玉米螺旋式清选装置的设计与试验

针对传统振动筛存在噪音大、筛分效率不高等问题，该文基于螺旋输送原理设计出一种玉米螺旋式清选装置，装置主要由输送搅龙、料槽、半圆筛片、减速电机、变频器等组成。输送搅龙外径为100 mm，螺距为100 mm，工作长度为2 000 mm，螺旋轴轴径为20 mm，6 mm孔径的筛片开孔率约为40%，16 mm孔径的筛片开孔率约为35%。以筛分效率和破碎率增加值为试验指标，对含水率为14.5%的玉米分别进行大杂清选试验和小杂清选试验。大杂清选试验结果显示，筛分主要在筛片前部分完成，且破碎率随着输送搅龙转速的增加而增加。小杂单因素试验表明，随着输送搅龙转速的增大，筛分效率逐渐增加，破碎率增加值逐渐增大；随着初始填充系数的增加，筛分效率缓慢降低，破碎率增加值逐渐增大；随着输送角度的增大，筛分效率先增加后减小，破碎率增加值逐渐增加。小杂正交试验结果表明，3种试验因素的最优组合为初始填充系数20%，输送角度0°，输送搅龙转速500 r/min；显著性检验结果显示，输送搅龙转速对筛分效率和破碎率增加值的影响均显著（P<0.05）；输送角度对筛分效率和破碎率增加值的影响均不显著（P>0.05）；而初始填充系数对筛分效率的影响显著（P<0.05），但对破碎率增加值的影响却不显著（P>0.05）。该装置工作过程中噪音较小，运行可靠，筛分效率达到98.5%，试验结果可为后期研发螺旋式清选设备提供参考。

Design and test of screw cleaning mechanism for corn

Screening is the most important part of post-harvest processing of grain, and it is mainly vibration screening. Traditional methods of vibration screening have many problems, such as large noise and low screening efficiency. The aim of this article was to solve the problem mentioned above in the traditional screening process, and the screw cleaning mechanism was designed based on the principle of screw conveying. The device was mainly composed of conveying auger, inlet charge hopper, frame, collection box, semicircular screen, discharge port, gear motor, variable-frequency drive, and so on. In terms of mechanism parameters, the inner diameter of semicircular screen was 130 mm, the external diameter of the conveying auger was 100 mm, the screw pitch was 100 mm, the working length was 2 000 mm, and the diameter of screw shaft was 20 mm. There were 2 types of semicircular screens, the first one was 6 mm circular aperture with the open porosity of about 40%, and the other one was 16 mm circular aperture with the open porosity of about 35%. The critical screw rotational speed was 205 r/min, and the maximum theoretical cleaning ability of the device was 6.8 t/h. In order to determine the screening effect of the device, the screening efficiency and the breakage rate increment were used as the test indices in this study, and the corn with 14% moisture was adopted in the test, which included the separation test of big-sized impurities and the separation test of small-sized impurities. In terms of separation test of big-sized impurities, it was a single-factor test. Appropriately sized corn cobs and stalks were selected as big impurities. Test samples were prepared according to the relevant standards, and corn samples were obtained, of which big-sized impurities content was 2%. The conveying inclination was 0°, the initial filling factor was 40%, the working length was 960 mm, and 30 kg corn samples were tested each time. The results of the separation test of big-sized impurities showed that screening separation occurred mainly at the front portion of the screen, and the main function of the latter portion of the screen was to separate corn entrained by corn cobs and stalks; and the breakage rate increased with the increase of the screw rotational speed. Although lower screw rotational speed reduced cleaning ability, it could protect corn from break, and higher screw rotational speed might increase the working length of the screen surface. For the separation test of small-sized impurities, the clay granules which had passed through 3 mm circular aperture grain sieve were selected as small-sized impurities and the test samples were also prepared according to the relevant standards; corn samples were obtained, of which small-sized impurities content was 5%, and 30 kg corn samples were tested each time. The single-factor test showed that screening efficiency and breakage rate increment increased with the increase of the conveying auger speed; with the increase of the initial filling factor, screening efficiency decreased slowly, but breaking rate increment increased gradually; screening efficiency increased initially and decreased afterwards as the conveying inclination increased, and breaking rate increment increased gradually. The orthogonal test selected conveying inclination (-10°, 0°, 10°), screw rotational speed (150, 200, 250 r/min) and initial filling factor (20%, 30%, 40%) as the test factors, and 9 groups of experiments were conducted. The orthogonal test results showed the optimal test levels of the 3 experimental factors: Initial filling factor was 20%, conveying inclination was 0°, and screw rotational speed was 500 r/min. The ANOVA (analysis of variance) results showed that initial filling factor had significant (P<0.05) influence on screening efficiency, but it didn''t have significant (P>0.05) influence on breakage rate increment; screw rotational speed had significant (P<0.05) influence on both screening efficiency and breakage rate increment; but conveying inclination didn''t have significant (P>0.05) influence on either screening efficiency or breakage rate increment. The device had low noise and reliable operation in working process, and screening efficiency of the device reached 98.5%. This study can provide reference for the design of the screw cleaning equipment in the future.