Fracture analysis of the pulley of a bucket wheel boom hoist system

This paper presents the results of the pulley fracture analysis. Experimental investigations confirmed that the chemical composition and basic mechanical properties of the pulley material, except the impact energy at a temperature of - 20 degrees C, meet the requirements of the corresponding standard. The impact energy value at the temperature of - 20 degrees C is for approximate to 45% lower than the prescribed value which has considerable influence on the appearance of the brittle fracture, especially having in mind the fact that the bucket wheel excavators operate at low temperatures. Metallographic examinations as well as magnetic particle inspections indicated that initial cracks in the welded joints occurred during the manufacture of the pulleys. Characteristic levels of the rope load cycle are obtained by using in-house software which includes the dynamic effects of the resistance-to-excavation. The FEA results pointed out that in the representative load cases the combinations of the mean stress and the alternating stress in the pulley critical zone lie considerably below the limit line of the modified Goodman's diagram. The conclusion, based on the presented results, is that the fracture of the pulley appeared as the result of the 'manufacturing-in' defects.