The AFS-GFN is one meands of measuring the grain fineness of a sand such as chromite sand.GFN is a measure of the everage size of the particles or grains of a sand,for example chromite sand .
The Optical GFN in a sand system is determined by the type of metal poured,pouring temperatures,casting product mix(heavy vs.light casting) and required surface finish,one that optical fineness lever is determined,maintaining a consistent grain structure becomes a critical factor in the quality of the final castings.Sand that is too fine(higher GFN) can creat low permeability and result in gas defects.Sand that is too coarse(Lower GFN) can creat high permeability and lead to problems with metal penetration,rough surface finish,burn-in and burn-on.
