Like Australia, coal is the United States' 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 an astronomical amount of undiscovered reserves. According to Simon Agar, General Manager, Air Springs Supply, and just as Australian power utilities and mining operations are seeking 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. Air Springs Supply distribute 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, utilising 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 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 pulverised 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 pulverisers' rollers at a consistent height.
After contacting air springs’ manufacturer Firestone, the same supplier of these products through Air Springs Supply 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% of the pressure on the rollers, but the Firestone air springs provide an additional six tons of force (up to a maximum of 100psi) as needed. A levelling valve on one of the air springs regulates all three springs on each pulveriser, applying equal force to all three rollers.
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 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. Some are used under machinery to protect surrounding areas; others are used under delicate equipment (such as computers) to protect it from ambient vibration.
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.