What is the reason of centrifugal blower in violent vibration?

Centrifugal blower in use process, if there is a severe vibration, so is very bad, because will affect the normal use of fan, can produce serious damage to the fan itself, and it also has certain security hidden danger, so be handled in time, timely solve, so, what are the causes of fan violent vibration? The following is for analysis.
The causes of fan violent vibration mainly include the following:

(1)The fan shaft and motor shaft not concentric;

(2)Basis, or the whole bracket stiffness is not enough;

(3)Bolts, rivets, etc to loosen, or the impeller deformation occurred;

(4)Between the impeller shaft plate hole and shaft with dense;

(5)There is dust or dirt on blade, or wear or deformation, which makes the rotor unbalance;

(6)Fan of import and export pipeline is not installed, a resonance phenomenon;

(7)Bearing temperature rise too high, or a violent vibration of the bearing box;

(8)Lubricating oil quality closes nevertheless, or only the impurities, or bad

(9)Rolling bearing friction between inside and outside the circle, or bending, damage;

(10)Casing or air inlet and the impeller friction;

(11)Motor current is too large, or the temperature is too high;

(12)Fan starts, adjust the door or gate no closed sealed inside gas pipeline;

(13)The input voltage is too low, motor power single-phase power condition

(14)The medium temperature is too low, makes the motor overload operation;

(15)System can not match with the performance of the fan, the fan at a lower pressure big flow area, will not run well.