Effects of break-roll speed differential on product yield and semolina granulation in a durum pilot mill system

Changes in break-roll speed differential in a 25-quintal (55-cwt) durum pilot mill system (136 kg/hr feed rate capacity) affected total yield of semolina, flour, and bran; semolina yield from different purifiers; and semolina granulation (150- to 841-mu m particle size range). By adjusting the speed differential of the break and chunk roll pairs from 1.5:1 to 2.5:1 to 3.5:1, semolina yield increased significantly from 55 to 67 to 72%, respectively, and bran yield decreased significantly from 24 to 15 to 11%, respectively. Shorts yield was not affected by speed differential. At 1.5:1, semolina contained 9% flour, compared with 5% flour at 2.5:1 and 3.5:1.