News Releases

November 2010

A simple cure can be best where NVH spells trouble for the environmentally unwary

One of the most persistent enemies of industrial and processing plants lies hidden beneath the innocuous- sounding acronym NVH (noise, vibration and harshness).

The NVH problem rears its head in applications as diverse as the mounting of compressors, generators and turbines; isolating shakers, crushers and vibrating screens and conveyors; taming the shock and impact of stamping presses, fabrication and packaging and loading machinery; or ensuring tranquil environments for delicate computers and other electronic equipment now used widely in production and production automation processes.

And, at the same time NVH is trying to disturb the daily function of instruments and computerised building systems, it is also disrupting employee comfort and safety - "In a recent five year period there were about 16 500 successful workers' compensation claims for industrial deafness involving permanent impairment due to noise. says pneumatic isolation specialist Simon Agar, who is General Manager of Air Springs Supply Pty Ltd (www.airsprings.com.au).

"Safe Work Australia Chief Executive Officer Rex Hoy points out that not only is there a high economic price for occupational noise-induced hearing loss, borne by workers and their families, business owners and managers and the wider society: Also, NVH has also been linked to annoyance and fatigue and to serious health conditions such as hypertension," says Mr Agar, whose company has greatly expanded its range of inflatable Airmount isolators and Marsh-Mellow isolators in response to industry needs for simple, reliable and highly efficient ways to tackle NVH.

The company's single, double and triple-convoluted Airmount isolators - as well as rolling sleeve models and complementary Marsh Mellow (R) isolators - have been refined by international pneumatics leader Firestone to achieve isolation efficiencies of more than 99 per cent, says Mr Agar, who has more than 20 years experience in engineering isolation installations. He is a firm advocate of simplicity and cost-efficiency in tackling industrial NVH problems.

"In essence, the Airmounts we distribute are highly engineered balloons - balloons which are carefully constructed to deliver a range of performance demanded across a very broad spectrum of needs, extending from suspension of a 30kg computerised control panel, for example, to total suspension of the entire 100-tonne bulk of a huge motor, crusher, press or production line.

"The Airmounts' extreme performance and reliability is outstanding across a wide weight range. They're so efficient as to be used beneath operating tables in surgeries and beneath the most delicate of computers, yet robust enough to suspend an entire swimming pool in a luxury hotel" said Mr Agar.

Airmounts are available in an expanded range of sizes which can individually support weights extending from under 100kg up to more than 40,000kg. Models range from palm-sized to nearly a metre across.

"One of the beauties of isolators as simple as the Airmounts is that they contain no internal moving parts to wear, or metal springs to corrode or break," says Mr Agar. "They are extraordinarily tough, being manufactured by Firestone in exactly the same way as the Air Springs used in the suspensions of luxury coaches, heavy trucks and express trains.

Simple Mounting

Airmounts are typically mounted in the four following ways, each of which involves the fabrication of metal brackets to connect the air spring and its load. The brackets are usually fixed to bolts ramset into floors or walls, and the Airmounts are bolted onto them by way of studs protruding from the air spring's metal heads. The Airmounts, in turn, are bolted to the equipment which they are isolating.

1. The simplest way is to mount the load to be isolated on sealed air springs equipped with a valve (just like a tyre valve). Airmounts used this way are inflated individually and each must be checked periodically, as part of a routine maintenance programme, to ensure they retain the correct operating pressure and, hence, isolation efficiency.

2. Alternatively, individually inflated Airmounts can be linked to a compressed air tank via a regulating valve which ensures they maintain a pre-set pressure.

3. More sophisticated and maintenance-free is a three-point regulated system, in which Airmounts are connected directly to a typical industrial (100psi - 7 Bar) compressor via pressure regulating valves. This eliminates the need for periodic inspections. The Airmounts involved are connected in clusters with the load supported by three regulators to ensure even distribution of load.

4. The most sophisticated of the mounting systems in general use is a three-point leveled system connected to a compressor, as above, but also incorporating leveling valves, actuated by sensors, to ensure the load is maintained precisely in the desired position.

Marsh Mellows®

A product which is complementary to Airmounts (and also engineered by Firestone) is Marsh Mellow® springs, are tubular isolators which comprise a solid rubber core surrounded by bias layers of fabric engineered to the needs of particular applications.

Simpler again than Airmounts, they don't even need to be inflated. Utilized beneath machinery such as stamping presses and vibratory screens, they prevent repetitive shock and vibration from being driven into the ground, where they can disrupt foundations and disturb electronic equipment used for quality and process control efficiency.

They also allow very low natural frequencies (down to 2.5 Hertz) to be achieved under load, says Mr Agar, and feature a construction that allows them to retain a constant natural frequency under compression. This means they are excellent in applications subject to frequent load changes, such as isolating diesel engines, centrifugal separators, feeder lines and stamping presses, which can disturb instruments and electronic controls. Marsh Mellow springs are particularly suitable for vibration isolation of machinery such as compressors, vibrating screens, bin hoppers, blowers and motors.

Marsh Mellow springs are a simple, robust and effective means of solving industrial shock and vibration isolation problems including:

• Noise
• Gallop through resonance
• Short spring life
• Corrosion, abrasion
• Surge loads
• Bottoming-out
• High maintenance costs
• Lengthy replacement downtime
• Limited space for high-load springs
• Metal fatigue and breakage
• Complicated mounting

Low natural frequencies of Marsh Mellow springs mean they provide excellent isolation of forced frequencies in the range of 800-1200 cycles per minute (13-20 Hz).

Their high load capability means fewer springs may be needed in an application, resulting in less overall cost. The springs range in size from the 0216 model with an unloaded height of 44 mm and outside diameter of 41 mm, through to models such as the 0243 with an unloaded height of 203 mm and an outside diameter of 279 mm.

Information about the full range of Airmount and Marsh Mellow isolators can be obtained through the website of Air Springs Supply Pty Ltd, www.airsprings.com.au which is one of Australia's most comprehensive guides to pneumatic actuation, isolation and suspension.

Free technical information

Would you like to learn more about the technology discussed here? Readers can receive more information by contacting Air Springs Supply Pty Ltd, PO Box 215 West Ryde, 2114, ph (02) 9807 4077, fax (02) 9807 6979.

For more information about Air Springs Supply's national distribution and technical support network, please contact Air Springs Supply Pty Ltd, 10 Angas St, Meadowbank, Sydney 2114, ph (02) 9807 4077, fax (02) 9807 6979, sales@airsprings.com.au