Air Springs Supply is a leading Australian supplier of air springs and associated pneumatic technology for the industrial and transport segments.
Simon Agar, the General Manager of Air Springs Supply has compiled a report on ‘The Overlooked Air Spring’ based on his experience with the ingenious actuators.
Many of the best engineering innovations are the simplest. Sometimes, however, their very simplicity can work against initial market acceptance.
This is certainly true in Australasia of the air spring. Compared with traditional and more complex hydraulic and pneumatic cylinders, these flexible wall bellows-type air cylinders are frequently overlooked for tasks for which they are ideally suited.
Generally known as air springs or air bags, they have capabilities and limitations that set them apart from traditional metal-wall cylinders driven by the pumps and compressors in nearly every production plant. It is important to remember, however, that, regardless of their appearance, they are indeed cylinders and that their performance has a critical bearing on the overall efficiency of pneumatic systems powered by pumps and compressors.
Most production and process engineers involved in food manufacturing, materials handling and motion control are familiar with the traditional cylinder design. It 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.
This design necessitates 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 uses none of these components to contain and channel its column of fluid. This difference is the key to its functionality - and also the cause of its anonymity.
An air spring contains its column of air in a fabric-reinforced rubber envelope or bellows. The ends are sealed by bead plates, which are crimped around the bead of the bellows. These plates contain the attachment hardware for the part, normally a blind tapped hole called a blind nut.
An air fitting, generally in one bead plate, allows fluid or air to be introduced into the chamber. The fabric in the side wall of the bellows restricts radial expansion, so pressure is built up, causing axial extension.
Air springs are available in a variety of styles, sporting differing components that control the shape and path of axial extension, but their basic design is the same.
In order to select the appropriate air spring, one would need to know the force necessary, the linkage motion and any special environmental concerns.
A broad range of air springs is available to Australian industry. Airstroke actuators from Air Springs Supply for example, give 40-40,000kg of pushing or lifting power. Offering power strokes of up to 350mm, Airstrokes are powered by simple, basic compressor equipment found in nearly every factory.
Benefits of Air Springs
- 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 in diameter.
- Compact installation: Air springs can be put in a very compact space and extended to more than twice their starting height. This is a tremendous benefit in floor-mounted lifting devices.
- Side load flexibility: An air spring has a flexible, compliant bellows wall instead of seals or guides. Since the bellows follows the path of least resistance, users don't have to worry about side loads caused by misalignment.
- Ease of attachment: Since the bellows bends, bead plates don't have to remain parallel. This significantly simplifies attachment, especially when linkage is at an angle.
- Constant force: The lack of seals also means lack of friction. In many cases, a constant force needs to be applied to a moving object.
- Durability: Air springs outlast cylinders in most high-speed applications. They don't require lubrication and thus have a lower system cost.
- Curtailed production losses: Air springs contain no moving parts to break, wear, leak or cause costly disruptions of production.
- Suitability for aggressive environments: Since there are no seals sliding against exposed surfaces, an air spring can often survive abrasive and corrosive environments.
Limitations of Air Springs
- Air springs are single-acting: Some amount of outside force is required to be used to retract them to their minimum, or starting height.
- The available stroke of an air spring is limited by the length of the side wall. This length is determined by stability concerns (length-to-diameter considerations). These design needs can frequently be met by specifying either single, double or triple-convoluted air springs.
- Air spring users should not stretch the wall in extension or pinch it in compression. This goes for linear as well as angular movements. Therefore, air springs are normally used for high-force, low-stroke applications.
- One critical component of an air spring is rubber. This must have good elongation, flexibility and abrasion resistance - factors which limit the choice of elastomers available.
- Normally, users should keep air springs away from petroleum-based fluids and chemicals that attack rubber.
And a bonus
Not only are air springs ideal actuators for many materials handling applications, but they are also highly efficient isolators. An air spring not only lifts, but also isolates an object. For instance, it can lift and support a vibrating load such as a shaker or vibrator without concern for wear on components.
Isolation efficiencies frequently exceed 99 per cent; in fact, an entire product line of air spring isolators called Airmounts is marketed in Australia.
As Australian states move toward more stringent workplace and environmental guidelines, this isolation capability is becoming a major factor in machinery design.