PSI - Issue 13

Filip Miletić et al. / Procedia Structural Integrity 13 (2018) 1644 – 1650 Author name / Structural Integrity Procedia 00 (2018) 000–000

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Figure.1. Cutting elements on rotor excavator SRs – 2000.32/5

3. Measuring the resistance of the material to the cutting One of the basic preconditions for satisfactory weather and capacity utilization of rotor excavators is their proper choice, more precisely in the conformity of the digging power of the excavator and the expected resistance to digging under the specific conditions of the working environment. An important requirement for the proper selection of basic mechanization on a particular surface mine is the knowledge of the specific resistance of the material to cut. The digging of material by a rotor excavator is a very complex process, and the indicators of the effectiveness of this process depend on numerous and diverse factors, from which the physical - mechanical and technical characteristics of excavated material, the operation mode of the excavator, the selection of technological parameters of the block, floor and cut, geometry and state of cutting elements. Measuring resistance to digging was performed on the SRs - 2000.32 / 5 rotor excavator, which was engaged in excavation of the waste material on the surface of the Tamnava – West field. The first measurement was performed in the middle of May, when the wearing of cutting elements was about 30%. After that, the excavator went for overhaul, and the new measurement was performed with new cutting elements. In this way, we tried to get the dependence on how the wearing of cutting elements influences the bucket wheel drive, that is, to increase the specific energy consumption, and hence the specific resistance to digging. By measuring the engagement force on the rotor wheel drive engine, the value of the specific resistance of the material to the digging. Since the lateral force of the resistance component of the digging has a significant impact on the digging process, the engaged engine power of the drive for the circular movement of the excavator is taken into account. In the case of the rotor drive, two engines are applied, with an installed capacity of 670 kW, while three engines, powered by 54 kW, are engaged for the drive of the circular movement of the excavator. In operation, electric motors are exposed to variable loads. This variability requires a special power measurement regime that is consumed in the digging process and this particular mode is in fact continuous measurement using a specific speed printer. The printer registers the current electricity, by which it calculates the total power which is consumed in the digging process, or effective force. By using effective force, we get the engaged power. To determine the specific resistance of the material to the dig, instruments have been used in the excavator, which are in function of the micro-technological parameters of the block an that:

 determining the height of the bench;  determining the cutting thickness;  determining the speed of circular motion and  determining of the angle position of arrow rotor wheel

Determination of the specific resistance to digging, that is, the engaged power of the engine of the rotor drive in the digging process was performed with several iterations. First of all, the thickness of the cut was changed, while the speed of the circular motion was fixed and amounted to 70% of the maximum speed of the turn of the upper construction. The height of the bench was 7 m. There were several iterations related to the thickness of the cut. It started with 25 cm, then with 40 and at the end 50 cm. The analysis of the results was performed by a well-known