Field Failure Investigation of 42CrMo4 Bottom Rollers in Bucket Wheel Excavators Operating Under Severe Mining Conditions

Abstract –Bucket Wheel Excavators are Specialized Mining equipment used mostly in open Cast Mines for excavatingthe overburdens and the minerals. BWEs use track system for movement of these heavy machineries. Bottom rollers usedin this track system carry heavy loads and play an important role in smooth operation of the machine. Any prematureroller failures will result in increased maintenance, production interruptions, and high operating costs. This studypresents a fieldbased investigation of failure in 42CrMo4 bottom rollers used in largescale mining operations. Thepresent study was carried out through systematic visual inspection of failed components, review of service records, andassessment of wear features, crack development, corrosion damage, geometric distortion, and manufacturing relateddefects.As per the service records for an operating BWE, it was discovered that 666 of 960 installed rollers failed within one yearof operation at a failure rate of 69.4%. The root cause of the failure was multiple degradation mechanisms acting at thesame time during service. The entrainment of mineral particles resulted in material loss, surface grooving, and plasticdeformation due to abrasive wear. Sliding wear was observed at bearing interfaces, where lack of lubricants and theingress of contaminants seemed to accelerate surface damage. Fatigue cracking normally starts from wear scars,corrosion pits and geometric stress concentration areas and grows slowly with a repeated load cycle. Several failuresassociated with corrosion damage, dimensional instability, metallurgical discontinuities, and defects due to repairwelding were also discovered in some failed rollers. The result of this study indicates that failure of bottom roller is due tothe combined effects of wear, environmental degradation, and cyclic loading instead of single failure. The study resultwill help in the development of improved inspection practices, maintenance planning, material selection and futuredevelopment of more reliable track roller systems for harsh mining applications.