Insurability of Large Gearless Mill Drives (GMDs)
ABB’s and Zurich Risk Services’ concept of a 24 h repair cycle in ring motors for GMDs is reviewed. The application of this concept to winding design is shown to be counterproductive.
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Cadia Girth Gear Failures
Three investigations into the Cadia gear failures are reviewed. The first and third investigations showed that the location of the failures can only be explained by the thermal expansion of the gear. The second investigation shows that pinion diameter was a primary contributor to the failure and that T-shaped gears have better load distribution than Y-shaped gears. In any case, the cause of the gear failures was a design fault.
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Literature Review: Gearless Motor Failures – A Mill Designer’s Viewpoint
This post presents a review of a paper by a mill designer on the state-of-the-art of ring motor design in gearless drives. The conclusions in the paper are not justifiable. Ring motors are much more complex than grinding mills and the simple remedies offered in the paper would not have avoided most of the past failures. It is shown that external influences and design culture were the root causes of most of the ring motor problems since 1996 and the problems in design culture also exist in some mill vendor design groups. The conclusion in the reviewed paper that the ring motor failures are not diameter related is incorrect.
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