AIR Springs Supply have released a document outlining the advantages, applications and limitations of bellows-type air cylinders for the engineering of assemblies for high-repetition tasks in food, beverage, packaging and metal stamping plants.
According to the company, these air cylinders are also applicable for use in conveyor and materials handling applications within aggressive factory, mining and quarry environments where maximising production is important.
Generally known as air springs or air bags, the company said these have capabilities and limitations that set them apart from traditional complex hydraulic and pneumatic cylinders driven by the pumps and compressors in nearly every production plant.
Air Springs Supply says despite their appearance, they are cylinders. The traditional cylinder design contains a piston sliding within a housing of circular cross-section connected to the work by a rod passing through one end of the device.
These cylinders require several guides and seals, which align and seal the sliding surfaces. These allow a pressurised, contained column of fluid to apply force to the piston.
An air spring contains its column of air in a fabric-reinforced rubber envelope, or bellows, with the ends sealed. Air is introduced into the chamber, driven by compressors through an air fitting. As a result, the air spring expands lengthways.
To select the appropriate air spring, specify the necessary force, the linkage motion, and any special environmental concerns. Air Springs Supply, for example, provides Airstroke actuators which give 40 to 40,000kg of pushing or lifting power.
According to Air Springs Supply, some key reasons for using air springs include cost benefits. Air springs can be used instead of more expensive hydraulic systems when applying large forces.
Sizes are available from fewer than 80mm to more than nearly 1000mm (3in to 38in) in diameter. The larger sizes allow force up to 40,000 kg each using only 7 bar (100psi) air pressure. The capital cost of an air spring is frequently less than half that of a pneumatic cylinder with equivalent capabilities.
Another benefit of using air springs is their compact installation. The way a flexible-wall air spring operates is as follows: it is compressed to its minimum height then extends when pressure is applied.
Side load flexibility and ease of attachment are also two significant benefits of air cylinders. Since the bellows bends, bead plates don't have to remain parallel. This significantly simplifies attachment, especially when linkage is at an angle.
The company added however that although air springs are beneficial for scores of applications where they are not currently considered, there are some limitations to consider when specifying them.
For example, air springs are single-acting. Unlike hydraulic cylinders, air springs need an outside force to retract them to their minimum height. This force can be gravity, or another air spring, or a coil spring.
Additionally, the available stroke of an air spring is limited by the length of the side wall. This length is determined by stability concerns. However, specifying single, double or triple-convoluted air springs can often help solve this problem.
Air Springs Supply also warns air cylinder users should not stretch the wall in extension or pinch it in compression. Therefore, air springs are normally used for high-force, low-stroke applications.
Air springs should also be used in temperature ranges from -20 to 95 degrees Celsius, and in applications where they can be kept away from petroleum-based fluids and chemicals that attack rubber.
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