Drive in most bucket wheel excavators (BWE) is accomplished through its electric motor, cardan shaft and planetary gearbox. In the BWE SchRs630/6×25, the planetary gearbox is cantilevered at the end of the hollow shaft which transmits the torque through the sprocket to the caterpillar track chain. In this BWE, a the drive shaft fracture occurs at the point of support on the penetration side.
Experimental testing of the chemical composition and mechanical properties of the material of the shaft and metallographic inspections of the fracture surface by means of electronic and light microscopes carried out in the first part of the paper have shown that there are no significant inhomogeneities and errors in the material of the shaft and that they do not cause damage. Further, the analysis of results referring to the mechanical properties and chemical composition of the repaired shaft at the point of welding, and particularly in the transition zone, shows that they considerably deviate from those prescribed for the material used. Significant inhomogeneity of the material, occurrence of cracks as well as the difference in the microstructure appear in this zone, which is the cause of shaft damage.
The second part of the paper presents the FEM analysis of effects of the cantilever type of support of the planetary gearbox and stress concentration at the point of support due to inadequate finishing, which caused the occurrence of an initial crack. The user unsuccessfully tried to eliminate this weakness by repair welding of the shaft.
► The cause of the drive shaft fracture of the BWE SchRs630/6×25 was examined. ► The shaft fracture did not occur due to any errors in the material. ► The cause of the initial crack is inadequate machining of the shaft. ► The cause of the shaft fracture is the badly performed repair welding process.