Reasons for vibration during equipment operation

It is possible to consider whether there have been changes in the quantity and quality of the lubricating oil. Has the medium being transported changed? Whether there have been any changes to the inlet and outlet pipelines, or if resonance is present. Foundation bolts are also areas that need to be checked frequently.

Reasons for excessive axial vibration: (1) Severe wear of the motor’s bearings or bushings, resulting in large gaps and the occurrence of a \"shaft lift\" phenomenon. (2) The motor air gap is uneven or there is a fault in the motor windings. (3) The motor rotor is unbalanced, or the balance weights shift after balancing, and the fan blades are damaged. (4) The motor shaft is bent or the bearing surfaces are severely worn. (5) Axial positioning offset of the motor rotor. (6) The motor’s mounting foundation is not level, or it lacks sufficient stiffness, or the anchor bolts are not fixed tightly enough, etc.

The magnitude of vibration = excitation force ÷ stiffness. 1 If vibration is high in a certain direction, it can generally be determined that either the excitation force in that direction is large or the stiffness in that direction is low. Using this as a guiding principle, identify possible faults based on the equipment’s structure. For example, I once dealt with a problem of excessive vibration in a dust collection fan; the vibration was very noticeable on site. Using a handheld vibration meter, it was found that the levels of horizontal and vertical vibration were similar, both being dozens of times above the acceptable limits, with the vibration displacement amount approaching 400μ. At that time, it was judged based on experience that the foundation was loose, and the excessive vibration was caused by a decrease in vertical stiffness. 2 Verify based on the characteristics of the potential faults identified. It was still the fan mentioned above; to verify this, vibrations were measured vertically at various points on the fan’s foundation. Several locations where the vibration levels differed significantly were identified, and tightening the bolts at those spots resolved the issue, resulting in an immediate reduction in vibrations. Vibration has three manifestations: \"velocity, acceleration, and displacement.\" These three aspects have different relationships with vibration, and a comprehensive assessment must be made based on the structure of the equipment. It’s still that fan there – why was it possible to determine based on experience that the problem lay with the fan’s foundation? The bearing is lightweight, and unless it is in an advanced state of wear, it would not cause such significant vibration in the equipment; therefore, the bearing issue can be ruled out (although the measured acceleration values are also above the limit). Imbalance of the fan impeller can cause such large vibrations, but these vibrations tend to decrease as one moves further away from the impeller; however, multiple vibration measurements taken at different locations showed no significant reduction in the vibrations. What if the couplings are not aligned? On both sides of the coupling, the vibration is high at the fan end and low at the motor end; therefore, this option is also ruled out.

Learned from Cat God: victory:

The main factors that increase the excitation force include imbalance, loose components, misalignment, shafting instability, and rubbing. The main factors contributing to the decrease and variation in dynamic stiffness include: loose bearing shells, loose connection bolts, loose foundation (including reduced tightening force), as well as changes in oil temperature and clearance