ANYONE who has ever ridden in air-suspended vehicles will have seat-of-the-pants knowledge of the quality of air isolation. But while many people know that air springs often provide the ultimate ride in stretch limos, luxury coaches and high-speed trains, not all are aware of their extensive applications in materials handling machinery.
Applications range from isolating heavy equipment for operational efficiency (conveyors, generators, compressors and vibrating screens) through to protecting of delicate equipment.
Air Springs are in essence immensely strong rubber and fabric-reinforced balloons or bellows. These bellows can be tubular, or come in convoluted shapes. These latter, doughnut-shaped, convolutions may be stacked one, two or three high depending on the performance required.
What makes air springs useful in many applications is that they are the only passive isolator that operates on the principle of compressing a gas rather than deflecting a solid.
Air springs are therefore the passive isolator with the lowest natural frequency, and the lower an isolator’s natural frequency, the better the isolation effectiveness. Furthermore, air springs are the only passive isolator that can achieve a reduction in the natural frequency.
With the use of an auxiliary reservoir, the natural frequency can be lowered to further improve isolation effectiveness to even finer degrees.
Air Springs Supply’s Firestone products are called Airmounts, and they have a variable spring rate. This quality is very useful to industrial engineers in that it allows the isolator’s natural frequency to remain nearly constant with changes in pressure and load.
Because Airmounts use air as the isolation media rather than a solid material, they provide less of a pathway for transmitting high-frequency vibration.
Any given Airmount (and they range in load carrying capacity from 40-40,000kg) can easily handle a substantial change in load by simply adjusting the air pressure.
Applications
A common materials handling problem is isolation of bin vibration, typically used to maintain a homogeneous mix or flow of material inside a hopper.
It must be isolated from bin supports so as to prevent structural fatigue. Solid rubber isolators or steel springs can be used, but they must be tuned to one specific load and a single height.
Air springs provide a high degree of isolation compared with other methods, where they are used down to disturbing frequencies of 3-4Hz. Isolator inflation can be changed to compensate for different loads or heights without compromising isolation efficiency.
Air spring isolators are generally used where weights exceed 100kg per mounting point. They can also be used on conveyors to prevent shock and vibration in a wide range of industries.
One of the most frequent applications of air springs is in isolating vibrating screens, which are widely employed in industries to process chemicals, minerals and food and beverage ingredients.
*Simon Agar is the National Sales Manager for Air Springs Supply sales@airsprings.com.au
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