Cluster article
Plansifter Sizing: How Much Sifting Area Does Your Mill Need?
The sifting-area rule (1 m² per 0.8 t/d), how to distribute area across streams, when to choose twin-bin over high-square, and what happens when sifting is undersized.
Key takeaways
- Sifting area (m²) = daily capacity (t/d) ÷ 0.8 for a standard 4B5M flow sheet.
- Area must be distributed by stream, not just totalled — five streams need five separate grading paths.
- Undersized sifting caps extraction and produces flour that is ground fine but not properly classified.
- High-square compartment count is chosen by stream count; frame size is chosen by total area.
The rule
Sifting area (m²) = daily capacity (t/d) ÷ 0.8
| Capacity | Area needed | Practical configuration |
|---|---|---|
| 20 t/d | 25 m² | 2 × twin-bin (5 m²/bin = 10 m² each) |
| 25 t/d | 31 m² | 2 × twin-bin, or 1 × FSFG4×24 (26.3 m²) + twin-bin |
| 30 t/d | 38 m² | 2 × twin-bin, or 1 × FSFG6×24 (39.5 m²) |
| 40 t/d | 50 m² | 1 × FSFG8×24 (52.7 m²) |
| 60 t/d | 75 m² | 2 × FSFG6×24 (79 m²) |
| 100 t/d | 125 m² | FSFG8×24 + FSFG6×24 (92 m²) + twin-bin, or 3 × FSFG6×24 (118 m²) |
| 200 t/d | 250 m² | 5 × FSFG8×24 (263 m²) |
| 300 t/d | 375 m² | 7 × FSFG8×24 (369 m²) |
The rule assumes a standard 4B5M flow sheet at 76–78% extraction on medium-hard wheat.
Adjustments:
| Condition | Adjustment |
|---|---|
| 3B2M flow sheet (fewer streams) | −15% area |
| 5B7M+ flow sheet | +20% area |
| Soft wheat, low extraction | −10% |
| Durum or very hard wheat | +10% |
| Whole wheat, no grading | −40% |
Distribution by stream
Total area is necessary but not sufficient. Sifting area must exist per stream.
A 60 t/d plant with 79 m² on two machines can handle:
- 1 sifter for break + scratch streams (4 passages)
- 1 sifter for reduction + flour streams (5 passages + tailing)
But it cannot handle eight independent products on one machine. High-square sifters solve this with 4, 6 or 8 physically isolated compartments.
| Machine | Compartments | Area | Best for |
|---|---|---|---|
| Twin-bin FSFJ-D | 2 | 5 m²/bin | 20–40 t/d, 3B2M–3B3M |
| FSFG4×24 | 4 | 26.3 m² | 30–40 t/d |
| FSFG6×24 | 6 | 39.5 m² | 40–60 t/d |
| FSFG8×24 | 8 | 52.7 m² | 60 t/d and above |
What happens when sifting is undersized
Extraction falls. Material that cannot be classified gets re-circulated or rejected as bran. Typically 2–5 points of extraction loss.
Ash rises. Improperly graded material carries bran into the flour streams.
Power rises. Recirculating material through the mill twice costs twice the grinding energy.
Sifter overheats. Overloaded sifter frames run hot and fatigue. Frame cracking follows.
Undersized sifting has no alarm and no visible symptom other than a plant that quietly underperforms its design figures.
Maintenance that protects area
Sifting area is only real if the screens are intact and tensioned.
| Item | Interval |
|---|---|
| Screen frame inspection | Weekly, under strong light |
| Frame replacement | When mesh sags or tears |
| Hanger rod bushes | 12–18 months |
| Gyration check | Annually with a vibrometer |
A worn hanger bush changes the gyration path. Every compartment on the machine degrades simultaneously, and the effect is subtle enough to be mistaken for wheat variation.