Rotor dynamic balancing knowledge sharing

Rotor dynamic balancing knowledge sharing

Knowledge point: rotor dynamic balancing

Accident overview

A compressor in a petrochemical company was recently sent to our company for repair due to the bending of the male rotor journal, which seriously affected the operation. After discussion, the equipment needed to replace a pair of rotors. Before replacing the new rotors, our company conducted a rotor dynamic balance test. After the dynamic balance test, it was found that the female rotor weighed 1000g and the male rotor weighed 2000g. Regarding the unbalance amount, the quality engineer analyzed that the metal bonded on the end face has an impact on the dynamic balance. In order to prevent the vibration of the equipment and the friction of the parts during operation, our company adopted the weight removal method to process the male and female rotors with one cut: the male rotor has a smooth end face, thus reaching the standard and meeting the assembly requirements.

After this case, our company summarized the possible reasons for rotor imbalance.

1. Processing and manufacturing reasons:

The rotor manufacturing process produces uneven wall thickness and uneven material density, such as blisters and pores;

During machining, the journal is eccentric and the end face axis is not vertical, such as the journal is eccentric, the end face is not perpendicular to the axis, etc.;

Uneven metallographic structure occurs during heat treatment;

2. Reasons for assembly:

The assembly quality error causes the center of gravity of the rotor to not coincide with the center line of rotation;

The coupling assembled to the rotor is misaligned with the rotation centerline;

3. Operational reasons:

Rotor bend;

The balance state of the rotor is damaged, such as parts defects, breakage, etc.;

Parts on the rotor are loose;

Precipitation of solid impurities on the impeller, etc.;

So what is the purpose and accuracy level of dynamic balancing?

Purpose:

Due to factors such as uneven material, process errors, uneven deformation of the rotor blades, uneven wear or local block loss, there is always an imbalance on the rotor. The unbalanced rotor causes rotor vibration, accelerates the wear of bearings, shaft seals and other components, and reduces the service life and efficiency of the equipment. For this reason, the rotor needs to be dynamically balanced during the maintenance process.

After the magnitude or phase of the rotor imbalance is measured, there are generally two correction methods: de-weighting method and weighting method. The weight removal method is to remove the heavy side by drilling, grinding, chiseling, milling andLaser perforation and other methods remove part of the metal; the weighting method is to add part of the metal to the lighter side using methods such as screw connection, riveting, welding and metal spraying.

Accuracy level:

Taking into account the advancement of technology and economic rationality, the International Organization for Standardization (ISO) formulated the world-recognized ISO1940 balance level in 1940. It divided the rotor balance level into 11 levels, with 2.5-fold increments between each level. The balancing machine ranges from G0.4, which has the highest requirements, to G4000, which has the lowest requirements. The unit is grams x millimeters/kg (gmm/kg), which represents the eccentric distance of the unbalance to the rotor axis. Our company adopts the measurement standard of balance accuracy G2.5 to ensure the smooth operation of the equipment.

Based on this case, our company’s experience is shared :

1. Before dynamically balancing the rotor, it is necessary to check whether there is contact friction on the end face.

2. If there is friction or metal adhesion, you need to consider polishing it first.

3. The rotor surface also needs to be polished first

4. Before dynamic balancing, the rotor should be in the default qualified state