At present, it is a complicated work to determine the allowable unbalance of the rotor, because in the mass production of the rotor, the necessity, possibility and cost of the process must be considered at the same time.Therefore, there is no authoritative theoretical calculation method to determine the allowable unbalance of machinery in the world, and only the most effective method to determine the allowable unbalance of rotor is to make statistics and analysis through durability experiment.Therefore, the state selects the accuracy level according to relevant standards and the technological capacity of the enterprise, and determines the balance quality level G value of the rotor.

The balancing quality grade G of the rotor is divided into 11 grades in gb9239-88, including G0.4, G1, G2.5, G6.3, G16, G40, G100, G250, G630, G1600 and G4000. The corresponding grade standard is selected according to the application type of rotor drive.

Table 1 classification criteria table below 

Note: general general motor rotor G value is 6.3 class

Rotor balance quality grade G and the unbalance of the rotor е maximum operating speed and rotor noise related omega, its formula is:G = е * / 1000 omega

(1) if n is the highest operating speed of the rotor, in r/min, =2 n/60. First, according to the actual application of the design of the motor to choose the balance level, then according to =2 n/60 to calculate the highest operating speed of the rotor, and finally according to the corresponding known parameters input into the formula (1).The deformation formula for: е = G * 1000 / omega

(2) however, at present, the motors of manufacturing enterprises are all batch products, and due to the influence of components and other factors, the rotational speed may fluctuate within a certain range. Therefore, manufacturing factories generally refer to table (2) to confirm the application range of unbalance.