balance weight effect 2

[cyw]

I am new to vibration issue, and very keen to know more about it. I need to balance a simple turbine rotor. The vibration level at bearing 1 is 4.3mil pp while bearing 2 is 1.8mil pp. I want to bring down the vibration level on bearing 1 without affecting bearing 2. Does anybody know how to calculate a weight placed near bearing 1 will effect bearing 2? Beside, how does influence vector calculated from first successful balancing will help in future balancing if a mass unbalance is introduced later (i.e. change of a set of rotor blade)?

 

[butelja]

This sounds like a standard 2 plane rigid rotor balancing problem. With the proper balancing machine, it will tell you exactly how much weight to add to each end. If you are doing it the "old fashioned" way without a computerized machine, it is still not all that difficult, providing that you can get accurate readings for amplitude and phase angle at each measurement plane.

The general the method is as follows:

1.) Do a trial run in the existing condition and record both amplitude and phase angle for each measurement plane.

2.) Add a trial weight to correction plane 1. You must record both the weight and its phase angle. Spin the rotor and record amplitude and phase angle at each measurement plane.

3.) Remove the trial weight from correction plane 1 and install it on correction plane 2. Spin the rotor and record the amplitude and phase angle at each measurement plane.

4.) By using the results of #1, #2, and #3 above, it is possible to solve for a 2x2 complex matrix of influence coefficients. Polar notation is most useful in expressing the complex numbers. The matrix equation is A*x=B, where A is the 2x2 influence coefficient matrix, x is the 2x1 correction mass vector, and B is the 2x1 vibration reading vector. A, x, & B are all expressed in terms of complex numbers.

5.) After completing #4, set vector B equal to 0 and solve for vector x. The resulting vector x gives the correction mass and phase angle at each correction plane.

I hope this is helpful.

 

[dgallagher]

Check out our application note on dynamic balancing at:

http://www.reliabilitydirect.com/appnotes/balance.html,

to make the job easier, take a look at the low cost 2 plane field balancing system at:

http://www.reliabilitydirect.com/balancingproducts/GT5052a.htm

 

[VibrationSpecialist]

Dear cyw,

I am sure that butelja response was beneficial.

In the case of the unavailability of a computerized balancing machine, you need to see the response after the first trial weight. A good response is considered when you have 10-20 % change either in the amplitude or the phase angle. If you notice that change on the other plane then it is indeed a Two Plane Balancing.

Remember to use removable trail weight.

Take Care.

 

[cyw]

Thanks butelja & VibtrationSpecialist. Can you elaborate more on the 2x2 influence coefficient matrix? What is in row 1 column 1, row 2 column 2, row 2 column 1 and row 2 column 2? I can back-calculate these value using the formula given by butelja, but I want to know what does each of these means. Thanks

 

[Franko]

Bruel and Kjaer has the equations and a 2-plane program written in Basic language in their No.3-1979 Technical Review. You could ask them for a copy -

http://www.bksv.com/bksv/

If you can't get it, call me @ 724-600-8140.

 

Go to:

http://br.briefcase.yahoo.com/microsyn1

Clik in Catalogos,
and download DEMO 1/2 and 2/2.
dudes?: tecnica@microsyn.com.br

 

Hi cyw,
You are new in Insitu Balancing field. So are you sure it is unbalance problem.
1. Can you give me analysis checks that you have performed for diagnosing the Unbalance problem i.e frequency analysis,reproducability, Bode plot analysis, mode shape analysis etc.
2. Can you tell be what is the type of unbalane i.e static,couple, 1st critical or 2 nd critical etc.
3. which equipment and transducers are you using?

Thanks
Kashif