Methodology for Studying Soil Cutting Modes by Bar-Type Earth-Cutting Machines and Processing Experimental Data
Abstract Generated abstract
This paper presents a methodology for experimentally studying soil cutting regimes of bar type earth cutting machines, with emphasis on frozen soils and on the comparability of productivity and power data. It describes the “Moroz” experimental installation based on an ETV-353 trench excavator, its variable chain speed and feed arrangements, instrumentation for measuring torque, chain speed, hydraulic feed force, and procedures for repeated tests under controlled soil conditions. The work also provides formulas for processing dynamometer records to obtain cutting force, torque, power, chip thickness, specific energy, and measurement errors, together with guidance on the required number of repeated experiments. The reported accuracy estimates indicate that the method yields data suitable for engineering calculations and for designing improved bar type machines for cutting frozen soil.
Full Text
O. D. Alimov, I. G. Basov, F. F. Zelinger, V. G. Yudin,
E. I. Lisovskii
METHODOLOGY FOR STUDYING SOIL-CUTTING MODES BY BAR-TYPE EARTH-CUTTING MACHINES AND PROCESSING EXPERIMENTAL DATA
The bar-type earth-cutting machines used in practice differ in the number, dimensions, and operating modes of their working members, in the devices for introducing the bar into the soil, and in engine power [1–6]. These machines operate and are tested under various conditions. Therefore, data on their productivity are in most cases not comparable. Very many questions connected with the selection of optimal operating modes for bar machines remain unresolved or insufficiently reliable. For example, it is not clear what the appropriate magnitudes of the cutting-chain travel speeds and feed speeds should be, and in what interrelation they must be applied. This necessitates special investigations that would make it possible to determine rational operating modes of existing bar machines and to outline ways for their further improvement and creation.
In the present work, a methodology is set forth for studying the cutting modes of soils by the bar working members of earth-cutting machines.
On the basis of experience in the creation and operation of coal-cutting machines in mines, and taking into account the engine powers of modern tractors and prime movers that can be used for creating bar machines, the study of the operating modes of earth-cutting machines must be carried out with variation of their parameters within the following limits [1]:
1) cutting speed from 0.4 to 3.0–5.5 m/sec;
2) feed speed from 0.2 to 3.0–4.0 m/min;
3) feed force from 200–300 to 5000–10000 kg;
4) depth of the cutting slot from 0.4 to 2.0 m;
5) angle of inclination of the bar to the horizon from 20° to 90°;
6) width of the slot being cut from 0.12 to 0.14 m.
The results of investigations of the operating modes of bar working members should clarify existing conceptions about the process of destruction of frozen soils when cutting with chain working members; the power expenditures required for pulling the chain at various feed and cutting speeds; feed forces at various feed and cutting speeds; power expenditures for driving the cutting part and for moving the bar installation; tooth wear and its influence
on the feed forces, the pulling of the chain, and the power consumption; the process of removing cuttings from the cutting slot, and the power consumption for carrying away cuttings under various operating modes of the chain-type working member.
For the study of cutting modes in frozen soils, soils should be selected that do not contain inclusions of gravel or other rock. This will make it possible to determine the parameters under study more accurately and to eliminate errors that may arise when a bar-type working member cuts hard inclusions whose physicomechanical properties differ significantly from those of homogeneous frozen soil.
Experimental Setup
To study the cutting modes of frozen soils, an experimental setup with a bar-type working member, called “Moroz,” was built at the Tomsk Polytechnic Institute. The “Moroz” setup (Fig. 1) was built on the basis of an ETV-353 trench excavator, from whose chassis the working equipment and the upper frame with the hopper had been removed [4]. On the freed frame of the excavator, the cutting part of a KMP-type cutting machine was installed (Fig. 2). The drive of the cutting part is provided by the engine through shaft 1 (Fig. 2) of the gearbox, which in normal excavator operation is used to drive the belt conveyor. The rotational speed of shaft 1 was increased by replacing the gearbox gear wheels with 15 and 28 teeth by a gear pair with 21 and 22 teeth. This made it possible to unload the output shaft 1 to some extent and to eliminate the possibility of its breakage when transmitting the greatest power from the engine to the cutting part of the machine. To obtain a large number of speeds of motion of the cutting chain, a transfer case 3 and a gearbox 4 were installed between the belt-conveyor drive shaft of transmission box 2 (Fig. 3) of the ETV-353 excavator and the driving shaft of the reducer of the cutting part of the KMP.
Fig. 1. General view of the setup for cutting frozen soils.
Fig. 2. Kinematic diagram of the drive of the cutting part of the “Moroz” earthmoving machine.
Labels visible in the figure:
- Auto-pen
- High-speed gearbox, TsU-353, \(Z = 18\), \(m = 6\)
- Distribution gearbox
- Box of speeds ZUP-64
- Tachometer
- Cutting-wheel reducer
| No. of group of interchangeable gears | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Number of teeth | 20 | 20 | 29 | 33 | 10 | 29 | 26 | 29 | 41 | 44 | 20 | 31 | 33 | 20 | 22 | 39 | 22 | 41 | [[unclear]] | [[unclear]] | 13 | 32 | 25 | 20 | 11 | 20 | 22 |
| Module | 2.5 | 2.5 | 2.5 | 5 | 5 | 2.5 | 2.5 | 3.75 | 3.75 | 2.5 | 2.5 | 3.75 | 2.5 | 3.5 | 3.5 | 7.5 | 4.2 | 4.2 | 4.2 | 4.2 | 7 | 7 | 7 | 9 | 9 | 9 | [[unclear]] |
of a ZIL-164 truck. The bar is lowered into the soil by means of hydraulic cylinder 5, but, unlike the bar-type installations created earlier [2—6], the working member is lowered when the rod is retracted, that is, when oil is supplied to the rod-side cavity of the hydraulic cylinder.
Fig. 3. Schematic diagram of the “Moroz” earth-cutting machine.
To measure the power and the pulling speed of the cutting chain on the “Moroz” installation, a ZIL-164 gearbox was used (Fig. 4); it is suspended freely (as a balance) on rolling bearings, forming a reduction dynamometer. A moment \(M_p\) acts on the balanced gearbox housing. This reactive moment \(M_p\) tends to rotate the gearbox housing about an axis coinciding with the axis of the primary and secondary shafts. Knowing the moment \(M_p\), one can determine the moment on the shaft of the drive sprocket of the operating member.
Determination of the moment \(M_p\) is reduced to measuring the force that prevents rotation of the gearbox. This balancing force is produced by means of an elastic force meter, for which a spring dynamometer 1 is used (Fig. 2).
One end of the cylindrical helical spring 2 of the dynamometer is fixed immovably, while the other is connected with the balanced housing and sets pencil 3 in motion. As a result, a diagram of the force of the reactive moment is recorded on the tape 4 of the recording instrument. With the aid of two drums 5, the tape is pulled at a constant speed.
The truck gearbox has a device for driving the speedometer shaft. In the present case this device 5 is used to drive a tachometer, by which the number of revolutions of the gearbox output shaft is measured. After the corresponding recalculation, the rotational speed of the sprocket of the cutting bar is determined.
The feed force of the cutting member into the soil is found by recording the fluid pressure in hydraulic cylinder 8 by means of two pressure gauges 9.
During the tests, the cutting chain of the bar was arranged in a “herringbone” pattern with nine and seven cutting lines (Fig. 5). The number of teeth in the employed
the chain was not a multiple of the number of teeth in the sprocket. Therefore, the chain consisted of four full and one incomplete “herringbone.”
Fig. 4. Diagram of the reduction dynamometer.
In the studies, KMZ-1 teeth with a normal holder were used.
Fig. 5. Diagram of the arrangement of cutters of the cutting chain.
The experimental installation “Moroz” has the following technical characteristics.
Engine power, hp — 54;
Depth of the slots cut in the soil with this method of fastening the bar, maximum, m:
for a bar length of 1.9 m — 1.3;
for a bar length of 2.2 m — 1.6;
for a bar length of 2.8 m — 2.2;
number of bars, units — 1;
width of the cutting slot, depending on the design of the teeth and chains, mm — 120–600;
speed of motion of the cutting chain (20 speeds), m/sec — 0.4 to 5.5;
travel speeds of the installation: operating, m/h — 20.4; 26.5; 35; 47; 103; 149.5; 186;
maneuvering, km/h — 1.28; 1.7; 3.8; 5.2; 6.8;
average hourly speed of cutting slots in frozen soil, m/h — 18–180;
overall dimensions, m: length, width, height — 7.8; 2.9; 2.5;
weight, kg — 9900.
The “Moroz” earth-cutting machine, in the variant described above, is intended for studying the cutting regimes of frozen soils by chain working members. It may also have industrial application. In this case the transfer case and gearbox are removed, and a cardan shaft 6 is installed between the drive shaft of the belt-conveyor gearbox of the ÉTU-353 transmission box and the driving shaft of the cutting section (Fig. 3).
Procedure for Conducting Experiments
Before the start of recording the quantities under study, the cutting section of the “Moroz” machine was switched on and the bar was lowered into the soil to the required depth. The cutting chain continued to operate until the crushed soil was completely removed from the slot. The working member was then switched off.
On the diagram recording the compression force of the spring, the number and date of the experiment are entered.
The recording of the spring-deformation diagram, by which the torque and power transmitted to the cutting member were subsequently determined, was carried out in the following sequence. With the feed and cutting mechanisms switched off, the mechanism for pulling the tape of the spring dynamometer was switched on. On the tape, the writing mechanism draws the zero line $a_1$ (Fig. 6) and a control line $a_4$ parallel to it. Then the cutting chain is switched on, and the deformation of the spring is recorded on the pulled tape (section $a_2$). This section characterizes the no-load losses in the transmission, beginning at the output shaft of the ZIL-164 gearbox and ending with the cutting chain of the bar. Section $a_3$ of the diagram reflects the total force expended on overcoming losses in the transmission, on cutting, and on removing crushed soil from the slot with the cutting chain switched on.
Having set a certain cutting speed, we conduct a series of experiments while changing the feed speed of the machine up to full engine load. After this, the next speed of motion of the cutting chain is switched on, and the feed speed is likewise increased successively, and so on. Before switching on each successive feed speed, the thickness of the layer of crushed soil remaining in the slot is measured with a measuring ruler,
and the slot depth. At each setting of the corresponding cutting speeds and machine travel speeds, the readings of the pressure gauges installed on the hydraulic cylinder are recorded. The pressure value recorded by the pressure gauges is proportional to the machine feed force. The change
Fig. 6. Diagram of force recording on the body of the reduction dynamometer
in the speeds of motion of the cutting chain was carried out by changing the transmission gear ratios. This was achieved by shifting the gearbox, the transfer case, and the reducer of the cutting part of the KMP machine. During the experiments, the number of revolutions of the bar sprocket is recorded by a tachometer. At each feed and cutting speed, no fewer than eight experiments were carried out. The length of the slot cut by this bar was 5--8 m. The feed speed of the Moroz machine is calculated by measuring the distance traveled by the machine during the experiment and the duration of the experiment.
The strength of the soil being worked was determined using the DorNII impact device [9]. All quantities obtained in the performance of each experiment are entered in the observation log.
Processing of Experimental Data
From the deformation diagram of the dynamometer spring, the following quantities are found by calculation:
a) the force deforming the spring;
b) the reactive moment \(M_p\);
c) the torque on the output shaft of the reduction dynamometer \(M_2\) (Fig. 4);
d) the torque on the drive sprocket of the cutting chain \(M_{\text{sp}}\);
e) the average pulling force of the cutting chain;
f) the average pulling force of the cutting chain referred to one cutter;
g) the average power expended on soil destruction, overcoming the friction forces of the chain against the walls of the bar trench and of the teeth against the soil;
h) the power expended on transporting the loosened soil.
The formulas for calculating all these parameters and for determining the errors of their calculation and the magnitudes of the relative errors are given in Table 1. Table 2 gives coefficients whose use substantially simplifies the calculation of the torque on the output shaft of the reduction dynamometer.
Table 1
| Name of the quantity to be determined | Calculation formula | Formula for determining the relative measurement error of the quantity | Relative error, % | Notes (machine constants are taken from the technical characteristic) |
|---|---|---|---|---|
| Average value of the deformation of the dynamometer spring, mm | $$L_{\mathrm{avg}}=\frac{L_{\mathrm{avg}}^{\max}+L_{\mathrm{avg}}^{\min}}{2}-L_{\mathrm{id}}$$ | $$\frac{\Delta L'_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L^{\max}}{L^{\max}};\qquad \frac{\Delta L''_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L^{\min}}{L^{\min}}$$ $$\frac{\Delta L''_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L_{\mathrm{id}}}{L_{\mathrm{id}}}$$ | 12 | \(L'\) and \(L''\) are, respectively, the maximum and minimum values of the deformation of the spring. They are found from the diagrams. |
| Average value of the minimum deformations of the spring, mm | $$L_{\mathrm{avg}}^{\max}=\frac{L'_1+L'_2+\ldots+L'_m}{m}$$ | $$\frac{\Delta L'_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L^{\max}}{L^{\max}};\qquad \frac{\Delta L''_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L^{\min}}{L^{\min}}$$ $$\frac{\Delta L''_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L_{\mathrm{id}}}{L_{\mathrm{id}}}$$ | 12 | \(L'\) and \(L''\) are, respectively, the maximum and minimum values of the deformation of the spring. They are found from the diagrams. |
| Average value of the maximum deformations of the spring, mm | $$L_{\mathrm{avg}}^{\min}=\frac{L''_1+L''_2+\ldots+L''_m}{m}$$ | $$\frac{\Delta L'_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L^{\max}}{L^{\max}};\qquad \frac{\Delta L''_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L^{\min}}{L^{\min}}$$ $$\frac{\Delta L''_{\mathrm{avg}}}{L_{\mathrm{avg}}}=\frac{\Delta L_{\mathrm{id}}}{L_{\mathrm{id}}}$$ | 12 | \(L'\) and \(L''\) are, respectively, the maximum and minimum values of the deformation of the spring. They are found from the diagrams. |
| Average value of the reactive force, kg | $$P_p=L_{\mathrm{avg}}k$$ | \(\kappa\) is the coefficient of proportionality of the calibration curve (Fig. 7). | ||
| Torque on the output shaft of the reducer dynamometer (Fig. 4), kgm | $$M_2=\frac{P_p A r}{B\left(1-\dfrac{r_2}{r_1}\right)}=P_p k_1 k_2$$ | $$\frac{\Delta M_2}{M_2}=\frac{\Delta L_{\mathrm{avg}}}{L_{\mathrm{avg}}}+\frac{\Delta S}{S}+\frac{\Delta l}{l}+\frac{\Delta A}{A}+\frac{\Delta B}{B}$$ | 10 | |
| Torque at the drive sprocket of the cutting chain, kgm | $$M_{\mathrm{sp}}=M_2 i_p$$ | \(i_p\) is the gear ratio of the reducer of the cutting unit. \(i'_p=6.25;\ i''_p=12.32\). | ||
| Force required for destruction by the cutting chain, kg | $$P_{\mathrm{cut}}=\frac{2\left(M_2-M_{\mathrm{fr}}\right)i_p}{D}=\frac{2M'_2 i_p}{D}$$ | $$\frac{\Delta P_{\mathrm{cut}}}{P_{\mathrm{cut}}}=\frac{\Delta M'_2}{M'_2}+\frac{\Delta D}{D}$$ | 10 | \(D\) is the mean diameter of the drive sprocket of the cutting chain. \(D=303\ \mathrm{mm}\). |
| Torque expended to overcome friction in the manual hoist, kgm | $$M_{\mathrm{fr}}=\frac{P_p fD}{2}$$ | |||
| Force of raising the working member on the ground, kg | $$P_p=\frac{P_{\mathrm{cyl}}\cos\delta+\lambda}{\dfrac{H_1}{\sin\lambda_{\mathrm{n}}}}$$ | $$\frac{\Delta P'_p}{P'_p}=\frac{\Delta p}{p}+\frac{\Delta R}{R}+\frac{\Delta\cos\delta}{\cos\delta}+\cdots$$ | The force on the cylinder rod \(P_{\mathrm{cyl}}=F_{\mathrm{cyl}}p\), where \(F_{\mathrm{cyl}}=226\ \mathrm{cm^2}\); \(p\) is the oil pressure in the cylinder; \(R=320\ \mathrm{cm}\). |
Continuation of Table 1
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| $\dfrac{-(90^\circ-\alpha)R+G_{\mathrm{n}}h_{\mathrm{n}}\cos\lambda_{\mathrm{n}}}{H_1/\sin\lambda_{\mathrm{n}}}$ | $\dfrac{\Delta\cos\alpha}{\cos\alpha}+\dfrac{\Delta H_1}{H_1}$ | 14.0 | $G_{\mathrm{n}}=320$ kg; $H_1=95$ cm; $l_{10}=120$ cm (Fig. 8) | |
| Number of simultaneously operating cutters, pcs. | $n_{\mathrm{p.r.}}=\dfrac{Hmz}{t_{\mathrm{p}}z_k}$ | $\dfrac{\Delta n_{\mathrm{p.r.}}}{n_{\mathrm{p.r.}}}=\dfrac{\Delta H_{\mathrm{c}}}{H_{\mathrm{c}}}+\dfrac{\Delta t_{\mathrm{p}}}{t_{\mathrm{p}}}$ | 4.0 | $H_{\mathrm{c}}=1.6$ m — cutting depth; $z=42$ cutters for bar length; $2.2$ m; $z_k=28$ cutters in the chain; $t=100$ mm — cutter pitch |
| Soil-cutting force per cutter, referred to one cutter | $P_{o,\mathrm{res}}=\dfrac{P_{\mathrm{res}}}{n_{\mathrm{p.r.}}}$ | $\dfrac{\Delta P_{o,\mathrm{res}}}{P_{o,\mathrm{res}}}=\dfrac{\Delta P_{\mathrm{res}}}{P_{\mathrm{res}}}+\dfrac{\Delta n_{\mathrm{p.r.}}}{n_{\mathrm{p.r.}}}$ | 14.0 | |
| Power consumed for cutting and transporting the frozen soil, hp | $N=\dfrac{M'_2 i_{\mathrm{p}} n_{\mathrm{zv}}}{71620}=\dfrac{P_{\mathrm{res}}D\,n_{\mathrm{zv}}}{143240}$ | $\dfrac{\Delta N}{N}=\dfrac{\Delta M'_2}{M'_2}+\dfrac{\Delta n_{\mathrm{zv}}}{n_{\mathrm{zv}}}$ | 12.5 | $n_{\mathrm{zv}}$ — number of revolutions of the drive sprocket |
| Cutting speed of the cutter, m/sec | $v_{\mathrm{r.c.}}=\dfrac{\pi D\,n_{\mathrm{zv}}}{60}$ | $\dfrac{\Delta v_{\mathrm{r.c.}}}{v_{\mathrm{r.c.}}}=\dfrac{\Delta D}{D}+\dfrac{\Delta n_{\mathrm{zv}}}{n_{\mathrm{zv}}}$ | 4.0 | |
| Operating feed speed of the machine, m/min | $v_{\mathrm{p}}=\dfrac{L}{t}$ | $\dfrac{\Delta v_{\mathrm{p}}}{v_{\mathrm{p}}}=\dfrac{\Delta L}{L}+\dfrac{\Delta t}{t}$ | 2.0 | $L$ — length of the path traversed by the earth-cutting machine over a time interval $t$ |
| Average chip thickness cut by the bar, mm | $h_{\mathrm{sr}}=\dfrac{b\,t_{\mathrm{p}}\,z_k\,v_{\mathrm{p}}}{60\,z\,v_{\mathrm{r.c.}}}$ | $\dfrac{\Delta h_{\mathrm{sr}}}{h_{\mathrm{sr}}}=\dfrac{\Delta t_{\mathrm{p}}}{t_{\mathrm{p}}}+\dfrac{\Delta v_{\mathrm{p}}}{v_{\mathrm{p}}}+\dfrac{\Delta v_{\mathrm{r.c.}}}{v_{\mathrm{r.c.}}}$ | 5.0 | $b=9$ or $7$ — width of the cut in cm |
| Specific energy expenditures for cutting soil, kgm/cm³ | $W=0.0272\,\dfrac{P_{\mathrm{res}}}{S}$ | $\dfrac{\Delta W}{W}=\dfrac{\Delta P_{\mathrm{res}}}{P_{\mathrm{res}}}+\dfrac{\Delta S}{S}$ | 10.0 | $S=0.22$ cm² — smallest cross-sectional area of the structure |
The differing granulometric composition, moisture content, and fluctuations in soil temperature predetermine the instability of its physico-mechanical properties. Therefore, in order to obtain reliable data on the measured quantities characterizing the process of destruction, with constant parameters the experiment was repeated many times.
The necessary and sufficient number of repeated experiments is determined as
\[ H_0=t_0^2 \frac{\kappa_{\mathrm{var}}^2}{\kappa_{\mathrm{allow}}^2}, \]
where \(t_0\) — 1.65–2.0 — the normalized deviation of the arithmetic mean of a series of experiments from a single measurement [8];
\(\kappa_{\mathrm{allow}}\) — 5–10% — the magnitude of the permissible error in carrying out research work [7].
\(\kappa_{\mathrm{var}}\) — the largest value of the coefficient of variation for the given series of experiments.
The necessary number of experiments when cutting thawed soil is
\[ H_{\mathrm{ot}}=1.8^2\frac{29.4^2}{8^2}=42.6\approx 43 \text{ experiments}, \]
for frozen soil
\[ H_{\mathrm{om}}=1.8^2\frac{15.8^2}{8^2}=12.7\approx 13 \text{ experiments}. \]
To assess the scatter of the experimental data from the calculated number of experiments relative to the averaging curve characterizing the pattern of variation of the given quantity as a function of some parameter, the coefficient of variation of the entire field of points is calculated:
\[ \kappa_{\mathrm{var.\,avg}}=\sqrt{\frac{\sum \kappa_m^2}{n-1}}, \]
where \(\kappa_m\) is the deviation of the given quantity relative to the averaging curve, %.
Table 2
| Feed speed | I | II | III | V | |
|---|---|---|---|---|---|
| Gear ratios of the ZIL-164 gearbox | 6.24 | 3.32 | 1.90 | 1 | 0.81 |
| \(\kappa_2=\dfrac{r}{1-\dfrac{r_2}{r_1}}\) | 0.141 | 0.160 | 0.247 | 0 | 0.513 |
| \(\kappa_1\cdot\kappa_2\) | 0.472 | 0.535 | 0.822 | 0 | 1.71 |
The results obtained in the course of conducting the experiments and in processing the diagrams are entered into the table of experimental data. On the basis of the experimental data, graphs of the investigated dependences are constructed.
Studies of the processes of cutting thawed and frozen soils carried out according to this methodology made it possible to determine the coefficients of variation of the data, which for torque in thawed and frozen soil are less than 20%, and for feed force are less than 30%. In the first
Fig. 8. Kinematic diagram of the mechanism for setting the bar.
In the diagram: \(1\), \(2\), \(3\), \(4\); \(R\), \(P_{\text{dyn}}\), \(P_{\text{n.o.}}\), \(G_{\text{tn}}\), \(D_n\), \(H\), \(\delta\), \(\alpha\), \(\lambda_n\).
Fig. 7. Stiffness curves of the dynamometer springs investigated for measuring the resultant force at cutting speeds: I—0.43 and 0.78 m/s; II—1.3 and 2.3 m/s; III—3.4 and 5.4 m/s.
Axis labels in the graph:
- Vertical axis: Load removed from the spring, kg
- Horizontal axis: Spring deformation, mm
in the first case the indicators belong to the second, and in the second case—to the third class of accuracy of indicators and calculations. Calculations that in engineering practice are customarily regarded as “exact” belong to the second class of accuracy. Data of the third class of accuracy are also suitable for use in engineering calculations [7].
Thus, the experimental setup “Moroz” makes it possible to obtain the data needed for the design and creation of new bar-type machines for cutting frozen soil.
REFERENCES
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