Analysis of the main causes of fan motor vibration failure and some effective treatment methods

Fan vibration is a common phenomenon during operation, and as long as it is within the vibration control range, it will not cause significant impact. However, excessive fan vibration can lead to damage to bearing housings or motor bearings, loosening of motor foundation bolts, damage to the fan casing, blades, and air ducts, and motor burnout and overheating, reducing fan performance and even causing it to become completely inoperable. In severe cases, vibration may cause accidents, endangering personal health and the working environment. Our company has experienced incidents where excessive fan vibration caused friction between the impeller and the casing.

I. Vibration of Fan Bearing Housing

A common fault in fans is vibration of the bearing housing, which can be initially diagnosed through external testing. The causes of bearing housing vibration are traceable; it's a slow process where the vibration gradually increases in intensity. Our company uses vibration meters to regularly measure the vibration values of fan bearing housings. By comparing these values, we can quickly make accurate analyses and take appropriate actions, proactively carrying out planned maintenance on fans that may experience malfunctions, thus ensuring the safe and stable operation of the fans.

1. Vibration caused by rotor mass imbalance.

Most of the vibrations in the fan bearing housings of the company are caused by the mass imbalance of the rotor system. The main causes of rotor mass imbalance are: uneven wear or corrosion of the impeller; uneven dust or deposits on the impeller surface; failure to perform dynamic balancing after impeller repair welding; loose parts on the impeller or loose connecting parts, etc.

The characteristics of vibration caused by rotor imbalance, as measured by the vibration meter, are: (1) the vibration value is larger in the radial direction and smaller in the axial direction; (2) the vibration value increases with the increase of rotational speed.

We have formulated a series of preventive measures for vibration caused by rotor imbalance. Since the induced draft fan used by the company is mainly used to promptly extract the asphalt fumes generated in the roasting furnace chamber out of the flue, the fan impeller is prone to corrosion, and dust easily adheres to the surface and other cavities, resulting in uneven dust or deposits, causing the fan rotor to be unbalanced and causing fan vibration.

Therefore, the company requires team members to measure and record the vibration of the fans daily. Technicians then statistically analyze the data, using changes in the amplitude curve to determine if the fan impeller needs maintenance, if accumulated dust and tar on the blades needs cleaning, or if dynamic balancing correction is required.

The changes in the vibration curve of the fan bearing housing are visually observed. When significant changes occur, appropriate measures can be taken to prevent system downtime caused by fan vibration failures. Based on years of production experience, the company performs impeller maintenance and cleaning on the induced draft fans quarterly, ensuring stable and reliable fan vibration, reducing impeller wear, and protecting the dynamic balance of the fan rotor.

2. Vibration caused by abnormal rolling bearings

(1) Improper bearing installation

When there are problems with the bearing assembly, such as improper bearing installation, using brute force to install, the bearing will be deformed; the installation is tilted, there is a deviation in the installation, or it is not installed in place, resulting in the bearing clearance being too small. The inner and outer rings are not in the same rotation center, causing eccentricity.

Its vibration characteristics are: the vibration value is larger in the axial direction and smaller in the radial direction; the vibration frequency is the same as the rotation frequency.

(2) Damage to the bearing surface

If the purchased bearing is of poor quality and the clearance is unreasonable; long-term overload operation, fatigue damage caused by exceeding the service life; inadequate lubrication, incorrect lubrication method or wrong lubricating oil selection; foreign matter entering and causing contamination, etc. It will cause damage to the bearing surface, wear and deformation of the balls, metal peeling off the raceway surface, severe wear of the raceway of the seat ring, and breakage of the cage, reducing the running accuracy of the shaft and causing the bearing housing to vibrate.

The vibration characteristics are: the amplitude may be large in both the radial and axial directions; the vibration stability is poor and is unrelated to the load; the bearing housing will show heat generation at the damaged bearing.

3. Vibration caused by insufficient rigidity of the bearing housing foundation

: Inadequate secondary grouting quality of the bearing housing foundation, such as shifting foundation shims, excessively high foundation shims, oil leakage in the bearing housing, insufficient concrete strength, and loose anchor bolts, nuts, and washers, can all cause severe resonance. In severe cases, anchor bolts may break, or the bolt holes in the bearing housing may fracture, rendering the bearing housing unusable.

Characteristics of this type of vibration: high vibration values in the bearing housing at the problematic anchor bolts, large radial amplitude, and vibration frequency generally an odd multiple of the rotational speed.

Handling this type of fault: Strengthen daily inspections and regularly tighten the anchor bolts and nuts of the bearing housing and motor.

4. Vibration caused by abnormal couplings:

Misalignment between the induced draft fan and motor shafts, or the lack of a pre-existing clearance between the induced draft fan and motor coupling, can also cause severe vibration of the bearing housing and motor. Its vibration characteristics are:

(1) The vibration is unstable. With the change of load, the amplitude is small when idling and large when fully loaded. The greater the shaft deviation, the greater the vibration;

(2) There is also obvious vibration on the output shaft side of the motor. When the fan and motor coupling are disconnected and the motor is run alone, the vibration disappears.

The method to deal with this type of vibration is to re-align the coupling center and make adjustments to reduce the misalignment of the fan and motor shafts; and to reasonably reserve the gap between the fan and motor coupling.

II. Vibration caused by the critical

speed of the rotor When the fan starts and accelerates, it will suddenly produce violent vibration when it reaches a certain speed. After passing this speed, the vibration will gradually decrease when the speed is increased. The same phenomenon will occur during the shutdown process. The speed corresponding to the natural frequency of the fan is called the critical speed of the fan. The greater the mass of the shaft and the smaller the stiffness (the shaft is slender), the lower its critical speed, and vice versa. When the working speed of the fan is higher than the critical speed, vibration is likely to occur.

Its vibration characteristics are: the relative vibration at the resonance point of the object is large; the vibration frequency is the same as or close to the rotation frequency.

III. Vibration of the Exhaust Fan Caused by Duct System Vibration:

Vibration caused by pressure pulsations and disturbances in the airflow within the duct system mainly includes vibration caused by vortex pulsations in the bellows, vibration caused by local vortices in the duct, vibration caused by insufficient rigidity of the fan casing and duct wall, and rotational stall. Its vibration characteristics are: pressure waves are often irregular, amplitude increases with flow rate, vibration is irregular, and amplitude increases with load. Addressing this type of vibration mainly involves tightening screws, reinforcing the volute and duct, or reinforcing the base.

Disclaimer: We respect originality and value sharing. We appreciate the hard work and creation of every author. The copyright of this article belongs to the author and represents only the author's views, not those of this website. It is for learning and reference purposes only. This article is not for commercial use and is solely for learning and exchange. If any content, images, audio, or video in this article infringes on the prior intellectual property rights of a third party, please contact us promptly for removal.