By Cliff Ortmeyer, Global Head of Technical Marketing at Farnell
Many industries depend on the continuous operation of critical assets such as motors and pumps. These devices must function to ensure that customers get the food products or water supply services they need. Failure to provide these products or services can result in significant financial penalties for companies, and even legal sanctions.
More and more companies are turning to predictive maintenance which seek to avoid these consequences by eliminating unexpected breakdowns and hence unplanned downtime. Such programs monitor machine condition and performance to determine which models are most likely to fail, and when. With this information, maintenance personnel can investigate machine condition more effectively, schedule maintenance tasks to comply with production schedules, and carry out repairs before a machine breaks down.
Working in this way can produce significant benefits, including:
Maintenance costs - down 50 %
Unexpected failures - reduction of 55 %
Repair and overhaul times - down 60 %
Spare parts inventory - reduction of 30 %
Mean time between failures - up 30 %
Availability - up 30 %
According to the book Plant Engineer's Handbook (2001), a 10 % reduction in maintenance costs can produce the same financial benefit as a 40 % increase in sales for a typical manufacturing plant.
Vibration analysis: a vital tool for predictive maintenance
One of the main tools for obtaining data for a predictive maintenance program is thevibration analysis. Measuring vibrations can enable engineers to react in real time to changes in a component's condition, and allow remote condition monitoring.
The type of vibration sensors The most common type is accelerometers, which must be in direct contact with the machine or component being measured. Piezoelectric accelerometers are the most widely used type. They are popular because they produce a strong, clean signal at most frequencies, although piezoresistive accelerometers, which produce changes in resistance, are also becoming increasingly common.
Microphone sensors are also popular. They can detect changes in high-frequency sound, and are a cost-effective way of obtaining basic information. They are often used in conjunction with accelerometers.
Strain gages operate through an electrically conductive grid that deforms when a component undergoes vibration. These deformations modify the electrical resistance of the grid and, by reading the time taken for an electric current to pass through it, the vibration of the object can be evaluated.
Non-contact techniques such as eddy current and laser displacement can also be used. As they do not need to come into contact with the asset, they are ideal for use with delicate assets.
There are also well-established vibration analysis techniques that can be used in predictive maintenance, such as peak acceleration analysis, frequency analysis and artificial intelligence techniques. Some suppliers offer compact vibration analysis equipment that can provide insights into vibration problems in motors, hydraulic components and other machines used in production.
IIoT boosts adoption of vibration analysis
The ongoing adoption of the Industrial Internet of Things (IIoT) is one of the main drivers behind the implementation of vibration sensors and analysis techniques. As manufacturing companies adopt plant-wide connectivity to share data from interconnected sensors and instruments, it becomes easier to access and analyze data and integrate it into predictive maintenance programs. This makes it easier than ever to integrate vibration sensors into a monitoring and maintenance program, and will undoubtedly lead to greater choice and wider adoption of these devices.
The cost savings that vibration analysis can bring mean that users of production machinery, particularly rotating equipment such as motors, pumps, compressors and turbines, can benefit financially from implementing this technology.
Misconceptions about vibration analysis
There are a number of preconceived ideas and misunderstandings about thevibration analysis and the need to introduce it as a major pillar of a predictive maintenance program. These include:
"Our machines don't vibrate, so we don't expect them to break down anytime soon."
All machines vibrate, and while it's normal for motors to generate small vibrations, strong vibrations or any change in the motor's vibratory behavior could indicate problems. All the vibrations experienced by a motor can be due to a number of factors. Knowing what these possible causes are will help you diagnose your engine more effectively.
One of the primary causes of vibration is motor imbalance, a point where an unbalanced weight moves around the machine axis, causing rotating components to vibrate. These types of imbalances can be caused by molding defects, machining errors or even maintenance problems, such as dirty fan blades.
Bearings can also be another major cause of vibration, as loose bearings can cause vibrations to propagate to other components. Lack of lubrication, poor insulation or contamination can quickly wear out bearing components, while a roller raceway with tracings can create movement every time a bearing moves over the damaged area.
Gears are also a potential source of vibration if misaligned. Worn or broken gear teeth can shock against each other, causing a potentially dangerous vibration.
"We don't need vibration analysis: if our machines heat up or make unusual noises, then we can study them."
Waiting until there are easily detectable signs of impending failure is a false economy. At that point, a catastrophic failure could occur within days or hours. On the other hand, a properly executed vibration analysis program could detect a possible breakdown several months before it occurs.
Figure 1 shows the detectable indications of component failure and the time scales over which these signs become apparent. Easily detectable indicators, such as noise and excessive heat, which can be detected by humans, are signs of impending failure. However, by the time they are detected, it may be too late to intervene, and production interruptions or catastrophic damage are real possibilities.
On the other hand, changes in the vibration profile of a component or machine can be detected several months before a breakdown occurs.
Many plant maintenance departments operate on a "use it or lose it" philosophy, where no action is taken until the machine actually breaks down. This results in high maintenance costs and lost production. In contrast, the benefits of early vibration detection include predictability, safety, reduced costs and improved reliability.
"Vibration analysis is too difficult and expensive."
Vibration data analysis requires software, hardware, training, an extensive asset information infrastructure and a rigorous schedule. Although the most complex analysis of multi-cause vibrations is best left to specialist vibration analysts, much can be done to detect basic problems with relatively inexpensive equipment.
Take the Fluke 805 vibration meteris an easy-to-use instrument that delivers precise, reproducible readings. The meter features a four-level scale for determining severity, and a built-in processor that calculates bearing condition and overall vibration with easy-to-understand text alerts.
Its transducers can read a wide range of frequencies, from 10 Hz to 20,000 Hz, broad enough to cover the vibration profiles of most machines and components. The Model 805 features a simple user interface through which the user simply enters the rpm range and equipment type. Fluke also offers the 810 Vibration Tester, a more advanced instrument with a diagnostic engine that uses a database of real vibration information.
While the implementation of a vibration analysis program entails certain expenses, the costs associated with the absence of vibration analysis can be considerably higher. Some examples, an analysis by ABB Motors highlighted the potential costs that could arise in the event of a motor failure. The analysis took the case of a 315 kW motor with an efficiency of 95.5 % used in a continuous process. With an energy cost of 12 cents/kWh and a motor running for 8,400 hours a year, the cost of running the motor over a 20-year life would be €7,096,176. This is extremely high compared to the typical purchase cost of €20,957.
However, the cost of engine downtime is just as significant. The analysis cites the example of an engine used in the oil and gas industry, where a breakdown could result in losses of €256,145 per hour. A single ten-hour breakdown over the 20-year life of the motor would thus result in losses of €2,561,425.
Similarly, significant losses are also possible in industries such as automotive, metal casting and food & beverage. Potential losses due to unplanned downtime have led more than 70 % of engine users to cite reliability as the number one priority in their engine maintenance programs, according to Reliable Plant.
"We don't have the staff to carry out a vibration analysis."
If an organization is large enough to have a dedicated reliability team, then vibration monitoring and analysis should be part of that team's responsibilities. Maintenance technicians can be trained in ISO 18436 via online courses for just a few hundred euros. One of the advantages of maintaining an in-house vibration analysis program is the ability to assess machine trends. In-house staff know the machines, processes, conditions and history, and can use this knowledge to supplement the information received from their monitoring tools.
With some training and inexpensive monitoring equipment, data that may indicate a fault can be collected. If sophisticated analysis is required, specialist consultants can be called in to use more advanced techniques to analyze difficult problems.
"Sourcing vibration analysis equipment takes too long and is difficult."
A growing number of suppliers offer specialized monitoring and analysis equipment, helping to democratize vibration analysis by emphasizing its benefits. Farnell provides solutions from a wide range of suppliers, including Fluke, Kemet, Omron, Murata, Amphenol Wilcoxon, TE Connectivity and Rohm. Many of these suppliers also provide online resources that explain vibration analysis and its practical application.
"In our plant, there are difficult conditions that prevent the use of delicate vibration sensors."
Sectors with harsh environments, such as industry, automotive and aerospace, already make extensive use of vibration sensors. Although these are difficult industries, careful consideration of issues such as housing/connector structure, sensing element material, signal conditioning and wiring has shown that these challenges are not insurmountable. Reputable manufacturers can advise on solutions for most applications. Moreover, demand is growing for sophisticated sensors that can also withstand extreme weather conditions, such as MEMS, ultrasonic, wireless and fiber optic sensors.
Today, more and more companies are realizing the need to implement a predictive maintenance program, especially for critical production assets. Vibration analysis is an essential part of this process. Many electronic component manufacturers and distributors offer sensors, analysis equipment and software, professional technical support and training to help customers at any stage of development.
By taking steps to implement a vibration monitoring and analysis program as part of an enterprise-wide predictive maintenance regime, plant managers can put in place a system that will deliver immense and lasting benefits, such as avoidable downtime, cost reductions, asset condition maintenance, improved productivity and a reputation as a reliable supplier.
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