Are AFS and GFN the same thing?

In practice they describe the same property. The AFS (American Foundry Society) grain fineness index is calculated by weighting the percentage retained on each sieve with the multiplier belonging to that sieve; the result is expressed as GFN (Grain Fineness Number). The chart shows the target range next to the actual GFN we measured for that range.

Does a low AFS mean coarse or fine?

A low AFS means coarse. 15-20 AFS is a coarse sand with high gas permeability, while 100-120 AFS is very fine and gives a smooth surface. The higher the number, the finer the grain.

Which AFS suits which casting work?

Coarse sand (low AFS) is preferred for large, thick-walled parts because it lets gas escape from the mould more easily. Fine sand (high AFS) is used for bronze, aluminium and thin-walled, detailed parts where surface quality is decisive. We can determine the range together based on your wall thickness and surface expectation.

Are the GFN values in the chart fixed?

They are the sieve analysis results of samples taken from our production batches and stay inside the target range. Every batch is analysed before shipment; when you place an order we share the analysis result of that specific batch.

What fractions exist besides AFS grades?

Alongside the AFS grades we produce millimetre-based fractions (from 0,8-1,2 mm up to 5-8 mm) and micron-based ranges. Filter products use a separate fraction set defined by the TS EN 12904 standard.

Silica Sand AFS Chart | Measured GFN Values

What Is AFS and Why Does It Matter So Much?

The AFS (American Foundry Society) grain fineness index reduces the average fineness of a sand to a single number. In foundry sand this number is the most decisive technical criterion, because it directly governs the gas permeability of the mould and the surface quality of the cast part.

The logic is simple: low AFS = coarse grain, high AFS = fine grain. Coarse grain helps gas escape from the mould; fine grain produces a smooth surface. The balance between the two is set according to the size and wall thickness of the part.

The 10 AFS Grades We Produce and Their Measured GFN Values

The GFN values below are not estimates — they are the results of sieve analyses carried out in our own laboratory. Each row corresponds to a production fraction:

Fraction	Measured GFN	Grain size equivalent
15-20 AFS	19,09	0,5-1,2 mm
20-30 AFS	27,28	500-1000 micron
30-35 AFS	32,13	300-700 micron
40-45 AFS	41,30	180-700 micron
50-55 AFS	50,49	100-500 micron
60-70 AFS	62,62	100-300 micron
70-75 AFS	72,50	—
80-100 AFS	88,70	—
90-110 AFS	101,40	—
100-120 AFS	109,92	—

No micron equivalent is given for the last four grades (70-75 AFS and above); these ranges are produced directly to the AFS target. The first six grades can be ordered either as an AFS grade or as a micron range — from the fraction cards on the product page you can see the full sieve analysis of each one and download its technical data sheet (TDS).

Which Grade Suits Which Work?

15-30 AFS (coarse): large, thick-walled castings and moulds that need high gas permeability.
30-55 AFS (medium): general purpose moulding sand; the most widely used range in iron and steel casting.
60-120 AFS (fine): bronze, aluminium and thin-walled parts; work where surface quality is decisive.

This split is a starting point. The final choice depends on the wall thickness of the part, the moulding method (green sand, cold-box, core) and the required surface roughness.

How Is the AFS Value Calculated?

In a sieve analysis, the percentage retained on each sieve is multiplied by a factor belonging to that sieve; the sum of these values is divided by the total percentage to obtain the GFN. In other words, AFS is derived from the whole grain distribution, not from a single sieve. Two sands with the same AFS can have different distributions — which is why you should look at the entire sieve analysis, not only the AFS number.

We explained how to read a sieve analysis table step by step in a separate article: How to Read a Sieve Analysis

Let Us Determine the Right Grade Together

Share your part type, moulding method and surface expectation, and we will recommend a suitable AFS range and send a sample. You can reach us through the contact form.

Related pages:

Silica Sand AFS Chart: 10 Grades and Measured GFN Values

What Is AFS and Why Does It Matter So Much?

The 10 AFS Grades We Produce and Their Measured GFN Values

Which Grade Suits Which Work?

How Is the AFS Value Calculated?

Let Us Determine the Right Grade Together

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