Case Study – Crown Wheel

Crown Wheel Testimonial

CAT Scraper Differential Single Tooth Crown Wheel Failures.

PROBLEM STATEMENT

 For the last fifteen years we have operated fleets of 637 and 657 Caterpillar scrapers, regardless of which model machine is in use we have suffered a high incidence of single tooth crown wheel failure predominantly in rear diffs but not limited only to rear differentials.

 During this time we did not experience a pinion gear tooth failure the tooth failures were concentrated 100% to crown wheel failure.

 Two years ago two differentials were treated differently with the CAT crown wheels being refinished and then treated to increase strength and special attention paid to fitting during the diff rebuilds.

 In early October 2012 one of these diffs failed, inspection found the primary failure was operator induced diff lock failure. All of the lugs were broken off one half of the diff lock, this metal made its way through the diff centre into the gear housing doing much damage in its passing.

 The pinion gear suffered significant damage with sections of gear teeth breaking away, the sections of broken pinion gear as well as the lugs from the diff lock were ground to a paste as they passed through the gears with only one lug remaining when the diff was stripped.

 The crown wheel that had previously been prone to losing teeth prematurely had not lost a tooth yet there was evidence that much of the metal had passed through the gear with evidence of metal bruising and deformation in the root of the gear without causing failure.

Previously the treatment of the diff was limited to theory however this is hard evidence that treating the gear significantly strengthened the component and had the diff lock not failed would most likely have continued to give good service.

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