## 3 Results and Discussion
### Tribological Test Results of the Benchmarks Showing the Greatest Wear  
In order to be able to analyze, under laboratory conditions, the behavior of the bucket teeth of the two machines mentioned in contact with the mined rock, several cylindrical samples were made of the material from which the excavator tooth is made, both for the Liebherr 944 L excavator and for the Volvo L220 E front loader. Ten samples (Figure 14) from each of the two tooth materials were thus studied. The average values of the coefficient of friction (metal with basalt) were 0.0361 for the Liebherr 944 L excavator bucket tooth sample (Figure 15) and \(-\)0.0385 for the Volvo L220 E front loader bucket tooth sample (Figure 16). The profile of the worn metal surface can be analyzed using the roughness parameter determined with the help of a tribometer and a profilometer, as described in Section 2.2. Following the friction test between the metal sample and the rock sample, the roughness parameter R\({}_{\text{a}}\) is obtained, which represents the arithmetic average deviation of the worn metal surface profile from the ideal profile (represented by a straight line). Regarding the amount of wear (Figure 17) on the surface of the metal sample of the Liebherr 944 L excavator tooth (Figure 18), a pronounced increase of 205.88% was found in correlation with its R\({}_{\text{a}}\) roughness value and 31.03% for the bucket tooth sample of the front loader Volvo L220 E (Figure 19). Figure 14: Cylindrical metal samples subject to wear. Figure 13: Volvo L220 E front loader (the dashed line) bucket teeth maintainability value (the solid line represents the same distribution fit but starting at time 0). Figure 16: Friction coefficient variation for Volvo L220 E front loader bucket tooth sample. Figure 17: Wear profile of a metal sample (3 mm). Figure 15: Friction coefficient variation for Liebherr 944 L excavator bucket tooth sample. Figure 18: Wear values for the Liebher 944 L excavator bucket tooth sample. The experiments carried out made it possible to appreciate that the material of the tooth allows charging by welding with covered electrodes in order to increase its life and recondition it after wear [33; 34; 35; 36; 37]. The practical tests led to the choice of the charging procedure by manual electric welding with coated electrodes so that the existing equipment in the quarry could be used but also to the rapid reconditioning of the worn teeth without dismounting them from the machines. The choice of filler materials was made on the basis of data on wear resistance and welding behavior in difficult deposition positions. The development of the self-protection system against tooth wear (Figure 21), which involves reconditioning areas through welding, was carried out differently depending on the wear surface position of the teeth, namely the worn edge of the tooth was protected with a compact layer of material, and the active surfaces were protected with rhomboidal systems. In the case of the technical equipment of the quarry, the concept of preventive-repetitive maintenance involved the repetitive development, realization, and reconditioning, in conditions of economic efficiency, of the bucket teeth of the Liebherr 944 L excavator and the Volvo L220 E front loader; experimenting with reconditioned teeth demonstrated the usefulness of applying the proposed method by actually increasing their service life by 60%. The cost-effectiveness of the optimized welding process for bucket teeth is estimated at 1700 euros, based on a consumption of 20 teeth per quarry during 1.5 production cycles. The proposed method can also be used on other components that show pronounced wear, for example, the blades in the equipment of the buckets of front wheel loaders. Figure 21: Self-protection system against wear of the bucket tooth: (**a**) active edges reinforced with welding; (**b**) tooth base reinforced with welding. Figure 20: Volvo L220 E front loader bucket tooth: (**a**) brand new tooth; (**b**) tooth that has undergone wear during the manufacturing process.