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Fault frequencies are very important in vibration analysis because they allow the analyst to correlate vibration data to specific components in the equipment that may be in some stage of failure (equipment faults). Fault frequencies change with any adjustment in the speed of the equipment being monitored. Most modern vibration data collectors and software will automatically re-calculate the displayed fault frequency information as the rotational speed of the equipment changes. Component information (bearing information, gear information, etc.) is required to calculate and display the fault frequencies of specific components in machinery.

It is important to create fault frequency setups at the beginning of a vibration analysis program. Not doing so will affect the overall success of the vibration analysis program.

When aligning a vertical flange-mounted machine, it can be helpful to tweak the flange configuration in your laser alignment system to take advantage of different shimming alternatives. For instance, if the OD of the flange is larger than the diameter of the mounting bolt circle, a good laser system will compensate for this by taking into consideration that when shimming your pivot point is not the bolt circle but the flange OD. Thus, all shimming corrections will be positive.

However, if you already have shims at all the bolt positions, you could take advantage of the opportunity to minimize the required shimming corrections by forcing the smallest correction position to be zero. Do this by entering a distance for flange OD as being equal to your bolt circle. Of course, the best laser systems already allow for all the different shimming alternatives (positive, negative, and zero-sum options) right in the software, so you don’t have to use this trick.

Knowing the exact bearing information for your equipment can make bearing defect analysis much easier.

However, it may not always be possible to acquire the bearing information for your equipment.  This can make it difficult to determine the bearing fault frequencies for correct analysis.

It is possible to remember easy formulas to calculate the approximate bearing fault frequencies for rolling element bearings.  The following formulas are easy to remember and can help you when the bearing information is not known:
FTF = 0.43 × RPM
BPFO = 0.43 × N × RPM
BPFI = 0.57 × N × RPM
Where:
FTF = Fundamental Train Frequency
RPM = Revolutions per minute
BPFO = Bearing Pass Frequency Outer Race
N = The number of rollers
BPFI = Bearing Pass Frequency Inner Race

The values derived from these formulas should be within 10% – 15% percent of the actual bearing fault frequencies.

Other formulas are available that will more accurately estimate bearing fault frequencies than the ones listed above.  LUDECA will be happy to provide those to you upon request.

If you are aligning very critical machines and your laser system does not offer you the ability to apply vector tolerances, you can still do so manually, by keeping these criteria in mind:

The standard industry norms of 2 mils offset and 0.3 mils per inch of angularity at 1800 rpm equate roughly to vectors of 1.4 mils of offset and 0.17 mils per inch of angularity. Therefore, you can apply a sliding scale when you look at your misalignment results: If you have misalignment only in one plane (either vertical or horizontal), apply the full value of the standard tolerance; if you have a roughly equal misalignment in both planes apply the more conservative values shown above to both. This way you will not exceed your vector limits in any direction.

To find the vector limits for any RPM, simply take the square root of the standard limits.

Of course, none of this would be necessary if you have one of the better laser systems that feature vector tolerances and calculates them for you automatically.

Your vibration software should have the capability to automatically import and export data from and to your CMMS system. Vibration programs like the OMNITREND® software can provide you with the means to address this issue.

Having the ability to automatically share information between your CMMS system and vibration software can be of great value. This capability can allow you to automatically build your vibration database with the same equipment names, equipment IDs, and hierarchy locations that are contained in your CMMS system. This can potentially save your company critical time and expense when starting a new vibration program or updating your current program.

Alarm condition information and much more can easily be shared between your CMMS software and vibration software. This provides the ability to alert your Maintenance Manager, planning and scheduling resources, and other team players about the important equipment conditions found by your vibration program.

Most CMMS and vibration software do not directly share information. Direct storage of data into another program greatly increases the risk of information corruption. Of course, this is never a good thing when it occurs and the risk should be minimized as much as possible. Most CMMS and vibration programs have the ability to map specific information for import and export via a file transfer process. A template is created that determines what information should be exported and in what format it should be stored. The template is stored and automatically executed on a scheduled basis determined by the user. Both the CMMS system and vibration software will create temporary files to share the required information with each other. Each system will automatically import this information and store it in their specific databases(s) from the temporary files. This type of process minimizes your efforts and provides routine and scheduled data sharing between both systems.

This type of data exchange will provide continuity in your reliability efforts and removes confusion when creating work orders based on the defect findings from your vibration program. The result will better integrate your reliability program with your maintenance process.

Measuring machinery misalignment with today’s tools, particularly computerized laser alignment systems, and well-designed bracketing is no longer as difficult a task as it once was when all you had were a straight edge, feeler gauges, and maybe a set of dial indicators with some make-shift hardware.

Why then, is it that aligning the machinery to given target values is so often still so cumbersome and time-consuming? There may be several reasons, among them unnecessarily tight tolerances specified by the machinery vendor, problems with worn-out bearings, inadequate bases, lack of jackscrews, etc. But by far the greatest obstacle to expeditiously reaching your alignment goal is soft foot. ‘Soft foot’, or machine frame distortion can be measured by various means, and indeed it must be measured and corrected before proceeding with the alignment. Why? Simply because an uncorrected soft foot condition will make alignment a trial-and-error procedure where indicated corrective shimming and lateral moves no longer bring you to the expected results.

Severe soft foot may also be quite harmful to the machinery itself.

Correcting soft foot may not be easy, but it is worth every minute you spend on it because once done, the alignment of the machines becomes a much easier task. Many alignment systems available today have soft foot measuring programs, and the most advanced system even features a soft foot ‘wizard’ which analyzes the type of soft foot measured (there are a number of different soft foot conditions) and suggests how to correct it.

Conclusion: If you want to make aligning your machinery easier, quicker, and more accurate, start by correcting soft foot.

Read: Types of Soft Foot

One of the problems we can encounter while performing an alignment is the re-use of old washers. Sometimes it isn’t enough to replace all the used bolts, nuts, and shims. You need to replace old washers too.

They are just as simple to replace and as inexpensive as the bolts and nuts you are also replacing. Dished washers will try to center themselves in the bolt hole of the foot and will pull your machine out of alignment, even if you are very careful in your torquing procedure. This effect is virtually impossible to overcome and at times even to detect (unless you are using the live move function on a ROTALIGN® laser alignment system), resulting in a difficult alignment to finish properly, even if you have followed every step correctly. Make sure to discard all damaged or inappropriate washers on the movable machine and replace them with thick, good quality Grade 8 new washers.

Another issue is the use of lock washers. Generally, a good flat washer under a bolt head with a good washer seat that has been correctly tightened to the proper torque does not need additional security; however, if your application requires a lock washer due to severe vibration, or because the join needs to be allowed to expand while still maintaining the required amount of axial force on the closure, then a high-quality lock washer may be the right solution. Avoid the use of cheap, one-time-use split-ring lock washers, and use a high-quality Belleville washer (a conical disc spring washer) instead. A split ring lock washer exerts 90% of its force in the first 20% of its travel range, therefore it is a very ineffective solution to the problem attempting to be solved; a Belleville washer, on the other hand, exerts 100% of its locking force over 100% of its travel range, and moreover also serves the functions of a flat washer. In addition, they can be stacked in parallel to increase the axial locking force, or in series to increase both the locking force and the travel range.

Do you archive your historical vibration data or keep it around forever?  If your Condition Monitoring department does not have a plan to deal with database management, then it is critical that you develop one.

Usually, the vibration data has lost any historical value after a couple of years, and keeping this data stored in your vibration database is of limited or no value.  Data collected on critical equipment or certain machines may have interesting analytical value and be worth keeping long term.  You should decide what data must be stored and for how long.  You may find that you have a lot of historical data in your vibration database that is no longer of value.

This data should be moved into another database for long-term storage or completely deleted.

Unwanted vibration data will increase the size of your database(s).  This unwanted data can decrease the performance of your vibration software, increase the risk of database corruption issues and cause the loss of the data that you actually do wish to keep long term.  Storage of huge amounts of historical data may make your vibration database become unreliable.  Some IT departments will charge your department based on the amount of storage space your database(s) consume.  Therefore, the storage of extra data could be costing your department additional money monthly and yearly.

Most vibration programs have a means to delete data based upon historical criteria (date ranges) and filter types (equipment types, etc).  You may determine that you wish to keep this data archived, but not stored in your primary database file(s).  Your vibration software should have the ability to transfer this data to another database.  This will allow you to keep the data stored in another location, but remove it from your primary database file(s).

The choice is yours, but you should beware of the positives and negatives of allowing your vibration data to increase year after year.  You should devise a plan on what works best for your facility and vibration department and execute this plan on a routine basis (yearly, etc).  Some vibration departments will use a specific holiday (New Year, for instance) to remind them that it is time to do database management.

For future reference, write the sizes & types of belts used in your equipment in a safe but noticeable area of the belt cover/guard of the machine.
Use a Reflectorized Arrow Sticker (yellow) for rotation direction especially on pulleys without direction indicators.

Tip provided by Garry Villamil of TRILUX ELECTRONICS & LUMINAIRES, INC.
By the way, don’t forget to always laser align your belts and pulleys.
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You are invited to submit a Maintenance Tip of your own and get a free LUDECA cap if we publish it!
By submitting a tip you acknowledge and consent that any tips submitted become the property of LUDECA, Inc. and may be submitted to third parties in LUDECA’s own name. Submission of a tip will not entitle the submitter to any other compensation whatsoever beyond what is promised above, as well as our everlasting gratitude. Thanks!
Send us your Maintenance Tip.

In lubricating an electric motor bearing, long grease purge pipes create backpressure, which increases the chance of grease being forced into windings or excess grease remaining in the bearing. Therefore, drain pipes should be as short as possible and not have any turns if possible.

Tip provided by Garry Villamil of TRILUX ELECTRONICS & LUMINAIRES, INC.
———-
You are invited to submit a Maintenance Tip of your own and get a free LUDECA cap if we publish it!
By submitting a tip you acknowledge and consent that any tips submitted become the property of LUDECA, Inc. and may be submitted to third parties in LUDECA’s own name. Submission of a tip will not entitle the submitter to any other compensation whatsoever beyond what is promised above, as well as our everlasting gratitude. Thanks!
Send us your Maintenance Tip.

Cross-head or Phillips screws have a plus-shaped slot in the head and are driven by a cross-head screwdriver, designed originally in the 1930s for use with mechanical screwing machines. They were intentionally made so the driver would ride out, or cam out, at a certain force to prevent over-tightening. After a piece of equipment has been disassembled and rebuilt numerous times, the Phillips head drive wears out in the screw head “by design.”

When removal is required but the driver continues to ride out of the slot, place a small amount of lapping compound in the +-shaped slot of the screw head and proceed with the removal, (always replacing the stripped screw with a new one.)

This method works like magic on all sizes of Phillips head screws and can save a lot of needless frustration. Not earth-shattering technology, but a pretty neat trick.

Tip provided by Thomas Keefer of Tennessee Valley Authority.
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You are invited to submit a Maintenance Tip of your own and get a free LUDECA cap if we publish it!
By submitting a tip you acknowledge and consent that any tips submitted become the property of LUDECA, Inc. and may be submitted to third parties in LUDECA’s own name. Submission of a tip will not entitle the submitter to any other compensation whatsoever beyond what is promised above, as well as our everlasting gratitude. Thanks!
Send us your Maintenance Tip.

Some vibration software and vibration data collectors allow the use of frequency bands to help the analyst measure and identify specific equipment faults.  These frequency bands are actually measured in the vibration data collector.  The results can be used for trending and alarm purposes.  You can create specific bands around specific faults that may occur in the equipment being monitored.  For example, bands for imbalance, misalignment, specific bearing defects, electrical defects, and much more can easily be measured.  Alarm thresholds can be created to alert you when attention is required.  These bands can help you identify equipment issues in your vibration data before you look at the FFT or time waveform data.  A review of the FFT and time waveform data should always be completed.  However, band alarms can keep you from overlooking an issue and reduce the amount of analysis that may be required.

Some coupling manufacturers will sell couplings claiming that the coupling can take shaft misalignment. While this is true for most flexible couplings, it can be easily misinterpreted. Flexible couplings are designed to withstand, without damage, some shaft misalignment. Sometimes it is perceived that, since the coupling can take the misalignment, the machines can run under this condition without any consequences. When running machinery with significant shaft misalignment, bearing and seal life may decrease immensely, and other damage results. Therefore, for longer machinery life, it is always recommended to have equipment laser aligned to standard industry tolerances for shaft alignment, and not to the looser alignment tolerances allowed by the coupling itself.

Learn about Shaft Alignment Tools with Built-in Tolerances. 

Oil data reports made available by laboratories to their customers are usually delivered in MICROSOFT EXCEL® files or text files.  The data is generally made available via an online download.  These reports contain information on many different substances found in the oil such as iron, aluminum, copper, and many more.  Other factors such as viscosity are included as well.

Oil analysis data provides a great insight into the health of your equipment and should be a routine part of any good reliability program.  It can be overwhelming to process all this data in a meaningful way.  You may not wish to trend and alarm on every single parameter contained in the oil report.  So what do you do?  The answer may be your vibration analysis software!

A good vibration analysis program like OMNITREND will allow you to create customizable imports for your oil analysis data.  A routine and automated process can be set up to import only the data of interest for specific machines.  Once the data is imported, then automated alarms can be created to alert you of any oil parameters that are of concern for your equipment.

Oil data can be visually trended over time and you will automatically be alerted when an oil parameter reaches a value of concern for a specific machine. This can allow you automatically manage selected oil parameters of concern and greatly reduce the amount of time required to manually review each parameter measured by your oil analysis lab.

Furthermore, it will allow you to use the routine vibration data collected and oil analysis data provided by your laboratory to detect and confirm equipment problems.  You should not underestimate the power of having your vibration and oil analysis data integrated.

Defects occur at specific frequencies in relation to the running speed of the equipment. Most vibration analysis software will allow these specific frequencies (bands) to be measured and trended over time. Trending this information will help identify problems as they occur in your equipment. This results in more accurate analysis of equipment problems that will help determine the severity and repair urgency of the problems identified.

For example, if the vibration trend is increasing slowly, then the failure may not be progressing rapidly. However, a sharp increase in a specific vibration trend over time indicates that a defect may have developed and failure is more imminent.­

We often hear about the need to acquire vibration measurements at precisely the same location each time we measure a point. Why is this important? In order for vibration measurements to be trendable they must be closely repeatable, and we need to eliminate measurement error. With high-frequency measurements, the vibration attenuates rapidly as it travels away from its source. The author has seen readings vary by as much as 50% when the collection transducer was moved by as little as ¼ inch.  If the transducer is not placed in the same location, the trended data will show an error that may be mistaken for a change in machine condition. When the collection point is different, the transmission path is either longer or shorter. This affects the amount of energy perceived by the transducer. Standing waves also exist in vibrating machinery. The transducer may sometimes be located at a nodal point of one of these waves; and if care isn’t taken in transducer placement, the next measurement may be at an anti-node. This is more apparent in larger machines because of the amount of surface area available for standing wave formation. There are several ways to precisely mark data points for measurement with a magnet-mounted transducer. Paint, glue-on-pads, stud-mounted pads, machined surfaces, and dimples made by a small drill bit are all used with success. Best of all are permanently mounted coded attachment studs (such as VIBCODE®) that guarantee precise re-placement of the transducer every time, at the same location, angle, and pressure. Regardless of the method employed, it is important to always precisely identify data collection points.

Many vibration programs fail because they become too complicated. Too much data can sometimes become more confusing than too little data. Many potential machinery problems can be eliminated with the analysis if one keeps in mind several simple concepts:

1. Vibration units such as acceleration are more sensitive to high frequencies than low frequencies.

2. Vibration units such as displacement are more sensitive to low frequencies than high frequencies.

3. Velocity units are evenly sensitive between about 60 CPM to 60, 000 CPM.

4. High-frequency vibration does not travel far and degrades rapidly through metal seams.

5. In general the closer your measurement is to the source of the vibration the higher the amplitude will be.
These differences can be used to zero in on machine faults.

Example: Take a generic 100 HP motor. If an outboard rolling element bearing begins to fail because of a lack of lubrication the first indicator is high-frequency ringing from the bearing. This is characterized by a large increase in acceleration amplitude and a small to no increase in velocity or displacement. Now you have identified that there is a high-frequency problem and not a low-frequency mechanical problem. You can eliminate low-frequency sources such as looseness, unbalance, or misalignment. What is the most likely source of high-frequency vibration on the back end of a motor? Probably a bearing or shaft or rotor rub. Now you can apply a simple test. Grease the bearing and see if the acceleration returns to normal. If it does, you have nailed the problem without knowing the bearing frequencies or even taking a spectrum. Come back the next day and see if the acceleration is back up. If it is, you either have a lubrication problem with contamination or a loss of grease, a damaged bearing, or both.

While not perfect, understanding the behavior of vibration units combined with a mechanical understanding of machinery can help you quickly identify machinery problems.

How fast is the data collection speed of your vibration data collector? You may feel that this is not an important characteristic. Does it really matter if a data collector is one or two seconds faster-acquiring data versus another? Data collection speed is very important and should be taken into consideration by your facility management and Condition Monitoring Group. For example, consider a vibration monitoring program that monitors 1000 machine trains per month with 10 measurement points per machine train. If a vibration data collector requires 8 seconds to acquire data for each measurement point, then it would necessitate 22 hours of real data collection time (this does not include time moving between each machine, reporting time or etc). Does a second really make a difference? A data collector that is one second faster acquiring the same data will result in 3 hours per month saved or almost one full man week per year. If the data collector is 3 seconds faster in acquiring the same data, then the time savings are more substantial. A savings of 3 seconds per measurement point will result in a savings of 2.5 man-weeks per year. Multiply the time savings by your labor cost per hour and the savings could be very important to your facility. The savings may surprise you!

Take a look at our new VIBXPERT II analyzer featuring a crisp color display, fast data acquisition, and powerful vibration diagnostics tools.