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 ??