Practical Solutions to Machinery and Maintenance Vibration Problems
Chapter 4, Rotor Resonance and Corrections
Section 5, Whip Correction Procedures for Resonant Whirl at Rotor's Second Critical Speed
Notice that the two bends are 180° opposite each other. Again, ignore the large couple unbalance that this creates, as this unbalance will be eliminated when the whip is removed and the roll is finally straight. The double bend will be corrected with two couple balancing type weights placed at the quarter points of the roll and two more couple weights placed at the ends of the roll.
The two larger whip correction weights at the quarter points form a couple. The couple is counterbalanced by the two smaller weights on the ends of the roll. The smaller end weights should be sized as follows:
Correction weights B = L2/L1 x Correction weight A
A similar procedure would be used for removing whip at the 3rd critical speed, 4th and so on. (Review section "Plotting the Mode Shape from Point-to-Point Amplitude Readings to Determine Whether or Not a Part is Resonant.”). (As such situations are extremely rare, the exact procedure will not be discussed in this book.)
This textbook contains only part of the information in our Practical Vibration Analysis seminar.