Any with antifriction bearings and gears of the machine […]
Any with antifriction bearings and gears of the machine will show the high-frequency vibration to some extent. Rotary screw air compressors is an example of such machines. Single-stage rotary screw compressor designed with two rotors, there are four to six lobes on each rotor. Rotor rotation in the opposite direction, lobe almost touch, forming a "screw", the compressed air. The compressor is usually driven by a motor directly connected to the male rotor, the motor has a coupling gear, the drive gear and thus the female rotor. Timing gear of the rotor never contact manner.
In view of such a mechanical arrangement, or may be several different dither occurs:
• rotors mesh frequency - equal to the number of lobes of the outer rotor is multiplied by the speed of the motor. Accordingly, the frequency will be synchronized with the running speed of the motor.
• gear mesh frequency - multiplied by the gear motor is equal to the operating speed. In the case of multi-stage rotary screw compressor, there will be more than one set of gear mesh frequency. This vibration will be synchronized with the running speed of the motor.
• Bearing frequency - depending on the particular bearings used in the machine. Typically, bearing frequency is not synchronized with the running speed of the motor. Internal and external frequency race will be the most common frequency.
• other frequencies - the machine resonance may be due to or caused by the compressed air flow.
Standard warning method typically natural vibration of the machine, such as a rotary screw air compressor, even in normal operation, can not function well. The overall vibration level is sometimes insensitive to small changes in the level of vibration caused by the deterioration of the bearings. This is due to the large number of natural vibrations occurring in the rotary screw compressor. Every time a high-frequency measurement trigger normally bearing inspection tools or techniques, which in turn is due to vibration caused by the gear and the rotor. This can result in "nuisance" alarms.
In view of these problems when using standard alarm technology, usually on the spectral data rotating screw air compressors. Typically the spectral data is compared with the measured value and the reference value before measurement. Considering the number of measurement points and many different frequencies that may occur, which can be a time-consuming and daunting task. One technique to speed up this process is synchronous and asynchronous vibration percentage comparison between two measurements. Many software program calculates the vibration data for each spectrum. Deterioration of the bearing is generally non-synchronous vibration. In other words, it is not an integral multiple or a harmonic of the operating speed of the machine.