Root cause for increase in vibration

Hi Friends,

                In one of the roller press the vibration of motor and gearbox gradually increases.In motor it increases from 1.5 mm/sec to 4.5 mm/sec(Tripping is 5 mm/sec).Dominant peak is at 1XRPM of Motor.During this scenario we change bearings in flexible coupling and the vibration gets drops in both motor and G.B. Again after two to three months the vibration increases and again we change the flexible coupling bearing.This is happening from last one year and we already changed the bearings four times.

Cardan shaft,G.B I/P bearings and Motors bearings checked and found OK.

what is the root cause for increase in vibration in Motor and G.B ??

Sagar

Original Post

Vidya, if you have the technology, use your vibration analyzer to perform an ODS (
operational deflection shape) test on the motor and gearbox to look for any possible flexing. If you do not have this capability, find a contractor that does, it may be instructive. This sounds very similar to a fan problem I troubleshot at a glass plant where the fan/motor kept coming out of alignment and showing high vibration at 1X. The key indicator was when the foundation finally fatigued to the point of cracking. You can also inspect for cracks in the motor base. 

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