Case-core separation on gear teeth. Photo courtesy GEARTECH © 2014.
Definition: Case/Core separation results from internal cracks that cause corners, edges, or tips of teeth to separate.
Identification: Fracture surfaces exhibit characteristics of brittle fracture.
Discussion: Case/Core separation occurs as a result of high levels of tensile residual stress due to excessive case depth.
Prevention: Control case depth, particularly at tooth tips. Avoid narrow top lands. Chamfer all edges of teeth. Use clean steel, with high fracture toughness. Temper gears immediately after heat treatment.
More Information: For more information on case/core separation, please submit a question to our “Ask an Expert” link. For assistance with a gearbox failure analysis, please visit our “Consulting” page.