Mori Seiki NZ2000 Spindle Failure



CHALLENGE

Mori Seiki NZ2000 main spindle, 4000 RPM, lifetime grease bearing lubrication, stator drive Our inspection of the front quad set of angular contact bearings in this modern turning spindle showed that the #3 bearing had suffered catastrophic failure. When the cage disintegrated, the debris contaminated the adjacent #2 bearing. We did not find evidence of excessive heat, coolant contamination or bearing misalignment, so we could only assume that the #3 bearing had simply reached the end of its useful life. Our dimensional evaluation did find that the rear housing bore was egged 10µ, but fortunately this had not adversely affected the rear roller bearing.

SOLUTION

We recommended green grinding, hard chromium plating & finish grinding the rear housing bore to forestall possible premature failure of the rear roller bearing. We also recommended substituting angular contact bearings with large steel rolling elements, rather than using bearings with small steel balls as found in the spindle. We felt that this modification would provide more appropriate axial & radial rigidity for our customer’s application while reducing their cost and still maintaining an appropriate speed rating. When final assembly was complete, we ran the spindle to break in the new bearing grease while checking the vibration & heat signature and delivered it to our customer.

DETAILED CAUSE OF FAILURE

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