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Mechanical vibration analysis and its elimination method

Wuxi JN Fan Co.,Ltd | Updated: Jul 23, 2018
Source:
No.

Cause

Characteristic

Factor analysis of vibration

Elimination method

1

Rotor static and dynamic unbalance

The same vibration is generated between the fan and the motor , and the vibration frequency is in accordance with the rotating speed .

Shaft and sealing ring strong friction, produce local high heat, so that shaft bending.

Blade mass is asymmetric, or one part of the blade is corroded or badly worn with uneven attachments, such as rust, ash, or tar.

The balance block is not in the right position, or the position is moving, or the balance has not been found after repair

The fan operates under unstable conditions (i.e. flying zone), or the load changes dramatically.

Air intake from both sides of the double suction fan varies (due to blockage in the pipeline or improper adjustment of the inlet baffles on both sides)

New shafts should be replaced and sealing rings should be repaired at the same time.

Replace bad blades, or replace new impellers and find balance.

To clean or wipe off appendages on a leaf. Retake the balance and fix the balance block firmly.

Open gate valve or bypass valve for condition regulation.

Clean the intake duct dust and adjust the baffle so that the negative pressure of the air intake on both sides is equal

2

Shaft installation

Vibration is uncertain, light when idling, high at full load (can be detected by reducing rotational speed)

When the shaft is not installed properly, the center of the fan shaft and the motor shaft is not positive, and the foundation is down.

The belt wheel is not properly mounted and the two-belt axle is out of balance.

The speed reducer shaft, the fan shaft and motor shaft in the timing, did not take into account the displacement compensation, or considered but did not meet the requirements

Make adjustments and re - alignment .

Make adjustments and re - alignment .

Adjust and set aside an appropriate allowance for displacement compensation.

3

Rotor fixed part slack, or active part clearance is too large

Local vibration occurs mainly in the moving part of the bearing box. The vibration of the body is not obvious and has nothing to do with the rotational speed.

The wear of the bushing and the journal causes the oil gap to be too large, and the tight force between the bush and the bearing box is too small or loosened with the clearance.

Rotor impeller, coupling or belt wheel loosening with shaft

Coupling bolt loosening, rolling bearing fixed round nut loose.

Weld the alloy lining, adjust the gasket, or scrape the bearing box to repair the shaft and impeller, and rematch the keys to tighten the nut.

4

The stiffness of a foundation or seat is not strong enough or firm

The resonance phenomenon in the production of adjacent rooms, the overall vibration of the motor and the fan, and the same in all kinds of load situations

The grouting of the machine room foundation is bad, the anchor nut is loose, the gasket is loose, the connection of the machine seat is not strong, and the nut is loose.

The rigidity of the foundation or seat is not enough to cause the rotor unbalance to cause strong resonance.

The pipeline is not left to expand, and the pipeline connected with the fan is not supported or installed or fixed.

After ascertaining the cause, apply appropriate repair and reinforcement, tighten nuts, fill gaps for adjustment and repair, and install support devices.

5

Friction phenomenon inside fan

The vibration is irregular and concentrated in a certain part. The noise is consistent with the rotational speed, and the metal touch sound inside the fan can be heard when starting and stopping.

Impeller skew against the inner wall of the housing, or the shell stiffness is not enough, left and right sloshing.

The impeller tilts against the inlet ring.

The thrust axis is skewed, unbalanced or worn.

The sealing ring and the seal teeth collide.

Repair impeller and thrust liner.

Repair impeller and inlet ring.

Repair thrust bushing.

Replace the seal ring and adjust the seal ring and teeth clearance.


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