Stress‐Strain Analysis and Visual Observation of Wheat Kernel Breakage During Roller Milling Using Fluted Rolls

Abstract

The endosperm and bran of a wheat grain have different mechanical properties and break differently under the same stresses. Stress‐strain analysis was used to model the factors affecting wheat kernel breakage during milling using fluted rolls. The planes of principal compressive and tensile stress and the maximum shear stresses, along which the kernel is most likely to be broken, were calculated for a sharp‐to‐sharp roll disposition. With the occurrence of compressive stress in the horizontal direction and shear stress in the vertical direction, a kernel tends to break along a principal tensile stress plane because the tensile strength of the endosperm is much smaller than its compressive strength. The model presented quantifies the mathematical relationship of three design and operational factors affecting the principal stresses and the maximum shear stresses: roll gap, differential, and roll diameter. High‐speed video was used to observe wheat breakage events during milling; the results show consistency with the theoretical analysis.

Effects of kernel hardness and moisture content on wheat breakage in the single kernel characterisation system

“…These particle sizes are much larger than would be expected from First Break roller milling, for which the x is 50 typically in the range 500-1500 mm (Fang & Campbell, 2003a). This suggests that the mechanism of breakage in the SKCS is primarily compression, which tends to produce larger particles, in contrast to roller milling in which shear contributes significantly, as well as compression, the relative contributions depending on roll disposition (Fang & Campbell, 2002a,b, 2003a. The large particles also reflect the relatively large final gap of 0.89 mm between the rotor and crescent in the SKCS (Martin & Steele, 1996).…”

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

“…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.…”

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.…”