rolling elements bearings defect frequency and harmonics
rolling elements bearings defect frequency and harmonics
(OP)
i have conducected a few experiments to detect rolling element bearings fault using envelope analysis. The envelope sepctrums showed that the fundamental bearing defect frequency and its harmonics are in exponentially decaying in their amplitude. Is there anyone know why this phenomenan happen. If possible pls email me leo9421@hotmail.com. Thanks.





RE: rolling elements bearings defect frequency and harmonics
Dave G.
www.reliabilitydirect.com
RE: rolling elements bearings defect frequency and harmonics
Actually in my experiments, i purposely created an artificial fault on the bearing raceways and rolling element for both ball and roller bearings. The results are presented using an envelope spectrums. The spectrums showed that fundamental spike and its harmonics are detected at their defect frequency location. The similar results are obtained when i repeat the experiments for a few times.
My quention is why the fundamental spike and its harmonics magnitude decayed over frequency?Is this due to the total energy spread or the calculation involved in the FFT algorithm? Thanks.
RE: rolling elements bearings defect frequency and harmonics
http://www.geocities.com/pschimpf/impacts/electricpete.htm
For that case the spectrum can be identified as the product of three components:
#1 - The natural frequency of the bearing components
#2 - The fourier transform of a single impact
#3 - A frequency pulse train which "samples" the frequency waveform at points f=k*f0, leaving only harmonics k*f0.
How would this be modified in looking at the demod spectrum? I believe that the demod spectrum would ignore/discard effect #1 (natural frequency of bearing), since the ringing at bearing frequency gets smoothed out by the demod/envelope. That leaves the primary factor that explains the relative shape of the demod harmonics as #2 - the fourier transform of a single impact.
If you have perhaps something between outer ring and the housing, then you will get a very smooth low frequency impact as a ball rolls over this location... much lower harmonics.
If you have a sharp defect on the inner race which causes a high-rise time high frequency impact, then your higher harmonics will show up higher.
There was a related article by Jan Krepela in one of the predictive maintenance magazines last June which gave several examples of bearing defects and the associated shape of the impact time waveform, and the associated spectra. I think his article answers your question exactly with good examples. I personally think he neglected to consider the effect of bearing ringing on the shape of the harmonics in the normal spectrum, but that's irrelevant to your question on demond spectrum.
Let me know if you want an exact article citation... I have it lieing around somewhere.
RE: rolling elements bearings defect frequency and harmonics
I will very glad if you can send me the article that u mentioned. Thanks again.
RE: rolling elements bearings defect frequency and harmonics