Hwacheon lathe with poor part finish



CHALLENGE

Our customer sent this turning center spindle in for rebuild because of poor part finish & excessive bearing noise. The front tapered roller bearing failed from contamination with coolant which had washed out almost all of the grease & allowed corrosion of the rolling elements & raceways. The contaminant had also largely displaced the grease in the rest of the bearing complement, including the rear tapered roller. Our dimensional inspection also showed slight damage on the tooling taper OD & face. We did notice that both the front & rear housing ID’s were on the loose side of ISO, but there was no fretting which would indicate that this condition contributed to the bearing failure. As the housing bores were likely manufactured this way, we did not recommend grind, plate & finish grind to tighten them up.

SOLUTION

We first performed a kiss grind on the tooling taper OD and face to remove the high spots. We replaced the full bearing complement, a worn pulley retention nut and the assembly hardware. When our customer initially contacted us about this spindle, they asked if we perform a run-in cycle which would be sufficient to break in the new bearing grease. Especially with tapered roller bearings, the spindle must be run in to disperse the grease and prevent overheating due to churning. According to our standard break-in procedure, we ran in this spindle at progressively increasing speeds for a total of eight hours while checking the vibration signature, then balanced the spindle with all rotating components installed, and shipped it to our customer ready to make parts.

DETAILED CAUSE OF FAILURE

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