Testimonial

Huge lifting success reveals industrial potential of safe, precise air spring systems.
 
Lifting technology developed in Australia is being used to safely, and with microscopic precision, hoist for installation
and maintenance some of the heaviest mobile machinery
on the face of the Earth.
 
Ellavale Engineering in the Hunter Valley employs a lifting system based on liquid-filled air springs to hoist, hold, level and lower the superstructure of mining draglines, which are some of the biggest land-based mobile structures ever built.
Typically weighing between 2500-6000 tonnes, and walking at three or four metres a minute in full flight, these giant crane-like structures scoop bucketfulls of more than a hundred tonnes of material a time as they swivel about open-cut mine sites stockpiling the overburden to uncover Australia's mineral riches for processing and transport.

The lifting exercise involved in servicing them is breathtaking in its scale and the technology involved is just as applicable to lifting bridges, buildings, generators, turbines and fixed machinery, says Andrew Cameron, Managing Director of Air Springs Supply Pty Ltd, which delivered the 90 model 215 double-convoluted Firestone air springs used in Ellavale's system.
The air springs, with a minimum deflated height of only 85mm and outside diameter of 710mm, are used when the draglines are split for regrouting of the circular rail system on which their revolving frame swivels. Draglines are mounted on either grouted or machined rail systems. Lifting them for refurbishment is a precision task, because the rail system must be set in a perfectly level plane to ensure ease of rotation. The air springs have to maintain the dragline in a dead level plane, whatever the temperature, day or night, during the maintenance shutdown period.

Expanding to the maximum 300mm height required by Ellavale, the air springs are inflated for the lift with a 70/30 water glycol mix at 175psi (12.25 Bar) to support the entire weight of the dragline's revolving frame while grouting takes place. The water/glycol mix is used instead of compressed air to ensure minimum compressibility when lifting, holding and lowering to an accuracy of two thousandths of an inch (.000508mm).
 
Using height sensors and sophisticated control sensors to govern the lift, holding and lowering, the air springs provide the high degree of precision and safety required when dealing with such phenomenal weights. 'In dozens of lifts we have never managed to blow an airbag,' says Ellavale Construction Manager Mr Steve Honey.
 
'They are amazingly tough. We have had absolutely no damage in use. The only time we have ever had any damage is when someone abuses them by scraping them or abrading them. This happens very rarely and never during lifts, when they are completely stable, strong, precise and safe'.

One of the attractions of the flexible rubber-and-fabric bags (identical in design to the airbags used in advanced truck and train suspensions) was that they spread their load-carrying capacity over the entire surface of the air springs, rather than using concentrated point-loading.
 
Also we could fit them into the confined space available for the job they gave excellent flat jacking capacity. The degree of control we got was outstanding, if anything starts to get out of level, you just adjust the pressure to keep it on the same plane. Not only is this precision important to the job in hand, but it is also critical to the safety policies in mine sites throughout Australia. Safety just isn't an option with this system - it is built in.
Andrew Cameron says that in addition to hoisting heavy mining machinery, air spring systems have already demonstrated their suitability to other civil and mechanical tasks. They are very suitable for precision lifts in electrical generation and precision manufacturing equipment, for example.

These same airbags are not only excellent actuators, but also they are so good as isolators that they are used to take vibration away from hospital beds in operating theatres, for example, or to provide a stable platform for theatre lighting or missile systems.
 
The Powerful model 215 Airstroke® actuators used by Ellavale weigh fewer than 20kg installed but can lift more than 20,000kg each when inflated to 5.5-7 bar on normal industrial compressed air.
 
The compact model 215s part of a broader Airstroke family from Air Springs Supply in individual capacities from a few hundred kilograms up to 40,000kg - feature a compact starting height of less than 85mm, which makes them easy to design into equipment where space is at a premium. Able to extend to more than 350mm, the double-convoluted model 215 Airstrokes are highly engineered and enormously durable fabric-and-rubber bellows that contain no internal rods, pistons or seals that can abrade, corrode or wear in dirty environments.

The scale of the lift is demonstrated by this
shot underneath it


Mining Dragline.


Air Springs being set in position.


Air Springs being readied for the lift.

This durability, combined with a rapid-cycling ability, makes them ideal for many materials handling applications, including actuation of conveyors, screens and bins, says Mr Cameron. Used singly or in sets,  they are suited to tasks such as hoisting components for maintenance, lifting drive tables and actuating belt scrapers, conveyor transfer sections and powerful scissors lifts. While highly sophisticated tasks such as Ellavale's require specialist ancillary equipment, far simpler but effective systems can be designed for more straightforward tasks.
 
Compared with alternatives, such as hydraulics, they can offer considerable savings in set up costs. Rather than dedicated pumps and sophisticated lifting infrastructure usually required for precision heavy lifts, Airstrokes connect to less costly general purpose compressors. Fine control of the lift can be obtained through valving and mechanical means, making the lift less of an engineering task then it might be otherwise.
 
Because of the comparatively low cost of Airstroke installations, they can be used either as mobile jacks or built into equipment for swift, trouble-free use when inspection and maintenance periods come around, he says. This helps operations staff to conduct periodic inspections and maintenance with minimum downtime an important consideration when individual items of equipment and production savings can be worth huge amounts.