Rotor dynamic balance knowledge sharing

Knowledge point: Rotor dynamic balance

Accident overview

A petrochemical company has a compressor recently sent to our company for maintenance due to the bending of the male rotor journal. After discussion, the equipment needs to be replaced with a pair of rotors. Before replacing the new rotor, our company conducted a rotor dynamic balance test. After the dynamic balance test, it was found that there were 1000g of the female rotor and 2000g of the male rotor unbalanced. The quality engineer analyzed that the metal bonded to the end surface has an impact on the dynamic balance. In order to prevent the equipment from vibrating and the friction of parts during operation, our company adopted the deduplication method to process the male rotor one-cut operation: the male rotor is optically end surface, thus meeting the standards and meeting the assembly requirements.

Through this case, our company summarized the reasons why rotor imbalance may occur.

1. Reasons for processing and manufacturing:

During the production of the rotor, the wall thickness and uneven material density occur, such as sand holes and pores;

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

Inhomogeneity of metallographic structure occurs during heat treatment;

2. Assemble reason:

Assembly mass error causes the rotor's center of gravity to not coincide with the rotation center line;

The coupling is assembled on the rotor and the center line of the rotation;

3. Reasons for operation:

Rotor bending;

Rotor equilibrium state damage, such as part defects, breakage, etc.;

The parts on the rotor are loose;

Precipitation of solid impurities on impellers, etc.;

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

Purpose:

Due to factors such as uneven material, process error, uneven deformation of the rotor blades, uneven wear or partial block loss, there is always an imbalance on the rotor. The rotor imbalance causes the rotor to vibrate, accelerating the wear of bearings, shaft seals and other components, reducing the service life and efficiency of the equipment. Therefore, the rotor needs to be dynamic balance detection during the maintenance process.

When the magnitude or phase of the rotor imbalance is measured, there are generally two correction methods: deduplication method and amplification method. The weight removal method is to drill, grind, chisel, mill andLaser perforation and other methods remove part of metal; weighting method is to use screw connection, riveting, welding and spray metal on the light side, and add part of metal.

Precision level:

Taking into account the advanced 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 each level in increments of 2.5 times, and the balance machine ranged from the highest G0.4 to the lowest G4000. The units are grams x mm/kg (gmm/kg), representing the eccentric distance of imbalance to the rotor axis. Our company adopts the measurement standard of balance accuracy G2.5, which provides guarantee for the smooth operation of the equipment.

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

1. Before the rotor is activated and balanced, it is necessary to check whether there is contact friction on the end surface.

2. If there is friction or metal bonding, you need to consider first

3. The rotor surface part also needs to be polished first

4. The rotor should be in the default qualified state before dynamic balance.