Case/Core Separation

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.

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