Vibration Fault - Imbalance

Vibration Fault - Imbalance

1. Judgment basis:

When the center of gravity of the rotating part is inconsistent with the center of rotation, that is, the mass is eccentric, an imbalance occurs. The unbalanced rotor generates centrifugal force, which damages the bearing and reduces the service life of the bearing. Only a few millimeters of displacement of the center of gravity will generate a very large driving force. Unbalance causes obvious frequency conversion vibration.

2. Unbalanced characteristics and spectrum phenomena:

The vibration cycle is the same as the working speed, and the main vibration energy is concentrated at twice the equipment speed;

Vibration intensity is very sensitive to changes in working speed;

Maximum radial amplitude;

Stable vibration amplitude and phase angle, good repeatability;

The phase angles of the vibrations differ by about 900 in the horizontal and vertical directions.

2. Analysis and confirmation of imbalance:

Spectrum double-speed amplitude is large, harmonics are small;

No other peak entrainment in significant amplitude;

Use high-resolution amplification or time-synchronous averaging to verify the exact characteristics of the dual speed;

There is no significant difference in the amplitude of one velocity frequency between the horizontal and vertical directions, unless there are asymmetrical steel properties in the structure;

The vibration intensity of axial frequency doubling is less than that of radial doubling

Each rotation cycle produces a symmetrical waveform with no roof cuts or top discontinuities;

In the phase analysis, the horizontal and vertical difference of the same bearing seat is about 90 degrees;

Causes and solutions:

The main factors that cause equipment to become unbalanced (correctable) are:

Incorrect machining tolerances and installation tolerances;

Manufacturing errors (eccentricity of rotating parts, etc.);

Inhomogeneous material (voids in castings, etc.);

Component defects (corrosion or wear of rotating parts, etc.);

There are thermal deformation or mechanical deformation, etc.;

bending of rotating parts;

Mass eccentricity caused by foreign body adhesion;

Other factors that cannot be corrected by dynamic balance:

Severe looseness of equipment (including large bearing clearance);

The device excites resonance near the operating speed;

Shaft fracture;

bearing damage;

Torque imbalance caused by wear of transmission components;

equipment misalignment;

Equipment installation tilt (such as equipment foundation settlement, equipment installation adjustment pad damage, etc.);

The factors causing poor dynamic balance are complex, so the real cause of abnormal vibration of the equipment must be carefully analyzed before dynamic balance. If the equipment has the above-mentioned uncorrectable reasons, these problems must be dealt with before dynamic balance, otherwise the dynamic balance correction will reach less than expected effect