Foundry Sand Lab & Defect Control, AFS Standard 2-Inch Specimen Permeability Formula
Foundry Green-Sand AFS Permeability & Blowhole Formula
Calculate Volumetric Air Venting Rate (cm³/min), Superficial Darcy Gas Velocity (cm/min), AFS Permeability Number P, and Iron/Steel Castings Steam-Blowhole Gate.
Every gram of green-sand moisture flashes 1,600x in volume to steam at 1,420°C iron pour—and if dust fines choke AFS permeability below 50, trapped steam boils right back into the casting!
When `1,400–1,580°C` molten ductile iron or steel hits `3.2%`-moisture bentonite-bonded **Foundry Green Sand**, interfacial water flashes explosively into superheated steam alongside sea-coal hydrocarbon and resin core gases! Under the **American Foundry Society (`AFS`) Standard `2 x 2`-Inch Cylindrical Rammed Specimen Test** (`Bell Air Volume V = 2,000` cm³, `Specimen Height H = 5.08` cm, `Cross-Sectional Area A = 20.268` cm², `Water-Manometer Pressure Head p = 10.0` gf/cm² = `10` cm `H_2O`, and `Measured Venting Time t` minutes), **Darcy Gas Conductivity** defines the dimensionless-industrial **AFS Permeability Number `P = (V * H) / (p * A * t)`** (`= 50.128 / (p * t)` on standard `2"` tooling)! Gray/ductile iron high-pressure molding lines require **`P >= 80–120` (`>= 50` absolute floor for medium iron/steel; `150–250` heavy steel)**—let dead-clay oolitics and baghouse silt drag `P` down to `20.5` (`t = 2.45` min) and cope surfaces riddle with **subsurface pinholes, gas blowholes, and scabbing**!
Verify in the Foundry Sand Lab Log—Bell_Air_Volume `V` = 2,000 cm³ (B2), Specimen_Height `H` = 5.08 cm (B3), Specimen_Area `A` = 20.268 cm² (B4), Manometer_Pressure `p` = 10.0 gf/cm² (B5), and Stop-Watch_Elapsed_Time `t` = 0.58 min (`34.8` s, B6): Volumetric Air Flow equals `3,448.3` cm³/min (E2), Superficial Gas Velocity equals `170.1` cm/min (E3), **AFS Permeability Number `P` equals `86.4`** (E4), clearing `"VENTING SAFE (>=50 AFS)"` for ductile-iron pouring (E5)!
| AFS 2x2-in Sand Lab Permeability KPI (V=2,000 cm³, H=5.08 cm, A=20.268 cm², p=10 gf/cm²) | Formula | Verified Output |
|---|---|---|
| Volumetric Air Flow (cm³/min) | Bell_Air_Vol_cm3 / Vent_Time_min | 3,448.3 cm³/min (816.3 @ silt-choked sand) |
| Superficial Darcy Velocity (cm/min) | (Bell_Air_Vol_cm3 / Time_min) / Area_cm2 | 170.1 cm/min (40.3 cm/min choked) |
| AFS Permeability Number P | (Vol_V * Height_H) / (Press_p * Area_A * Time_t) | 86.4 AFS (20.5 AFS over-rammed/silty!) |
| Iron/Steel Gas-Venting Gate | IF(AFS_Perm >= 50, "VENTING SAFE...", "BLOWHOLE...") | VENTING SAFE (>=50 AFS) |
AFS Darcy Sand Permeability Number & Steam-Venting Defect Formula
Validate `Air_Volume V` in `[500, 5,000]` cm³, `Specimen_Height H` in `[2.0, 10.0]` cm, `Specimen_Area A` in `[5.0, 50.0]` cm², `Manometer_Pressure p` in `[1.0, 50.0]` gf/cm², and `Elapsed_Time t` in `(0.05, 20.0]` min!
=LET(va_c, B2, hs_c, B3, as_c, B4, pm_g, B5, te_m, B6, IF(OR(va_c < 500, va_c > 5000, hs_c < 2, hs_c > 10, as_c < 5, as_c > 50, pm_g < 1, pm_g > 50, te_m <= 0.05, te_m > 20), "Invalid AFS Input", ROUND(va_c / te_m, 1)))Dead-Clay Fines Buildup + Over-Tempering (`t = 2.45` min -> `20.5` AFS) Blowhole Defect Check
Skip new-silica dilution so dead-clay fines and excess temper water stretch `2,000` cm³ bell drop time to `B6 = 2.45` min: AFS Permeability E4 plunges **`4.2x` down to `20.5`** (`40.3` cm/min velocity in E3), flipping E5 to **`"BLOWHOLE / PINHOLE RISK (<50)"`**—requiring fresh `AFS GFN 55` silica makeup and mechanical cope vent pins!
=IF(ISTEXT(E2), E2, ROUND((B2 * B3) / (B5 * B4 * B6), 1))Try the example
Use the original values or change them to test your understanding.