玉米籽粒收获机分段式振动筛清选装置设计与试验

针对目前玉米籽粒收获机籽粒清洁率和损失率不能满足国家标准要求的问题,设计了一种分段式振动圆孔筛清选装置。利用CFD-DEM耦合技术对传统双层往复振动筛清选装置内气固两相运动进行仿真,根据上筛纵向区域内籽粒透筛规律和上筛长度,确定合适的分段式振动筛前筛长度,并设计分段式振动筛后筛,使玉米脱出物在前筛尾部下落到后筛之前可以被前筛上下混合气流继续分散、分层,以提高籽粒清洁率,降低籽粒损失率。在保证分段式振动筛前筛清选性能不变的条件下,以后筛频率、后筛振幅、前后筛垂直间距、前后筛水平间距为试验因素,以籽粒的清洁率和损失率为评价指标,设计二次正交旋转中心组合试验,建立各因素与指标之间的回归数学模型。利用Design-Expert 8.0.6软件的多目标优化算法获得最佳参数组合:后筛频率为4.44 Hz、后筛振幅为15.65 mm、前后筛垂直间距为114 mm、前后筛水平间距为18.53 mm。在清选装置入口气流速度为12.8 m/s、气流方向角为25°、清选装置入口玉米脱出物喂入量为5 kg/s时,分段式振动筛清选装置使籽粒清洁率提高到98.34%,籽粒损失率降至1.45%,籽粒清洁率比传统双层往复振动筛清选装置提高1.26个百分点,损失率降低0.81个百分点,满足国家筛分质量评价技术规范要求。

Design and Experiment of Segmented Vibrating Screen in Cleaning Device of Maize Grain Harvester

In view of the fact that the cleaning rate and loss rate of maize grain could not meet the requirements of national standards for maize grain harvester, a cleaning device with segmented vibrating screens whose holes were round was designed. The CFD-DEM coupled method was used to simulate the gas-solid two-phase motion in cleaning device with traditional reciprocating vibrating double screens. Based on the law of grain penetration along the longitudinal area of the upper screen and the length of the upper screen, the suitable length of the front screen was determined and the rear screen was designed. The maize mixture could be dispersed and layered by the combination air from the upper and lower of the front screen before they fell on the rear screen from the end of the front screen. The cleaning rate of the grains could be increased and the loss rate of the grains could be decreased. Under the condition that the cleaning performance of the front screen remained constant, the frequency, amplitude of the rear screen, the vertical and horizontal distances between the front and rear screens were taken as the experimental factors. The cleaning rate and loss rate of the maize grains were taken as the performance indexes. The quadratic orthogonal rotational-combinational simulation tests were designed. The regression mathematical models between factors and indexes were founded. The optimal parameter combination was obtained by using the multi-objective optimization algorithm of Design-Expert 8.0.6 software. The best combination of parameters were the frequency of rear screen of 4.44Hz, the amplitude of rear screen of 15.65mm, the vertical distance between the front and rear screens of 114mm, horizontal distance between the front and rear screens of 18.53mm. Under the condition of inlet air velocity of 12.8m/s and the air direction angle of 25°, when the feed rate of maize mixture at the inlet of the cleaning device was 5kg/s, the cleaning rate of maize grain was 98.34% and the loss rate of maize grain was 1.45%. Compared cleaning device with traditional reciprocating vibrating double screens, the cleaning rate of maize grain of the cleaning device with segmented vibrating screens was increased by 1.26 percentage points and the loss rate of maize grain was decreased by 0.81 percentage points, which could meet the requirements of technical specification for quality evaluation of screening in China.