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Vibration Analysis: Predictive and Preventive Mechanical Maintenance Through Vibration Measurement

Because smooth running leads to less stresses, fatigue and noise, most machines and structures are required to operate with low levels of vibration. The information on this page provides a brief overview of the principles and methods used to analyze the vibration of rotating or reciprocating industrial machinery.


What causes vibration in industrial machinery?

  • out-of-balance rotating components
  • motor shaft not magnetically centered
  • cavitation/recirculation (as in pumps)
  • loose and/or worn chains and sprockets
  • loose or worn bearings
  • worn gears (inside gearbox)
  • loose anchoring bolts on gearboxes, motor mounts or idlers
  • application demands greater than machine's rated specification
  • alignment drift of components (e.g. couplings; chain/sprocket)
  • resonance (materials and components may have natural resonant frequencies)

What can lead to vibration in industrial machinery?

  • insufficient lubrication
  • improper alignment of components during set up (e.g. couplings; belts, pulleys; chain/sprocket)
  • ambient environmental temperature
  • component-level manufacturer or material defect
  • application demands greater than machine's rated specification

Noise vs. vibration: can a vibration always be heard?

Many industrial environments are noisy so a problem may exist long before it's "heard". Sometimes, the failing component never be will be loud enough before failure. A low frequency vibration (below 100Hz) may also not be audibly detectable.

Noise vs. heat.

A tell-tale clue that a component or machine is experiencing abnormal mechanical stress is heat. Example: a noisy gearbox that is hot to touch.


Vibration Monitoring:

The purpose of vibration monitoring is to ascertain the normal operation of equipment or machinery in a manner that is objective and scientific. While "expert" opinions regarding how a machine is running are useful, they cannot substitute for scientific "metering" and analysis to obtain the actual condition of rotating or reciprocating machinery. In addition, there is no better criteria for operational reliability in rotating machinery than its vibrational characteristics.

Companies that use vibration monitoring and vibration analysis enjoy the following benefits:

  • Less Downtime
  • Less Spare Parts Inventory
  • Improved Management Time Allocation
  • Less Maintenance
  • Longer Production Runs
  • Improved Product Quality

Recording vibration data can be done with tools as basic as a meter, pencil and paper. Modern technology, however, offers a far better option: computer-assisted data collection, which can provide far greater (and more accurate) detail in a fraction of the time. There are many suppliers that carry such instruments; alternatively, your company you may choose to out-source a vibration-analysis team.

Predictive and preventive maintenance programs that employ this technology allow for a promising new source of profit potential. Greater profit can indeed be attained with a minimum of capital expenditure, no layoffs and greater acquired skills.

Vibration Analysis

Using a vibration analyzer, trained personnel can pinpoint the causes of rough machinery condition. Such problems as rotor imbalance and misalignment make up a great proportion of mechanical deficiencies and can be identified and rectified. Other problems such as bearing wear are not only detected, but also "rated" as to the severity of wear. In many cases, an historical case study can prognose the remaining life of bearings so that repair schedules can be prioritized.

Techniques for analyzing machinery are well documented and are taught by instrument suppliers and formal education facilities. We have also put together a list of the best books on topics such as Machinery Vibration, Alignment, Measurement and Analysis by noted experts. You will find them useful if you need more in-depth information.

Analysis-based Correction: Getting to the Root Problem

A predominant use of vibration analysis-based correction is that of balancing. Balancing with an analyzer is a methodical, stepped process -- it's more than a trial and error method of achieving dynamic trueness.It's one of very few techniques where machinery which is deemed "rough" can be corrected in place, without disassembly and where, in almost all cases, the results can meet virtually any level of precision. Diagnosis and cure are achieved with the same instrument.

Vibration analyzers can be used for running alignment. For example, an analyzer can be used throughout the alignment procedure to detect the source of high vibration or to detect the effects of fastening. Also, soft-foot conditions can be detected and corrected while the machine is operational. This allows for a quick diagnosis and correction without having to stop and start the equipment.

There are many other instances of vibration monitoring, analysis, balancing and corrective measures that make this technology so effective.

False Beliefs, Assumptions and Wishful Thinking

"We don't have a vibration problem"

"vibration" is not a "problem" per se. It's a physical manifestation of machinery imperfection. It can be used as a tool to help find obvious and subtle deviations in machines. No machine runs "perfect".

"Align or balance that machine"

This is a request that is made before a condition of imbalance is established. It's not just a matter of semantics either. If the machine is imbalanced, corrective action can be taken and the machine can operate within tolerances. If it's not imbalanced, the vibration analyst will advise the corrective action but cannot use the analyzer to fix the problem directly. It's a matter of expectations and in some cases, disillusionment.

"That machine is running fine -- we just changed the bearings"

This is often stated as a reason for not analyzing a machine. Bearings do fail. After a certain amount of time, maybe a month, maybe a years, bearings will finally succumb to slight or severe wear criteria and will fail. Assuming that bearing replacement is the final solution is a wishful thinking.

The bearing replacement trap occurs when the old bearings are noisy or fail. The technicians replace them and the new ones are now quiet. Problem solved, right? Wrong!

Bearing failure could be an indication of the natural expected life of the bearing itself but it should send alarm bells that this is a primary candidate for analysis. The failure could be the result of the mechanical deviations in a machine that could be corrected if one were to know about them. Also, the best time to get a vibration profile for future comparisons is when the machine has been reconditioned. This helps to find any inherent fault in the machine as well as determine if the work performed on it was done to specification. Also, remember the best maintenance programs are the ones that have the most historical information.

"That machine always runs like that"

And it always will until you fix it! Vibration analysis can tell you how.

"When it breaks, we will fix it"

The fact is, the machine will fail at its discretion and not to your schedule. When it fails, it will cause secondary damage. The parts for many machines must be kept on hand ahead of time to minimize the time it takes to repair. Plant production will cease. Personnel will be reallocated.

However, A more sensible approach leads to efficient, cost-effective action:

"We replace worn parts before they fail"

Using vibration analysis, you have a list of "invisible" anomalies. This list will show problems long before failure which will allow repairs to be scheduled during off hours. Problems with bearings are detected long before they fail so that other associated mechanical components are unaffected. Parts are not seized, no shafts are broken so the repairs are done in a fraction of the time. During repairs, other machines that have impending problems detected with vibration monitoring can be corrected. The parts have been ordered as needed. top of page | How to choose a Vibration Analyzer

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Books

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Below you will find our highly-recommended reading list for learning the fundamentals of Vibration Analysis in Maintenance and Engineering applications.

Rotating Machinery Vibration: From Analysis to Troubleshooting Rotating Machinery Vibration: From Analysis to Troubleshooting
By: Adams, Maurice L.
Published By: Marcel Dekker, Inc.

This comprehensive reference/text provides a thorough grounding in the fundamentals of rotating machinery vibration—treating computer model building, sources and types of vibration, and machine vibration signal analysis.

Presents case studies and troubleshooting techniques gleaned from the author’s extensive industrial experience.

Illustrating turbomachinery, vibration severity levels, condition monitoring, and rotor vibration cause identification, Rotating Machinery Vibration

-provides a primer on vibration fundamentals
-highlights calculation of rotor unbalance response and rotor self-excited vibration
-demonstrates calculation of rotor balancing weights
-furnishes PC codes for lateral rotor vibration analyses
-treats bearing, seal, impeller, and blade effects on rotor vibration
-describes modes, excitation, and stability of computer models
includes extensive PC data coefficient files on bearing dynamics
and more! Providing comprehensive descriptions of vibration symptoms for rotor unbalance, dynamic instability, rotor-stator rubs, misalignment, loose parts, cracked shafts, and rub-induced thermal bows, Rotating Machinery Vibration is an essential reference for mechanical, chemical, design, manufacturing, materials, aerospace, and reliability engineers; and specialists in vibration, rotating machinery, and turbomachinery; and an ideal text for upper-level undergraduate and graduate students in these disciplines.

Use this link for more information and price: Rotating Machinery Vibration: From Analysis to Troubleshooting

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Vibration Analysis for Electronic Equipment by Dave S. SteinbergVibration Analysis for Electronic Equipment
by Dave S. Steinberg

"The natural frequency of many single-degree-of-freedom systems can be determined by evaluating the characteristics of the strain energy and the kinetic energy of each system..."

From Book News, Inc.
Without noting the dates for the first two, Steinberg (U. of California-Los Angeles) has made extensive changes in the third edition to reflect the dramatic reduction in electronics that makes them affordable in many applications that were once good enough as mechanical devices. A major concern of his is the adoption of commercial equipment and standards by the military. Among the new chapters are discussions of the effects of manufacturing methods and tolerances on the reliability of the electronic hardware, methods for improving the ruggedness of commercial hardware for improved reliability in harsh military environments, the bending distortion of the circuit board at its resonant condition, and environmental stress screening.Book News, Inc.®, Portland, OR

Book Description:
This book deals with the analysis of various types of vibration environments that can lead to the failure of electronic systems or components.

Reviews:

Application beyond just electronics
The author is obviously an engineer who understands the everyday practical problems a dynamicist faces. Some theory, but chock full of easy to understand, and more importantly, *useful* information necessary to put properly designed product out the door.

Don't let the title fool you. The focus of this book is electronics, but the material here is applicable to any vibration problem.

If you're doing any dynamics work, you NEED this book.

A tool for success
If a mechanical engineer has chosen a career in the world of electronics, I strongly recommend this easy to follow gold mine of a book. I say it's a gold mine because it applies directly to the engineers' job. There are no fluff chapters or topics. Everything applies. Steinberg has made it easy (and almost fun) to solve those every day shock, vibration and acoustic challenges. Finding the natural frequency of a body such as a PC board is so much simpler for me now. And a surprising tidbit was for me to discover some amazing facts concerning acoustics. This is especially important as applied to fan cooled electronic packages. Another important area of study was packaging for transportation. How many times have we simply said "Just pack it in foam"? Before reading this book, I couldn't be sure what foam density to use or what the optimum thickness was. Why guess? Do it right.

I borrowed this book from my employer, took it home and read it over the long Christmas weekend. I was so impressed, that I am purchasing my personal copy tonight. I won't be without it.

This Book is to the point, get it done, structural dynamics.
This reference is a must read for any structural engineer entering into the the electronic packaging world. You can't go wrong with the easy to understand examples and extra insight the book gives to the rapid engineering production world we live in today.

Michael Rogers - Structural Engineer

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Machinery Vibration: Measurement and Analysis by Victor Wowk There are generally two situations in which vibration measurements are taken...Machinery Vibration: Measurement and Analysis
by Victor Wowk "There are generally two situations in which vibration measurements are taken..."

From Book News, Inc.
Ninety percent of all machine failures are signaled months, even years, in advance by changes in machine vibrations. Wowk shows how to use state-of-the-art instrumentation--transducers and fast Fourier transform (FFT) spectrum analyzers--to monitor machine conditions using the vibration "signature" of the machine. Includes a diagnostic chart for assessing the severity of vibration, and case histories that illustrate strategies for solving machinery problems. Annotation copyright Book News, Inc. Portland, Or.

Book Description:
Presents, in a single source, a practical, "hands-on" approach to vibration analysis and measurement, field balancing and shaft alignment, and how to understand and solve typical vibration problems. It covers balancing, resonance, gears and bearings, structural vibration, isolation, alignment, instruments, diagnostics, and trending. Includes extensive coverage of the FFT spectrum analyzer as well as numerous ``fixes'' to help solve immediate vibration problems. Presents principles applicable to all mechanical equipment as well as many case histories covering various mechanical devices such as fans, common motors, and pumps

Reviews:

Overall Best Vibration Book Yet
As a practicing mechanical engineer and vibration analyst for over eight years, I have found Mr.Wowk's book the best yet. In particular, I have found this book to have a good index and sensibly ordered so information can be obtained quickly. Also, Mr.Wowk has smartly avoided extensive mathmatical discussions in his book and focused the content towards common problems and solutions. To improve his book I would recommend more case histories and more extensive content on topics such as electrical problems and bearing faults. Overall it's the best book of its type I have read yet.

About the books description from the author's wife
This textbook is basically about the technology of machinery vibration measurement and analysis. It touches on topics such as balancing and alignment, but does not cover these subjects in detail. Victor has written subsequent textbooks that cover balancing and alignment in detail. The [above] description about this book is correct except for the Synoposis which describes the textbook: Machinery Vibration: Balancing. I know Victor's textbooks intimately--since I word processed all three of them. Of course I highly recommend reading them. As an office manager with no experience in plant maintenance, I gained a basic understanding in the field of vibration analysis. I have seen that when companies utilize this technology, production downtime is minimized, and costs in maintaining rotating equipment and facilites are dramatically reduced--a must read for company decision makers, such as facility or plant managers, purchase agents, and executives. Of course maintenance techs and engineers also can benefit from reading this book. (Victor teaches private and public workshops based on his books--visit www.machinedyn.com for details.)

Well written with a focus on the fundmentals
A great book for anyone interested in basic vibration analysis. Good coverage of vibration theory and application. Included are case histories that help demonstrate how to apply vibration techniques. If you want a better understanding of machinery vibration with a focus on real world application this is a best buy.

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Machinery Vibration: Alignment by Victor Wowk Misalignment is a major source of vibration on machines with components that have relative motion...Machinery Vibration: Alignment
by Victor Wowk "Misalignment is a major source of vibration on machines with components that have relative motion...

From Book News, Inc.
A 127-page handout for alignment courses at the Los Alamos National Laboratory designed to provide practical knowledge to the hands-on person who must perform the task has here developed into a broad overview of the alignment process that contains all the common methods and tools, including a chapter on lasers. Wowk points out that misalignment is a major source of vibration in machines with components that have relative motion. Two earlier volumes on machinery vibration cover measuring and analysis, and balancing; a fourth, on resonance and isolation, will complete the series.Book News, Inc., Portland, OR

Product Description:
How-to-do-it guide to eliminating machine vibrations

One of the most common causes of severe machinery vibration is the misalignment of drive shafts and other components. Machinery Vibration: Alignment, by Victor Wowk, gives you a practical resource for aligning shafts, bearings, gears, pulleys and a wide variety of power transmission components in machines without further training. You get step-by-step procedures for balancing, resonance, structural vibrations, isolation, instruments, diagnostics, and trending. Many of the methods described require only simple tools, eliminating the need for a $20,000 laser alignment system.

Case studies covering everything from simple fans to high-speed turbines give you examples of real-world problem solving. You will find the extensive coverage of the FFT spectrum analyzer a valuable addition to this hands-on toolkit.

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