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?
What can lead to vibration in industrial machinery?
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.
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:
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.
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
Below you will find our highly-recommended reading list for learning the fundamentals of Vibration Analysis in Maintenance and Engineering applications.
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
Use this link for more information and price: Rotating Machinery Vibration: From Analysis to Troubleshooting
Analysis for Electronic Equipment
"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.
Application beyond just electronics
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
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.
Michael Rogers - Structural Engineer
Machinery Vibration: Measurement
From Book News, Inc.
Overall Best Vibration Book Yet
About the books description from the author's wife
Well written with a focus on the fundmentals
Machinery Vibration: Alignment
From Book News, Inc.
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.