What would you do if you had to move a heavy load across your factory? What if your factory was outdoors? What if the load was fragile? What would happen if the load fell?

The most common methods of moving heavy loads across factory floors are cranes, trolleys, belt conveyors, roller conveyors etc. All these methods have their uses - however cranes require that the infrastructure be forced to support the load and in many cases electric power; trolleys on the other hand are economical - the flooring however must be built so as to support the weight of the load. Some trolleys need rails, loading and unloading docks, and other infrastructure. Belt and Roller conveyors are directional.

In the above cases you either have to build support columns and beams to carry the weight of the load or set up a system of trolleys, rails, rollers etc..

Advances in material sciences have now made possible a safer, more reliable, and cheaper method of moving heavy loads - air ! Yes, air! Loads that are fragile wont break, the load cannot fall, and if you lost power the worst that will happen is that the load will "stay put".

All one needs to do to move a heavy load is put it on an cushion of air (called an air cushion - how simple!) - like a hovercraft. The reduced friction allows one to move a 1 Ton load with approximately 1 Kg of force. Remember however, that one still has inertia to work against.

To harness this "air cushion" what one needs is an "air cushion mobility system".

The benefits of Air Cushion Mobility Systems are felt because of the "Force Equation". One part of the "Force Equation" (in general) states that "the force required to move a load over a surface is the product of the weight x the coefficient of friction". This resistance to movement (friction) is dramatically reduced when the load is floated on a "air cushion".

Air because of it's easy availability and general characteristics is an ideal fluid to use for reducing the frictional drag between the load and it's supporting surface. Since air buoyancy is omni- directional there are no directional restraints (as in the case of trolleys, belt conveyors and roller conveyors) and loads can be rotated and/or moved in any direction with the same ease. Air cushion mobility systems also allow very accurate positioning of the load.

An "air cushion mobility system" is any system that employs a cushion of air to separate the load from the ground (or other load bearing surface). The common HOVERCRAFT is just one well known application of an "air cushion mobility system".

An "air cushion mobility system" could be any one or a combination of the following: Air Casters, Air Pallets, Air Pads, Air Cells, Air Lift Tables, Air Vans, Air Jacks, Air Tractors, Air Cushion Table Conveyors, Air Cushion Glass Conveyors, Air Cushion Feed Tables, Air Cushion Gravity Conveyors, Air Cushion Sheet Metal Conveyors, etc. All of them employ air to lift the load. The lateral movement can sometimes be provided by the same air or by any other external force.

Air cushion mobility systems can be broadly bifurcated into Air Casters and Air Conveyors.

Air Casters are building blocks in a variety of other air cushion mobility systems (like Air Pallets, Air Pads, Air Cells etc.). They usually operate on the ground and specialise in moving skid- mounted loads.

Air Conveyors consist of a range of specially made conveyors such as Air Cushion Table Conveyors, Air Cushion Feed Tables, Air Cushion Gravity Conveyors etc.

Air Casters (and it's relatives)

The principle of operation of Air Casters is also applicable to it's relatives - Air Cells, Air Pads, Air Pallets, Air Tables, etc.

Air casters employ the most advanced air seals. These seals employ a flexible wear foot mounted below a completely protected inflatable hanger. Since this inflated hanger does not come in contact with the surface over which the seal in operated, all wear is taken by the wear foot. This inexpensive wear foot can be replaced whenever necessary without replacing the remainder of the seal assembly.

Air is forced into the hangers which inflate. After the hangers are inflated fully, air is forced under the wear foot. The air lifts the wear foot just enough to create an air gap. Once this is created a very small approximately 1 kg for every 1 ton of load) force is needed to move the load.

Air Casters thus provide omni-directional virtually frictionless mobility for the load. This allows effortless movement and accurate positioning of heavy loads. Unlike trucks and trains they require no turning radius, i.e., they can rotate around their own axes. Also the pressure exerted (on the supporing surface) in the case of Air Casters is much lower (usually in the range of 50 P.S.I. -- about 3.6 Kgs/cm/sq.)

If for some reason the air supply is cut off the load come to a quiet, smooth, safe rest almost immediately. The air still in the hanger acts like a shock absorber.

If the floor surface is covered with (loose) metal shavings, chips, cutting oil, and solvents, the load floating Air casters simply push and blow the debris aside leaving a clean path. No damage can possibly occur to the inflated diaphragm (hanger) protected as it is by the wear foot.

The seals can also be inflated independently of the "air cushion". This makes it possible to float the Air casters at reduced heights under a skid-mounted load and then inflate the seals fully to lift the skids clear of the floor transferring the weight to the air casters.

Air Casters do have some limitations. The floor over which this equipment is to be operated should be reasonably smooth, flat, and continuos. Rough floor surfaces will require more volume of air (to maintain the air pressure). The floor surface should be non- porous to minimise loss of air. If expansion joints, cracks, air- gaps, etc. exist in the floor they should be filled with epoxy or mastic. Furthermore if the floor surface is sloping, there should not be any abrupt change in the slope.

A Few Applications of Air Casters, Air Pads, Air Cells, Air Tables, Air Jacks, Air Vans, etc.

• Moving Heavy Machinery like Presses, Engines, Turbines, Fixtures, Dies, Moulds, Transformers etc.
• Accurate Positioning of Heavy items like Propeller Shafts, Aircraft Engines, etc.
• Moving Bulky Objects such as Containers in open areas without crane facilities.
• Moving Fragile Equipment like Aircraft Fuselages, Under Carriages, Wings, Engines, etc.
• Handling Heavy and Odd shaped Material like Paper Rolls, Generator Sets, Large Motors, etc.

Air Casters can also be used for such specialised tasks as:

• Shifting Spectator Stands (skid-mounted)
• Accurate Positioning of Cranes and scissor-type lift tables (carrying load) Exact Positioning of Sheets for loading into machining equipment
• Shifting and Positioning of Ship sections
• Shifting Large (10 Ton and more) Cable Drums
• Rotating Large Pressure Vessels
• Moving Large Sensitive Electronic and other Laboratory Equipment like Mainframe Computers etc.
• Mounting Heavy Propeller Shafts on Ships (in conjuction with a crane)

Air Conveyors are made of "tables", which form the supporting surface, that are attached with "nozzles". Air is supplied to the nozzle by means of hoses or a plenum. Different methods are used to control the air flow to the supporting surface. Depending on the application the two principal methods are a series of nozzles arranged in a particular geometric pattern or a porous medium.

Efficient air regulation is the key factor in the design of this type of system of material handling. To conserve the air supply while providing optimum buoyancy the nozzles are based on the "check-valve" principle. These nozzles are mounted in the supporting surface with a ball actuator protruding above the "table" top.

Air flows only when the load moves over the nozzle and depresses the ball actuator. The entire air flow is thus directed and restricted to the area beneath the load. The load serves as it's own "switch" to automatically turn the air supply "ON" and "OFF".

The "ball" of the nozzle is usually made of Nylon or Stainless Steel.

The nozzles can either be press fit or can be "screw" fit into holes on the supporting surface. The "screw" fit nozzles are more expensive but they have virtually no leakage since they are sealed to the supporting surface with an integral "O"-Ring seal -- effectively economising the use of plant air. They can be designed to operate at all pressures up to 100 P.S.I. (7 Kgs./cm.sq). Systems utilising such precision nozzles are usually supplied by blower or plant air through a regulator to provide air at the required pressure. These systems are used when higher pressures and accurate control of the pressure is needed. The pressure requirements vary, depending on the load involved and the flatness of the supporting surface.

Press fit nozzles are cheaper but unlike the "screw" fit nozzles have no "O"-Ring seal. Hence there is a slight loss of air due to leakage. Recent advances have reduced the leakage of these nozzles by incorporating urethane balls for the ball actuators. These nozzles are specifically intended for use in low pressure, high volume blower systems hence the leakage is of little consequence.

With a porous medium Air Conveyor the entire "table" top becomes an air film surface and the air flow is a function of the porosity of the porous medium. Such systems are used where the moving load may be too light to depress the ball actuator or where the material conveyed may not have the rigidity necessary to depress the ball actuator.

Materials with controlled porosity are used to closely regulate air flow and buoyancy of the flotation surface. Particularly those adaptable for the use as either a buoyant air film or vacuum air clamp. This is accomplished by means of a shuttle valve at the blower which shifts the plenum from the exhaust side to the intake port of the blower, thereby switching the air table from pressure to vacuum by simply actuating a valve.

This type of system is also easy to clean and free of the hazards associated with moving sprockets and chains in the proximity of workers. Automatic conveying is readily accomplished by either tilting the table by 5o or utilising air jets in the table as the horizontal propelling force.

• Automatic Packaging and Processing Equipment
• Feeding and Handling Steel Metal, Glass, Paper and other planar or
• Rolled material
• Machine Flotation Devices
• Guillotine Cutters
• Stretching and Cutting Tables for Garments, Glass, Paper, etc.
• Tilt Tables