MACHINES FOR CUTTING FROZEN GROUND WITH CHAIN-TYPE WORKING TOOLS

O. D. ALIMOV, I. G. BASOV, B. L. STEPANOV

With each passing year the volume of construction in our country increases. In connection with this, the volume of winter construction work is growing, among which one of the most labor-intensive operations is the excavation of frozen soils. Various methods are being sought to carry out this operation. One of the most promising methods for mechanizing the excavation of frozen ground is its preliminary division into blocks by special earth-cutting machines, followed by further excavation with ordinary earthmoving machines. As earth-cutting machines, various self-propelled units with cutting members borrowed from coal-cutting machines—the so-called bar-type units—are finding ever wider application. With the aid of such machines, the frozen ground is cut into a series of longitudinal and transverse slots, and sometimes only longitudinal ones. Further excavation is carried out by ordinary construction excavators. Sometimes blocks of frozen ground are loaded onto dump trucks by means of excavators or truck cranes.

In the present work a brief survey is made of domestic machines for excavating frozen soils with a chain-bar working tool. Such units have been used in practice, with varying success, since 1940–1941. Naturally, at first builders tried to use coal-cutting machines for cutting frozen ground in the same form in which they are used in mining.

In 1941, Associate Professor P. N. Demidov conducted tests of a GTK-3 coal-cutting machine in cutting frozen ground. Mounted vertically on special skids, the machine cut a slot in the ground, moving at a speed of 0.56 m/min. This experiment enabled Associate Professor P. N. Demidov to conclude that a coal-cutting machine could be used for cutting frozen ground [18]. In the course of the tests it was established that the machine operates more smoothly when the bar is inclined; moreover, the operation of the machine in cutting frozen ground proceeds with less strain than in coal.

Experiments on the use of a coal-cutting machine for cutting frozen soils, carried out by the Office of Construction Mechanisms of the Moscow Housing Construction Administration in the winter of 1940–1941, were not entirely successful, and their results did not satisfy the requirements of builders. In 1951, NII-200 built a machine on the same principle and tested it at the construction of a reinforced-concrete plant in Lyubertsy. The tests did not yield positive results [14, 16].

In 1953, at the Intaugol combine, at the suggestion of mechanic Sennikov, the GTK-3 slot-cutting machine was used for excavating frozen ground. Apparently, because of the machine’s low power (17 kW), no substantial effect was achieved. The greatest success in the use of slot-cutting machines in construction practice was achieved at the construction sites of the Intaugol combine in 1959–60, when the KMP-2 slot-cutting machine with an engine power of 47 kW was used [17]. The machine was mounted on skids and, during operation, was moved by a cable with the aid of its own traction winch (Fig. 1). The speed of winding the cable onto the drum of the slot-cutting machine when cutting frozen loamy soils averaged 30 m/hr.

Fig. 1. Diagram of operation of the KMP-2 slot-cutting machine when cutting frozen ground:
1—anchor; 2—machine body; 3—bar; a—before the start of cutting; b—bar cutting in; c—cutting the ground while feeding the machine with the traction winch.

During operation the machine was set in the direction required for cutting the slots. The traction cable was unwound from the drum and attached to an anchor post installed at a distance of 25 m in the same direction. The cutting chain was then put into operation.

With the cutting chain running, the bar, under the action of its own weight, turns in a vertical plane, tending to assume a vertical position (Fig. 1, b). If the depth of freezing corresponded to the length of the bar, the latter was set in the vertical position. If the freezing depth was smaller, the bar was fixed at a certain angle ensuring cutting through the entire layer of frozen ground. After this the traction winch was engaged, and the machine was pulled toward the anchor post (Fig. 1, c), cutting in the frozen ground a slot 140 mm wide. The cycle was then repeated.

The ground was cut by longitudinal and transverse slots. Then a bulldozer, with teeth fastened to the blade, broke off blocks of frozen ground, and a crane with self-grabbing tongs removed them and stacked them on the edge of the trench or excavation pit, or loaded them onto dump trucks.

For cutting transverse slots when digging trenches, the slot-cutting machine was mounted on an automobile loader. The dimensions of the blocks of frozen ground were determined by the lifting capacity of the working with

by a truck crane and a dump truck. Moreover, the more powerful the transport equipment used in excavating frozen soils, the better the economic indicators were (Table 1).

Table 1

For the cutting chains of the cutting machine, “Uralets” teeth were used, with the edge hard-faced with a hard alloy. Their service life depended on the physical and mechanical characteristics of the soil being excavated. They were replaced after cutting 600–700 linear meters of slot.

The use of cutting machines proved more advantageous in excavating pits and less advantageous in excavating trenches [17].

One of the shortcomings of using cutting machines with cable feed is the considerable expenditure of workers’ time and labor on maneuvering operations. It is therefore more expedient to use cutting machines on crawler tracks or special self-propelled bar-type installations.

For cutting slots in frozen ground, the Ukrstroimekhanizatsiya Trust used a universal cutting machine on crawler tracks of the VTU-1 type [15]. In one shift it cut two slots in frozen ground, 1.2 m deep and 40 m long. VTU-1 machines were produced as a pilot batch for the coal industry and did not find practical application in the construction industry.

Modern cutting machines are generally produced with electric drive. This substantially limits their use in construction practice.

A more progressive approach proved to be the installation of bar-type working members on various self-propelled units driven by internal-combustion engines. In the winter of 1953–1954, at the Magnitostroi Trust, interchangeable equipment was made for the ET-352 trench excavator [6, 9, 10, 16, 19, 20]. It consisted of a boom comprising a supporting part fastened to the excavator’s gantry shaft in the same way as the boom of bucket equipment, and of one, and later two, bars with the excavator’s bucket chains, fitted with cutters (Fig. 2). The cutting bar had 60 cutter heads, including 40 two-cutter and 20 three-cutter heads. The cutters were made of round steel 20 mm in diameter, hard-faced with hard-alloy electrodes.

A safety friction clutch was installed on the machine, necessary in the event that the cutters encountered hard inclusions in the frozen ground [9].

At the beginning of operation the cutting chain was set in motion, and the bar gradually, under its own weight, sank into the frozen ground to a depth of up to 2 m. After this the excavator began to move, cutting a slot 0.13 m wide.

The first production tests of the machine, equipped with one bar, took place in the winter of 1953–1954; in 337 hours of operation it was pro-

2,167 m of slots were cut, with an average cutting rate of 6.4 m/h. On some days the cutting rate reached 37 m/h in light sandy-loam soils and 20–27 m/h in loams [9, 10].

Fig. 2. Diagram of the Magnitostroi machine for cutting frozen ground:
1—support section of the excavator boom; 2—support for two bars;
3—cutting chain; 4—bar.

The approximate service life of a set of cutters before restoration was: in dense, highly moist and frozen clays—up to 800 m of cut; in loams—900 m; and in sandy loams with inclusions of pebbles—1,000 m of cut. In the three-cutter head, when the end cutters became dull they were interchanged, after which they cut up to another 200 m of slot. Accidental loss of up to 10% of the cutters had no noticeable effect on the cutting rate. These and subsequent tests showed that breakage of the cutters is extremely rare, since they project from the cutter head by only 30 mm. The round cross-section of the cutter is favorable in this respect.

The tests also showed that when working with one cutting chain, the power of the excavator engine is not fully utilized, and subsequently the excavator was equipped with two chains. In the winter of 1954–1955, production tests were carried out on an excavator with two chains. The excavator cut 12.5 m/h of paired slots to a depth of up to 1.5 m in soils of categories II and III. The operating speed of the excavator’s forward travel ranged from 0.03 to 0.4 m/s. The highest productivity was achieved when the cutters were replaced after 400–500 m of cutting, without allowing them to become completely dull [10].

In 1955–1956, the Transvodstroi trust used an installation for cutting frozen ground with two bars; it cut two slots at a rate of 8–10 m/h [6]. In the winter of 1956–1957, five such installations operated on construction sites in the Southwestern District of Moscow. The greatest hourly productivity of one installation when cutting a double slot was 20.2 m, and the lowest was 6.4 m. The cutting depth reached 2 m [19].

As practice showed, after only longitudinal slots had been cut in frozen ground, spaced 0.7–0.8 m apart, an OM-202 excavator with a bucket capacity of 0.5 m³ freely excavated the frozen ground in the foundation pit [9].

Operation of machines based on a trench excavator under production conditions revealed the need for a number of improvements. Because of

because of the insufficient weight of the bars, the cutters penetrated poorly into heavy soils. To eliminate this drawback, it was proposed that additional weights be hung on the bars.

Because the weight of the bars did not ensure rapid deepening of the bars and holding them at the required slot depth, the motion of the unit during operation was intermittent. Long stops for deepening the bar reduced the productivity of the unit, and the intermittent motion complicated machine control. To eliminate these shortcomings, the authors considered it necessary to install in the cab a special device indicating the degree to which the cutting chains lagged behind the travel of the excavator. Suggestions were made [10] that the machine design should permit the cutting chains to be reset to the required width.

Despite the noted shortcomings, earth-cutting units based on the ET-352 are used on construction sites. Their technical characteristics are presented in Table 2. The labor input for excavating frozen soils with earth-cutting units based on the ET-352 is 0.029-0.033 man-days/m³, and the cost is 0.765-0.886 rubles/m³ [20]. The unit is serviced by one person.

Single-bar units developed on the basis of S-80 and S-100 tractors [3, 4, 12, 14] have found wider application in construction practice. They are produced by various construction organizations. In 1958, the Tsentrospetsstroi trust of the Ministry of Construction of the RSFSR created such a unit on the basis of the S-80 tractor (Fig. 3, Table 2). In the winter of 1958-1959, 6 such units operated on the construction sites of this trust, and in the winter of 1959-1960, 20 such units [12].

The cutting part of the KMP-2 slot-cutting machine is mounted on the rear wall of the S-80 tractor and is driven by the tractor power take-off shaft. Lowering the bar onto the ground at the start of cutting and lifting it out of the slot are carried out by means of a hand lever winch with a tractive effort of 1.5 t. The cutting part is engaged by the speed-shift clutch of its reducer.

Fig. 3. General view of a single-bar unit for cutting frozen ground of the Tsentrospetsstroi trust.

During operation the tractor is positioned in the direction of the slot to be cut, the bar-lifting cable is slackened, the reducer of the cutting part is engaged, and the bar, under its own weight, cuts into the frozen ground. The maximum deepening of the bar corresponds to an angle of inclination to the vertical of 30°-45°. Cutting of the slot can be performed only while the tractor is stationary. When the bar has deepened to the required depth, the tractor moves forward. As the tractor moves, the bar rises slightly, and after stopping it again cuts in to the required depth. The resulting slot has a stepped shape with projections up to 0.5 m high. This, of course, complicates the subsequent excavation of the soil by an excavator. After the slot has been cut to the required length,

the tractor operator, with the aid of a winch, raises the bar above the soil into the transport position, turns the tractor through 180° and begins cutting the second slot at a distance of 60–70 cm from the first, and so on.

Frozen ground cut in this way is, in most cases, excavated by a backhoe-type shovel excavator without further loosening.

Single-bar installations of this type are used by various construction organizations of the Soviet Union. In the winter of 1958, on construction sites in the city of Perm, such an installation cut 9,300 m of slots at a frost depth of up to 1 m. The cutting speed, not counting the time for turns, transfers, etc., was about 1 m/min [3].

In December 1960, the trust Vostoknefteprovodstroi (Ufa) used the installation to excavate ground for a district-heating trench. At a distance of 1.5 m from one another, two parallel slots were cut to a depth of 1.5 m, after which a backhoe excavator dug the trench quite freely. The installation was also used on other jobs. The cost of excavating frozen ground with the installation was 0.60 rubles/m³ [4].

Construction organizations, mounting cutting parts of trenching machines on tractors, introduced their own modifications in comparison with the design of the installation developed by the Tsentrospetsstroi trust. All these modifications mainly concerned the mechanism for raising and lowering the bar. For raising and lowering the bar, hand winches and hoists were used, as well as winches driven from the gearbox of the cutting part of the trenching machine, with these winches controlled both at the place where they were installed and from the tractor operator’s cab.

The designs and operating technology of the single-bar earth-cutting installations described above, created on the basis of S-80 and S-100 tractors, did not allow the power of their engines to be fully utilized. Without substantially changing the design of such machines, their productivity could be increased by installing several bars on one machine. Two-, three-, and even four-bar earth-cutting installations appeared.

The two-bar installation VU-2 was created on the basis of the S-100 tractor and, since 1959, has been manufactured by the Kizel Ore-Repair Plant (Fig. 4, Table 2) [8]. It consists of the gearbox 1 of the KMP-3 trenching machine with two cutting members—bars 2, a safety friction clutch 3, a mechanism for raising the bars 4, a boom with weight 5, and control levers 6.

Fig. 4. Diagram of the two-bar installation VU-2.

The presence of two cutting members led to a number of changes in the mechanism of the cutting part. A second unified drive unit for the cutting-chain sprocket was installed in the gearbox housing. Both units are connected by a toothed coupling. Transmission of rotation from the tractor power takeoff shaft to the cutting-chain sprockets is effected through the gearbox of the KMP-3 trenching machine.

The operation of the two-bar installation is analogous to that of the single-bar installation considered above. Cutting of frozen ground is carried out

Table 2

also only while the tractor is stopped. The bars are cut into the ground under the action of their own weight and the weight of the boom with replaceable weights mounted on it.

After cutting slots to the depth of ground freezing, the tractor moves in the prescribed direction by 0.8–1.5 m; at the same time the cutting members are raised somewhat by means of a friction winch, and after the tractor stops the bars again cut in to the required depth. Thus two parallel slots are cut simultaneously.

During the period of mastering the experimental model, the slot-cutting speed reached 38 m/h at a ground-freezing depth of 1.1 m, which corresponds to a capacity of 187 m³/h of frozen ground (with a utilization factor of the installation of 0.8).

A similar two-bar installation based on the S-80 tractor was developed at the Tsentrospetsstroi trust of the Ministry of Construction of the RSFSR, and was produced by the Mikhnevo Repair and Mechanical Plant (Fig. 5) [12, 14]. The speed of movement of the cutting chains was 0.7 and 1.4 m/s; the maximum cutting depth was 1.7 m. Lowering and raising of the bars is carried out by means of hand-operated lever winches. Its principle of operation is the same as that of the VU-2 installation.

Fig. 5. Two-bar machine for cutting frozen ground with hand-operated lever winches for raising the bars.

As a result of operation of single- and two-bar installations mounted on S-80 and S-100 tractors, the need for their further improvement was revealed. For the most complete utilization of tractor power and for achieving high productivity, the design of the installations must include devices for mechanizing the setting and raising of the bars and for combining ground cutting with machine feed.

If the operating experience of coal-cutting machines is taken into account, then in order to combine frozen-ground cutting with movement of the machine, the working travel speeds of the earth-cutting machines should be on the order of 0.2–1.5 m/min (12–90 m/h). Modern tractors have minimum travel speeds on the order of 1–2 km/h, that is, 20–80 times greater. Therefore, the problem of combining ground cutting and feed of earth-cutting installations built on the basis of tractors can be solved either by replacing the tractor gearboxes or by installing additional reduction gears.

In improving two-bar installations, the Tsentrospetsstroi trust of the Ministry of Construction of the RSFSR developed a two-bar installation with one hydraulic lift for raising and lowering the bars, which in 1960 was exhibited at VDNKh; then in the same year it created the RMTs-2 installation on the basis of the S-100 tractor, on which two hydraulic lifts and a gearbox from an ER-4 excavator were installed, making it possible to combine ground cutting with tractor movement. The installations are manufactured at the Mikhnevo Repair and Mechanical Plant (Table 2, Fig. 6) [14].

The two-bar mounted mechanism consists of a reducer of the cutting

part of the KMP-3 slot-cutting machine with two bars and a hydraulic system for raising the bars. The bars are located on both sides of the reduction gear, parallel to one another.

The reduction gear of the cutting part of the unit is mounted at the rear of the tractor. The primary shaft of the reduction gear is connected to the tractor power take-off shaft.

Engagement of the cutting chains and their disengagement are carried out by the cam clutch of the reduction gear of the cutting part of the KMP-3.

The hydraulic system for raising the bars consists of an NSH-60V gear pump, two hydraulic cylinders, a control valve, an oil tank, and a system of pipelines. The pump is driven by the tractor engine. Raising, lowering, and pressing each of the bars against the ground can be performed independently. Owing to this, it is possible to cut either two slots at once or only one with either bar. The combination of cutting and feeding of the machine is achieved by installing on the tractor the gearbox from an ER-4 rotary excavator instead of the tractor gearbox. The resulting speed of 62 m/hour is the operating travel speed of the unit. The tractor’s transport speeds are thereby retained as before.

Fig. 6. Two-bar machine for cutting frozen ground, RMTs-2.

During operation the tractor is placed on the cutting line, the drive of the cutting chains is engaged, and the ends of the bars are lowered by the hydraulic lift. Under the action of their own weight and the pressure force of the hydraulic lift, the bars cut into the frozen ground, making a slot in it. After the bars have penetrated to thawed soil or, in the case of great freezing depth, to the extreme lower position, the tractor’s working travel is engaged. The unit, moving forward, cuts two slots in the ground. In this process the bars are held in the prescribed position by the hydraulic lift.

After cutting the slots to the end of the planned section, the tractor is stopped, the bars are raised out of the slots, the cutting part is disengaged, the unit is turned through 180°, and the slots are cut in the opposite direction parallel to the first ones at a distance of 40–60 cm. On short cutting sections it is advisable to drive the unit back to the starting point in reverse.

The design of the unit includes an original device for fixing the bars in the transport position. Before moving the unit, the bars are raised to a position somewhat above horizontal, until the automatic catches, located on both sides of the reduction gear of the cutting part, engage. The catches are also released automatically before the bars are lowered. For this purpose the bars are raised somewhat above the transport position.

According to data from the Tsentrspetsstroy trust, the cost of a machine-shift for the operation of the unit is 38 rubles 34 kopecks. In practice, over the winter period

In 1960–1961, the cost of preparing 1 m³ of frozen ground for excavation by means of the installation amounted to 17–33 kopecks.

When calculating the technical productivity of the installation, the Tsentrospetsstroi trust adopted a shift utilization coefficient equal to 0.5. Under these conditions the installation was to travel 217 running meters and cut 434 running meters of slots.

In the Ryazan Specialized Administration, from February 8 to March 16, 1961, the installation cut 6,975 m of double slots at a ground-freezing depth of 1.2 m. On average, the installation traveled 225 m per shift and cut 450 m of slot.

In the Vologda Specialized Administration, in dense soils at a freezing depth of 0.6 m, a maximum productivity per shift of 350 running meters of double slots was achieved. With proper operation, during a working shift an average of 7–10 cutters out of a total of 108 are replaced. Machines based on the model of the Tsentrospetsstroi trust installation were also built by other organizations. Operation of these machines under various conditions made it possible to reveal the shortcomings of these designs. It turned out that such installations cannot simultaneously cut two slots in dense soils [21]. The reason for this is the excessively high operating feed speed of the tractor (62 m/h), at which the 100 hp engine power proved insufficient to drive the cutting chains of the two bars.

Thus, it was established that merely installing an ER-4 gearbox on S-100 tractors cannot provide synchronization of the operation of the cutting and feed mechanisms. It is necessary to seek other design variants for reduction gearboxes and for earth-cutting installations as a whole.

In this connection, the design of the self-propelled URMG-60 installation is of interest (Fig. 7, Table 2) [2].

In the winter of 1961–1962, the staff of the Department of Mining Machines and Mine Transport of the Tomsk Polytechnic Institute developed and built the self-propelled URMG-60 installation (an installation for cutting frozen ground; 60 is the engine power in hp). In manufacturing the installation, components of machines whose production had already been mastered by industry were used to the greatest extent possible in its design, in order to facilitate both the manufacture of the prototype and the subsequent production of such machines. A TDT-60 skidder tractor was selected as the base for the URMG-60 installation, on the grounds that its design permits, without major changes, the installation between the engine and the main chassis transmission of an additional speed-reduction gearbox—a demultiplier.

To place on the TDT-60 tractor the cutting section from a KMP-type coal-cutter, the device for combining ground cutting and installation travel, and other units, the loading shield and winch were removed from it. The cutting section of the coal-cutter 1 (Fig. 7) is fastened by means of plate 2 to an additional frame 3, secured to the tractor side members 4. The hydraulic lift 5, intended for raising and lowering the bar, is hinged by the cylinder lug to the A-shaped frame 6 and by the rod lug to the lower saddle of the bar 7.

The drive of the cutting section and of the running gear of the installation is effected from the tractor engine. To distribute the engine power, a transfer case from a ZIL-157 truck is used. The cutting section is driven from the engine through the transfer case 8 and cardan shafts 9, 10; the crawler running gear—through the transfer case 8, cardan shaft 11, demultiplier 12, and the tractor gearbox 13.

Fig. 7. Schematic diagram of an installation for cutting frozen ground, type URMT-60.

A ratchet mechanism from the feed unit of the GTK-35m cutting machine was used as the reduction multiplier, with certain modifications (a housing for the drive shaft with an additional spur gear was welded to the cover of the reduction multiplier; splines were cut on the end of the ratchet-wheel shaft, instead of the bevel gear, to connect it by a coupling to the gearbox shaft of the TDT-60 tractor, etc.). With the aid of this reduction multiplier, the working travel speeds of the unit can be varied over a wide range. To obtain high maneuvering travel speeds, the ratchet mechanism of the reduction multiplier is disengaged.

The hydraulic lift is a hydraulic jack from a TDT-60 logging tractor. Its cylinder is hinge-mounted on the A-shaped frame, and the rod is likewise hinge-connected to the bracket of the lower saddle of the cutter bar. The cylinder chambers are connected by high-pressure hoses to the hydraulic distributor of the NSh-60/75 gear pump.

Owing to the combination of a two-speed transfer case, a four-speed ratchet reduction multiplier, a five-speed tractor gearbox, and a two-speed reducer of the cutting unit, the machine has 40 working speeds, 12 maneuvering travel speeds, and three cutting-chain speeds (Table 2). This enables the operator of the unit, depending on the soil being worked, to select operating modes that ensure maximum utilization of the drive power.

For cutting frozen ground, the unit is positioned in the direction of the route of the future trench or foundation pit. Then, by means of the hydraulic lift, the cutter bar is raised slightly and, after the locking roller is turned, is lowered from the transport position down until it contacts the ground. At the same time the cutting chain of the bar is switched on, and, by the force of the hydraulic lift, the bar is sunk into the ground to the depth of its freezing. After this, the working travel is engaged by means of the reduction multiplier, and the most rational feed speed is set, depending on the depth of soil freezing, its physical and mechanical characteristics, and the degree of wear of the cutting tool.

As a result of the cutting element being located along the axis of the machine, the URMG-60 unit maintains the specified direction of travel well when cutting soil, without constant intervention by the tractor driver. This makes it possible to have only one person service the unit.

The URMG-60 unit was used for preliminary breaking of frozen ground when excavating foundation pits for house foundations; when driving trenches for cable, sewer, and water lines; for loosening the surface layer of soil at a construction-material quarry; and for transplanting trees.

From time studies of observations of the operation of the URMG-60 machine, it was established that the average technical speed of cutting a slot 0.9–1.2 m deep was 48–78 m/h. The large range of variation in technical productivity is explained by differences in soil strength, the degree of wear of the cutting teeth, and, chiefly, sharply differing volumes of maneuvering operations when it was operating on construction sites. Over the entire period of industrial tests, the average technical productivity was 50 m/h, which is 4–7 times higher than the productivity of single-bar units built on the basis of the S-80 tractor, operating simultaneously with the URMG-60 at construction sites in Tomsk and having no forced bar advance or device for combining soil cutting and unit travel. The specific consumption of teeth,

that is, the number of worn teeth referred to the area of the slot cut in this process, when working with the URMG-60 unit, is 4 times less than with units built on the basis of the S-80 tractor. This is explained by a considerable increase in the specific feed and a reduction in dynamic loads.

Operating experience with the URMG-60 unit confirms the possibility of using ratchet mechanisms as speed reducers for transport machines when creating frozen-ground cutting machines on their basis. In the further improvement of ratchet speed reducers, attention should be given to increasing the service life of the springs of the ratchet dogs.

On the basis of the accumulated operating experience with the URMG-60, the Department of Mining Machines and Mine Transport of TPI has developed a number of variants of frozen-ground cutting units based on TDT-60 and TDT-40 tractors, with one and two bars.

In the autumn of 1962, a thematic exhibition of machines for excavating frozen soils was organized in the “Construction” pavilion of the USSR Exhibition of Achievements of the National Economy. In addition to the machines described earlier, several new variants of bar-type frozen-ground cutting machines were displayed at the exhibition.

In Administration No. 1 for the Mechanization of Construction Work of the Promstroymekhanizatsiya Trust of Azerbaijan, a frozen-ground cutting unit SAI was created on the basis of the S-100—the self-propelled unit of engineer I. M. Iskenderov (Table 2) [1]. This unit is a two-bar frozen-ground cutting installation. Unlike the Tsentrospetsstroy units, it has a greater range of feed and cutting speeds. Of interest is the experience in using the SAI units for cutting rock.

The process of excavating rock ground with the unit is as follows. With a bulldozer blade, the rock cutter removes the surface layer of soil; after that, two slots 2.5 m deep are cut in the rock. Without stopping the unit, an auxiliary working member—a hydraulic breaker connected to the tractor hydraulic system—breaks off the piece of rock between the slots. Then a truck crane with a special grab carries the stone slab out onto the trench shoulder.

The SAI rock cutter was used in the construction of the Novobaku oil refinery for excavating pits, working together with an excavator. Using one of the bars, the SAI cut slots 140 mm wide for small pipelines and for cables in rock with a Protodyakonov strength coefficient of up to $f = 2$, and it is being tested in rocks with $f = 4$. In excavating each cubic meter of rock, the machine saves up to seven rubles [1]. The administration has created a four-bar SAI rock-cutting unit on the basis of a 140-hp tractor, which in one pass cuts four slots for a trench 1.6 m wide.

The Moscow RMZ of the Transvodstroy Trust of the Ministry of Transport Construction manufactured and demonstrated at the exhibition the two-bar machine BMRMG-1. In the design of the mounted equipment and of the base machine (S-100), this unit is analogous to the two-bar machines of Tsentrospetsstroy (Table 2). It is equipped with a special planetary demultiplier. As a result, its technical characteristics differ somewhat from those of the Tsentrospetsstroy machine. In particular, the working travel speed is reduced from 62 to 45 m/h, but even at this speed the machine is recommended for use only with slot depths of 1.2 m [7]. It is stated that, when the BMRMG-1 machine is used, the cost of loosening frozen ground, in comparison with loosening by a wedge ram, is reduced by a factor of 4.2.

Visitors to the exhibition showed considerable interest in bar-type units created on the basis of trench excavators. This also...

It is advisable because, first, most trench excavators stand idle in winter, and their use at that time with cutter-bar equipment will increase the efficiency of these machines in the national economy; second, converting trench excavators into cutter-bar installations does not require significant expenditure, and the availability of a wide range of low feed speeds in trench excavators will allow cutter-bar installations to operate most effectively in soils of different hardness.

In terms of their technical characteristics, the trench excavators of the ETU-353 type are the most suitable as a base for cutter-bar installations. The working feed speeds of these excavators can vary from 21 to 205 m/h.

At the Exhibition of Achievements of the National Economy of the USSR, cutter-bar installations created on the basis of ETU-353 excavators with two and three cutter bars were presented (Fig. 8). In

Fig. 8. ETU-353 trench excavator equipped with cutter bars of a coal-cutter machine.

all these variants the cutter bars are suspended from the upper frame of the excavator. The drive sprockets of the cutting chains are mounted on the turret shaft, which is driven from the gearboxes by a chain transmission. The cutter bars are raised by a cable with the aid of the excavator’s hoisting winch. The cutter bars penetrate into the ground only under the action of their own weight. This is a considerable disadvantage of the indicated installations, since the engine power cannot be used to the fullest extent. Evidently, in order to make greater use of the engine power, in the absence of forced setting of the cutter bar, the designers of the machines demonstrated at the exhibition were compelled to suspend 2 and 3 cutter bars on the excavator.

In this connection, of considerable interest is the proposal of the Department of Mining Machines and Mine Transport of the Tomsk Polytechnic Institute for re-equipping ETU-353 excavators, which provides for the installation of a hydraulic device for starting and raising the cutter bars.

An interesting variant of an earth-cutting unit is a single-bar machine built on the basis of the ETN-124 excavator (Fig. 9).

Fig. 9. ETN-124 excavator with mounted cutter-bar equipment.

The wheeled undercarriage is convenient for using the unit in urban construction, while the hydraulic travel reducer installed on the excavator makes it possible to vary continuously the feed speed when cutting soils of different strengths. Detailed information on the results of operation of cutter-bar units based on the ETN-124 is not given. It is known that the maximum cutting depth of the soil was 1200 mm, the working travel speed was from 6 to 30 m/h, the speed of the cutting chain was 0.16 and 1.1 m/sec, and the bar was raised and lowered by means of two hydraulic cylinders.

Some data were given earlier [11] on tests of ETN-124-type excavators when working in hard and frozen soils. In these cases, to make trenches for cables, wideners are attached to the bars; these are brackets 265–275 mm wide, to which knives are fastened that cut directly into the soil when the trench is being excavated. Experience in operating cutter-bar earth-cutting machines has shown the expediency of using them on frozen soils that do not contain inclusions of rock, with a freezing depth of up to 1.7 m. The cost of preparing 1 m³ of frozen soil for excavation is 20–35 kopecks [13].

On the basis of a review of the designs of cutter-bar earth-cutting machines, the following conclusions and recommendations may be made.

1. Cutter-bar earth-cutting units are effective machines for preliminary loosening of frozen soil.

2. Many organizations in the country have created various designs—

bar-type installations. The operating indicators of these machines, reported in various literature sources, differ and in most cases are not comparable.

1. A progressive direction is the creation of self-propelled bar-type machines on the basis of standard tractors and trench excavators with the cutting parts of mining machines. The most appropriate parameters of the installations (engine power, feed forces and speeds, cutting speed, number of simultaneously operating bars) must be determined on the basis of special studies.

2. To ensure high operating performance, the installations must have devices for forced starting of the bar and for the necessary combination of feed and cutting speeds.

3. One of the urgent problems is the creation of speed reducers.

To solve this problem it is necessary to carry out research and exploratory design work. Promising variants of speed reducers may be ratchet and hydromechanical types.

1. To determine the best variants for using earth-cutting machines in combination with excavators, it is necessary to conduct production tests of these machines under various conditions and to determine the economic efficiency of their application.

LITERATURE

1. Averyanov K., The Rock-Cutting Machine Requires Recognition. “Ekonomicheskaya gazeta,” No. 48/69, November 24, 1962.

2. Alimov O. D., Basov I. G., Pratussevich Z. M., Cutting Frozen Soils with the URMT-60 Installation. Tomsk, 1963.

3. Apollonov S. P., Experience in the Use of Mounted Equipment for Excavating Frozen Ground. “Novaya tekhnika montazhnykh i spetsializirovannykh rabot v stroitelstve,” No. 5, 1959.

4. Berdyuk V. V., Excavation of Frozen Soils with a Cutting Machine. “Stroitelstvo truboprovodov,” No. 3, 1961.

5. Galperin M. I., Analysis of Existing Mechanisms for Excavating Frozen Soils by Cutting and Impact. “Razrabotka merzlykh gruntov rezaniem i udarom” (materials of a conference). Moscow, 1955.

6. Gusakov S. F., Vaigant A. S., Production of Earthworks in Winter. “Stroitelnaya promyshlennost,” No. 9, 1956.

7. Two-Bar Machine BMRMG-1. VDNKh USSR, Moscow, 1962.

8. Kozdoy I. L., The Two-Bar Installation VU-2 for Excavating Frozen Ground. “Byulleten tekhniko-ekonomicheskoi informatsii,” No. 11, 1960.

9. Kuznetsov F. F., Use of the ET-352 Trench Excavator for Cutting Frozen Ground. “Stroitelnaya promyshlennost,” No. 10, 1954.

10. Levitin L. E., Excavation of Frozen Ground by Cutting. “Mekhanizatsiya stroitelstva,” No. 4, 1957.

11. Mazunov I. F., Bars on the ETN-251 and ETN-123 Excavators. “Mekhanizatsiya stroitelstva,” No. 1, 1962.

12. Mechanism for Cutting Slots in Frozen Ground with Two Bars on an S-80 Tractor. VDNKh USSR, Moscow, 1960.

13. Production of Earthworks in Winter. VDNKh USSR, Gosstroiizdat, Moscow, 1962.

14. Rudakov V. I., Shcherbov A. I., Mechanization of Frozen-Ground Excavation in the Tsentrospetsstroi Trust. “Stroitelnye i dorozhnye mashiny,” No. 10, 1961.

15. Stadnik N. K., Feldshin Z. D., Instructions for the Excavation of Frozen Ground. BTI NIISK ASiA Ukrainian SSR, Kiev, 1959.

16. Tyazhelov B. P., Shnipko E. V., Earthworks under Winter Conditions. Gosstroiizdat, Moscow, 1958.

17. Fedorin L. A., Excavation of Frozen Soils by Cutting Machines (Experience of the Builders of the Intaugol Combine of the Komi ASSR). Gosstroiizdat, Moscow, 1961.

18. Fedulov A. I., On the Question of Choosing a Method for Excavating Frozen Soils. Transactions of the Mining-Geological Institute of the West Siberian Branch of the USSR Academy of Sciences, issue 16, 1956.

19. Cherkashin V. A., Methods and Mechanisms Used for the Production of Earthworks under Winter Conditions. BTI NIIOMTP ASiA USSR, Moscow, 1959.

1. Cherkashin V. A., Gorbachev V. P. Production of earthworks under winter conditions (reference manual). Gosstroiizdat, Moscow, 1961.

2. Shtobbe V. A., Troyanovskii Yu. V. Application of the two-bar machine RMTs-2 for loosening frozen ground. Mechanization of Construction, No. 9, 1962.