A balancing machine is a machine for measuring the magnitude and position of the unbalance of a rotating object (rotor).
When any rotor rotates around its axis, the centrifugal force is generated due to the uneven mass distribution relative to the axis. This kind of unbalanced centrifugal force will cause vibration on the rotor bearing, generate noise and accelerate bearing wear, which will seriously affect the performance and service life of the product. In the manufacturing process, the rotating parts such as motor rotor, machine tool spindle, crankshaft of internal combustion engine, turbine rotor, gyro rotor, clock and pendulum wheel need to be balanced to operate smoothly and normally.
The mass distribution of the rotor relative to the axis can be improved by correcting the unbalance of the rotor according to the data measured by the balancing machine, so that the vibration or the vibration force acting on the bearing can be reduced to the allowable range. Therefore, balancing machine is an essential equipment to reduce vibration, improve performance and improve quality.
Generally, the balance of the rotor includes two steps: the measurement and correction of the unbalance. The balancing machine is mainly used for the measurement of the unbalance, while the correction of the unbalance is often done by means of drilling machine, milling machine, spot welder and other auxiliary equipment, or by hand. Some balancing machines have made the correction device a part of the balancing machine.
Gravity balancing machine and centrifugal force balancing machine are two kinds of typical balancing machines. Gravity balancing machine is generally called static balancing machine. It depends on the gravity action of the rotor itself to measure the static unbalance.
As shown in the figure, if the rotor placed on two horizontal guide rails has unbalance, its gravity moment to the axis makes the rotor roll on the guide rail until the unbalance is at the lowest position.
The balanced rotor is placed on the support supported by hydrostatic bearing, and a reflector is embedded under the support. When there is no unbalance in the rotor, the light beam emitted by the light source is reflected by the mirror and projected on the polar origin of the unbalance indicator. If there is unbalance in the rotor, the support of the rotor will tilt under the action of the weight moment of the unbalance, and the reflector under the support will also tilt and deflect the reflected beam, so that the light point on the polar coordinate indicator will leave the origin. According to the coordinate position of the deflection of this light point, the magnitude and position of the unbalance can be obtained.
Gravity balancing machine is only suitable for some disc-shaped parts with low balancing requirements. For rotors with high balance requirements, centrifugal single-sided or double-sided balancing machine is generally used.
The centrifugal balancing machine measures the unbalance according to the bearing vibration caused by the rotor unbalance or the vibration force acting on the support when the rotor rotates. It can be divided into single side balancing machine and double side balancing machine according to the different number of correction planes. The single-sided balancing machine can only measure the imbalance (static imbalance) on one plane. Although it is measured when the rotor rotates, it still belongs to the static balancing machine. Double sided balancing machine can measure dynamic unbalance, static unbalance and even unbalance, which is generally called dynamic balancing machine.
The centrifugal force balancing machine can be divided into soft bearing balancing machine and hard bearing balancing machine according to different bearing characteristics. Balancing speed higher than the natural frequency of rotor support system is called soft support balancing machine. The support stiffness of the balancing machine is small, and the signal detected by the sensor is proportional to the vibration displacement of the support. The balance speed is lower than the natural frequency of the rotor support system, which is called the hard support balancing machine. The support stiffness of the balancing machine is large, and the signal detected by the sensor is proportional to the vibration force of the support.
The main performance of the balancing machine is represented by two comprehensive indexes, i.e. the minimum achievable residual unbalance and the unbalance reduction rate. The former is the minimum value of the remaining unbalance that the balance function makes the rotor reach, which is the index to measure the maximum balance capacity of the balance machine; the latter is the ratio of the reduced unbalance and the initial unbalance after one correction, which is the index to measure the balance efficiency, generally expressed by percentage.
In modern machinery, because of the wide application of flexible rotor, people have developed a flexible rotor balancing machine. This kind of balancing machine must be stepless speed regulation within the working speed range of the rotor; in addition to measuring the vibration or vibration force of the support, it can also measure the deflection of the rotor. Flexible rotor balancing machine is sometimes installed in the vacuum protection room to fit the balance of the steam turbine and other rotors. It is equipped with a large number of auxiliary equipment, such as vacuum pumping system, lubrication system, lubricating oil degassing system and computer system for data processing.
According to the needs of mass production, the automatic balancing machine and automatic balancing line that can automatically complete balance measurement and balance correction for specific rotors have been equipped in a large number of modern industrial departments such as automobile manufacturing and motor manufacturing.