Class K Axle Design and Repair by Machining

Until the introduction of AAR Standard S-259 (circular C-8287) in November, 1994 the Class F axle was the only officially designated roller bearing axle design permitted for 100 ton freight car service in North American interchange service. The increase in Gross Rail Load permitted by the Standard was correlated to increased failures at the journal ends of the axle. A 1998 redesign of the bearing and axle resulted in lower stresses in the journal; the new axle was designated as Class K and was to be used in service loads of 100/110 tons (263,000 to 286,000 pounds GRL). The redesign was highly successful in reducing axle journal failures and improving bearing life. An increase in axle failures between the wheel seats was reported several years after the redesign. Better inspection requirements and repair procedures were implemented to reduce failures resulting from surface damage. This investigation considers the effect on stresses of the accepted practice of repairing the body of the axle by machining.