Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1206285
By Roger Story, Owens Corning www . machinerylubrication.com | January - February 2020 | 9 denotes lubricant failure, either due to an absence of lubrication, excess lubricant or contamination. When the lubrication team is integrated with the vibration analysis team, these cases can be well-controlled. Other symptoms include an oil vortex or dry vortex. Symptoms of these defects are characterized in the frequency spectrum by 0.42 to 0.48 times the revolutions per minute (rpm). ey usually are found in sliding bearings with oil that operates under pres- sure at high speeds. When this occurs, the oil pushes the shaft into the bearing, accelerating its wear. is can be minimized or eliminated by changing the oil speed. Oil instability is very severe and can lead to bearing play. is instability sometimes happens when the oil whirl frequency coincides with the critical machine speed. is special condition of shaft resonance with the oil's turning frequency results in a more serious form of whirlwind, called oil whip. In this case, the vortex speed will keep up with the critical rotor speed and will not disappear even if the machine operates at higher speeds. is event is highly destructive. Rolling vibrations can also be caused by improper lubrication. is is easily noticeable in the spectrum, as the friction of the bearing with the shaft raises the carpet. is frictional force can excite other machine frequencies as well. Figures 1-2 illustrate this symptom, which is called carpet. Figure 3 shows an example of slight oil instability, which in this case is still within the acceptable values. is frequency is from a bearing within a power gener- ator. It can serve as a monitoring target, as it indicates the health of the machine. Oil Analysis Oil analysis is also widely used to diagnose the condition of equipment. is technique has produced considerable information and contributed greatly to asset reliability. It is very useful in monitoring the condition of reducers, compressors, turbines, pumps, transformers and hydraulic systems. When a machine is in operation, there is continual friction of its components due to particle generation. e particles generated by this friction typically are charged by the lubricant, which can be easily identi- fied through oil analysis. Just as vibration analysis has several tools that can be used according to the failure mode to be monitored, oil analysis has parameters that must be selected based on the machine's characteristics. It is critical to choose the appropriate analysis tests for identifying abnormal oil wear particles, customizing each test according to the different types of equipment. Figure 1. A bearing vibration spectrum before lubrication Figure 2. A bearing vibration spectrum after lubrication Figure 3. Oil instability frequency ML