Plant & Equipment

Stroke speeds, loads place stress on conveyor actuators

Due to the higher stroke speeds, coupled with greater tolerance to side and uneven loads for reliability, process and plant engineers have to look outside their traditional terms of reference for fresh approaches.

?Most process and production engineers will agree the simplest solution to a problem is often the best. Fewer moving parts and reduced complexity equate to less wear and more reliability,? says James Maslin, the industrial manager for pneumatic actuation and isolation specialists Air Springs Supply.

{{image3-a:l-w:200}}The actuation alternative offered by Air Springs involves Firestone Airstroke actuators, some of the simplest pneumatic actuators available. They are tough, flexible wall bellows engineered into different shapes to perform different tasks. They contain no internal moving parts to break, bend, cause internal scoring or require lubrication.

?Another of their advantages for conveyor applications is side load flexibility. 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 do not have to worry about side loads caused by misalignment,? said Maslin.

The lack of seals also means no friction. In many cases, a constant force needs to be applied to a moving object. With traditional cylinders, the sliding seals can stick, providing a jerky motion that can damage equipment. As Airstroke actuators have no sliding seal, there is no breakaway friction.

Airstrokes can also stroke through an arc without a clevis. An angular motion of up to 27 degrees is possible, along with the design advantage of less complex linkages.

Airstroke sizes are available from 31mm diameter to 940mm. These offer compact starting heights of 30.48mm and 139.7mm respectively (the tiny plastic moulded Airomatic polyactuator has a 16mm starting height).

{{image2-a:r-w:200}}The smaller sizes provide a wide range of forces required for conveyor and processing operations. The largest sizes allow force up to 40,000kg each with only 7 bar air pressure.

Yet the capital cost of an air spring is less than half that of an hydraulic or pneumatic cylinder with equivalent capabilities, says Maslin, adding that Airstrokes may also be considered in installations requiring:

? Compact installation. A flexible wall air spring can be put in a very compact space and extended to over twice its starting height.
? Ease of attachment. Since the bellows bend, bead plates do not have to remain parallel, this significantly simplifies attachment.
? Durability. Air springs outlast cylinders in high speed applications. They do not require lubrication and cost less.
? Curtailed air and production losses. Air springs have no moving parts to break, wear, and leak compressed air.
? As there are no seals against exposed surfaces, an air spring can survive in abrasive, corrosive environments that a conventional cylinder could not.

Source: Air Springs Supply Pty Ltd

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