## 3 Results and Discussion  
### Qualitative Analysis  
The most frequent changes observed for the surface structures and properties included abrasive and corrosive wear. Figure 5 shows an example of abrasive wear demonstrated in the removed upper layer of the surface of the steel element during contact with the transported material. This is the most frequent failure type found in ore transfer devices [24]. In order to enable the comparison of the wear level of steel elements in the receiving bin, the technical condition of these elements after repairs has been shown in Figure 5a. Further,  
Figure 4: Locations of the bunkers within the transportation system of the mine. Figure 5b-d show the abrasive wear on the vertical sealings, the lining of the carriage trough and the lining of the front wall of the hopper, respectively. The movement of ore against the working device caused a drastic decrease in the thickness of the steel sheet, until it was perforated (Figure 5b,c) and as a result partially bent, which caused an ore blockage in the receiving bin (Figure 5c). In such case, repairs of the receiving bin consist in the replacement of linings made of ordinary quality structural steel sheets 20 mm in thickness. The use of linings allows only those elements to be replaced which are subjected to the most intensive wear, without the necessity to disassemble the entire device. This procedure significantly accelerates the replacement of worn elements and reduces the operating costs. Figure 6 shows the wear on the running rail of the feeder carriage. In this case, the wear is due to rolling friction [24]. The rail, together with the entire feeder trough, reciprocates on the wheelsets. In the case of this element, the rate of the wear process is influenced not only by the aggressive operating condition, but also the pressure force exerted on the wheelsets by the trough. The wheelsets are typical for rail transportation systems. Therefore, they can be modeled and their behavior can be simulated on the basis of the solutions from the railway industry, which follow the Archard model [25]. Figure 5: Examples of abrasive wear observed in the receiving bin: (**a**) newly installed steel elements of the bin, (**b**) abrasive wear on the vertical sealings, (**c**) abrasive wear on the feeder carriage lining, (**d**) wear on the front lining of the hopper. A bunker failure can also be due to corrosive wear, caused by subjecting the steel elements to a specific, highly humid microclimate, and to highly mineralized underground waters [24]. Figure 7a-d show examples of corrosive wear on the elements of the bunker. Figure 7a is a view of the back part of the hopper shown from the side of the feeder motor. The character of this surface damage is well visible in contrast with the newly installed lining of the feeder carriage. Corrosion which develops so fast causes the technical condition of the structure to be difficult to evaluate, and the corroded parts of the bolted joints are not easily replaced, thus extending the potential repair time. Figure 6: Example of the wear on the wheelset: (**a**) abrasive wear on the running rail in contact with the wheelset, (**b**) material loss in the running rail. Figure 7: Corrosive wear: (**a**) on the back wall of the receiving bin and on the feeder carriage, (**b**) on the motor of the feeder trough, (**c**) on the hopper, (**d**) on the linings in the bin. The rate of the corrosion processes is also influenced by intensive venting of the excavations with forced oxygen supply (a normal mine ventilation process). Importantly, the majority of steel structures in mines is made of low-alloy structural steel. Despite additional anti-corrosion protection means (protective coatings), the corrosion advances at a significant rate [26]. Extreme loads from the mass of the transported material also result in a type of damage described as deformation wear.