Chaoying Fang

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

ABSTRACT Breakage 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 μm. By contrast, a dull-to-dull disposition gave a U-shaped distribution with more larger and smaller particles and fewer in ...

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

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.

Complex Permittivity of Solid, Liquid and Granular Materials using a four layer boundary cell

The four boundary cell is an important arrangement for the measurement of complex permittivity of bulk solids and liquids. Transcendental equations for reflection and transmission are derived and previous errors in the literature are noted. This measurement method is extended to granular samples where a compression technique is introduced to minimize the dispersion in S-parameter measurements associated with interface problems.

Effect of Measurement Method and Moisture Content on Wheat Kernel Density Measurement

Wheat kernel breakage is a critical factor in the flour milling process, and is affected by kernel density. Kernel density measurement is not routinely performed, and depends on the measurement technique used and the moisture content of the grains. This study compared currently available wet and dry methods based on gas displacement and liquid displacement (using water, water-ethanol mixtures and xylene) to determine the density of Hereward (hard) and Consort (soft) wheat kernels of different sizes and moisture contents. A gas pycnometer was used to measure the average density of a sample of wheat kernels, while a double cup system was used to measure individual kernel density by weighing kernels in air and immersed in liquid. The hard wheat variety, Hereward, had kernels of slightly higher average density, with a narrower distribution, than the soft variety, Consort. Kernel density was independent of kernel size, while increasing moisture content decreased the measured kernel density. The dry technique using the gas pycnometer gave the highest kernel densities, followed by xylene immersion, with water immersion giving the lowest density values, lower than the dry technique by 6.2% for Hereward and 9.9% for Consort. This was attributed to the effect of surface tension effectively increasing the kernel volume measured by the wet method. Further investigations with water-ethanol mixtures of varying surface tension supported this. The current trend in cereal quality testing is to measure distributions of single kernel physico-chemical parameters. The wet method allowed the measurement of the distribution of single kernel densities, but with poor accuracy due to surface tension; what is needed is a dry single kernel density method.