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Balancing machine is a machine for measuring the unbalance and position of rotating objects (rotors).
When any rotor rotates around its axis, centrifugal force is generated due to uneven mass distribution relative to the axis. This unbalanced centrifugal force will cause vibration, noise and accelerated bearing wear, which will seriously affect the performance and life of products. Rotating parts such as motor rotor, machine tool spindle, internal combustion engine crankshaft, steam turbine rotor, gyro rotor, clock balance wheel, etc. all need to be balanced in the manufacturing process in order to run smoothly and normally.
Correcting the unbalance of the rotor according to the data measured by the balancing machine can improve the mass distribution of the rotor relative to the axis and reduce the vibration generated when the rotor rotates or the vibration force acting on the bearing to the allowable range. Therefore, the balancing machine is a necessary equipment to reduce vibration, improve performance and improve quality.
Generally, the balance of rotor includes two steps: measurement and correction of unbalance. Balancing machine is mainly used to measure unbalance, and the correction of unbalance is often done by drilling machine, milling machine, spot welding machine and other auxiliary equipment, or by manual methods. Some balancing machines use the calibration device as part of the balancing machine.
Gravity balancing machine and centrifugal balancing machine are two typical types of balancing machines. Gravity balancing machine is generally called static balancing machine. It relies on the gravity of the rotor itself to measure the static imbalance.
As shown in the figure on the right, if the rotor placed on two horizontal guide rails is unbalanced, its heavy torque on the shaft makes the rotor roll on the guide rails until the imbalance is at the lowest position.
The balanced rotor is placed on a pedestal supported by a hydrostatic bearing, and a reflector is embedded under the pedestal. When the rotor is not unbalanced, the light beam emitted by the light source is reflected by this mirror and projected to the polar coordinate origin of the imbalance indicator. If the rotor is unbalanced, under the action of unbalanced heavy torque, the rotor bracket will tilt, and the mirror under the bracket will also tilt and deflect the reflected light beam, so that the spot projected by the light beam on the polar coordinate indicator will leave the origin. According to the coordinate position of this spot deflection, the magnitude and position of the unbalance can be obtained.
Gravity balancing machine is only suitable for some disc parts with low balance requirements. For rotors with high balance requirements, centrifugal single-sided or double-sided balancing machines are generally used.
Centrifugal balancing machine measures unbalance according to bearing vibration caused by rotor unbalance or vibration force acting on bearing when rotor rotates. According to the different number of calibration planes, it can be divided into single-sided balancing machine and double-sided balancing machine. One-sided balancing machine can only measure the imbalance (static imbalance) on one plane. Although it is measured when the rotor rotates, it is still a static balance machine. Double-sided balancing machine can measure dynamic imbalance, static imbalance or even imbalance respectively, which is generally called dynamic balancing machine.
Centrifugal balancing machines can be divided into soft supporting balancing machines and hard supporting balancing machines according to different supporting characteristics. The balancing speed is higher than the natural frequency of the rotor-support system, which is called the soft-support balancing machine. The support stiffness of this balancing machine is small, and the signal detected by the sensor is directly proportional to the vibration displacement of the support. The balancing speed is lower than the natural frequency of the rotor-support system, which is called hard support balancing machine. The support stiffness of this balancing machine is large, and the signal detected by the sensor is directly proportional to the vibration force of the support.
The main performance of the balancing machine is expressed by two comprehensive indexes: the minimum achievable residual unbalance and the unbalance reduction rate. The former is the minimum value of the residual unbalance that the balancing machine can make the rotor reach, and it is an index to measure the highest balancing ability of the balancing machine; The latter is the ratio of the reduced imbalance after correction to the initial imbalance, and it is an index to measure the balance efficiency, which is generally expressed as a percentage.
In modern machinery, due to the wide application of flexible rotors, people have developed flexible rotor balancing machines. This kind of balancing machine must carry out stepless speed regulation within the working speed range of the rotor; In addition to measuring the vibration or vibration force of the support, the deflection of the rotor can also be measured. Flexible rotor balancing machine is sometimes installed in vacuum protection room, which is suitable for balancing rotors such as steam turbines. Equipped with vacuum pump system, lubrication system, lubricating oil degassing system, data processing computer system and other huge auxiliary equipment.
According to the needs of mass production, automobile manufacturing, motor manufacturing and other industrial departments have been equipped with automatic balancing machines and automatic balancing lines since modern times, which can automatically complete the balance measurement and balance correction of specific rotors.