Analysis of Vibration Caused by Abnormal Coupling and Failure of Low Speed ​​and High Speed ​​Shaft

　　XNUMX. Vibration caused by abnormal coupling

　　Because the shaft of the induced draft fan and the motor are not concentric, or there is no gap between the induced draft fan and the motor coupling, it will also cause severe vibration of the bearing seat and the motor.Its vibration characteristics are:

　　(1) The vibration is unstable. As the load changes, the amplitude is smaller when idling and larger when fully loaded. The greater the axis deviation, the greater the vibration;

　　(2) There is also obvious vibration on the motor output shaft side. Disconnect the induced draft fan and the motor coupling, the motor runs alone, and the vibration disappears.The method to deal with this kind of vibration: realign the center of the plum blossom coupling and adjust it to reduce the misalignment of the induced draft fan and the motor shaft; reasonably reserve the gap between the induced draft fan and the motor coupling.

　　For the assembly of rigid coupling, the radial displacement of the two shaft centers shall not be greater than 0.03mm, and the contact between the end faces of the two half couplings should be close.

　　When the fan reaches a certain speed during the start-up and speed-up process, the wind machine will suddenly vibrate severely. After passing this speed, the wind will continue to rise, and the vibration will gradually decrease. This will also occur during the shutdown process. One phenomenon, the speed corresponding to the natural frequency of the fan is called the critical speed of the fan.The greater the mass of the shaft, the smaller the rigidity (the shaft is slender), the lower the critical speed, and vice versa.When the working speed of the fan is higher than the critical speed, vibration is prone to occur.Its vibration characteristics are: the relative vibration at the resonance of the object is relatively large; the vibration frequency is the same or close to the rotation frequency.

　　The vibration caused by the pressure pulsation and turbulence of the air flow in the air duct system mainly includes the vibration caused by the vortex pulsation of the wind box, the vibration caused by the local vortex of the air duct, the insufficient rigidity of the fan casing and the air duct wall causes the vibration, and the rotation stalls.Its vibration characteristics are: the pressure wave is often irregular, the amplitude increases with the increase of the flow, the vibration is irregular, and the amplitude increases with the increase of the load.

　　Dealing with this kind of vibration is mainly to tighten screws, strengthen volutes and air ducts or strengthen the base.

　　The above faults are not common faults. According to statistics, 70% of the faults of rotating machinery are related to the unbalance of the rotor. Therefore, the main fault is the unbalance of the rotor, which needs to be solved by on-board balancing and on-site dynamic balancing.

　　The possible situations of the crane in the working process will be analyzed separately: First, when the hoisting mechanism is fully loaded with goods, because the coupling between the motor and the reducer falls off, the hoisting mechanism loses power and the goods are free from a higher point. When falling, the brakes are not working. In the model, the right brake wheel rotates at a high speed under the drive of the cargo. At this time, the inertial force generated by the brake wheel may make the high-speed shaft fail; second, the whole machine runs normally, but due to installation errors. The misalignment of the shaft or the motor shaft and the shaft of the reducer causes an accessory force to be generated at the left end of the high speed shaft of the reducer, and with the rotation of the shaft, the direction of this force is alternating. If it is used for a long time, it will cause fatigue Fracture, the fatigue failure analysis will not be analyzed here, and it will be studied from the combination of bending and torsion; third, the whole machine works normally, due to an emergency, the two high-speed axle brakes brake at the same time, which is added to the brake wheel. The torque is very large, and the high-speed shaft of the reducer may fail due to insufficient torsional strength; fourth, when the misalignment and two brakes are simultaneously braked, the high-speed shaft may also fail.

　　Second, low-speed and high-speed shaft failure analysis

　　　　Wind turbines usually have high practicability, but this is not because of their stable quality, but because of frequent maintenance.In fact, the working environment of the wind turbine is harsh, and the wind speed has high instability. The severe weather such as heavy rain, lightning, ice and snow severely tests the operation quality of the wind turbine.Under the action of alternating load, the wind turbine blades are prone to fatigue damage, and the tower system is easily damaged.In fact, all mechanical components are affected by damage. Most of the sub-systems of wind turbines in the wind turbine may fail during operation, including rotors and blades, switch control systems, gearboxes and bearings, yaw systems, and generators. , Power control system and brake pads, etc., coupled with the power conversion system of the wind turbine, its damage is more serious than other rotating machinery.However, the wind turbine is a relatively inaccessible structure because it is installed in a remote area, and the nacelle itself is tens of meters or even hundreds of meters above the ground, making it difficult to get to the nacelle.In addition, the maintenance and care of the wind turbines require additional cranes, elevators and other equipment, and even the way to enter the cabin through a helicopter, which incurs extra costs.

　　Wind turbines belong to rotating machinery. No matter how high the processing technology is, the shafts in the gearbox will have more or less problems such as imbalance, but as long as these imbalances are within the allowable range, they will not affect normal wind power. The operation of the unit has an impact.However, during the long-term operation of the wind turbine, these unbalances will gradually increase, causing faults and affecting the normal operation of the wind turbine.Wind turbine low-speed shafts and high-speed shafts often have typical faults such as shaft imbalance, misalignment, and bending in harsh working environments.

　　(1) Shaft imbalance

　　Unbalance is a typical failure of rotating machinery. It is mostly caused by the eccentricity of the shaft components or the failure of the components. According to statistics, about 70% of the failures are related to the imbalance of the shaft.The main cause of shaft imbalance is mostly the centrifugal torque caused by the eccentric mass and eccentricity, and the alternating force will cause vibration. When the shaft rotates for one revolution, the direction of the centrifugal force changes for a period. The frequency and speed of the unbalanced vibration are Consistent.The main vibration characteristics of the shaft unbalance fault are: 1) The time-domain waveform of vibration is similar to a sine wave; 2) The harmonic energy in the frequency spectrum is concentrated on the fundamental frequency, and smaller high-order harmonics appear, which is the so-called " "Fir tree shape"; 3) Below the critical speed, the amplitude increases with the increase of the speed. When the speed increases above the critical speed, the amplitude tends to a smaller stable value. When the speed is close to the critical speed, resonance will occur. The amplitude has a large peak. 4) The phase is relatively stable at the working speed; 5) The axis track of the rotor is generally embodied in the shape of an ellipse.

　　(2) Shaft misalignment

　　The shaft misalignment faults in the gearbox mainly occur in the drum-shaped gear couplings that connect the gearbox and other components. These faults are mostly caused by conditional restrictions during assembly or after long-term operation.Its vibration characteristic is that the measured gearbox vibration signal appears as a very low frequency vibration signal, its acceleration signal is generally not easy to measure, and the speed signal and displacement signal are generally more sensitive.The main faults of shaft misalignment can be summarized as follows: 1) The gear meshing frequency and its harmonics are used as the carrier frequency for meshing modulation, and the modulation frequency is 2 times the frequency component of the modulation frequency. The amplitude of is larger; 2) The meshing frequency of the gear and the amplitude of its harmonics are larger; 3) The vibration energy is increased to a certain degree; 4) The envelope energy is increased to a certain degree; 5) Misalignment The excitation force to the rotor caused by the fault increases with the increase of the speed, and it increases linearly.

　　(3) Shaft bending

　　When the shaft in the gearbox fails during operation, it is easy to cause the failure of the entire gearbox. When the shaft is bent, it will directly affect the normal operation of the shaft components such as gears and bearings.The main faults when the shaft is bent can be summarized as: 1) The number of modulation sidebands is the number of modulation sidebands when the gear shaft rotation frequency and its multiplication frequency are used as the modulation frequency, and the gear meshing frequency and its harmonics are used as the carrier frequency. If there are multiple pairs of gears meshing on the bending shaft, multiple pairs of meshing frequency modulation will appear; 2) The vibration energy is increased to a certain degree, especially the axial vibration energy is greatly increased; 3) The envelope energy is increased to a certain degree.