1. Materials info consultancy private limited www.materials-info.com
Crown wheel and pinion failure
Materials info consultancy private limited

2. Crown wheel and pinion failure
Contact Pattern
Top land
Materials info consultancy private limited

3. Crown wheel and pinion failure
Failure during vehicle level test at kms
Spalling
Materials info consultancy private limited

4. Crown wheel and pinion failure
Materials info consultancy private limited

5. Crown wheel and pinion Failure
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.
Materials info consultancy private limited

6. Crown wheel and pinion Failure
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
Materials info consultancy private limited

7. Crown wheel and pinion Failure
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.
Materials info consultancy private limited

8. Crown wheel and pinion Failure
Check list
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
Materials info consultancy private limited