Side loads are one of the big killers of conventional hydraulic and pneumatic cylinders used in materials handling applications.
Even as little as a degree or two of off-centre loading can spell doom for the rods, seals or bores of common types of actuators used for lifting and placing objects or providing constant loads on conveying belts or materials webs.
Bent rods, scored bores or damaged seals can lead to downtime on such essential apparatus in industries as diverse as bulk materials handling, manufacturing, minerals processing and packaging, say the suppliers of a simpler, robust alternative: Airstroke actuators from Firestone.
Airstrokes’ national distributor, Air Springs Supply Pty Ltd, says the tough, flexible wall bellows contain no internal moving parts to break or bend, cause internal scoring or require lubrication. Because an air spring has a flexible, compliant bellows wall, instead of seals or guides, the bellows follows the path of least resistance. This means users don't have to worry about side loads caused by misalignment, says Air Springs
Unlike a conventional cylinder (which extends a rod, or plunger, to provide actuation) Airstrokes themselves inflate to provide actuation force.
Using standard factory compressed air at 7 bar – or other compatible gases and liquids such as nitrogen and water-glycol solutions - Airstrokes inflate like enormously robust tubular balloons, extending to deliver actuating forces between 40-40,000 kg a unit. The range is being progressively expanded by Air Springs Supply to encompass models from palm-sized mini-actuators (ideal for conveyors) to triple-convoluted types almost a metre across that can lift semi-trailers.
Airstrokes can also cycle rapidly - the lack of seals also means lack of friction - which makes them ideal for conveying or stamping tasks.
Or Airstrokes can be inflated slowly and with great precision, such as when they have been used to lift giant mining shovels and heavy industrial plant for maintenance.
Airstorkes are very suitable for uses where a constant force needs to be applied to a moving object, like a web or belt. With traditional cylinders, the sliding seals can stick, providing a jerky motion that can damage equipment. Because Airstroke actuators have no sliding seal, there is no breakaway friction, as there is with conventional cylinders.
Airstrokes also possess the unique capability of stroking through an arc without a clevis. Angular motion of up to 30 degrees is possible, along with the design advantage of generally less complex linkages.
Airstroke sizes are available from about 31 mm diameter (2.2 in) to 940mm (37 in). These offer compact starting heights of 30.48mm and 139.7mm respectively (with the tiny new plastic moulded Airomatic polyactuator - a different design - having a starting height of just 16mm.
The smaller sizes provide a wide range of forces required for conveyor and processing operations, while the largest sizes allow force up to 40,000 kg each using only 7 bar (100psi) air pressure. Yet the capital cost of an air spring is normally less than half that of an hydraulic or pneumatic cylinder with equivalent capabilities.