting part of the cutting machine.

The research results obtained with the aid of the “Moroz” experimental installation can be used for further improvement of earth-cutting machines. Conversion of the ETU-353 excavator into BETU “Moroz” earth-cutting machines and back does not require significant funds and can be carried out in practically any construction organization. But in the interests of the national economy of the country, it is advisable that the additional units required for converting ETU-353 excavators into BETU-type bar installations be produced centrally, according to consumer orders. There is no doubt that most users of ETU-353 excavators in the northern and central parts of our country are interested in using these machines year-round and will purchase excavators with additional devices for winter operation. If one proceeds from the minimum expenditures of funds for converting ETU-353 excavators into bar earth-cutting machines, then the BETU machine should first of all be taken as the basis for the design of the bar machine and of the additional units. In developing the units needed to convert most ETU-353 excavators into earth-cutting machines, it is advisable to carry out a number of improvements in the design of the excavator as well, in order additionally to increase the productivity and reliability of the machine and to improve the working conditions of the service personnel.

Thus, the design of the intermediate-shaft supports should be changed in such a way as—

so that when converting the excavator into a bar-type earth-cutting machine they could be fastened directly to the upper frame, i.e., without an additional insert. At the same time, it must be possible to vary the position of the bar within the same range as in the BETU machine. At the maximum penetration of the bar into the ground, it must occupy a vertical position. The design of the countershaft assembly must provide devices for the rapid replacement of the drive sprockets and for their reliable locking in the required position. The auxiliary equipment must include replaceable toothed wheels of the chain drive of the countershaft, to change the rotational speeds of the countershaft when converting the excavator back into a bar-type earth-cutting machine.

Because of the substantial increase in the rotational speeds of the countershaft required for driving the bar-type operating mechanism, the plain bearings of the countershaft supports should be replaced with rolling bearings.

Since the excavator will operate year-round, an insulated cab must be provided for the excavator operator. The cab must be equipped with a heater ensuring normal working conditions for the operator throughout the entire shift, even in the most severe frosts. The cab windows must provide good visibility, including toward the bar-type working member. All control mechanisms must be located in the cab, including the hydraulic distributor.

Conversion of ETU-353 excavators according to the “Moroz” machine scheme can also be recommended for practice. This is especially true in cases where construction organizations have at their disposal the bars of machines together with the gearboxes of the cutting section. An advantage of this scheme is also that the entire set of the working equipment of the multi-bucket excavator is removed from the machine; it can be repaired and thus prepared in advance for operation in the summer season.

In the future, it would be desirable, instead of gearboxes for the cutting sections of undercutting machines, to develop universal bar-drive units so that they could be installed both on trench excavators according to the “Moroz” scheme and on standard tractors. In our opinion, the design of such universal drives should include a two-speed toothed gearbox for the chain drive and a hydraulic mechanism for setting the bar. The universality of this mechanism should also consist in the fact that, in addition to driving bars for cutting frozen soils, they should be adapted to drive chain-type working members for excavating trenches of small cross section, for laying cable, etc.

Trench excavators produced by the Tallinn Excavator Plant can be used to great advantage as a base for creating bar-type earth-cutting machines. These excavators have travel speeds that meet the requirements of bar-type machines; a hydraulic drive for controlling the working equipment; and enclosed cabs that protect the operators from bad weather.

The author, together with engineers V. G. Yudin and Yu. P. Sadakov, has developed a proposal for converting the ETN-171 trench excavators of the Tallinn plant into BETN-171 bar-type earth-cutting machines.

Compared with the BETU, the speeds of the cutting chains in these machines have been increased somewhat. This makes it possible to make the fullest use of

increase the engine power and achieve a productivity somewhat higher than that of machines of the BETU type.

Earth-cutting installations on a crawler chassis have good stability, low specific ground pressure, and can provide high feed forces for a bar-type working member when cutting frozen soils of various strengths. All this makes it possible to use them widely in various construction operations. These machines are especially effective when large volumes of earthwork are being carried out on new construction sites that are not littered with construction debris in the form of scrap metal, fragments of concrete slabs, etc.

When these machines are used for loosening soil in urban conditions, where the volumes of earthwork are small and the machine often has to be moved from one place to another, difficulties arise. They are connected with the need to have bulky auxiliary equipment: trailers and tractors for transporting crawler machines on city roads covered with asphalt. The work of loading, transporting, and unloading crawler earth-cutting machines increases the cost of earthwork and significantly reduces labor productivity.

Therefore, for loosening frozen soil in various earthworks within city limits, it is desirable to have earth-cutting machines on pneumatic-wheel running gear.

As a base for such machines, tractors and excavators on pneumatic-wheel running gear, as well as trucks, may be used. Particularly noteworthy are trench excavators on pneumatic wheels of the ETN-124 type. These excavators, like other trench excavators, are either idle in winter or are used with comparatively little benefit as ordinary wheeled tractors for small transport jobs.

The conversion of an ETN-124 excavator into a bar-type earth-cutting machine is facilitated by the fact that this excavator, like the ETN-171, already has a hydraulic system that can be used to mechanize the setting and lifting of the bar, and also to change the speed of movement of the machine during operation.

Several bar-type earth-cutting machines based on the ETN-124 have been built and are operating successfully at construction sites in the cities of Tomsk and Novosibirsk. These machines were created by researchers of TPI jointly with engineers of construction administrations.

It should be noted that attempts to create earth-cutting machines based on ETN-123 and ETN-124 excavators had been known earlier. At the thematic exhibition of earth-cutting machines at VDNKh in 1962, an earth-cutting installation, manufactured by one of the construction organizations of Moscow on the basis of the ETN-123, was demonstrated. It is also known that the Tallinn Excavator Plant in the spring of 1962 tested an ETN-123 with a bar-type working member. Unfortunately, however, the literature still lacks sufficiently detailed data on the design of such machines and on the results of their application. From an inspection only of the external appearance of these machines it is difficult to obtain answers as to how stable these machines are when working with long bars from coal-cutting machines. There are no data whatever on suitable chain speeds, on the reliability of operation of the hydraulically driven travel reducer under severe frost conditions, etc.

Therefore, the creation of BETN earth-cutting machines (B—bar-type; ETN—the base machine is the ETN-124 excavator) at the Tomsk Polytechnic Institute was accompanied by exploratory design, calculation, and experimental research work.

The general view of the BETN bar-type earth-cutting machine is shown in Fig. 5. When converting the ETN-124 excavator into a bar-type earth-cutting...

To create the BETN earth-cutting machine, the entire assembly of the scraper-type working member of the trench excavator is removed from the excavator—the frame with the chain and augers—and in its place a newly fabricated suspension with a bar fastened in it is installed. The suspension is hinged to the bosses of the excavator’s reduction gearbox. Rotation of the suspension with the bar fastened in it is carried out by the excavator’s hydraulic jacks. The rods of the jack cylinders enter the lugs of the suspension and are connected to it by pins. The geometry of the bar suspension and of the fastening of the jack rods was selected in such a way that, with the unchanged design of the jacks and their fastening on the excavator reduction gearbox, the suspension with the bar turns through an angle which, in the working position, ensures that the bar is positioned vertically downward. The vertical position of the bar during cutting contributes to the best use of the machine’s coupling weight for producing the greatest feed forces. In this case, the force of cutting the soil, acting through the cutting chain on the machine body, presses the excavator chassis downward. Owing to this, the coupling weight of the machine increases. This circumstance is especially important for such earth-cutting machines as the BETN, built on the basis of wheeled chassis. The light weight of the ETN-124 and the small coefficient of adhesion of the wheels to the ground substantially limit the possible feed forces. “Mobilization” of the cutting force for this purpose is highly desirable in this case.

Fig. 5. Bar-type earth-cutting machine BETN.

When the rods of the hydraulic jacks are retracted into the cylinder, the bar is positioned upward at an angle of 10–16° to the horizon. In this position the machine is convenient for maneuvering operations and for moving from one work site to another.

For better stability of the BETN machines during maneuvering operations and to achieve sufficiently high productivity when cutting slots in the ground, the length of the bars was adopted as somewhat shorter than in other earth-cutting machines. At the same time, however, the suspension design made it possible to cut slots to a relatively great depth—1.1–1.5 m—which proved quite sufficient for the successful performance of most various earthworks under urban conditions.

The cutting chain of the bar is driven by a sprocket mounted on the output shaft of the excavator reducer. The pitch and design of the chains in the working equipment of the ETN-124 excavator and in the bars of modern cutting machines are different. Therefore, before installing the bar-type working element, the driving sprocket of the excavator chain is removed and replaced with the sprocket from the cutting machine.

The design of the excavator reducer may be left unchanged. In this case, soil-cutting speeds of 0.95 and 1.4 m/s are obtained. But these speeds, in our opinion, are insufficient for effective use of engine power when cutting frozen ground, especially for machines with pneumatic-tire drive. Therefore, changes were introduced into the reducer design of one of the machines, as a result of which the speeds of motion of the cutting chains were increased to 1.6 and 2.3 m/s.

Tests of the machine confirmed the advisability of such an increase in speeds. Thus, BETN machines with cutting speeds of up to 1.4 m/s cut slots in frozen soils with an average productivity of 50 m/h. The same machines, but re-equipped to operate with cutting-chain speeds of up to 2.3 m/s, provided, in the same frozen soils, twice the productivity, that is, 100–120 m/h.

BETN machines are successfully used for mechanizing various operations: for preliminary loosening of soil when excavating trenches for cable and water mains, pits for house foundations, trenches for blasting work, for mechanizing winter transplantation of trees, etc.

It proved very convenient that the BETN machines also have a bulldozer blade. Such a machine can prepare its own work front, clearing the site of snow and debris, removing loosened soil, etc. All this increases work productivity.

BETN machines were operated at various temperatures. Frosts often reached −30° to −40°C.

In all these cases the hydraulic drive of the creeper gear operated properly. Difficulties in these cases arose only when starting the machine engine in the morning after the machine had stood for a long time in the cold. These difficulties can be eliminated by storing the machines in heated garages. Storage of the BETN machine in a heated garage will naturally also increase the reliability and service life of the hydraulic part of the machine. The possibility of garage storage of the BETN machine is also ensured by the fact that the overall dimensions of the machine with the shortened bar allow it to be placed in any garage intended for GAZ-51-type trucks and others. The mobility of the BETN and the possibility of travel on roads with any type of surface make it possible at the beginning of a shift to deliver the machine quickly to any place in the city, and at the end of the shift to return it to the garage without particular difficulty.

Work on the investigation and improvement of bar-type earth-cutting machines based on trench excavators is continuing. But even now the design of the additional attachments developed at TPI for re-equipping ETU-353, ETN-171, and ETN-124 excavators into bar-type earth-cutting machines can be recommended for wide use. It is advisable that these additional mechanisms be manufactured centrally and supplied to consumers complete with bars, spare chains, and teeth. The cost of these additional units and parts is low. Experience in the use of bar-type earth-cutting machines of the BETU and BETN types in Tomsk and Novosibirsk shows that the costs of re-equipping trench excavators are recovered after only a few days of operation of the bar-type earth-cutting machines. One such machine during the winter season of operation gives an economic eff—

Table 1

effect only due to a reduction in the cost of earthwork by 10—15 thousand rubles.

REFERENCES

1. A. S. Selensvich, Machines for excavating frozen soils at the Exhibition of Achievements of the National Economy of the USSR, Construction and Road-Building Machines, No. 2, 1963.

2. O. D. Alimov, I. G. Basov, Z. M. Pratusevich, Cutting frozen soil with the URMG-60 installation. Tomsk, 1963.

3. O. D. Alimov, I. G. Basov, F. F. Zelinger, V. G. Yudin, Some results of creating machines for cutting frozen soil on the basis of the ÉTU-353 excavator. Proceedings of the Tomsk Polytechnic Institute, vol. 123, 1963.