The air compressor is driven by the motor and is compressed in two stages. The unit consists of a frame, a rubber metal damper and a support platform. The support platform is made of angle iron air compressor unit structure and measuring point layout. Volume 26, Issue 2, June 2006 Vibration, test and diagnostic welding support Above the bottom tank of the ship. The measuring points 1, 2, and 3 measure the vertical vibration of the motor at the free end, the coupling, and the rear of the air compressor, that is, the vertical vibration of the damper; the measuring points 4, 5, and 6 are measured. It is the vertical and horizontal radial vibration of the bearing at the free end of the motor, the bearing at the end of the motor shaft, and the bearing at the input end of the air compressor.

The measurement vibration measurement of the signal requires the selection of the most sensitive diagnostic parameters for the fault. This parameter is called the “sensitivity factor”, which means that the characteristic parameters change greatly when the machine state changes slightly. Since the structure of the device varies widely and the types of faults are various, it is impossible to determine a sensitive factor for each fault signal. For most machines, the best diagnostic parameter is speed because it is the ideal parameter to reflect the vibration intensity. Many vibration diagnostic standards in the world use the speed effective value as the discriminant parameter. In the past, some industry standards in China used displacement (amplitude) as the diagnostic parameter. This article uses Entek data collector, which can directly collect vibration speed, displacement, acceleration and other signals, and process and analyze the signal.

Measurement Signal Analysis Signal acquisition is performed based on the placed measurement points. It is the data measured at 1, 2, and 3 points. From the measured data analysis, the vibration intensity of the unit is up to 117mm/s and the displacement is 2076.91m, which has serious troubles. The whole unit is strongly vibrated. Even if the rubber metal damper is damped, the vibration energy transmitted to the bottom of the cabin is still quite large. For example, the lower end of the coupling is nearly 1200m, causing local structural vibration of the hull. Figure 3 shows the vertical velocity spectrum of the horizontal radial and air compressor damper at the input end of the air compressor.

Air compressor horizontal radial velocity spectrum diagram Air compressor damper vertical velocity spectrum diagram From the measurement data and spectrogram analysis, the unit vibration is mainly concentrated at the fundamental frequency of 25Hz (motor speed is 1500r/min) with obvious Directionality. The vertical vibration is greater than the horizontal vibration. The vertical vibration intensity is up to 117mm/s and the displacement is 2076.91m. The horizontal radial vibration intensity is up to 70mm/s and the displacement is 1200m. After the vibration absorber is damped, the vibration transmitted to the platform remains. Very large, the maximum vibration intensity is 67.39mm/s, and the displacement is 1192.27m. From the spectrum analysis of the measurement and acquisition, the vibration is concentrated at the fundamental frequency, and the judgment may be caused by unbalance, looseness, etc. (after inspection of the unit and foundation and There are no rigid connections and contacts in other surrounding facilities, and there is no looseness in the unit and damper bolts). However, the vertical vibration before and after the vibration is quite large, which is 2 to 3 times of the horizontal radial direction. Therefore, the basic resonance can be initially determined.

The cause analysis is due to the fact that the vertical vibration before and after the vibration is quite large, and it is represented by a simple power frequency 25 Hz vibration. It can be considered that the fundamental resonance is generated, and the damper does not play a damping role. The basis mentioned here refers to the entire support system of the frame-damper-support platform below the air compressor unit. This support system and the machine generate the same-frequency vibration of 25 Hz, resulting in local structural vibration of the hull.

There are two reasons for causing the fundamental resonance, one is due to the rotor dynamic imbalance; the other is that the natural frequency of the support system is consistent with the frequency of the machine excitation force, resulting in resonance. From the analysis of the test results, the vertical vibration is much larger than the horizontal radial vibration, and the performance is 25 Hz. In the repair, the damper was replaced. Therefore, the first consideration is the resonance caused by the fundamental change causing the natural frequency change, but since there is a large horizontal radial vibration, the cause of the vibration caused by the imbalance cannot be excluded. For comprehensive analysis, we should first solve the problem of the foundation, that is, the support system, and change the natural frequency of the system.

The natural frequency of the computer group support system is related to the relevant data. The unit uses the E-300 rubber metal damper with a rated load of 300kgf, a natural frequency of 18Hz, a damping coefficient of 0.15~0.3, and an ultimate deformation of 12mm. Installed 6 shock absorbers, a total of 12, the unit weight 1.6t.

According to the calculation, the natural frequency of the system is f=1212KM1+M2+F1+F2=24.27Hz, where: K is the dynamic stiffness coefficient; M1 is the unit quality; M2 is the frame quality; F1 is the motor disturbance; F2 is the air compressor disturbance. force. It shows that the natural frequency of the unit support system is consistent with the unit excitation force frequency (25Hz).

Natural frequency measurement research The current test method for the natural frequency of large structures is the modal test method. The frequency response function is obtained by multi-point excitation and multi-point measurement, and the natural frequency and modal damping are identified by computer parameter fitting. And modal parameters such as vibration shape. This method requires the use of multiple exciters, which must be very energetic and require a variety of vibration testing instruments. Because the marine air compressor unit is driven by the motor, the speed cannot be adjusted, and the installation space is narrow and compact. This paper proposes to measure the fundamental natural frequency by the impact method.

Any vibration system has its own natural frequency. Under an initial disturbance force, the damped vibration is generated at the natural frequency. After testing the unit support system (rack, damper and supporting lower platform) by impact method, it is found that its natural frequency is between 25 and 31 Hz, which is close to the unit's natural frequency of 25 Hz. It is the measured time domain and frequency domain diagram respectively. From the data analysis of the impact measurement, the unit should belong to the same frequency vibration of the supporting foundation and the unit, that is, the fundamental resonance.

Through the above calculations and measurement analysis, it is determined that the natural frequency of the unit system is close to the unit power frequency, and there is a fundamental resonance. Therefore, first consider adding two dampers (one left and one right, mounted under the frame) at the coupling where the vibration is maximum before and after vibration reduction, so that the system is changed from the dynamic stiffness of the support system. Natural frequency. It is calculated to be 27.5 Hz, but the actual effect is not ideal and the vibration is still large.

The effect of damper selection by increasing the number of dampers to change the dynamic stiffness is not obvious, and then consider changing the static stiffness of the unit. Since the air compressor unit is filled with fuel oil tanks and the basic support static stiffness is increased, it is very troublesome to carry out welding construction. Therefore, in order to solve the problem fundamentally, the natural frequency of the unit support system must be changed to avoid the occurrence of resonance.

According to the design principle of vibration reduction, the ratio of the disturbance frequency f to the natural frequency f0 of the damping system (f/f0) should be greater than 2, and the actual application of the project is between 2.5 and 4.5. At present, f/f0=25/18=1.38<2, therefore, the selection of the currently used damper is not suitable, and the damper with lower natural frequency should be selected to increase the f/f0 value and enhance the vibration damping effect.

Finally, the HT-30 rubber metal damper was selected, and the natural frequency was 12 Hz. The actual measurement after installation proved that the basic resonance was effectively eliminated, and the vibration values ​​were significantly reduced to reach the allowable range. The measured data and spectrogram are as shown.

Conclusion (1) Although the fundamental resonance is a relatively complex vibration phenomenon, it is possible to find the root cause through rigorous and meticulous analysis, calculation and measurement. (2) According to the analysis and research of the monitoring data, the basic resonance of the unit is eliminated by replacing the damper, which ensures the safe and stable operation of the unit, and provides experience for solving the problem of severe vibration of the air compressor unit coexisting with the same type of ship. .

High speed/Precise Injection Molding Machine

Trolley System Parts,Clutch System Parts,Ups System Parts,Precision Lathe

Shen Zhou Machinery Co., Ltd. , http://www.szmouldmachine.com