FLUID POWER HANDBOOK
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AIR
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springs have been used in heavy-duty vehicle suspension systems for nearly a century, where they have been able to provide usefulness by taking advantage of the compressed air required for vehicle braking systems. Air springs have provided a two-fold advantage over mechanical leaf or coil springs. One advantage with air suspension is the extra comfort provided by being able to vary the air pressure inside the spring, which changes the spring rate, and therefore, ride quality. Additionally, because variable control over air pressure adjusts the deck or trailer height, aligning loading docks to the level of the deck is possible when dock plates are unavailable. The usefulness of air springs or actuators didn’t go unnoticed in the industrial machine industry, and it was clear they could offer unique solutions for various applications. Air actuators have seen duty as shock absorbers, linear actuators, vibration isolators and tensioners, to name a few examples. They can be used to absorb shock in material handling applications, such as a saw mill,
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when logs are dropped onto processing stations. Air springs make some of the best vibration isolators on the market, such as would be used on a vibrating hopper or commercial laundry machine. In summation, air springs are a high-force, low-cost actuator that can operate in a linear fashion or at an angle. They can be stacked to provide longer strokes or greater angular rotation. As air is directed into air springs, the bladders allow them to expand in a linear fashion. This permits them to be used as force developing actuators — like pneumatic cylinders — and as such, rod attachments are available to mimic the function of them. Most often, however, an air actuator is simply two end plates connected by a bladder, and as they are pressurized, force pushes the plates away from each other. As linear actuators, they can provide up to 35 tons of force, making them useful in various press applications, such as a forming press or small stamping press. Air actuators are also excellent for constant force applications, such as pulley tensioners or drum roller compression devices. All air springs are singleacting, unless they are coupled together so one extends while the other retracts. The two major types of air springs are the rolling lobe (sometimes called
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reversible sleeve) and the convoluted bellow. The 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 high usable stroke length — but it is limited in strength because of its tendency to bulge, and therefore has limited force capacity. The convoluted bellow type air spring uses one to three shorter bellows, with the multiple units being reinforced by a girdle hoop. Convoluted air springs are capable of ten times the force of a rolling lobe version and twice the life cycle rating, but have less usable stroke to work with.
