Abstract
Abstract: Buckwheat belongs to Fagopyrum mill, which is one of the grain crops in China. Buckwheat is rich in protein, fat and other nutrients, as well as food fiber, sugar alcohol, phenolic acids, bioflavones and other disease-resistant ingredients. In recent years, buckwheat has become the preferred functional staple food for people which with cardiovascular disease and diabetes and are highly recommended for its high medicinal and edible value by the public. At present the mechanized production level of buckwheat is relatively low. The stress modes of relative working parts on grain are extrusion, impact, kneading and so on during the design process of buckwheat segmenting, combined harvesting, threshing, husking, milling, processing and other equipment. Therefore, the selection of design parameters for key components requires a comprehensive mastery of the conventional biomechanical properties that contain compress, impact and friction of different buckwheat grains. Viscoelastic properties of buckwheat powder were studied in this paper: 1) Basic physical parameters that contain triaxial size, 1000-grain weight and bulk weight of different buckwheat varieties (Jinqiao-1, Yuqiao-4, Heifeng-1, Heifeng-10, Zhaoku-1 and Chuanqiao-1) with different moisture content (22.8%, 19.4%, 15.6%, 13.2%, 11.1%)were measured. The results showed that the length, width, height, 1000-grain weight and geometric mean diameters of buckwheat grain decreased as the moisture content decreased, and the bulk density increased as the moisture content decreased. The Fagopyrum esculentum moench length, width and thickness range from 6.16 mm to 6.87 mm, 4.16 mm to 4.60 mm, 3.87 mm to 4.32 mm, and 1000-grain weight range from 32.34 g to 37.70 g, respectively. The Fagopyrum tataricum length, width and thickness range from 4.39 mm to 5.90 mm, 3.10 mm to 3.90 mm, 2.93 mm to 3.61 mm, and 1000-grain weight range from 21.32 g to 27.67 g, respectively. 2) The static sliding friction coefficient and the angle of repose of buckwheat grain were measured by inclined plane instrument and repose angle measuring device. The results showed that the friction coefficient decreased on Q235 steel plate, 7075 aluminum alloy plate and 304 stainless steel plate in turn. The friction coefficient and angle of repose decreased as the moisture content decreased, and the friction coefficient and angle of repose of Fagopyrum esculentum moench were smaller than those of Fagopyrum tataricum. The friction coefficient was not only related to grain moisture content, surface roughness of contact materials, but also related to grain surface characteristics and grain shape. 3) The dynamic viscoelastic test of buckwheat (powder) was carried out on DMA (Q800), and the storage modulus, loss modulus and loss factor of buckwheat powder were obtained. The storage modulus decreased as the moisture content increased. For the same buckwheat, the loss modulus and loss factor increased as the moisture content increased, and the lower the moisture content, the smaller the loss modulus, the bigger the storage modulus, the greater the elasticity and the smaller the viscosity. 4) The mechanical properties of grain, which contain failure force and failure energy, were measured by physical property analyzer. As the moisture content increased, the failure force, apparent modulus of elasticity and maximum contact stress decreased gradually, the amount of deformation gradually increased, and the failure energy showed a downward trend. The failure force and failure energy of Fagopyrum esculentum moench were lower than that of Fagopyrum tataricum, so Fagopyrum esculentum moench was easier to peel than Fagopyrum tataricum. In order to increase the whole and half kernel rate of Fagopyrum tataricum, the grain could be pretreated first to reduce the hardness and strength of shell and increase the hardness and strength of kernel. 5) The impact force was measured by ZBC50 pendulum hammer impact tester. The broken rate of Yuqiao-4 and Heifeng-1 was approximately 0 when the impact force was 20.70 and 42.58 N respectively. Under the same impact force, the broken rate first decreased and then increased as the moisture content increased. And the experimental results were fitted. According to the fitting formula, the broken rate (p1, p2) was the lowest when moisture content was 18.2% and 18.4%, respectively. The experimental results showed that: the broken rate was 2.9% when the impact force was 27.77 N and the moisture content of Yuqiao-4 was 18.2%; the broken rate was 11.7% when the impact force was 48.27 N and the moisture content of Hefeng-1 was 18.4%, and the experimental results were consistent with the model. The results can provide comprehensive foundation support for the development of buckwheat mechanized production equipment and parameter optimization.
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