Why analyse machinery vibration?

04 October 2021

Jason Tweedy discusses the benefits of vibration monitoring and analysis.



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In the 1970s and 80s condition monitoring was largely restricted to audible monitoring with technology playing little part. You literally listened to the equipment!  There is a lot to be said for this and an experienced pair of ears can pick up useful information. Similarly, a visual inspection can also provide some information such as discolouration on bearings’ raceways, cages and balls which can often be the result of increased vibration leading to wear.

Of course, it’s not always possible to see all parts on a machine or hear every nuance and there’s not always a person on site who has worked with that specific machinery for years and can tell when something isn’t quite right. Plus, by the time you can hear or see something isn’t right, the damage has often already been done.

So, new forms of technology-reliant condition monitoring have been introduced over the years which are more effective, require less labour (and experience. The human ear has been replaced by ultrasonic devices and the eye by thermography which looks for heat which can be caused by friction. Either of these are good identifiers of potential issues and which is used depends on the process and machinery being monitored.  In the case of rotational equipment, and bearings in particular, ultrasonic is ideal as these parts often produce ultra-high frequency sounds when vibrating. Where access is an issue, thermography is the better solution.

Vibration analysis
Analysing machinery for vibration is becoming increasingly popular. We are increasingly finding that maintenance related tenders have Vibration Analysis stipulated within them.  

There is a good reason for this: Vibration Analysis allows early detection of wear, fatigue and failure in rotating machinery because vibration occurs in all rotational assets, but generally highlights an issue discovered by higher readings and particular frequencies, mostly as the result of wear and tear but also as a consequence of poor maintenance practices. Vibration builds and leads to equipment failure. 

Vibration Analysis identifies potential problems and a predicted time to failure (in some cases up to one year in advance of equipment failure) to enable replacement parts to be ordered in a timely way and helping to reduce unexpected downtimes.  

Vibration Analysis also saves money on repairs and maintenance.  This can be clearly seen By one of our customers who was replacing all the bearings on a particular machine every month as they couldn’t afford to have that machine fail. We implemented a Vibration Analysis service which has stopped this practice. Instead, we are able to identify which bearings need to be replaced. 

In-house or outsource?
Technology has not replaced human knowledge and experience altogether. The data presented by the Vibration Analysis equipment needs to be read, understood and interpreted into meaningful action. So, while organisations can buy relatively inexpensive monitoring equipment, they also need the expertise to understand the data.  This is why many companies now outsource Vibration Analysis to specialist companies who provide Vibration Analysis. 

If you do decide to outsource this service, you can expect a typical analysis visit to take around two days to complete; one day to data collect from the machinery, and a further day to interpret the data and produce a report. Larger routines sometimes need a days’ setup to create a database. Obviously, this depends on the size of the site and the number of points to be analysed.

The engineers will measure the absolute and relative vibration on machinery. The level of vibration can be compared with historical baseline data to assess the severity. The report supplied should detail the findings for each of the assets, along with clear photographs, and a remedial list of actions required to remedy any faults.

The frequency of the analysis will depend on the nature of the process and machinery to be measured.  Monthly in-depth analysis is recommended for sites where you can’t easily stop a line. Other processes, where the components are low cost and easily replaced, would require less.  

Delivering results
While the market for Vibration Analysis is growing, the reality is that the majority of businesses remain either unaware or unconvinced of the benefits. For many, it’s the cost of the service which puts them off and a lack of awareness of the ROI. 

My advice is to ask the prospective company for samples of the reports they have produced for customers and read them to see if your engineers would be able to take appropriate action based on those reports. Ask to speak to other customers to find out if the analysis has really delivered a good ROI; whilst many companies may not want to put cost savings in writing, they are often happy to speak to a fellow colleague on a one-to-one basis.

For one such customer, our Vibration Analysis service certainly made a good first impression. On the first day of setting up a Vibration Analysis programme at their site, we made an unexpected discovery. Day one involves identifying what and where to analyse and taking sample readings, with the actual analysis to start the following day.  However, even within that brief time frame the sample analysis clearly showed one of the motors to have serious issues. We mentioned it to the customer as we left for the day and just half an hour later the motor blew up. Although it was too late for this motor, the customer was very impressed that we had been able to identify an issue in such a short time frame. From that moment on he clearly understood how Vibration Analysis would benefit his business going forward.

But it’s not just ageing or worn parts that can be identified by Vibration Analysis. One customer uses our Vibration Analysis service to firstly identify potential issue during the biannual shutdowns for repair and major maintenance. Then we return after the repair work has been done to ensure it has been carried out correctly. We have been able to identify some poor repair work, which would have reduced the life of the component part and led to unnecessary downtime, enabling it to be remedied all before the site returned to production.  

Similarly, we were asked recently by a ¬ customer —¬ a manufacturer of bricks — to look at a repair done on a critical fan used to regulate the kiln temperature. The Vibration Analysis showed the repaired fan, that had originally been out of balance and at risk of breaking, was actually worse than when initially removed. The company who had conducted the repair work was unable to fix it. We found a catalogue of mistakes, including poor alignment of pulleys and motor, broken anti-vibration feet and inadequate fan balancing causing vibrations which were reverberating through the structure. Ultimately the customer decided to buy a new fan, but this was on a long lead time so, in the meantime, we helped to make the existing fan work until the new one arrived. We also installed a temporary wireless Vibration Analysis unit to monitor severe fluctuations in the fan, so they could be caught before breaking the fan beyond repair.  

Condition monitoring has seen a significant uptake over the past decade, with vibration monitoring and analysis gaining greater traction. Manufacturing, engineering and processing sites are seeing genuine benefits and in many instances Vibration Analysis is becoming business critical. 

Jason Tweedy is head of condition monitoring at Brammer Buck & Hickman.


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