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Sr. Member
Posts: 1,914
Reply with quote  #1 
I just got a lot of data from a pressure plastic mold machine that have a double ball screw, one in each direction thread, 2 servo drives and 2 sort of hypoid or worm type of gears and it got the sound of disaster. Motor bearings was likely replaced 1.5 years ago as the motors filled with oil. I get no real good bearing signature only one or another odd frequency. When they tighten the adjusting on the ball screw nuts/bearings it got worse. They have a plastic soft insert at the end cover that fallen apart spreading silicon type residue all over. Ball screw can be inspected as it can be transported outwards and seems ok. A similar machine runs smooth as silk. Anyone seen a similar monster?
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
Danny Harvey

Sr. Member / Moderator / Supporter
Posts: 1,402
Reply with quote  #2 

I have a limited amount of experience with ball screws but it predates my experience with VA so I can't give you any data.

I'm sure there are more types of drives but most I have encountered have been worm drives. As I recall, the most common issues within the drive is wear in the worm wheel. It is probably cast bronze or something soft like that and the worm is steel. Wear is visible on the load side. Proper lubrication is critical and contamination leads to rapid wear. I think the same is true for the balls in the ball screw. Bronze sludge sinks to the bottom with prolonged wear.

I would guess that it would vibrate like any other worm drive, the number of leads times the running speed. I don't do much VA on worm drives but the ones that I did, I just tracked overall because I never got much of anything but noise out of them.
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