Repairing of cracks on tooth gear ring of a bucket-wheel excavator

Bucket-wheel excavators are continuously working machines for removal of waste and useful materials in open-pit mines, mainly used for mining of lignite. The purpose of a tooth gear ring is to rotate the excavator using two reducers. Due to this, the structural integrity of such elements is of great importance for the safe and reliable operation of the bucket-wheel excavator as a whole. In order to ensure its proper function, non-destructive testing (NDT) methods (namely magnetic particles testing) was performed after casting of gears. NDT revealed the presence of cracks with varying lengths (10-110 mm), which were located in the gear teeth, its main body and the openings used for connections between segments. For this reason, it was necessary to adopt a repair welding technology which would eliminate the cracks. Since the tooth gear ring was made of GS-40MnCrSi3V low-alloyed cast steel, electrode 42 4 B 42 H5 (designation according to EN 499E) was selected as filler material, due to its exceptional mechanical properties, suitability for welding of low-carbon low-alloyed steels and low hydrogen content. Manual arc welding was the procedure used in this case. Since these repairs were all performed on the surface of the tooth gear ring segments, final NDT included only magnetic particle and penetrant testing, both of which had shown that the repair technology was successfully applied, i.e. not new defects were detected in the repaired gear ring elements