×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

balance weight effect
2

balance weight effect

balance weight effect

(OP)
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)?

RE: balance weight effect

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.

RE: balance weight effect

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.

RE: balance weight effect

(OP)
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

RE: balance weight effect

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.

RE: balance weight effect

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources