Eccentric rotor:

The geometric centerline of the rotor shaft does not coincide with the center of the rotor. This causes the weight on one side of the rotation centerline to be greater than the weight on the other side, causing the shaft to oscillate in an irregular trajectory. This is an inherent instability problem, potential fault source or vibration source. Sometimes, although the effect of partial eccentricity can be "balanced" by dynamic balancing, there is still more oscillating motion. If the eccentricity of the rotor is large, it is even impossible to achieve good dynamic balance of the rotor. The increasing speed is now emphasized, so it is important to eliminate eccentricity.

1、 Vibration characteristics of eccentric wheel

The belt pulley is eccentric. The maximum vibration often occurs in the belt stretching direction, and the vibration frequency is twice that of the eccentric belt pulley. Eccentric pulley is one of the main causes of undesirable vibration in belt transmission. At present, the dynamic balance method is usually used to correct the vibration problem caused by the eccentric pulley.

2、 Vibration Characteristics of Eccentric Gears

The gear is eccentric, and the maximum vibration will occur in the central direction of the two gears, as well as 1 time the speed of the eccentric gear. Its vibration characteristic signal is similar to the imbalance of this kind of gear, but it is not unbalanced. If the eccentricity of the gear is large, a very high dynamic load will be generated on the gear teeth when the gear teeth are forced into and out of engagement with the mating teeth.

A phase analysis can be performed on a gear with a large 1X vibration to determine whether it is unbalanced or eccentric. Eccentric gears will not only generate 1X large vibration, but also generate high amplitude gear meshing frequency and its harmonics. The sideband frequency is higher than the normal amplitude on both sides of the meshing frequency, and the sideband frequency is twice that of the eccentric gear. Frequency. Sometimes these sideband frequencies will be 2 times the speed frequency of the eccentric gear. These sidebands will modulate the magnitude of the gear meshing frequency itself.

3、 Vibration characteristics of eccentric motor rotor

The eccentric motor rotor generates a rotating air gap between the rotor and the stator (note the difference with the eccentric stator), which generates vibration between 2X power frequency (100Hz) and 100Hz and the nearest rotating resonance. For 2-pole motors, the resulting beat frequency vibration will produce a beat between 2X speed frequency and 2X power frequency, and for 1480 rpm motors, it will produce a beat between 4X speed frequency and 2X power frequency. Pole passing frequency (FP) sidebands are generated on both sides of 2X power frequency.

Finally, the eccentric motor rotor motion itself will cause the magnetic field vibration between the stator pole and the eccentric rotor, so there is 1X rotation frequency vibration between the rotor and the stator.

4、 Eccentric vibration characteristics of pump impeller

The eccentric pump impeller will cause unequal hydraulic interference between the rotating impeller and the fixed diffuser blade. This will not only produce large vibration of pump speed, but also produce blade passing frequency and its harmonic frequency due to the "hydraulic imbalance" generated by eccentric impeller.

5. Phase characteristics of eccentric rotors

The eccentric rotor may cause the vibration in the radial direction to be significantly greater than that in other radial directions (therefore, the impact bearing may sometimes cause looseness).

Phase analysis determines whether 1X vibration is caused by eccentric torque or other 1X vibration sources (such as imbalance).

The phase difference between the H and V directions is approximately 0 or 180 degrees. The force generated by eccentricity is very directional. Unlike the situation where unbalanced faults dominate, the phase difference between the horizontal and vertical directions is 90 degrees.