News Releases

September 2010

Conveyor killers friction and grit come to an unsticky end with the indomitable Airstroke

Friction and grit can kill conveyors - and their favourite accomplice is aggressive environments such as those found in mines and mineral processing plants.

Aggressive atmospheres laden with dust, waste and water can speedily despatch the seals in traditional cylinders that actuate the conveyor equipment involved, including belt scrapers, belt tensioners and brakes, conveyor guides and hinged actuator gates.

Eliminating this weak link is especially critical in environments where pneumatic and hydraulic cylinders can clog up and wear prematurely over the millions of cycles for which they must operate.

One simple way to avoid this potential problem is to employ cylinders that totally lack such seals, says pneumatic actuation and isolation specialist Simon Agar. Mr Agar - who is General Manager of Air Springs Supply Pty Ltd - has more than 20 years experience with Firestone air spring actuators known as Airstrokes®.

These extraordinarily rugged Airstrokes are identical in construction and durability to the Firestone airbags used every day in the suspensions of heavy trucks and semis, including the big vehicles that abound in mines all over the country, so their reliability and suitability for the conditions has been proved over decades.

The highly engineered rubber and fabric Airstorkes are flexible-wall, bellows-type air cylinders which are ideally suited to engineering of assemblies for high-repetition tasks, for which they are inflated and deflated rapidly to achieve their purpose.

"Traditional cylinder designs contain a piston sliding within a housing of circular cross-section connected to the work by a rod passing through one end of the device," says Simon Agar

"This design necessitates several guides and seals, which align and seal the sliding surfaces to allow allow a pressurised, contained column of fluid to apply force to the piston.

"An Airstroke air spring uses none of these wear-vulnerable components to contain and channel its column of fluid. 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 (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.

"Each style is, in essence, a heavy-duty balloon. 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, you need to know the force necessary, the required stroke 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.

An example of conveyor uses for which Airstrokes are particularly suitable is belt scrapers, an unglamourous but essential component of conveyor systems. Their blades or brushes bear against the moving conveyor belt to remove material sticking to it. Using an effective, continuous method for cleaning conveyor belts - one that prevents material buildup on the belt - can help extend the life and productivity of the entire belt system. By preventing material buildup, it helps keep the belt from drifting off track, prevents erratic loads on the motor, eliminates uneven wear on pulley bearings and damage to return idlers, and minimizes belt stretching.

"In addition to ensuring that scrapers are made from the correct material (not too hard, so as to damage the belts, not too soft, so as to be ineffective on material being conveyed) it is important to pay special attention to the style of actuation, says Mr Agar.

While in some instances metal springs, flexible blocks or torsion bars will satisfactorily position the scraper adjacent to the belt surface, other applications increasingly require more sophisticated, flexible and continuously supple arrangements. These can be provided by flexible pneumatic actuators, such as Airstroke® air spring actuators.

Because the amount of force they exert against a surface varies in continuous proportion to the amount of air pressure contained within them, they can adjust to different load requirements simply by varying this pressure. In addition, air springs (whether egg-sized mini actuators or triple convoluted models half a metre in diameter) provide force evenly over the surface upon which they are acting, rather than imposing sharp point loads, Further, they will undulate over irregular loads passing beneath them, flexing with the load profile if necessary, rather than fighting irregularities in the load and causing jerking, jamming and strain on the production line.

Another major advantage for design engineers is the Airstrokes' ability to rotate through an angle without a clevis.

In addition to making air springs easy to install in compact spaces, this ability to bend with load (and to tolerate high side loadings) means the air springs will perform where more rigid alternatives would break or wear. Air springs' other advantages (including no internal moving parts to break or wear) have been widely proven over a wide range of materials handling uses. These extend from conveyor direction gate actuation, lift sections and bumper stops, through to ram cylinders, die cushions, counterbalances, clamps, lifters, valve operators, flexible connectors, shock absorbers and isolators.

Key reasons for using air springs include cost benefits, says Simon Agar. 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 normally less than half that of a pneumatic cylinder with equivalent capabilities.

They are also compact and easy to install, because of the way the flexible-wall air spring operates: it is compressed to its minimum height then extends when pressure is applied. In most cases, the minimum height is considerably less than the available stroke. As a result, 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 and conveyors.

Free technical information

Would you like to learn more about the technology discussed here? Readers can receive more information by contacting Air Springs Supply Pty Ltd, PO Box 215 West Ryde, 2114, ph (02) 9807 4077, fax (02) 9807 6979.

For more information about Air Springs Supply's national distribution and technical support network, please contact Air Springs Supply Pty Ltd, 10 Angas St, Meadowbank, Sydney 2114, ph (02) 9807 4077, fax (02) 9807 6979, sales@airsprings.com.au