A manufacturer of ski lifts discovered damage to one of the gears in the gearbox used in one of its lifts. The lift manufacturer contacted the gearbox supplier, who sent a service team to examine the damaged gearbox. According to the gearbox supplier, the damage was caused by a faulty maintenance action performed on the lift. The ski lift manufacturer wanted a third party expert opinion, and contacted GearboxFailure.com to perform an investigation.
GearboxFailure.com engineers visited the project site and performed a thorough visual inspection of the gearbox. Using a portable hardness tester, we discovered locations on the gear teeth that did not meet the required hardness values. We also observed grind notches in the roots of the gear teeth. These grind notches act as mechanical stress risers, and decrease the life of gear teeth. Based on evidence we obtained during our inspection, we decided to perform additional metallurgical analysis in the laboratory. The gear was submitted to an etching process used to visually identify the induction hardened zone on the gear teeth. Additional hardness measurements of the gear teeth were made as well. Our analysisproved that the combined effect of the grind notch and the insufficient hardness of the gear teeth resulted in the gear damage. The analysis also identified the source of the inadequate hardness as due to incorrect location of the induction hardening head during heat treatment of the gear.
Result for the Customer:
With the results of the GearboxFailure.com investigation, which showed clearly and convincingly that the failure did not occur due to a maintenance action, but was the result of incorrect heat treatment combined with the presence of grind notches in the roots of the gear teeth. Due to our investigation, the lift manufacturer was able to reach a favorable agreement with the gearbox manufacturer.