Preload and Stiffness:
Air bearings are often preloaded to increase their stiffness, which is crucial for maintaining stability at high speeds. Preload can be applied using different methods, such as opposing air bearing surfaces or adjustable pressure settings. This creates a more rigid air film that can effectively support the load and resist disturbances that might cause instability.
1. Calculating Preload
Preload in air bearings is typically achieved by applying a controlled air pressure that slightly exceeds the minimum required to separate the bearing surfaces. This creates a stiff air film that can handle additional load or external disturbances more effectively.
Determine Required Pressure: Calculate the air pressure required to just lift the load, usually based on the area of the bearing and the load (weight) it needs to support.
Apply Preload Factor: Increase this pressure by a certain factor to ensure the bearing has enough capacity to handle dynamic loads or variations in external conditions.
Equation:
P=(A/F)(1+k)
P = required preload pressure
F = load to lift
A = area of the air bearing surface
k= preload factor
Damping Characteristics:
Air bearings naturally possess damping properties due to the air film's viscosity. When the bearing moves relative to the surface, the air film compresses and decompresses, which dissipates energy and stabilizes the motion. This damping is especially important at high speeds where vibrations and oscillations need to be controlled to prevent resonance
.
Geometric Design:
The design of air bearings, including their shape and the way they distribute air pressure, is tailored to enhance stability. As an example OAV aerostatic bearings use air pressure supplied externally and feature porous surfaces to control air flow. This ensures a uniform air film thickness even at high rotational speeds or linear velocities, leading to greater stability.
Thermal Management:
Air bearings help manage heat generation at high speeds, which is a common source of instability in traditional bearings due to thermal expansion. The air film between surfaces provides thermal insulation and reduces heat transfer, maintaining dimensional stability and performance consistency.
