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Crown wheel and pinion failure

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Crown wheel and pinion failure

• Contact PatternTop land

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Crown wheel and pinion failure

• Failure during vehicle level test at 50000 kms

Spalling

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Crown wheel and pinion failure

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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.

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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

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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.

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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