Hi all!

I'm new here. i'm a student and taking vibration as my final project subject.

I know that a damage in a rotating machine will have a signature at the vibration signal, so, we can use vibration to monitor the machine condition. But i still not understand the concept of vibration for rotating machine. want to understand things like, why unbalance only create vibration at 1x speed, what if there are multiple mass concentration/unbalance? would the harmonics increase? Why looseness create a series of harmonics and subharmonics? Why misalignment increase the 2x freq further than the 1x? And how to use the vibration phase to locate the damage?

Can any of you point out a good reading material regarding this? or,, can you kindly explain for me?

Thanks in advance

p.s: i post my project at http://veemont.wordpress.com if any of you interested

Hi
You we get all your answer in the below link
WWW.viabration school.com
Ali

Wow!
Thank you very much! That's very helpful!

btw, i still don't understand one thing about imbalance. If there is multiple mass consetration in a rotor, does it still gives out 1x vibration or will it give harmonics? why?

hello

you can get all of your answers in the below link

www.dliengineering.com/vibman

you will find a complete information about vibration analysis and fault diagnosis.

best regards

thank you for the link, i got additional information from there.

but i still can't find the answer to my question regarding imbalance. anyone can explain to me?

Opiq-

Not 100% sure I know what you are asking here but if you have a situation where imbalance is present regardless of if it is due to one area or multiple it is still creating a center of rotation that is different than the center of mass thus it would generate a 1x because the sensor would feel the high spot bump due to the change in center of rotation a multiple due to the weights. These are not free moving pieces of equipment. The only way harmonics are created in a situation like that is if the tolerances of the bearings have been lost. Or if you think of it in terms of a journal bearing which has looseness as part of it you will get harmonics off the get go. That is why an accelerometer is not the best way to monitor this as it reads overall movement and a bearing that has an allowable clearance needs to monitored in a better way for better diagnosis.
http://www.dliengineering.com/vibman/journalbearings.htm

Hope this helps and welcome the the world of vibration, you'll enjoy the ride.

Dear Opik,

Going back to your very first post where you ask :But i still not understand the concept of vibration for rotating machine. want to understand things like, why unbalance only create vibration at 1x speed, what if there are multiple mass concentration/unbalance?

From what I know about balancing here goes :

A rotor with multiple mass distribution will display one single component of all of the 'unbalances' in a particular plane. In other words, they are summed up as one. If you were to draw on a polar vector diagram the various spots of unbalance that you visually notice on the rotor, you can sum up thru a vector the angle of the resolution of the equation.

I am in the process of preparing a small manual on the basics of balancing and I hope to produce it before I kick the bucket.

Good Luck in this sometimes dark as night world of vibration analysis.
May you find as much pleasure and satisfaction as I did during my years as a vibration analyst with the prehistoric instrumentation of the times.

MarkoLeo

aaahh, i see then! so the unbalance is summed up! thank u Markoleo.

as for the harmonics,, if i don't misunderstand oju's explanation, it come from the rotor's "rubbing", right?

Thank you guys! u had shed some light1

Cheers!