Due to frequent breakdowns of the gear spindle pair, a Hot Strip Mill in India experienced a huge loss of productivity and an increase in maintenance costs. The breakdowns caused damage to many elements of the gear coupling, including: The end rings running in contact with the flex-hub, excessive wear at the gear teeth, cracked sleeves, and end plate bolt failure. However, an initial observation of the damaged parts and even the installed spindle would not reveal the root cause.

Perceptiv™ Services Solution

The Perceptiv team studied the spindle in operation and at the repair bay over four visits. A detailed analysis was done using mill layouts provided by the customer to calculate the distance from a reference point on the mill stand to the thrust button on the pinion stand. A comparison of that calculated distance versus actual field measurement lead to identifying the root cause. The measured distance was fairly larger than the calculated distance.

Based on this clue, the Perceptiv team later observed a flaw in the work roll change procedure. The roll sleeve was being pushed by the workroll during installation leading to permanent deformation of parts, including the thrust plate at the pinion end. This would result in increased distances, leading to loss of designed gap between the flex-hub and the end ring. When the flex-hub was operated with inadequate gap, it would lead to the locking up of the gear pair, resulting in premature wear and damage to the gear spindle elements.

The Perceptiv team provided recommendations to properly align the work roll so that it does not push the spindle sleeve excessively during the work roll change. With the knowledge and support of the steel mill personnel, the Perceptiv team could solve a critical issue for the customer, saving thousands of dollars in lost production as well as maintenance costs.

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