We were asked to determine the cause of cracking on a conveyor chain used for material transfer in a gypsum kiln.
The failed links were fabricated from AISI-SAE 1045 steel in the hardened and tempered condition, with Rockwell C Hardness (HRC) values measured at 41 to 43 HRC. The cracking was observed primarily at the side link pin and sleeve holes that exhibited notches from the punching operation, with limited cracking also observed in the rollers. Excessive wear and galling was also observed on the bearing surfaces of the link pins that exhibited low hardness.
Chains are assumed to be subjected to impact loaded during service, and when excessively hard, become notch sensitive and susceptible to brittle fracture. The chain links failed due to the presence of notches in the highly stressed pin and sleeve holes, coupled with high hardness of the links that initiated fatigue cracking at the notches. OCE recommended to utilize chains exhibiting hardness within the range of 32 to 38 HRC to increase toughness and still provide sufficient strength and wear resistance for this application. It was also recommended to verify chains exhibit smooth link and sleeve hole surfaces to eliminate notches.