## 3 Results and Discussion
### Dragline Excavator  
On the territory of Russia, handling equipment is often used in difficult climatic conditions. Fluctuations of the temperature, cyclic operating loads lead to the nucleation and propagation of the  
Figure 23: AE signals received during the diagnosis of shafts. The beginning of the destruction of the shaft surface during frictional contact. Figure 24: Waveforms of AE signals recorded on shafts of 2 roller bearings (**a,b**) and linear location results (**c,d**). defects in a load-carrying structure component, which reduces its residual life and, as a result, can lead to an emergency destruction of the structure. Using AE monitoring can prevent a sudden occurrence of an accident, reduce economic damage and prevent human casualties. Despite the fact that the operation of the lifting equipment is accompanied by a high level of acoustic noise, AE monitoring is possible by optimizing the location of the sensors and applying special methods of data processing [25; 26]. Studies were conducted to assess the feasibility of developing an AE monitoring of metal structural elements of a walking dragline excavator. The work of such dragline excavator is carried out all year round, continuously in 3 shifts. Most of the dragline excavators on the mine where the studies were conducted worked out their normal service life; however, it continues to be actively used. The most stressed and, as a consequence, the most susceptible to the formation of defects are the struts. Emergency situations with dragline excavator lead to downtime, whose duration, for example, in 2016 at one mine was 812 h. Currently, in accordance with the recommendations of manufacturers two times a year periodic diagnostic tests of dragline excavator by ultrasonic method are performed. Research work was carried out on booms and struts of dragline with bucket capacity--20 m\({}^{3}\) and boom length--90 m, which previously had damage at the left strut near the weld (Figure 25). The work was carried out without dragline excavator decommissioning. A 30-channel A-Line DDM AE system and GT200 AE sensors with a working frequency range of 130-200 kHz were used. A-Line DDM system provides the principle of digital data transmission. The system consists of several sequentially connected measuring lines. The amplification of AE signals, filtering, AD conversion and threshold impulse detection and calculation of AE parameters are carried out in the AE module, which is located next to the AE sensor directly in the tested structure. AE sensors were installed on the main structural elements of the dragline: 3 on the left and right struts, 8 on the upper boom belt and 4 on the lower boom belt, 4 on the lower struts and 3 on the column. The distances between the AE sensors were from 5 to 15 m. In addition, 5 AE sensors were mounted on the anchor links where the zone location was carried out, since they consist of structural elements between which there is no acoustic contact. AE monitoring of a rope was not carried out, as the damage to the rope does not lead to prolonged downtime. In addition, the rope is a movable part, that greatly complicates its AE testing. Data was collected directly during the work of the dragline. At the first stage, the frequency range and threshold were selected and the acoustic properties of the monitored object were determined. Two frequency ranges were tested: 30-500 and 150-500 kHz. When using a wide frequency range (30-500 kHz), an extremely high AE activity was observed, which did not have a visible dependence on the operating mode of the dragline excavator, that is, on the value of the load. Such noise is associated with the continuous operation of the equipment (working winch, loose structural elements, engine operation, vibration, etc.). Therefore, a filter of 150-500 kHz was used. Complete noise detuning by the threshold method was still impossible, since the noise reached 100 dB\({}_{\text{AE}}\). As a compromise, a threshold value of 50 dB\({}_{\text{AE}}\) was chosen.