Vol 32 Iss. 1

Soviet mining science and the Leningrad Mining Institute suffered a heavy loss - on November 30, 1953, one of the founders of the modern Russian school of mining mechanics, Academician, Doctor of Technical Sciences, Deputy Director for Research and Head of the Department of Mining Mechanics of the Leningrad Mining Institute Alexander P. German died after a long and serious illness. A. P. German's scientific works covered almost all sections of mining mechanics. He showed the greatest interest in all complex theoretical questions and, being a brilliant analyst and a great mathematician, usually solved difficult and obscure questions of mining mechanics with talent and success. Considering numerous works of A. P. Hermann, we can conclude that his favorite field of research was technical thermodynamics or, more precisely, the application of thermodynamics to the resolution of technical issues. The works of A.P. German devoted to the theory of effective process of reciprocating compressors are of great interest and practical importance.

Lift automation at skips with bottom unloading in the period of deceleration can be realized by application of dynamic braking mode of asynchronous lifting motor. In Fig. 1 the calculated diagram of velocity during the deceleration period t₃ is shown by the dotted line λr. During the unloading period t4', a constant velocity v3 (line ρϕ) is assumed, which drops to zero during the period t₄' along the line ϕѱ. According to the force diagram of the induction machine shown in Fig. 2, the acceleration of the hoisting motor during the start-up period occurs along the broken line BCDEFGHIKLT, varying about the given (design) force value F₁ as about the average value between the extreme limits F₁' and F₁“. At the end of the start-up period, there is a full stroke period during which the driving force follows all changes in the static force. Assuming a statically unbalanced lifting system, let the static force, and hence the driving force developed by a motor operating on the natural characteristic R2, vary from the value of F'_s2 at the beginning of the full stroke period (point N') to the value of F“_s2 at the end of this period (point N). At the end of the full stroke period, there comes a deceleration period t3, during which a braking mode is assumed, which is realized in the form of dynamic braking.

Advantages of automatic hoisting consisting in increase of productivity, increase of reliability of work and safety, and also release of labor of a highly skilled machinist and a great spread in the Soviet Union of hoisting installations with asynchronous motors make the problem of automation of hoisting with asynchronous drive very actual. The solution of this problem has been started since 1932-1933. However, despite the twenty-year period since the first studies on this issue, the problem has not been completely solved so far. The reason for this lies in the unfavorable mechanical properties of the induction motor, which make it difficult to automate the lifting, as well as in the known one-sidedness of the solutions offered so far, based, as a rule, on the use of mechanical shoe brakes during the deceleration period. In spite of numerous researches, conducted mainly by V. B. Umansky and V. S. Tulin, it is impossible to create a good solution. S. Tulin, it has not yet been possible to create good stroke controllers acting on the mechanical brake of a hoisting machine. And if the automation of starting the hoisting machine is solved today, the question of controlling the hoisting machine during deceleration requires theoretical and experimental study. The analysis of operation of various systems of hoisting automation, based on comparison of mechanical characteristics of various braking devices, allows us to critically evaluate these systems and outline new directions in solving the problem of automation of freight hoisting with asynchronous drive.

At present, in conditions of coal mines the main type of transportation along the main horizontal workings is electric locomotive rolling. At gas mines, electric locomotives are used for pumping by battery locomotives, and at mines not dangerous by gas and dust - by contact locomotives. This type of transport in modern conditions - under complex mechanization of coal mining - has a number of significant disadvantages. Often it is the cause of violation of the continuity of the process of transportation of minerals. Often there are violations of movement schedules. For modern large mines - at complex mechanization of coal mining with full automation - the most progressive type of transport is conveyor. It is easier to automate, allows to keep the continuity of the process of transportation of minerals from the face to the railway bunkers or preparation plants and is less dangerous for the operating personnel.

In mine conditions, the track profile of an electric locomotive haulage system is usually very complex. There are significant changes in track gradients, small radii of curves, sharp transitions from one radius of curves to another, etc. This causes a sharp change in the magnitude of the resistance forces to the train movement and, consequently, in the traction force of the electric locomotive. The change in traction force is also caused by frequent starting of the locomotive at very short track distances. Improvement of traction conditions can be achieved by correction of rolling tracks, elimination of sharp breaks in the track profile and small radii of curves, application of heavy rail profile. In this light, the possibility of increasing the coefficient of adhesion of electric locomotive wheels with rails by electromagnetic means should also be considered. The magnetic attraction forces arising between the links of the magnetic force line contour can create additional electromagnetic coupling between the wheel and the rail. To this end, a force magnetic field closed along the points of contact between the electric locomotive and the rails should be created

In conditions of coal mines regulation of centrifugal pumps is either not applied at all, or is carried out by a gate valve, which leads to deterioration of efficiency of the pumping unit and, consequently, to overconsumption of energy for drainage. As the survey data of a number of mines show, the nominal head of the installed pumps often significantly exceeds the head required to overcome static and dynamic resistances at the nominal capacity of the pumping unit. This, in turn, in order to avoid inadmissible overloading of the drive motor, leads to the need for prolonged operation of pumps with the gate valve closed, i.e. with significant unproductive losses. According to A. I. Veselov, the gauge nominal head of the installed pumps often significantly exceeds the head required to overcome the geodetic height of discharge, and the capacity of pumps is selected with a large reserve. Referring, for example, to the mines of Kizelovsky district, A. I. Veselov writes: “The largest dewatering installations of the mines named after V. I. Lenin and M. I. Lenin. V. I. Lenin and M. M. Volodarsky mines work with an excessive head reserve, and hence, of course, low efficiency of the unit. Lenin mine at the main pumping stations has an excessive installed capacity of pumps, which is equal to almost five times the normal inflow.

Currently used calculation of hoisting mine ropes for strength is clearly conditional in nature. This calculation is based on the so-called static safety factor, which represents the ratio of the breaking load to the static load (weight of the rope and end load). It goes without saying that in this method of calculation the dynamic load is not taken into account at all and the actual value of the safety factor (dynamic) remains unknown. It was natural to expect that the above provision led, for obvious reasons of caution, to somewhat exaggerated values of the safety factor, especially for deep mines, where the weight of the rope plays a significant role. Because of this circumstance, in American practice, the value of the said coefficient is set differentially, depending on the depth of the mine and the smaller the greater the said depth. Apparently, the working conditions of the rope in deep mines are considered more favorable in terms of the magnitude of stresses. It should still be pointed out that the latter statement, although more or less probable at first glance, is still not fully substantiated and, moreover, has as its starting point an assessment of stresses in the normal lifting mode.

The existing method of calculating the traction body of mine rope pullers is similar to the method of calculating the rope of mine hoisting installations, developed by A. P. Herman. The method consists in determining the weight of a linear meter of rope by the maximum static load on the rope, including also its own weight, and in the selection of rope according to factory data on the basis of the weight found. The currently used method of calculating the traction organ of belt conveyors consists in the preliminary determination of power on the shaft of the drive drum conveyor, for which is tentatively taken the weight of moving parts of the conveyor, then sequentially determined: the traction force, the maximum tension of the belt, the required number of pads and, finally, the weight of a linear meter of belt. After the approximate weight of the belt is determined, the final calculation is repeated. With the current calculation methodology, the weight of the moving parts of the conveyor must inevitably be taken tentatively, since the exact weight of the belt is not known at the beginning of the calculation.

In the practice of production and design works there is often a need to determine the maximum length of a scraper conveyor per drive for specific transportation conditions. However, to date, this issue in the technical literature is not sufficiently covered. This article sets the task of establishing design formulas for determining the length of the conveyor per drive depending on the main parameters of the transportation unit - the strength of the traction body and the installed engine power.

In recent years, oil shale production in the Soviet Union has increased significantly. The rate of development of the oil shale mining industry significantly exceeds the rate of development of the coal industry. In the directives of the XIX Congress of the CPSU on the fifth five-year plan for the development of the national economy of the USSR for 1951-1955 it is stated: “...to increase oil shale production by 2.3 times, especially in the Estonian SSR”. Such a rapid development of the oil shale industry is possible only on the basis of the highest technology. Oil shale mines are equipped with modern powerful machines and mechanisms. However, this technology is not used efficiently enough yet, which is explained mainly by insufficient study of the processes of mining machines operation in specific conditions of oil shale mines. There is a great number of researches on coal cutting, but there are absolutely no works on oil shale cutting. The material presented in this paper is based on experimental studies of notching in oil shale. The researches were carried out for several years at the mines of Leningradslanets and in the laboratories of the Leningrad Mining Institute. The experiments were carried out without self-recording instruments, only a set of small-sized electrical measuring devices was used, which slightly reduced the accuracy of readings (within 5-7%)

Mine No. 32 of the Snezhnyananthracite Trust, where the measurements were made, develops the H8 - Fominsky formation with a total thickness of 1.08-1.10 meters. The dip angle of the seam is 15°. The roof control is partial filling. The longwall face length is 167 m. The working mode is three-shift: two shifts are mining shifts and one shift is preparatory. Formation H8 is usually classified as anthracite of medium strength. However, the presence of a clearly pronounced jib and squeezing of the coal massif with a lowering roof allows us to refer it to the lower-middle strength: 0.04-0.05 pieces of KMZ-1 type victorite teeth are used to cut 1 m2. A Donbass combine harvester worked in the face. The total length of the bar was 1.6 m; useful length - 1.45 m; height - 0.83 m. There are three disks on the bar, as the anthracite is viscous and the target cut by the ring bar is not destroyed into transportable pieces. The cutting chain is set according to the scheme of a seven-line “herringbone” with an increased number of teeth in the extreme positions. Measurements were taken at the beginning of the cycle (at the pullback drift). All teeth in the cutting chain were tucked in and set according to the scheme. The pincers on the rod and teeth on the disks were made of carbon steel and reinforced with T-590 hard alloy.