Aerostatic air bearings

01

Choose orifice or porous media, and check stiffness

A University of Arizona optomechanics tutorial (OPTI 521) explains that aerostatic bearings keep their air gap even without motion because air is supplied continuously, unlike aerodynamic (foil) bearings. Orifice bearings distribute air through precisely sized holes or grooves; porous bearings feed it through a material such as porous carbon across the whole surface, so they are less likely to fail from scratches and more tolerant of an air-supply shortage. Static and dynamic friction are extremely low and equal, removing stick-slip. [1]

On stiffness, the tutorial cites a 6 in air bearing at 60 psi with 2,000,000 lb/in stiffness under a 1,000 lb load, under half a millionth of an inch of deflection per pound, and notes that as the bearing deflects the gap narrows and stiffness rises. [1] Semicorex's porous graphite for air bearings is an isostatic graphite with about 0.5 µm mean pore size and 15–18% porosity, using millions of sub-micron pores as the restrictor; it describes a gentle, non-galling landing on air loss and oil-free operation for cleanrooms. [2]

Editorial calculation: 2,000,000 lb/in × 4.448 N/lb ÷ 25,400 µm/in ≈ 350 N/µm, so 100 N of extra load would move such a bearing by roughly 0.3 µm. [1]

A 2022 study from Yancheng Institute of Technology built a porous aerostatic bearing with a reaction-sintered SiC ceramic restrictor: a 43 mm diameter, 5 mm thick disc in a 48 mm body, with 25.8% porosity, 20.55 µm pore size, a permeability coefficient of 2.78 × 10⁻¹³ m² and 256 MPa flexural strength. At 0.5 MPa supply pressure and a 6 µm gas film, its static stiffness peaked at 20.9 N/µm with a load capacity of 632.5 N, and the measured results matched the Fluent simulation. The authors found load capacity rises with supply pressure and permeability and falls as the film thickens, while static stiffness rises with supply pressure and falls as permeability rises. [4]

Editorial calculation: 632.5 N spread over the 43 mm porous face (π × 21.5² ≈ 1,452 mm²) is about 0.44 MPa of average film pressure from a 0.5 MPa supply; the graphite Semicorex describes has 0.5 µm pores and 15–18% porosity against 20.55 µm and 25.8% for this SiC, so ask a porous-media supplier for permeability and the stiffness curve it gives at your supply pressure. [4] [2]

Give the supplier the load and its direction, required stiffness and motion (linear, rotary, spindle speed), guide surface material, flatness and finish, available supply pressure and flow, cleanroom or vacuum needs, and space and mounting constraints.

02

Supply clean air and mount with alignment

The tutorial stresses that air bearings need a constant source of pressurised air relatively free of particulates, water and oil; with clean air, wear is practically eliminated because surfaces only erode. Flat bearings must be parallel to the guide surface within a few microns, so they are mounted on ball studs in spherical sockets to take up misalignment; air bushings are pressed into pillow blocks on O-rings, and the shaft is inserted only after air is supplied. [1]

Stages are built from multiple flat bearings, for example eight at the corners of a linear slide for roll stiffness, or five for a stable guidance system, and rotary tables can combine flat bearings with an air bushing. [1]

03

Read stiffness, fly height and air quality from a maker's design guide

New Way Air Bearings' Air bearing application and design guide (Revision F, 2021) states that a 6 in diameter bearing at 60 psi can exceed 2,000,000 lb/in stiffness under a 1,000 lb load, less than a millionth of an inch of deflection per extra pound, and calls 60 psi a standard air bearing input pressure. In its orifice example, a 2.5 in bearing at 60 psi flies at 300 microinches under 150 lb (about 30 psi average gap pressure); raising the load to 200 lb raises average pressure to about 40 psi and closes the gap to 200 microinches, so stiffness rises as the gap closes. [3]

The guide says porous media bearings are not sensitive to particulates such as thread tape or tube liner shedding because the media acts as a sub-micron filter, whereas such contamination would be catastrophic for orifice or step-compensated bearings; water contamination can be cleared with clean dry air. It warns that a stiffness curve is non-linear, so stiffness must be read at the operating load. [3] This adds numbers to the clean-air and porous-versus-orifice guidance described above. [1] [2]

Editorial calculation: 2,000,000 lb/in is about 350 N/µm; 300 µin ≈ 7.6 µm and 200 µin ≈ 5.1 µm fly height.

Ask the supplier for the lift/load curve at your supply pressure, stiffness at your working load, air consumption, compensation type and the air quality class it requires.

04

Compare what suppliers offer

The suppliers linked to this page list air bearings, air-bearing spindles or porous graphite for them; their cards link to the pages reviewed.

Ask any supplier for load capacity and stiffness curves versus supply pressure, air consumption, gap, compensation type, face material and flatness, required air quality, mounting hardware, and for spindles the speed, runout and power.

05

Trace the bearing parts

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your machine

An air bearing quotation needs values for your machine. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the load, motion and air data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Load: [magnitude; direction; moments]
Stiffness: [required]
Motion: [linear; rotary; speed]
Guide: [material; flatness; finish]
Air: [pressure; flow; filtration; dryness]
Environment: [cleanroom; vacuum; temperature]

See manufacturer records Send an enquiry through CNFX