玉米收获机清选曲面筛设计与试验

为提高玉米收获机风筛式清选装置的清选效果,通过筛上颗粒受力分析,确定筛上颗粒运动状态与筛面方程f(x)存在函数关系。以编织筛为研究对象,利用CFD-DEM耦合技术,通过对比清选装置内平面、凸面、凹面3种编织筛的气流场及不同区域筛分特点,提出一种正弦曲线编织筛,并与去除尾筛的正弦曲线筛进行性能对比,确定保留尾筛筛分性能更好。以正弦曲线筛筛形系数、入口气流速度、气流方向角为试验因素,以籽粒清洁率和籽粒损失率为评价指标,设计二次正交旋转组合试验,建立了各因素与指标间回归数学模型,运用Design-Expert软件的多目标优化算法进行参数优化。获得参数最优组合为:筛形系数32. 35 mm,入口气流速度13. 73 m/s,气流方向角23. 86°。当玉米脱出物喂入量为5 kg/s,筛面振动频率为5. 15 Hz时,利用高速摄像及室内台架进行了正弦曲线筛工作机理试验和性能对比试验。试验结果表明,正弦曲线筛可实现对杂余的快速推移,并提高籽粒透筛概率。正弦曲线筛清选装置的籽粒清洁率为98. 07%,籽粒损失率为1. 16%,相较平面编织筛清洁率提高2. 45个百分点、损失率降低0. 79个百分点,满足国家筛分质量评价技术规范要求。

Design and Experiment of Curved Screen for Maize Grain Harvester

In order to improve the screening performance of the air-screen cleaning device of maize grain harvester, the relationship between the motion of grain on the screen and the function f(x) of screen-shape was determined through the mechanics analysis of particle. In order to propose a type of sinusoidal-shape screen, the woven screen was studied. Computational fluid dynamics and discrete element method (CFD-DEM) were coupled to compare and analyze the airflow in the cleaning device and the characteristics of flat, convex and concave screening. The screening performance of the sinusoidal-shape screen, compared with this one with tail screen was removed, was better. The quadratic orthogonal rotational-combinational simulation tests were designed. The coefficient of screen-shape and the inlet velocity of airflow and the direction angle of airflow were taken as factors, and the loss and cleanliness of maize grains collected were taken as indexes. The regression mathematical models between factors and indexes were multi-objective optimized by using Design-Expert software. The best combination of parameters was obtained, including the coefficient of screen-shape of 32.35mm, the inlet velocity of airflow of 13.73m/s, the direction angle of airflow of 23.86°. The best combination of parameters was set in the bench test. The flat weave screen was compared with that of the screening performance of sinusoidal shape screen. The experimental results showed that the sinusoidal shape screen can realize the fast passage of maize debris, and increase the possibility of maize grains passing the screen when the total feeding quantity was 5kg/s and the vibration frequency of the screen was 5.15Hz. The working mechanism and screening performance of the sinusoidal-shape screen were tested by high speed camera and indoor bench. The experimental results showed that the state of movement of maize mixture on different screens was more favorable to the performance of the cleaning device. The cleaning rate of maize grains collected was 98.07% and the rate of maize loss was 1.16% after screening. Compared with the flat weave screen, the cleaning rate of maize grains was increased by 2.45 percentage points and the rate of maize loss was reduced by 0.79 percentage points, which met the requirements of technical specification for quality evaluation of screening in China.