Effect of Roll Fluting Disposition and Roll Gap on Breakage of Wheat Kernels During First‐Break Roller Milling

Abstract

Cereal Chem. 79(4):518-522Breakage of wheat kernels during first-break roller milling depends on many factors, including the disposition of the fluted rolls: sharp-to-sharp, sharp-to-dull, dull-to-sharp, or dull-to-dull. Wheat kernel breakage under different dispositions during milling was studied using high-speed video imaging. The results show significant slippage between kernels and the flutes when a dull working angle is used, especially when the dull angle is on the fast roll. Experiments were conducted to compare the size distributions resulting from the four dispositions. Representative hard and soft wheat cultivars were milled using fluted rolls at five different roll gaps, and the resulting size distribution of the milled stocks was measured by sieve analysis. A sharp-to-sharp disposition gave a relatively uniform or straight line size distribution over the particle size range of 212-2,000 mm. By contrast, a dull-to-dull disposition gave a Ushaped distribution with more larger and smaller particles and fewer in the middle size range. The size distributions from the other two dispositions lay between these, giving a transition from a straight-line distribution for sharp-to-sharp disposition, slightly U-shaped for sharpto-dull, more curved for dull-to-sharp, and highly U-shaped for dull-todull. The effect of roll gap was to change the balance between large and small particles.The particle size distribution resulting from first-break roller milling of wheat is of critical importance because it directly affects the mill flows and effectiveness of the rest of the milling process. A review of the literature by Fang and Campbell (2002) indicated that much research has been performed on various factors affecting first-break roller milling of wheat, including physicochemical properties of the wheat kernels and aspects of roll design and operation. However, relatively little work has addressed the effect of roll disposition on the breakage patterns of wheat kernels and the resulting particle size distribution delivered by first-break roller milling.In an accompanying article (Fang and Campbell 2002), we applied stress-strain analysis to identify the fracture mechanics principles describing wheat kernel breakage during milling with fluted rolls. By studying the deformation of a wheat kernel engaged between two fluted rolls in sharp-to-sharp (S-S) disposition, the planes of principal stresses and maximum shear stresses along which the kernel is most likely to be broken were calculated. As tensile strength is much smaller than compressive strength (Glenn et al 1991;Glenn and Johnston 1992), the most probable fracture plane was calculated to be that perpendicular to the principal tensile stress. The effects of roll gap, differential, and roll diameter on the stresses and strains were also discussed. High-speed video pictures of wheat kernel breakage under sharp-to-sharp milling were presented to illustrate the breakage patterns and fracture planes occurring during kernel breakage.

Dry processing of oats – Application of dry milling

“…The effects of roller milling parameters on oat breakage were investigated using the versatile Satake STR-100 test roller mill (Satake Corporation, Hiroshima, Japan) Fang & Campbell, 2002, 2003, using a feeding rate equivalent to 300 kg h À1 , and fitted with either corrugated or smooth rolls. All rolls were manufactured to industrial configurations for wheat flour milling, having diameters of 250 mm, but only 100 mm in length (compared with 1000 mm typically for industrial roller mills).…”

Wheat Mill Stream Properties for Discrete Element Method Modeling

“…This can be attributed to the difference in the hardness index of the different wheat classes. SRW wheat kernels, having the lowest hardness index, break into a greater proportion of smaller particles compared to hard wheat kernels (Fang and Campbell, 2002). Cohesion and agglomeration were not as evident in the HRW and HRS flours as they were in the SRW flour.…”

“…Subsequently, Fang (1995) found that feed rate played the most crucial role during first break grinding. In a similar study, Fang and Campbell (2002) found that using a dullto-dull roll disposition for first break milling gave a Ushaped distribution of particle size, while a sharp-to-sharp disposition gave a straight-line distribution for first break mill streams. These studies indicated the important effects of roll parameters on flour extraction percentage.…”

“…Grain hardness is another important factor that determines the breakage behavior of grain during milling. It also dif-ferentiates wheat classes (Dziki et al, 2010;Delwiche, 2000;Fang and Campbell, 2002;Jirsa et al, 2008).…”

Predicting the size and compositional distributions of wheat flour stocks following first break roller milling using the breakage matrix approach

“…The value of q 2 (x) is found by integrating the mass of outlet particles of size x created by any given inlet particle of size D, multiplied by the mass of inlet particles of size D. Assuming that only breakage not aggregation occurs, outlet particles of size x cannot be created from inlet particles of size D < x, so the integration takes place over the range of inlet particles for D P x. However, in the later papers (Fang & Campbell, 2003a, 2003b the authors corrected the limits of the integration (D = 0 instead of D = x) considering the fact that, particularly under dull-to-dull disposition, under the compressive crushing forces, it is entirely possible for a wheat kernel to break so as to produce flattened bran flake with dimensions larger than the kernel from which it came (Fang & Campbell, 2002a, 2002b. Secondly, the dimensions of the wheat kernel (D) and dimension of the broken particle (x) are measured in different ways, so they are not comparable.…”