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Practical Solutions to Machinery and Maintenance Vibration Problems


by Ralph T. Buscarello

This text has been written for the person working with already-built machinery rather than for the designer. Details covered are needed by the person new in vibration as well as the vibration specialist who already has hands-on experience.

This text is not a complete vibration textbook with all varieties of terminology needed by the reader completely new to the subject. Instead, it has been written to help and assist those who have already attended Update's machinery vibration seminars. Link to Seminar Schedule.

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I. Basic Information  
  1. What to Look For, Most of the Time
  2. Basic Understanding of the Sine Wave Representation of Vibration
  3. Using Phase to Determine How One Part of a Machine is Shaking Compared to Another
  4. The Most Common Vibration Amplitude Units in Use
  5. Precautions in Determining Pickup Direction
  6. Vibration Tolerances


II. Mechanical Resonance
  1. Understanding Resonance
  2. Considerations for the Probability of Resonance
  3. Probability of "Foot-Related Resonance”
  4. Why Some Machines do not Seem to Resonate as Often as Others
  5. Factors that Affect Natural Frequency
  6. Resonance at Frequencies other than the Natural Frequency or First Critical
  7. Resonant Vibration at Multiples of RPM
  8. Resonating a Rotor's First Critical Speed that is Twice its Operating Speed
  9. Detuning Resonant Part versus Reducing Vibration at the Source


III. Detuning and Proving Resonance
  1. Plotting the Mode Shapes from Point-to-Point Amplitude
  2. Where to Measure Plotting Points
  3. Further Considerations
  4. Fatigue Cracks and Failure Due to Resonance
  5. Resonance Bump Tests
  6. Bump Test Vibration Spectrum
  7. Bump Test While the Machine is Running
  8. "Reverse Bump" or Plucking the Suspect Part
  9. Understanding the Orbit of a Rotor's Centerline Due to Unbalance (when Running Above Resonance)
  10. Vibration Phase Relative to Resonance
  11. Using Phase Change to Determine a Resonant Condition
  12. Watching Phase vs. RPM Change to Determine Resonant Ranges
  13. Using Phase Change to Determine a Resonant Condition when Machine cannot be Shut Down
  14. Resonance in a Total System of Connected Parts Rather than in its Individual Parts
  15. Using Braces to Temporarily Change the Resonant Frequency
  16. Further Considerations when using Jacks and Braces
  17. Use of Variable Speed Vibration Shaker
  18. Positioning the Vibration Shaker on the Test Part of Structure
  19. Using Shaker to Determine whether Fault is Due to Weak Structure or Vibration Source
  20. Using Shaker to Determine Torsional Resonance
  21. Vibration Due to Foot-Related Resonance (FRR)
  22. Use of Dynamic Absorbers
  23. Summary of Approaches to Cure a Resonance Problem


IV. Rotor Resonance and Corrections


  1. Resonant Whirl
  2. Understanding Resonant Whirl Correction for All Types of Susceptible Rotors through "Whip" Correction of Papermachine Rolls
  3. Removing Whip from a Previously Balanced Rotor or Roll
  4. Whip Correction Procedure for Resonant Whirl at Rotor's First Critical Speed
  5. Whip Correction Procedures for Resonant Whirl at Rotor's Second Critical Speed


V. Unbalance
  1. Unbalance as the Resultant of Many Unbalance Forces in a Rotor
  2. Unbalance Units
  3. Various Combinations of Dynamic Unbalance
  4. Static Unbalance in a Uniform Rotor
  5. Static Unbalance in a Non-Uniform Rotor
  6. Couple Unbalance Forces
  7. How a Single Unbalance Force Can Cause Some Couple Unbalance
  8. Complications Created by Unbalance in Overhung Rotors
  9. Improving Field Balancing of Overhung Rotors
  10. Single Plane versus Two Plane Balancing
  11. Unbalance in Couplings
  12. Unbalance Tolerances
  13. Helpful Balancing Facts
  14. Field Balancing Exercise
  15. Update Method for Easier Balancing of Papermill Rolls with the Benefit of Reducing or Eliminating the Possibility of Whip
  16. Unbalance Due to Assembly Errors - Key Length Considerations
  17. Assembly Errors Due to Sharp Corners
  18. Improper Surface-to-Surface Fit Due to Stretched Threads
  19. Improper Mating of Surfaces Due to Burrs or Dirt in Bolt Holes
  20. Variances in Weights or Added Parts
  21. Setscrew Tightening Order
  22. Non-Square Spacers
  23. Centerline Shift Between Balancing Machine and Final Assembly
  24. Slightly Cocked Rotors
VI. Guide for Possible Sources of Vibration Based on Frequency and Amplitude
  1. Vibration Frequencies
  2. Less than 1 x rpm
  3. 1 x rpm (Rotor Speed)
  4. Lower Harmonics
  5. Higher Frequencies
  6. Miscellaneous


VII. Misalignment
  1. Reasons for Vibration Due to Coupling/Shaft Misalignment
  2. Most Usual Sources for Misalignment Errors
  3. For Machines where Drive and Driven Units Operate at Different Temperatures
  4. Machinery Soft Feet
  5. Misalignment Vibration at 1 x rpm of Rotor
  6. Axial Vibration Symptoms Due to Shaft/Coupling Misalignment
  7. Evaluating Harmonics Due to Shaft-to-Shaft/Coupling Misalignment
  8. Harmonics that are Measured in Velocity Terms
    (not Displacement or Acceleration) as Units
  9. Comparing Misalignment with Unbalance Symptoms
  10. Possible Confusion with Electrical Hum Frequency
  11. Quick Review of Other Higher than Usual Amplitudes of Harmonics not Caused by Shaft Coupling Misalignment
  12. Lower Frequency Harmonics
  13. Higher Frequency Harmonics
  14. Peaks at Higher Frequencies that are not Harmonics
  15. Separating Electrical Hum from a True Harmonic
  16. Why Symptoms of a Vibration Source are not Always Perfectly Clear (Mixtures of Vibration Vectors from More than One Source)
  17. Basic Vector Understanding
  18. Using Understanding of Vectorial Addition for Vibration Analysis
  19. Phase and Vibration Due to Coupling Misalignment
    (as Compared to Unbalance as a Source)
  20. Examining Phases from One Side of Coupling to the Other
  21. Evaluating Phase Relationships Between the Horizontal and Vertical Directions at the Same Bearing
  22. Determining the True Vibration Mode of Overhung Rotors
  23. Unclear Phase Symptoms Regarding Unbalance or Misalignment
    Caused by Machines with Unequal Flexibilities in Two Directions
  24. Coupling/Shaft Running Alignment


VIII. Vibration in Bearings
  1. Vibration Due to Rolling Element Bearings
  2. High Frequency/Ultrasonic Measurements
  3. Considerations for Evaluating Amplitudes Due to Bearing Defects
  4. Importance of Pickup Mounting and Location
  5. Use of IBF Units to Accurately Determine Bearing Lubrication
  6. Use of Velocity Spectra to Determine Bearing Condition
  7. Calculations for Bearing Defect Frequencies
  8. Further Considerations for Bearing Defect Vibration Amplitude and Frequency Symptoms
  9. Estimating Remaining Bearing Life
  10. Vibration Symptoms of a Loose Bearing
  11. Further Considerations Regarding Calculated Bearing Defect Frequencies
  12. Vibration Due to Oil Whirl (in Plain or Sleeve Bearings)


IX. Fluid Flow
  1. Cavitation
  2. Recirculation
  3. Turbulence
  4. Summary


X. Gear Vibration
  1. Gear Vibration Frequency of 1 x rpm
  2. Gearmesh Frequency Harmonics and Sidebands
  3. Gearmesh Vibration at Gearmesh Frequency
  4. Gear Vibration Frequency of 2 x rpm
  5. Gear Alignment
XI. Beats
  1. Vibration Due to Beats
  2. Beat Originating from Only One Vibration Source
  3. Effect of a Beat on Phase
  4. Minimizing the Effect of a Beat on a Tuneable Filter-Type Instrument
  5. Minimizing the Effect of Magnetic Field on Velocity-Type Pickups
  6. Minimizing the Effect of a Beat on a FFT-Type Instrument


XII. Low Frequency Vibration
  1. Slow Speed Machinery Such as Cooling Tower Fans, Other Low Speed Fans and Blowers, Mixers, Papermachine Rolls, etc.
  2. Measuring Low Frequency Vibration with Accelerometers
  3. Summary


XIII. Additional Vibration Sources
  1. Vibration Due to Pulleys/Sheaves and Drive Belts
  2. Vibration Due to Mechanical Looseness and Rubs
  3. To Determine a Bent Shaft (using Phase)


XIV. Mental Approach
  1. Most Usual Reasons for Vibration Increase (for Rotors that Once Ran Smoothly)
  2. Approaching a Machinery Vibration Problem


XV. Improvement Routines
  1. New Machinery
  2. Reworked and New Motors
  3. Vibration Checks by the Technician (Before Releasing Machine for Production)

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