News Releases

June 2009

Flexible air springs pulverize preconceptions in mining and energy materials tasks

"It comes in as coal and leaves as electricity."

As professional engineers often do, this pithy quote from an engineer at a major US power utility company cuts right to the basics: just as it is in Australia, coal is critical to the electrical needs of the residents of North and South Carolina.

Like Australia, coal is the United States' most abundant fossil fuel. According to the U.S. Geological Survey, the United States has approximately 1.7 trillion tons of known coal reserves, not to mention a potentially astronomical amount of undiscovered reserves. 

And just as Australian power utilities and mining operations are constantly seeking more efficient ways to process their product, so also has this US utility employed air springs of a type widely used in Australia to achieve higher reliability and less downtime, says the General Manager of Air Springs Supply Pty Ltd, Mr Simon Agar, whose company distributes throughout Australia the type of air springs involved.

Coal-fired stations accounted for about half of the electricity used by local customers of this regional US power company which also operated nuclear power plants, hydroelectric stations, plus combustion turbine units (oil/gas-fired stations) at six sites.

Processing coal is a 24/7 operation, utilizing multiple mills to pulverize gravel-sized coal into a talcum-powder consistency. It is then mixed with hot air and blown into the firebox of a boiler. Burning in suspension, the coal-air mixture provides the most complete combustion and maximum heat possible& an important factor in generating steam to turn massive turbines for electricity.

To attain the super-fine consistency needed for optimal combustion, the coal is pulverized by massive rollers in large mills. Each mill contains three rollers that roll on a rotating turntable, similar to an old-fashioned flour mill. Steel springs have traditionally been used to exert the pressure necessary to grind the coal. But a common problem is that different consistencies of coal may require different amounts of force; softer coal may cause the rollers to scoot or skid rather than roll.

Although steel springs are adjustable, making any adjustments to them requires shutting down the operation& a costly and inefficient factor in the process.

The power company's engineering specialist got the idea of using air springs while he was driving behind a trailer on the highway.  As he watched the air springs keeping the trailer level, he wondered whether a similar application could keep the pulverizers' rollers at a consistent height.

After contacting air springs' manufacturer Firestone,  the same supplier of these products through Air Springs Supply Pty Ltd in Australia,  the company developed a special rectangular yoke to attach a Firestone 113-1 air spring to each of the existing steel spring assemblies. Preloaded to 10 tons of pressure, the steel springs continue to exert 60-70 percent of the pressure on the rollers, but the Firestone air springs provide an additional six tons of force (up to a maximum of 100 psi) as needed. A leveling valve on one of the air springs regulates all three springs on each pulverizer, applying equal force to all three rollers.

"The air springs have given us flexibility we didn't have before," says the engineer.
With the air springs, we're running tests and gathering data so we can gain more control of the pulverizers and keep them operating regardless of the quality or quantity of coal."

Mr Agar says identical springs are frequently used in Australia for processing equipment such as conveyors and conveyor scrapers, an application in which they  prevent material buildup, helping keep the belt from drifting off track, preventing erratic loads on the motor, eliminating uneven wear on pulley bearings and damage to return idlers, and minimising belt stretching. In addition to being easy to install in compact spaces, the flexible actuators' 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.

Using Airstroke® air springs in capacities from a few hundred kilograms to tens of thousands, engineers here have completed installations for machinery as diverse as high-speed metal stamping plants to heavy lift dragline maintenance jacks.

Similar Airmount® air springs have been used as isolators to overcome severe occupational health and safety issues through high isolation efficiencies of 90-99 per cent. Some are used under machinery to protect surrounding areas; others are used under delicate equipment (such as computers) to protect it from ambient vibration.

"Because air springs contain no internal moving parts to break or wear, and they curtail friction, they are very suitable for high-repetition tasks involving either isolation or actuation," says Mr Agar.

The flexible air springs' ability to arc without a clevis, to bend and to tolerate uneven and fluctuating loads, also means they are suitable for minerals and energy materials handling tasks such as tensioning webs, belt take-up on conveyors, or powering scissors lifts.

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