Machine Design

Air casters 101

Air casters make it easy to move heavy machines and equipment without damaging floors.

It only takes a few men to move a 15,000-lb machine using AeroCasters.

When the AeroCaster's donut-shaped bag inflates, it forms a seal against the floor. When pressure in the bag is enough to lift the load, air slowly and evenly escapes between the bag and the floor, creates a thin layer of air on which the load floats and can be moved.

John Massenburg
Applications Engineer
Seattle, Wash.

Moving heavy loads on wheeled casters or rollers, either routinely as part of production or just once in a while for maintenance or cleaning, can damage floors. Wheeled casters can wear grooves in concrete and epoxy floors, and moderately heavy loads being wheeled on casters can break through raised cleanroomflooring. Wheeled casters present other problems as well. For example, even those touted as "heavy duty" with low friction and little start-up resistance or equipped with vibration damping are difficult to maneuver when loaded. In fact, often the load has to be lifted to turn the wheeled casters.

The problem is that all heavyduty wheeled casters must touch the ground while rolling. This automatically implies friction, floor wear, and, ultimately, floor damage.

So how do you move loads that weigh from hundreds of pounds to thousands of tons? You literally make it float above the floor with air casters.

That's what Aero-Casters do using compressed air. Compressed air inflates a donutshaped balloon beneath a square aluminum plate that is under the load being moved. When the balloon completely inflates, it creates a pocket of pressurized air beneath the plate. Air leaks out from under the balloon, creating a 0.003 to 0.005-in. layer of air. The load then floats on this nearly frictionless layer and can be moved in any direction. The load is lifted up to 3.5 in. vertically, depending on the size of air caster.

AeroCasters require a maximum of 50 psi of air pressure, but it is the volume of air that is more important. The volume depends on the floor surface and caster size and pressure rating. In general, on a smooth, nonporous floor, a 28,000-lb air-caster system made up of several air casters and a distribution network for air, will use about 65 ft3/min of air.

On most floors, a 5,000-lb load on air casters takes only 5 to 25 lb of force to move. With wheeled casters, it may take 300 lb of force to move the same load. Changing direction with air casters just means applying force in the direction you want to go, thanks to their omnidirectional travel. With wheeled casters and rollers, changing directions is time consuming and difficult. Air casters also spread the load out over a larger area so there's less risk of damaging floors. They are a safer and more ergonomically sound way to move heavy loads.

Air casters work on any smooth, nonporous surface, including vinyl, linoleum, raised tiles, and smooth concrete, like that found in most factories. They will also work on porous surfaces, provided a sheet-metal or plastic overlay is laid down first. For floors with gaps, steps, machinetool bases with slots, and woodplanked floors, a Gapmaster model will accommodate the unevenness. Air casters won't handle floor protrusion sharp enough to pierce the air-caster's balloon. Some loads are sensitive to vibration and jarring. The inflated balloon (or caster bag) is flexible and conforms to imperfections in the floor, providing a compliant suspension. Caster wheels are much less flexible and transfer every bump in the floor to the load. Air casters can even carry loads across wet floors and sheets of water, as long as the liquid doesn't degrade any air-caster components. There are also air casters that use water or machine-tool coolant as the working fluid in the air caster.

One potential danger, one it shares with traditional wheeled casters, is slanted or sloped floors. The rule of thumb is that a person can move 5,000 lb on a shop floor with a 0.25-in. slope over 10 ft.

Air casters are about 2-in. tall, letting them slide beneath most loads. Our company has manufactured custom casters that are less than an inch tall. If no space is available, the load has to be hoisted or jacked up. To get around this and for convenience, some users permanently mount air casters under heavy equipmentso it is always ready to be easily moved.

The casters have no moving parts, require no lubrication, and have no maintenance schedule. If they get dirty, they can be easily cleaned.

AeroGo AeroCasters can be a logical replacement for wheeled casters in many applications. They help protect delicate floors, let you move and precisely align heavy loads without powered equipment, and protect delicate machinery during moves. They also work in situations that casters won't. For example, they've been used to move 6,000-ton caissons and the entire bank of seats on the eastern side of Denver's Mile High Stadium.

AeroGo Inc.,

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