Vacuum-preloaded air bearing, porous ring feed — fixed reference geometry

Reference-geometry calculator (76mm outer diameter, 5µm film, 0.5MPa supply — fixed, matching the original) for a vacuum-preloaded aerostatic thrust collar bearing fed through a porous ring. Vary the remaining diameters and pressures.

✓ validated against legacyoriginal: /calculators/c12_6a.htm

Vacuum-preloaded air bearing, porous ring feed — fixed reference geometry — original diagram from /calculators/c12_6a.htm

Outer diameter of porous ring, 2R₁10⁻³ mInner diameter of porous ring, 2R₂10⁻³ mInner diameter of collar bearing, 2R₃10⁻³ mOuter diameter of vacuum preload, 2R₄10⁻³ mInner diameter of vacuum preload, 2R₅10⁻³ mAmbient pressure, pₐ10⁶ PaVacuum level, p_V10⁶ PaRestrictor pressure, p_R10⁶ Pa

Flow through porous surface, ṁ_b3.092 10⁻⁶ kg/s

Flow through porous surface, Q_b156 10⁻³ l/min

Flow through vacuum system, ṁ_V0.296 10⁻⁶ kg/s

Flow through vacuum system, Q_V14.9 10⁻³ l/min

Load capacity of collar bearing, F_b67.1 N

Tensile force of vacuum preload, F_V-23.1 N

External load of vacuum-preloaded bearing, F44 N

Axial stiffness, S = −dF/dh33.4 10⁶ N/m

The legacy "please login" demo lock froze D0/H0/pS to these exact values. Per docs/phase6/OWNER-DECISIONS-BACKLOG.md K4, this fixed geometry is kept exactly as in the original and only the inputs that were already free under the lock are exposed. Generalizing it is a deliberate future decision for Anton, not made here. Restrictor pressure pR is a free input — solve iteratively (adjust pR) until the external load F matches the intended operating point.

Method & references

Vacuum-preloaded bearings need only a single flat guide surface (no opposed bearing pair) and allow tunable stiffness/flying-height by adjusting vacuum and pressure.
The pressurized part behaves as a collar bearing loaded internally by vacuum on the inner region; the ambient-connected groove reduces the vacuum-system flow.
FIXED GEOMETRY: outer diameter 76 mm, film thickness 5 µm, supply pressure 0.5 MPa — the original demo lock froze these three together.

The computation is a literal port of the original client-side JavaScript from /calculators/c12_6a.htm. Results are verified equal to the original by an automated golden-master test. No formula has been re-derived or “improved”.

Vacuum-preloaded air bearing, porous ring feed — fixed reference geometry — Engineering ABC