Crown weel pinion failure

Approach to failure investigation of a specific failure in crown wheel pinion assembly

Transcript

1. Materials info consultancy private limited www.materials-info.com Crown wheel and pinion failure
2. Crown wheel and pinion failure Materials info consultancy private limited 2 • Contact Pattern Top land
3. Crown wheel and pinion failure Materials info consultancy private limited 3 • Failure during vehicle level test at 50000 kms Spalling
4. Crown wheel and pinion failure Materials info consultancy private limited 4
5. Crown wheel and pinion Failure Materials info consultancy private limited  What is Spalling  The specific failure mode observed on the pinion is spalling, or surface durability distress.  Specifically, spalling is a fatigue mechanism that occurs when very high, local stresses initiate cracks at or near the tooth surface.  These cracks progress into the hard case on the tooth surface and progress up along the tooth surface, from the lowest contact point, in the direction of sliding on the tooth surface.  As the cracks progress, material on the tooth surface is undermined, and eventually relatively large, somewhat fan-shaped pieces of tooth surface are liberated. 5
6. Crown wheel and pinion Failure Materials info consultancy private limited  Possible Causes of spalling  Over crowning of pinion teeth may act as high stress concentration  High loads may exist locally as the tip of the gear makes contact with the pinion. These very high local loads, combined with the normal, very high sliding that exists at the lowest contact point on the pinion, cause an abnormal, very high, local stress condition  Carburized case depth improper  Improper lube selection  Contamination of the lube 6
7. Crown wheel and pinion Failure Materials info consultancy private limited  Remedial actions proposed  Contact stresses on the gear surface can be reduced below the endurance limit of the material  Proper hardening case depth and hardness levels need to ensured . Also the hardenability of the materials to be ensured  A higher fatigue strength material can be selected if required  Complete redesign of gear set may need to be looked as the spalling indicates insufficient surface capacity of gear  The grade and contamination of lube need to be verified which otherwise may give rise to this defect. 7
8. Crown wheel and pinion Failure Materials info consultancy private limited  Check list 8 S. No What needs to be checked Pinion Material Chemistry, Hardenebility( to ensure) Heat treatment Case depth , core strength, case strength Microstructure Case and core for the transformation to Martensite with intermediate phases less than 5% Design Crowning, contact pattern and loads on surface Oil ( lube) Contamination, selection