Vibration is a persistent and costly problem across many industries. This is demonstrated by the fact that the global vibration monitoring systems market, for example, is expected to double over the next 10 years, to exceed an estimated $US 5 billion ($AU 7.5 billion). Companies are investing in monitoring and predictive maintenance to identify potential equipment issues before they cause failure, downtime, and OH&S maintenance hazards.
The burgeoning trend – especially strong in manufacturing, mining, oil and gas and energy generation – aligns closely with the broader trend of Industry 4.0 and the integration of technologies like AI and IoT into industrial processes to optimise efficiency and safety. Today’s machines can even indicate what they need and when – before a failure occurs.
Such spending is a wise investment in ensuring higher standards of production quality, consistency and on-time delivery – as well as preventing budgetary blowouts and reputational damage by ensuring statutory safety and environmental compliance, helping to foresee and prevent spills of oil, process fluids, and nasty chemicals passing into communities’ water and air.
“But monitoring vibration is just one side of the coin. The other side of preventative maintenance focuses on getting Noise, Vibration and Harshness (NVH) out of the workspace in the first place – sometimes by cutting it 90-99 per cent,” says pneumatic actuation isolation and suspension specialist Air Springs Supply.
“Oddly, isolation of NVH is thought of as an expensive business, which it doesn’t always need to be. While it is true that the best NVH individual solutions are tailored to particular applications (there is no single silver bullet), much can be gained by looking at the possibilities of active and passive isolation of bad vibration sources. And simpler can be better,” says Air Springs, which is national distributor for Firestone Airide actuation and isolation products through a network established over more than 50 years.
So as engineers, operations managers, and maintenance teams search for the best answer to their particular NVH issues, the first question they have to ask is whether they need an active isolation system or a passive system.
This applies whether they are:
- Mounting the source of the NVH on isolators to prevent it transmitting problems to nearby equipment (such as vibrations emanating from a stamping press, metal machining installation, heavy motor, compressor or conveyor, for example),
- Or where a sensitive piece of equipment is being mounted on isolators to remove it from surrounding NVH (such as isolating a control panel, or even a complete automation installation).
Both active and passive systems involve isolators that join two entities yet allow each to remain in its natural state without influence extending to the other.
Active Systems are usually more expensive and more complex. They involve a system that supports and isolates an object by providing motion that counteracts the disturbing motion that needs to be isolated. This requires extremely fast-acting actuators and high-gain feedback devices to sense the motion and control the actuators. It is usually the stuff of experts dedicated to the field, because so many applications are unique and challenging, to need this level of attention.
Passive Systems are typically simpler and more cost-effective. Passive isolators are mounts that support and isolate an object without the contribution of any outside energy source. Passive systems are often therefore an ideal low-maintenance solution to isolation of equipment such as vibratory conveyors and vibration tables, large drying machines, centrifugal separators, measuring tables and machinery, commercial laundry machines, compressors and electronic equipment involved in production automation. And plenty more too.
Air springs Supply says anyone who has been in the actuation, isolation and suspension industry in the longer term knows that the usual response to passive isolation needs has long been provided by metal coil springs.
“And people tend to stick with what they know, even if it is noisy, stiff, and its cost-effectiveness has been overtaken for many applications. (Not all, because it is horses for courses).
“But coil springs have some endemic issues, including constant spring rates that will only achieve their published isolation effectiveness at a single operating point. Any variation of load or input frequency will dramatically change the isolation achieved. This can be engineered out, but at a cost of cash and complexity.
“Plus, equipment mounted on coil springs can react quite violently to start-up and shut-down conditions. Also, coil springs are only able to provide isolation in one axis. If there is any lateral loading, coil springs will not provide good isolation.”
Metal can also fail in harsh environments, deteriorating through rust and corrosion, leading to hygiene and safety precautions. These can cost extra.
Also, metal construction does not allow for much overload capacity. Overloading a coil spring will most generally cause it to fail. Because coil springs can cause great damage if they do fail, spring cages or other means must be used to protect equipment and personnel from this possibility. These cost extra too.
Durable and versatile alternatives
So, it makes sense to at least consider alternatives, says Air Springs.
Several materials and designs offer effective industrial passive vibration isolation as durable and versatile alternatives to traditional coil springs. These include, extensively, rubber, as well as specialised materials, each offering unique advantages for different applications.
Metamaterials can fall at the more expensive end of the spectrum, being artificially engineered materials with properties not typically found in naturally occurring substances.
Rubber isolators’ viscoelastic properties, on the other hand, cost-efficiently provide both elasticity and damping, making it a common choice for vibration isolation.
Natural rubber is widely used, but synthetic options like neoprene and nitrile rubber offer better resistance to different industrial and environmental factors.
The simplest rubber isolators include rubber pads and laminated rubber cushioning designs, which are effective in some household and industrial uses where load capacity, environmental conditions, and spatial constraints have been considered. They also need regular maintenance to extend the isolator’s lifespan, where they are subject to environmental degradation. So, again, horses for courses.
“Which brings us to rubber-based products further up the performance and no-maintenance scales, the products for which the Air Springs Supply team are responsible as national distributor for Firestone Airide products proven globally and locally.”
The first of these attractive, no-maintenance and silent alternatives is provided by Firestone’s Marsh Mellow™ springs, which can achieve outstanding isolation efficiencies of up to 97 per cent.
These ingeniously designed Marsh Mellow springs appear similar to a solid rubber mount at first glance. But look deeper and you will see their unique construction with layered and angled fabric plies around a hollow core, which make Marsh Mellow springs much different in performance.”
Marsh Mellows’ hollow centres surrounded by a solid rubber core and fabric ply-reinforced body deliver constant vibration isolation with changing loads. Their unique construction delivers low natural spring frequencies to provide excellent isolation of forced frequencies in the range of 13-20-Hz (800-1200 cycles a minute).
This type of performance – and a maximum load range now extending from 0.64 kN up to 88 kN (on special order) – makes them particularly suitable for vibration isolation applications beneath equipment commonly used by the mining, quarrying, primary production, food and beverage processing, and manufacturing industries. They can be used beneath machinery ranging from vibrating screens to stamping presses, mixers, motors, compressors, conveyors, crushers, blowers and bins, and generators.
Marsh Mellow springs are a variable spring rate device which allows for a nearly constant natural frequency over a range of loads. This allows for changes in load without significant change in isolation effectiveness.
They can also function well over a range of input frequencies and endure overload conditions of up to 40 per cent deflection. If they ever do fail because of catastrophic conditions that could crush other suspensions, the design of these supple but strong springs means they will not fail catastrophically – so they don’t pass metal fragments into any primary or secondary machinery downstream on the production line. They will still provide some support, as well as being easier to get in and out of machinery, because a few of these springs do the job of a larger number of metal springs (also making them cost-efficient).
“This overload capacity is a big deal to staff at the production face, who sometimes have to crawl into confined and hazardous spaces to get machinery working again” says Air Springs Supply.
And because they reduce structurally transmitted noise caused by vibration, Marsh Mellows have considerable OHS and comfort benefits by being quiet in operation.
OHS professionals readily understand the importance of reducing the risks of hearing and nerve damage caused by NVH. It is a no-brainer, as statutory and compliance expand. Protecting people is always a priority.”
Marsh Mellows can also make ideal shock absorbers for conveyor, primary product, and other materials handling applications, particularly in situations where their corrosion-resistant durability means they will survive damp and corrosive environments in which alternatives may fail.
“So, Marsh Mellows are a highly cost-effective solution to a wide range of NVH issues. They will offer exceptional value and performance many applications for which they may never have been considered. But as with any good NVH technology, seek advice from someone who has long experience with the product and will be there to provide guidance long after the actual installation.
“Poor service and poor advice just transfer problems further down the timeline, when they will be even more expensive to fix. The Air Springs Supply team will be pleased to help, of course – and we may offer alternatives where our product and application knowledge demands these.”
Airmount™ isolators – the vibration isolation champion
Some of the absolute best performance in terms of industrial vibration isolation is offered by another product range distributed by Air Springs Supply. These are Airide Airmount isolators, quiet achievers (quite literally) which are among the world champions in their field.
So good they can be used beneath hospital operating tables, weapons guidance systems, industrial technology platforms, thumping generators in buildings and all manner of motors, drives, crushers, screens and the whole range of NVH-prone paraphernalia of factories, mine and infrastructure sites and energy plants.
These carefully engineered rubber-and-fabric bellows of whatever shape (above) contain a column of compressed air as their spring medium. They are constructed with multiple layers to contain this for maintenance-free durability, including an inner layer, two plies of cord-reinforced fabric, and an outer layer. Each features specific metal end closures, their bead plates, which are crimped onto the bellows for a secure seal.
“Firestone air springs utilise high-strength fabrics and durable rubber compounds, often neoprene. They offer extraordinary maintenance free performance – we had sets beneath a multi-storey sonar testing tank for more than a decade. The air springs were still good when the tank wore out its usefulness and was demolished.” These are enduring passive isolators because systems using them typically have:
No external control or feedback loop: Unlike active vibration isolation systems, passive isolators like air springs don’t require external energy input or feedback mechanisms to adjust their behaviour based on the vibration they are experiencing. They can be permanently sealed for their task – or fed by compressed air from a standard 7bar (100psi) compressor.
Spring-like behaviour, without the limitations: Air springs function by using the compressibility of air to provide a spring-like response to vibrations, effectively decoupling the vibrating source from the isolated component.
Natural frequency – this is important: The natural frequency of an air spring is determined by its design and operating pressure. Lower natural frequencies lead to better isolation, especially at lower vibration frequencies.
Designs such as Airmounts are also unique in that they have a variable spring rate, which allows the natural frequency to remain nearly constant with changes in pressure and load. This allows for the use of the same Airmount at different mounting points on unevenly loaded equipment.
Because Airmounts use air as the isolation media, rather than a solid material, they provide less of a pathway for transmitting high frequency vibration. Therefore, they reduce structurally transmitted vibration and hence reduce noise transmission.
Also, Airmounts do not exhibit the chatter that conventional coil springs do – or the crashing when a metal spring breaks or a bank of springs suffers from permanent compression, called “spring set”.
Further, Airmounts are also adaptable to overload conditions. Any given Airmount can easily handle a substantial change in load by simply adjusting the air pressure, whereas coil springs are often designed for a very narrow opening range. And finally, because of the nearly constant natural frequency, Airmounts react in a much less violent manner than coil springs during start up and shutdown.
How good are they? Better than 99 per cent
“It is interesting from an engineering viewpoint that Airmount air springs are the only passive type of isolator that operates on the principle of compressing a gas rather than deflecting a solid. Because of this, Airmounts are the passive isolator with the lowest natural frequency (and the lower the frequency, the lower the NVH transmission).
“They are so effective, in fact, that they are used beneath some hospital operating beds and to support weapons guidance. By using these qualities, severe engineering and OH&S issues have been overcome through their isolation efficiencies typically in the high nineties and sometimes well exceeding 99 per cent.
Airmounts performance can be further enhanced by using auxiliary reservoirs to lower the natural frequency. This makes them suitable for a wide range of applications, from sensitive instruments to heavy machinery.
Airmounts are also unique in that they have a variable spring rate, which allows the natural frequency to remain nearly constant with changes in pressure and load. This allows for the use of the same Airmount at different mounting points on unevenly loaded equipment.
Further, Airmounts are also adaptable to handling changing loads or overload conditions. Any given Airmount can easily handle a substantial change in load by simply adjusting the air pressure, whereas coil springs are typically designed for a very narrow opening range.
Because these air springs use air as the isolation media, rather than a solid material, they provide less of a pathway for transmitting high frequency vibration. Therefore, they reduce structurally transmitted vibration and hence reduce noise transmission. Also, Airmounts do not exhibit the chatter that conventional coil springs do.
And finally, because of the nearly constant natural frequency, Airmounts react in a much less violent manner than coil springs during start-up and shut-down conditions as the input frequency changes.
Conclusion
Often the cheapest passive isolation option is rubber pads. They can be useful where you don’t expect too much. The least engineered of these thin rubber mounts are, just as they sound, a thin sheet of rubber material.
They are very limited in their deflection capacity. Since deflection is inversely proportional to natural frequency, the rubber mounts’ inability to provide much deflection means it will have a high natural frequency, which will result in lower levels of isolation effectiveness. Better engineered pads are better, but they cost more than their basic cousins and perform less than the options above.
“This article suggests where very good natural isolators – such as Marsh Mellow and Airmount technologies – can provide superior performance in a wide variety of passive isolation applications. It does not for a moment assert that these technologies are the optimum for every application; after all, no isolator technology is that.
“But the performance and flexibility of designs such as Marsh Mellow and Airmount air springs are increasingly being appreciated as providing durable, high-performance and cost-effective alternatives to conventional methods of passive isolation.
“Particularly as Industry 4.0 drives the ongoing digital transformation of manufacturing, mining, utility and infrastructure industries.
The integration of technologies – such as the Internet of Things (IoT), cloud computing, artificial intelligence (AI), and big data analytics to create smart, connected, and efficient industrial systems – all demand ultimate protection and reliability of the plant they govern, both for both production efficiency and for the protection of the valued workers on whom these systems depend.