Online Textbook

Practical Solutions to Machinery and Maintenance Vibration Problems

FOURTH REVISED EDITION MAY 2002

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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INDEX

I. Basic Information
	What to Look For, Most of the Time Basic Understanding of the Sine Wave Representation of Vibration Using Phase to Determine How One Part of a Machine is Shaking Compared to Another The Most Common Vibration Amplitude Units in Use Precautions in Determining Pickup Direction Vibration Tolerances
II. Mechanical Resonance
	Understanding Resonance Considerations for the Probability of Resonance Probability of "Foot-Related Resonance” Why Some Machines do not Seem to Resonate as Often as Others Factors that Affect Natural Frequency Resonance at Frequencies other than the Natural Frequency or First Critical Resonant Vibration at Multiples of RPM Resonating a Rotor's First Critical Speed that is Twice its Operating Speed Detuning Resonant Part versus Reducing Vibration at the Source
III. Detuning and Proving Resonance
	Plotting the Mode Shapes from Point-to-Point Amplitude Where to Measure Plotting Points Further Considerations Fatigue Cracks and Failure Due to Resonance Resonance Bump Tests Bump Test Vibration Spectrum Bump Test While the Machine is Running "Reverse Bump" or Plucking the Suspect Part Understanding the Orbit of a Rotor's Centerline Due to Unbalance (when Running Above Resonance) Vibration Phase Relative to Resonance Using Phase Change to Determine a Resonant Condition Watching Phase vs. RPM Change to Determine Resonant Ranges Using Phase Change to Determine a Resonant Condition when Machine cannot be Shut Down Resonance in a Total System of Connected Parts Rather than in its Individual Parts Using Braces to Temporarily Change the Resonant Frequency Further Considerations when using Jacks and Braces Use of Variable Speed Vibration Shaker Positioning the Vibration Shaker on the Test Part of Structure Using Shaker to Determine whether Fault is Due to Weak Structure or Vibration Source Using Shaker to Determine Torsional Resonance Vibration Due to Foot-Related Resonance (FRR) Use of Dynamic Absorbers Summary of Approaches to Cure a Resonance Problem
IV. Rotor Resonance and Corrections
	Resonant Whirl Understanding Resonant Whirl Correction for All Types of Susceptible Rotors through "Whip" Correction of Papermachine Rolls Removing Whip from a Previously Balanced Rotor or Roll Whip Correction Procedure for Resonant Whirl at Rotor's First Critical Speed Whip Correction Procedures for Resonant Whirl at Rotor's Second Critical Speed
V. Unbalance
	Unbalance as the Resultant of Many Unbalance Forces in a Rotor Unbalance Units Various Combinations of Dynamic Unbalance Static Unbalance in a Uniform Rotor Static Unbalance in a Non-Uniform Rotor Couple Unbalance Forces How a Single Unbalance Force Can Cause Some Couple Unbalance Complications Created by Unbalance in Overhung Rotors Improving Field Balancing of Overhung Rotors Single Plane versus Two Plane Balancing Unbalance in Couplings Unbalance Tolerances Helpful Balancing Facts Field Balancing Exercise Update Method for Easier Balancing of Papermill Rolls with the Benefit of Reducing or Eliminating the Possibility of Whip Unbalance Due to Assembly Errors - Key Length Considerations Assembly Errors Due to Sharp Corners Improper Surface-to-Surface Fit Due to Stretched Threads Improper Mating of Surfaces Due to Burrs or Dirt in Bolt Holes Variances in Weights or Added Parts Setscrew Tightening Order Non-Square Spacers Centerline Shift Between Balancing Machine and Final Assembly Slightly Cocked Rotors
VI. Guide for Possible Sources of Vibration Based on Frequency and Amplitude
	Vibration Frequencies Less than 1 x rpm 1 x rpm (Rotor Speed) Lower Harmonics Higher Frequencies Miscellaneous
VII. Misalignment
	Reasons for Vibration Due to Coupling/Shaft Misalignment Most Usual Sources for Misalignment Errors For Machines where Drive and Driven Units Operate at Different Temperatures Machinery Soft Feet Misalignment Vibration at 1 x rpm of Rotor Axial Vibration Symptoms Due to Shaft/Coupling Misalignment Evaluating Harmonics Due to Shaft-to-Shaft/Coupling Misalignment Harmonics that are Measured in Velocity Terms (not Displacement or Acceleration) as Units Comparing Misalignment with Unbalance Symptoms Possible Confusion with Electrical Hum Frequency Quick Review of Other Higher than Usual Amplitudes of Harmonics not Caused by Shaft Coupling Misalignment Lower Frequency Harmonics Higher Frequency Harmonics Peaks at Higher Frequencies that are not Harmonics Separating Electrical Hum from a True Harmonic Why Symptoms of a Vibration Source are not Always Perfectly Clear (Mixtures of Vibration Vectors from More than One Source) Basic Vector Understanding Using Understanding of Vectorial Addition for Vibration Analysis Phase and Vibration Due to Coupling Misalignment (as Compared to Unbalance as a Source) Examining Phases from One Side of Coupling to the Other Evaluating Phase Relationships Between the Horizontal and Vertical Directions at the Same Bearing Determining the True Vibration Mode of Overhung Rotors Unclear Phase Symptoms Regarding Unbalance or Misalignment Caused by Machines with Unequal Flexibilities in Two Directions Coupling/Shaft Running Alignment
VIII. Vibration in Bearings
	Vibration Due to Rolling Element Bearings High Frequency/Ultrasonic Measurements Considerations for Evaluating Amplitudes Due to Bearing Defects Importance of Pickup Mounting and Location Use of IBF Units to Accurately Determine Bearing Lubrication Use of Velocity Spectra to Determine Bearing Condition Calculations for Bearing Defect Frequencies Further Considerations for Bearing Defect Vibration Amplitude and Frequency Symptoms Estimating Remaining Bearing Life Vibration Symptoms of a Loose Bearing Further Considerations Regarding Calculated Bearing Defect Frequencies Vibration Due to Oil Whirl (in Plain or Sleeve Bearings)
IX. Fluid Flow
	Cavitation Recirculation Turbulence Summary
X. Gear Vibration
	Gear Vibration Frequency of 1 x rpm Gearmesh Frequency Harmonics and Sidebands Gearmesh Vibration at Gearmesh Frequency Gear Vibration Frequency of 2 x rpm Gear Alignment
XI. Beats
	Vibration Due to Beats Beat Originating from Only One Vibration Source Effect of a Beat on Phase Minimizing the Effect of a Beat on a Tuneable Filter-Type Instrument Minimizing the Effect of Magnetic Field on Velocity-Type Pickups Minimizing the Effect of a Beat on a FFT-Type Instrument
XII. Low Frequency Vibration
	Slow Speed Machinery Such as Cooling Tower Fans, Other Low Speed Fans and Blowers, Mixers, Papermachine Rolls, etc. Measuring Low Frequency Vibration with Accelerometers Summary
XIII. Additional Vibration Sources
	Vibration Due to Pulleys/Sheaves and Drive Belts Vibration Due to Mechanical Looseness and Rubs To Determine a Bent Shaft (using Phase)
XIV. Mental Approach
	Most Usual Reasons for Vibration Increase (for Rotors that Once Ran Smoothly) Approaching a Machinery Vibration Problem
XV. Improvement Routines
	New Machinery Reworked and New Motors Vibration Checks by the Technician (Before Releasing Machine for Production)

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