Home > Which airbags are best as actuators and isolators in challenging environments?

Which airbags are best as actuators and isolators in challenging environments?

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article image Rolling sleeve air spring, centre, and single, double and triple convoluted types

Air springs offer a cost-efficient, low-maintenance and proven alternative to conventional pneumatic cylinders in applications involving challenging environments ranging from grimy heavy industrial mining and energy settings to ultra-hygienic food, beverage and primary processing.

Air springs or airbags are an excellent alternative to metal springs in tasks where they are subjected to shock and varying loads, because metal spring plates are susceptible to breakage. Air springs are also clean, quiet and extremely tough, and are being used in big trucks and trains in place of metal springs because of their comfort, durability and load-friendly smooth performance.

To those who are unsure about which type of classic airbag shapes to choose for their application from rolling sleeve and convoluted options, James Maslin, an air spring actuation and isolation specialist, advises that the right type comes down to the application. He explains that rolling sleeve as well as single, double and triple convoluted airbags are all designed for different tasks.

Mr Maslin is National Marketing Manager for Air Springs Supply, the long-established national distributor for Firestone Airstroke actuators and Airmount isolators as well as the structurally identical Airmount airbags.

Actuation

Offering load/force capabilities from a few dozen kilograms to nearly 40 tons each, both types of air spring operate the same simple way with compressed air directed into the air springs, expanding their fabric-reinforced rubber bladders in a linear fashion from their compact collapsed state to become force-developing actuators.

Mr Maslin explains that an air actuator is basically two end plates connected by a bladder, with the two plates pushed away from each other by the force exerted through pressurisation. In most cases, the minimum (or deflated) height is considerably less than the available stroke, allowing the air springs to be installed in a very compact space and extended to more than twice their starting height. This is a tremendous benefit in floor-mounted lifting devices.

The smallest Airstroke actuator is 2.3 inches (58mm) in diameter and collapses to just 1.2 inches (31mm) in height. The largest triple convoluted Airstroke actuator is 37 inches (940mm) in diameter and will collapse to a very compact 5.5 inches (140mm).

Airbag actuators also offer considerable side load flexibility, resulting from a flexible, compliant bellows wall, instead of seals or guides. The bellow follows the path of least resistance, eliminating any worries about side loads or damage caused by misalignment. The seal-less design also means lack of friction, removing the equipment-damaging jerky motion associated with sliding seals in traditional cylinders.

As linear actuators, they can provide anything from a few hundred kilograms of force up to multiple tons of force, making them useful in various press applications, such as a forming press or small stamping press or conveyor actuators, lift tables and conveyor buffers. Air actuators are also excellent for constant force applications, such as pulley tensioners, web tensioners or drum roller compression devices.

The convoluted bellow type air spring comes in stacked convolutions, single, double or triple, with the convolutions reinforced by a girdle hoop. Convoluted air springs are capable of up to ten times the force of a rolling lobe version, but have less usable stroke to work with, although they can be stacked to provide longer strokes or greater angular rotation.

The rolling sleeve (or rolling lobe) air spring uses a single rubber bladder, which folds inward and rolls outward, depending on how far and in which direction it is moved. The rolling lobe air spring is available with very high usable stroke length.

Although both the reversible sleeve and convoluted air springs are based on the same principle, there are subtle differences between the two options. Unlike convoluted air springs, the reversible sleeve air spring has a piston, which is fastened to the mount and plunges in and out of the air cavity within the rubber bellows. Having this piston gives the reversible sleeve air spring an advantage over the convoluted air spring in that spring rates can be further tuned using a variety of piston profiles. For straight-sided pistons, the reversible sleeve air spring is able to maintain a constant load for a given internal pressure over a range of heights.

Isolation

As isolators, both rolling sleeve and convoluted air springs offer outstanding isolation efficiencies of 99.5-99.9 per cent. A flatter performance curve, which helps achieve the same isolation efficiency through a broader range of expansion and compression, makes the rolling sleeve the preferred option for transport applications.

Convoluted and rolling sleeve air springs have been used as linear actuators, vibration isolators and tensioners among many other applications. They can be used to absorb shock in material handling applications, such as when logs are dropped onto processing stations in saw mills. Air springs make some of the best vibration isolators on the market, especially in applications such as vibrating hoppers, commercial laundry machines or generator and motor mountings.

Users of air spring isolators and actuators should consult their supplier to determine temperature and chemical tolerances for particular applications. Through permanent inflation or adjustment by standard factory 7 bar (100 psi) compressed air, Airmounts can be used in diverse isolation applications from suspending tanks, pressure vessels and liquid containers in which delicate processes are undertaken, through to suspension of process control technology including mixing tanks and computer and production automation equipment.

Airmounts are also recommended for isolating the source of noise, vibration and harshness (NVH) by suspending compressors, vibrating screens, bin hoppers, packers, blowers and stamping equipment that pass disruptive impacts into the area surrounding them.

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