Is there a type of bearing that won’t produce friction and wear as long as it operates within its design load? The answer is yes, and it’s called an air bearing.
Today, let’s delve into what air bearings are and why they’re used.
What is air bearing?
When people discuss bearings, they typically refer to ball bearings. In ball bearings, lubricated balls isolate the fixed and moving surfaces, and these balls move along specialized tracks or raceways. The most prevalent use for this type of bearing is a shaft rotating in a fixed hub, such as a drive shaft on a bicycle or car’s front wheel.
Air bearings, on the other hand, employ an air cushion in place of the ball. Hovercraft are a well-known application of air bearings.
Large fans blow air underneath the hovercraft and prevent the escape of air by means of an elastic rubber skirt.
The high air pressure created beneath the hovercraft is capable of supporting the weight of the hull, enabling it to float on an air cushion.
This air cushion not only supports the hull’s weight, but also acts as a soft spring, allowing the hull to glide smoothly over rough land or water surfaces.
The same principle can also be applied to shaft bearings.
High-pressure air is injected into the narrow gap (about 0.01 mm) between the rotating shaft and the fixed bearing, maintaining constant air pressure within the gap. The small gap significantly reduces the “elasticity” of the air cushion, ensuring precise fixation of the shaft with low dynamic eccentricity.
Due to the low friction, the shaft can rotate freely while the air pressure prevents the rotating shaft from making contact with the fixed bearing’s surface. Air is the most commonly used medium for air bearings, but depending on specific requirements, nitrogen, hydrogen, helium, carbon dioxide, and other gases may also be used.
In advanced mechanical equipment, air bearings are increasingly preferred due to their ability to provide higher precision, longer service life, and greater bearing capacity.
Why use air bearings?
- Non contact bearing, low friction;
- Wide range of speed operation capacity: from 0rmp to 350000rpm or above;
- These spindles have unique high rigidity and high load capacity, can be cooled by liquid, and only produce low dynamic eccentricity;
- High rotation accuracy and low spindle movement error;
- Long service life due to non-contact surface;
- Low heat production.
- High geometric accuracy is required in the manufacturing process;
- Clean and dry pressurized air supply is required.
The main drawback of air bearings is their high precision requirements and challenging production technology. This is the reason why this type of bearing, which can achieve zero friction and wear within the design load, is not widely used.