“Ural-20R” combines loading drives evaluation in two-stage development of the face

The technological features of the use of high-performance Ural-20R combines in the conditions of potash mines in Russia are described. It is shown that when the capacity of the worked potash seams is over 4 m, a two-layer ore extraction is used. The formation of cutting process, implemented by the second course of the combine in the treatment chamber, is carried out by an incomplete section of the executive bodies. The standard control system, display and protection of the Ural-20R combine does not allow monitoring and reliable estimation of the magnitude of dynamic components on the drives of the mining machine loads, as well as tracking the feed rate of the combine to the face. The regulation of the operating parameters and the assessment of the degree of loading of the drives of the excavating machine in real time are assigned to the operator. The fundamentals of the experimental research methodology for assessing the loading of drives of Ural-20R combines with the destruction of the potash mass by an incomplete section of the executive bodies are described. The device and the operating procedure of the “Vatur” software-recording complex, which measures, records and records the electrical parameters of the drive motors of a mining machine, is described. The process studies results of forming loads on drive elements of Ural-20R combines when mining a face with an incomplete section of executive bodies are presented. It is proved that the work of combine harvesters on the undercut of the formation with a high feed rate is accompanied by significant dynamic loads on the drives of planetary organs and an overload of the drives of the Berm organs, which leads to an accelerated consumption of the resource and emergency failures of the gearboxes and motors of the extraction machine.

loads in mechanical transmissions of combines, which, in turn, leads to increased accident data of mining machines [2,11].
The instant load on the drives of the executive bodies of the "Ural-20R" tunneling machines can be mathematically described as the sum of three components: N(t) = N 1 (t) + N 2 (t) + N 3 (t), (1) where N(t) -instantaneous value of the load on the drive of the executive body of the combine; N 1 (t) -the component determined by the physicomechanical properties of the destroyed potash mass and the geometrical parameters of the face; N 2 (t) -component determined by the technical condition and kinematics of the executive bodies of the tunneling machine; N 3 (t) -a component determined by the operational parameters of the "Ural-20R" tunnelling machine, in particular, the feed rate to the face. The important technical characteristics of tunneling machines with executive bodies of the drilling type are the shape and dimensions of passable workings, since the rational scope of the excavation machines when used in the treatment chambers of potash mines, the magnitude and nature of the load changes on the drive elements, power ratio harvesters and the possibility of using mine self-propelled wagons of increased carrying capacity [9,10,15].
Combines "Ural-20R" carry out tunneling workings with a cross section of arched form. The number of moves in the practiced chamber is determined by the stability of the roof. The width of the interchamber pillars is taken from 1.5 to 7 m and depends on the width of the chamber, the thickness of the reservoir and the physico-mechanical properties of the ore being mined.
The completeness of extraction and loss of potassium-magnesium ores depends on the form of production. The amount of ore loss in the treatment chamber is calculated by the formula: where S ra -the area of the rectangle described around the contour of the cross section of the mine worked by the combine, m 2 ; S к -crosssectional area of the completed development, m 2 . When the thickness of the potash ore layer is more than 4 m, a two-layer mining of the chamber is applied with overlapping crosssections in height, with the first stroke the tunneling machine excavates the upper layer (it works with full face). After distillation of the combine, the lower layer is worked out by the second move. At the same time, the face area is less than the cross-sectional area of the executive organs of the extraction machine -the combine harvester performs the undercut of the formation (Fig.1).
The destruction of the potash massif by the full cross section of the executive bodies is the most favorable condition for the operation of the "Ural-20R" combine, which ensures the maximum technical productivity of the excavating machine with the minimum specific energy consumption and dynamic loads on the drives [4,6,16]. The technological operation of the tunneling is characterized by significant dynamic loads on the drives of the executive bodies of "Ural-20R" sinking and harvesting combines. The lack of effective damping devices and the pulsating nature of the loads determine the occurrence of impacts transmitted to shafts, bearings, gears, which leads to accelerated wear and emergency destruction of expensive gearboxes, and downtime of mining machines.
According to the reviews of service specialists, whose field of activity includes tasks related to the repair of "Ural-20R" combines, the majority of emergency failures of drive electric motors and gearboxes occur during operation of the combines with an incomplete section of executive bodies. Examples of the most frequent emergency failures of gearboxes of "Ural-20R" combines: The standard control system of the Ural-20R combine is equipped with indicators of current loads of drive electric motors, the ultimate loads are monitored by "KORD" devices. When the induction motor overturns, a prolonged start-up (more than 2 s) or during technological overloads (more than 10 s), the device is activated and opens the power supply circuit of the corresponding motor with its contact [3,4].
It should be specially noted that the standard electro-hydraulic control and indication systems of the "Ural-20R" combines do not allow controlling the magnitude of the dynamic component loads on the drives of mining machines.
In order to identify the basic laws of the process of forming loads on the drive elements of "Ural-20R" tunneling machines while working the face with an incomplete section of the executive bodies, the authors performed experimental studies in real operating conditions of these mining machines.
Methods of experimental research. Employees of the Department of Mining Electromechanics of the Perm National Research Polytechnic University developed and manufactured the "Vatur" software-recording complex, which provides measurement, recording and preservation of electrical parameters of the drive motors of "Ural-20R" tunneling and treatment combines (Fig.2.). The "Vatur" complex also includes an encoder-sensor, which makes it possible to record the values of movement and the feed rate of the combine to the face [6,14].
"Vatur" registers the operation parameters of the drive motors of the "Ural-20R" combine for two voltage inputs. At each input (feeder), the loads of energy consumers are recorded, which can be either individual electric motors or a group of several consumers. To measure active power in a three-phase alternating current circuit, the method of one wattmeter with an artificial zero is used. The connection diagram of the current and voltage sensors on the Ural-20R tunneling machine is shown in Fig.3.
The instrument measures 5 kHz, i.e. during one period of voltage fluctuation of the supply network, 100 measurements are implemented. The primary processing of instantaneous values of currents and voltages, as well as the calculation of the effective values of these values, are carried out by the software of the computing unit directly during the experiment. In the process of primary data processing, the following parameters are determined.
The effective value of the phase voltage for each feeder (cable entry) is calculated by the formula: where I k -instantaneous value of current at the k-th point in time, А. The total and active power of the drive electric motors of the combine are determined by the formulas: where S -total power of the corresponding drive electric motor of the "Ural-20R" combine, kVA; N a -active power of the drive motor of the combine, kW. Power factor cosφ = S N a .
Combine feed rate  where l k and l k -1 -the position of the harvester at the current time k and the preceding time k -1, respectively, m.
The calculated values are stored in non-volatile memory of the software-recording complex. Further processing and analysis of the data array is carried out on a personal computer using the specially developed software "PC-Vatur". In the "PC-Watur" software environment (Fig.4), the data array of each measurement is visualized as a set of graphs on one-time axis. In the process of data processing, the researcher selects the boundaries of the analyzed sections of the graphs by setting the start and end measurement marks on the time axis. In order to determine the operating parameters of the "Ural-20R" tunneling machine in steady state, the corresponding measuring section is selected without transitional modes.
Evaluation of the variability of the loads on the drive elements of the executive bodies of the "Ural-20R" tunneling combines was carried out by determining the variance, mean square deviation and coefficient of variation of the active powers of the engines of mining machines [1,6,9].
The procedure and results of experimental studies. Investigations of the operation of the Ural-20R combine with an incomplete section of the executive bodies were carried out when the productive layer of the "Krasnyi II" layer was cut in one of the mines of the Verkhne-Kama deposit of potassium and magnesium salts. According to the data provided by the mine surveying service of the mine, the height of the massif to be destroyed was 1.0-1.1 m, the face area was 5.5-6.1 m 2 , the angle of inclination of the mine varied in the range + 1-3 (the movement of the combine from the bottom up) .
In the course of the measurements, the "Ural-20R" tunneling combines worked with feed speeds close to those established by the operators in practice when performing such operations. The average feed rate of the combine was 0.40 m/min. The operator limited the feed rate of the excavating machine, focusing on the readings of the current indicators of loading drive electric motors. Based on the measurement data, we plotted the active power graphs of the electric motors of the Ural-20R tunneling combines (Fig.5).
The average values of the active powers of the drives of the surveyed combine were calculated, the mean square deviations and the coefficients of variation of the signals of the active powers were determined (see table).  The most loaded engines of the "Ural-20R" tunneling machine are the engines of the Berm executive bodies, which destroy the potash mass near the excavation soil and load the broken rock mass onto the scraper conveyor. The active power of the engines of the Berm organs exceeds the nominal value, while the variability of the loads is the lowest among the examined drives. This is due to the filling of the loading augers driven by the same electric motors as the berm cutters of the combine. Most of the power consumed by the engines of the Berm executive bodies is spent not on the destruction of the face, but on loading, circulation and overgrinding of ore in the spiral channels of the augers.
The most significant load variability is observed on the drives of the portable and relative motion of the incisal discs of the twin planetary actuators. When performing cutting of a productive formation, the mean square deviations of the capacities of these drives increase by 2.3-2.5 times in comparison with the mining of the bottom by a solid section. It should be especially noted that during the operation of the "Ural-20R" combine in the conditions under consideration in contact with the face, only one of the two rotary gearboxes of the planetary actuator is alternately located. Thus, the standard display system of the combine signals the presence of excess loads during double overload of rotary gear. This explains the fact that over 35 % of the total number of emergency failures of gearboxes of combines "Ural-20R" is accounted for by rotary gearboxes of planetary executive bodies.
The analysis of the research results showed that the feed rate of the combine harvester V r exceeded the permissible value by the criterion of the maximum permissible chip thickness h max , the value of which is determined by the design of the rock cutting tool and the planetary executive body. The destruction of the potash mass by the planetary executive bodies of the Ural-20R tunneling machine with a feed speed of V r > 0.25 m/min allows contact with the face of the fist tool holders. During visual observations of the movement of the "Ural-20R" combine during the cutting of a productive formation, significant vibrations of the body of the extraction machine, the mass of which is 110 tons, as well as slippage of the tracks of the running equipment, were noted [6].
Conclusion. The results of experimental studies presented in the article and the analysis of the statistics of emergency failures of "Ural-20R" tunneling combines allow us to draw the following conclusions.
When operating the "Ural-20R" combines with an incomplete cross-section of the executive bodies (carrying out the technological operation of cutting), the feed rate of the extraction machine to the bottom should be limited by the criterion of the maximum allowable chip thickness. The most loaded drives of "Ural-20R" combines are drives of berm executive bodies, since a substantial part of the energy in the process of their work is spent on moving and grinding potash ore. The loads of the drives of the relative movement of the incisor discs of the planetary actuators are characterized by the greatest variability, which determines the high probability of emergency failures of these drives.
The regular control and display systems of the "Ural-20R" combine need to be improved, since they do not allow controlling the dynamic load components of the combine drives and registering the feed rate of the combine to the face in real time.
The operation of the "Ural-20R" combine with an incomplete section of the executive bodies with a high feed rate leads to accelerated resource consumption and emergency failures of gearboxes and drive motors of the extraction machine.