Sieve analysis, from grains to a number.
Sieve analysis turns a handful of sand or powder into a particle-size distribution, and in the foundry into a single grain fineness number. Here is how it works, and how to choose the sieves that make the number trustworthy.
What sieve analysis is
A weighed sample is placed on the top sieve of a nest arranged coarse to fine, with a receiver at the bottom. The nest is agitated, each sieve retains the grains too large to pass its aperture, and the mass held on every deck is weighed. Those masses, read as percentages, are the particle-size distribution.
Reading the distribution
The retained masses convert to percent retained and cumulative percent passing. Plotted against aperture, they draw the grading curve, and the aperture at which half the sample has passed gives a median size. The shape of the curve tells you whether a material is tightly graded or spread across many sizes.
Grain Fineness Number, worked through
The AFS GFN weights the percentage retained on each sieve by a multiplier for that sieve, sums the products, and divides by the total percentage retained. A finer sand carries more mass on the fine decks, so it earns a higher number.
| Sieve | % retained | Multiplier | Product |
|---|---|---|---|
| 425 µm | 4 | 20 | 80 |
| 300 µm | 12 | 30 | 360 |
| 212 µm | 27 | 40 | 1080 |
| 150 µm | 31 | 50 | 1550 |
| 106 µm | 18 | 70 | 1260 |
| 75 µm | 6 | 100 | 600 |
| Pan | 2 | 140 | 280 |
Illustrative worked example. Sum of products 5210, divided by total percent retained 100, gives an AFS GFN of about 52. Multipliers follow the AFS method. For the full method and background, see the guides below.
Aperture, grade and shake.
Match the material
Bracket the size range you expect with enough decks to see the shape of the curve, not just its ends. For foundry sand, the AFS series is the accepted set.
Match the stakes
Compliance for routine QC, inspection for audited method work, calibration for reference sieves and referee testing. Compare the grades.
Make it repeatable
A timed mechanical shaker removes the operator from the result, so the distribution is the sample’s, not the analyst’s.
Compliance, inspection or calibration grade?
How often should a working sieve be re-certified?
Do you certify sieves you did not manufacture?
Wet or dry sieving?
Ready to specify a set?
Send the material and the standard you report to. We will propose the apertures, the grade and a shaker to match, and quote for delivery worldwide.