Bent shaft vibration is caused by a bent shaft in a machine. A bent shaft can occur due to manufacturing defects, shipping damage, or uneven wear over time. Key signs of a bent shaft include high 1x axial vibration, a dominant 1x peak in spectral analysis, and 180 degree phase difference in axial vibration measurements across the machine. Identifying these vibration characteristics can indicate the presence of a bent shaft requiring repair or replacement.

1. BENT SHAFT VIBRATION
Thareq Akbar Arya Yudhistira (15/381210/TK/43388)
Muhammad Khautal Ardi Putra (15/381352/TK/43420)
Maurissa Hasina Rosyi (15/381209/TK/43387)
I Nyoman Nalendra (15/380152/TK/43336)

2. Bent Shaft Vibration
Bent shaft vibration is a vibration which caused by bent shaft. Bent
shaft generates high vibration and creates a lot of stress on other
components during operation.

3. Type of Shaft Bent based on the cause
1. Bent out of usage
1. Installation
2. Failure in manufacturing process
3. Shipping
2. Bent Because of usage
1. Uneven heat distribution in the rotor caused by a defect rotor bar
2. Eccentricity of shaft mass

4. How to Know when a Shaft is Bent
• Use overall vibration measurements
• Spectral analysis
• Phase measurements.

5. Bent Shaft Causes
• Cold bow – As a result of gravity, a shaft with a high length to width
ratio can, at rest, develop a bend.
• Improper handling during transportation
• High torque
• Catastrophic failure

6. Characteristics
• A bent shaft predominantly causes high 1x axial vibration
• If the bending is situated at the centre of the axle the dominating
vibration frequency is 1 x RPM.
• If the bending is situated near a coupling the dominating vibration
frequency is 2 x RPM (narrow band, possibly with 2x, 3x multiples)

7. Spectrum Analysis
A bent shaft typically produces spectra that have misalignment type
characteristics. A higher than normal 1x/2x amplitude may occur. A
high 2x amplitude can vary from 30% of the 1x amplitude to 100 to
200% of the 1x amplitude.

8. Spectrum Analysis
Look for a high 1x peak in axial. If the
bend is close to the coupling then
you will see a higher 2x peak. You
may also observe higher than normal
1x and 2x peaks in the radial
direction.

9. Phase Analysis
It’s important to note that all phase values are ±30°
• Radial phase measurements (vertical and horizontal) typically appear “in
phase”
• Axial phase measurements are typically 180° out of phase
If both the above conditions are true, the problem is probably a bent
shaft.

10. Conclusion
If the primary vibration plane is in the axial direction, and there is a
dominant 1x peak, and there is a 180° phase difference in the axial
direction across the machine, then there may be a bent shaft.

11. Reference
• http://www.skf.com/group/services/services-and-
solutions/introduction-to-condition-monitoring/how-to-know-when-
a-shaft-is-bent.html
• http://www.vtab.se/training/vibration-school/bent-shaft/?lang=en

12. TERIMA KASIH