Why Is The Fan Rotor Unbalanced? How To Solve It?

Next, Xiao Yang will introduce the reasons, characteristics and treatment methods of fan rotor imbalance.

01 Causes of unbalanced fan rotor

Fan rotor imbalance is the most common fault in fan operation. Therefore, maintaining the balance of the fan rotor is an important measure to eliminate the mechanical vibration of the fan rotor and ensure the normal operation of the fan.

The main reasons for the imbalance of rotor mass are:

1. Local corrosion and wear of impeller blades during operation;

2. Condensation occurs due to scaling on the blade surface;

3. The airfoil hollow blades of the fan are partially worn through and enter the fly ash;

4. The quality and setting position of the balance block on the impeller are not correct;

5. After the overhaul, the dynamic and static balance is not carried out;

6. Insufficient strength of the impeller causes cracking or deformation of the impeller, loose parts on the impeller or loose connections.

These factors can cause the rotor to vibrate violently.

02 Causes of unbalanced fan impeller

The cause of the imbalance of the fan impeller is the wear of the impeller. This is because a small amount of large particles and many tiny dust particles pass through the induced draft fan together with the high-temperature and high-speed flue gas, so that the impeller is continuously scoured. Blade-like wear is formed at the blade outlet. Since this wear is irregular, the impeller is unbalanced.

In addition, the surface of the impeller works at a higher temperature, which is easy to oxidize and generate a thick oxide scale. The bonding force between these oxide scales and the surface of the impeller is not uniform, and some oxide scales will automatically fall off under the action of vibration or centrifugal force, which is also one of the reasons for the imbalance of the impeller.

Because the impeller of the powder exhaust fan is washed by the coal powder, it is also easy to cause the imbalance of the impeller.

03 Characteristics of rotor unbalanced vibration

Rotor unbalanced vibration characteristics Through vibration spectrum analysis, the amplitude of various vibration frequencies and the main frequency components that cause vibration can be identified. In most cases, the cause of vibration and fault type can be inferred.

Characteristics of vibration caused by rotor unbalance:

1. The vibration stability is relatively good, and it is not sensitive to load changes;

2. The amplitude does not change with the increase or decrease of the load, but it is related to the speed of rotation, and increases with the increase of the rotation speed, and the vibration frequency is equal to the frequency of the rotation speed;

3. The vibration value is the largest in the horizontal direction, while the axial direction is small, and the vibration at the bearing bearing of the bearing seat is greater than that at the thrust shaft;

4. When the interior of the hollow blade is stained with dust or the individual parts are not welded and displaced, the measured phase angle value is unstable, and the vibration frequency is 30% to 50% of the working speed, which is the method to distinguish it from other similar vibration faults.

If there is a large fundamental frequency vibration at the working speed, and the insufficient dynamic rigidity of the bearing seat, the non-concentricity of the rotor connected by the coupling, or the excessive straightness deviation, and the non-circular shaft diameter have been eliminated, then it is possible to A diagnosis is made that the cause of excessive vibration at operating speed is rotor imbalance.

If you need to further determine the cause of the imbalance, you can also drill down to see if the vibration increases slowly or suddenly. Usually, it takes a period of time for the fan blades to condense and condense, so the vibration gradually increases with time. If the scale of the scale is large and some parts fall off, the vibration of the rotor will suddenly increase.

04 The treatment method of rotor unbalance

1. The impeller mass distribution is unbalanced due to the uneven ash deposition on the blades. Usually, it is only necessary to remove the ash deposition or condensation on the blades, and the impeller will re-balance, thereby reducing the vibration of the fan.

2. Because of the vibration caused by blade corrosion or wear, the treatment at this time is to remove impurities and repair the blade, but in severe cases, the blade or impeller must be replaced.

3. When the quality of the balance block on the impeller is not correct and the setting position causes vibration, it is necessary to adjust the static balance. The implementation method is to place a correction weight of equal weight at the unbalanced symmetrical position, so that the center of gravity of the rotor can be returned to the rotation axis.

4. In the rotating state, if the additional imbalance caused by the deflection of the rotor can be ignored, the rotor is called a rigid rotor; on the contrary, it is called a flexible rotor. The failure of the fan commonly used in the cement production line can be regarded as the unbalance problem of the rigid rotor on a single plane. The solution is to increase the weight on one plane, so that the vibration of the two bearings supporting the rotor can be satisfied. This is because the weighted plane is basically consistent with the unbalanced surface of the rotor, and the rotor can achieve the balance of force and force couple through the weighting of a single plane.

Whether the trial weight is appropriate is related to the success or failure of the rotor balance. The general performance of the inappropriate weight is too small, which will lead to the failure of the rotor balance. However, if the weight is too large, it may cause an accident. In order to ensure the safety of the fan and to balance the rotor smoothly, it is necessary to use an appropriate trial weight. Appropriate trial weight includes weight size and weighting direction to complete on-site balance adjustment.