Machinery Lubrication

Reliable Plant | www . reliableplant.com Machinery Lubrication | www . machinerylubrication.com 2025 Annual 23 • Imbalance • Bearing failures • Mechanical looseness • Misalignment • Resonance and natural frequencies • Electrical motor faults • Bent shafts • Gearbox failures • Empty space or bubbles (cavitation) in pumps • Critical speeds Distributor and alignment and mainte- nance training provider VibrAlign uses the example of taking an industrial fan, removing a fan blade and starting it up. As expected, the fan vibrates due to an unbalanced fan wheel. is unbalanced force will occur one time per revolution of the fan. Another example would be a damaged bearing track causing a bearing roller to generate vibration each time it contacts the spall (similar to a pothole on a highway). If three bearing rollers hit the spall per revolution, you should see a vibration signal of three times the fan's running speed. VIBRATION ANALYSIS METHODOLOGY While accelerometers are still the most common tool used to collect vibration data, modern technology and improved sensor technology have allowed for non-contact, high-speed laser sensors that can detect issues accelerometers can't. is allows for a more accurate and more localized analysis, and opens up vibration analysis to more method- ology. Vibration analysis is generally broken down into four principles, and each principle gives you specific information on the working conditions and features of the vibrating parts. 1. Time domain: When a vibration signal is picked up from a transducer (device that converts a physical quantity into an elec- trical signal) and displayed on the screen of an oscilloscope, it's called a waveform. is signal is in the time domain. e time domain is amplitude plotted against time. While most machine vibration issues are detected using spectrum analysis, some types are more easily seen in waveform. 2. Frequency domain: When the wave- form discussed earlier is subjected to spectrum analysis, the end result is a picture of frequency vs. amplitude, known as a spectrum. The spectrum is in the frequency domain like the vibration is in the time domain. Most in-depth analysis of machinery vibration is done in the frequency domain or using spectrum analysis. 3. Joint domain: Because vibration signals vary with time, calculating more than one spectrum at once can be useful. To do this, a joint time technique called Gabor-Wigner- Wavelet can be utilized. is technique is used to calculate variations of the fast Fourier transform (discussed below), including short- time Fourier transform (STFT). 4. Modal Analysis: Modal analysis takes measured frequency response functions of a piece of machinery and puts them into a computer model. e computer model can be displayed with animations of all the different vibration modes. e model can be adjusted by either adding to or taking away things like mass or stiffness to see the effects. Outside of these four basic principles lie numerous forms of analysis, calculations and algorithms used to determine different aspects of vibration analysis. ese include: • Time Waveform: A time waveform is acceleration vs. time displayed as tables and plots. Time waveforms show a short time sample of raw vibration, revealing clues to the condition of machinery not always clear in the frequency spectrum. A method of employing time waveform vibration signals as a vibration analysis tool is by using FFT. • Fast Fourier Transform (FFT): FFT is defined as an algorithm used to calculate a spectrum from a time waveform. In other words, it's a calculation intended to break down a signal into all its frequencies. If you'll recall time domain and frequency domain, FFT converts a signal from the time domain into the frequency domain. Fast Fourier transform is most often used for

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