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Analysing machinery for vibration

18 October 2021

Jason Tweedy discusses the benefits of vibration monitoring and analysis. 

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 as an experienced pair of ears can pick up useful information.  Similarly, a visual inspection can 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 is not always possible to see all parts on a machine or hear every nuance and there is 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 it is possible to hear or see that 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), but obviously come at a price. The human ear has been replaced by ultrasonic devices and the eye by thermography which looks for heat which can be caused by friction.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, and there is a very good reason for this: Vibration analysis allows early detection of wear, fatigue and failure in rotating machinery. 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. A wide range of components and machinery are impacted by vibration, with some of the most common being bearings and gearboxes.

Vibration analysis identifies potential problems and a predicted time to failure (in some cases up to one year in advance of equipment failure) this ensures that replacement parts can be purchased in a timely manner to allow for scheduled proactive maintenance, thereby reducing unexpected downtime.  

Furthermore, vibration analysis can help save money on repairs and maintenance. This can be demonstrated easily — one customer was replacing all the bearings on a particular machine every month as machine failure was unacceptable. We implemented a vibration analysis service with the company which has stopped this practice. Instead, we are able to identify which bearings need to be replaced. At the same time, we were able to highlight to the customer a number of issues that they were not aware of, allowing them to take proactive action.

In-house or outsource?
Technology has not altogether replaced human knowledge and experience. The data presented by vibration analysis equipment needs to be read, understood and interpreted into meaningful action. So, while organisations can buy relatively inexpensive monitoring equipment, they need to have the expertise to use that equipment and understand the data. This is why many companies outsource their vibration analysis to a specialist company.

Companies who provide  a vibration analysis service will have trained staff who can read frequency patterns and understand what they mean in relation to a wide range of machinery and its component parts. They are also likely to use more sophisticated machinery which provides accurate readings and detailed information. The type of low-cost monitoring equipment we see some companies using in-house is pretty basic and frequently misses nuances.

A typical outsourced analysis visit takes 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. 

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

The frequency of the analysis very much depends on the nature of the process and machinery to be measured. Monthly in-depth analysis is recommended for sites where it is not easy to 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 is the cost of the service which puts them off and a lack of awareness of the return on investment (ROI). This has not been helped by a number of companies professing to offer a professional vibration analysis service when in fact they do not have the training and skill levels, leaving the customer with a negative experience.

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 some of their customers to find out if the analysis has really delivered a good ROI; while 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 — a food production site in Manchester — our vibration analysis service proved invaluable in preventing unplanned downtime. As part of the survey, high readings were detected from a mill roof fan, which is part of a grain production process. The unit was swiftly removed for overhaul and the fan impeller and motor were sent to be balanced. Following the overhaul, the rotational frequency out of balance peak fell from a reading of 54.8mm/sec to 7.4mm/sec, a level which is within the normal working range. The planned overhaul and balance prevented at the very least 12 hours of unplanned downtime and lost production.

Condition monitoring in all its forms 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. Some insurance companies are even insisting on vibration analysis for safety, as we have regularly seen when it comes to electrical panels. If you haven’t previously considered it, or maybe you’ve not had a positive experience, it’s worth looking at the return a professional vibration analysis service can bring to your business for a relatively modest sum. 

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


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