April 01, 2002
by Suzi Fraser
A useful measure in grinding is the grist spectrum; it is used to describe the gradient from the largest particle to the smallest particle in a ground product and is derived by sieving particles and determining the average percentage of each size.
For example, a typical grist spectrum of a product ground with a hammer mill through grinder screens with 1.5 mm openings might read: 100% smaller than 1.5 mm; 80% smaller than 1.0 mm; 50% smaller than 0.7 mm; and 20% smaller than 0.3 mm.
Grist spectrums can be used to compare differences between hammer mill types caused by varying diameters, hammer speeds, hammer configurations and other parameters. In addition, as hammers and screens wear, the grist spectrum may shift; changes in grist spectrum can result in differing product quality or appearance.