| Coarse cereals crops have been northern cultivating crops in China for a long time.and their planting areas have been expanding gradually in recent years.The coarse cereals industry is developing and growing,but the coarse cereals crops were mainly harvested by manual work.The manual work’s efficiency was low,and the labour intensity was high.There was no specialized harvest machine type researched to support the harvest of coarse cereals.The market mainly adopted the modified combine harvester for wheat,rice or cereals to harvest coarse cereals crops,which caused the high loss ratio and impurity content during the cleaning process,which limited the increase of planting benefit and the development of coarse cereals industry.Therefore,we studied the cleaning characteristics and device for the threshed materials of coarse cereals crops harvested by machinery via theoretical analyses and experimental study,and the results are as follows:(1)We have conducted the theoretical analysis and experimental study on the cleaning characteristics and device for the threshed materials of foxtail millet,buckwheat and oat crops harvested by machinery.Based on the Chinese national standard for the measurement methods,we measured the physical properties related to cleaning for the threshed materials of the three kinds of coarse cereals crops harvested by machinery,including the grain-grass ratio,composition of extruded matter,moisture content of each component of extruded matter,morphological size,1000-grain weight,density,volumetric density,friction coefficient with different materials,friction Angle and suspension characteristics.The measured physical properties provide data support for the subsequent research on cleaning characteristics and equipment.(2)In this paper,we design an air-blown test equipment for measuring suspension velocity of agricultural materials,which suitable for three kinds of grain crops such as emerging agricultural material,and using the device,according to the relevant National Standard suspension speed measurement,the piecewise suspension test was designed to measure three grain crops rotor suspension speed of each composition,the result is: millet crops mechanical rotor grain harvest,disc,stem and leaf of suspension speed are: 4.29-8.88,1.03-6.48,1.71-6.09,1.03-3.09 m/s;The suspension rates of grain,branch,stem and leaf of buckwheat crop are: 4.47-10.18,1.85 ~ 5.18,2.80-8.37,0.76-2.99 m/s,respectively.The suspension rates of grain,seed coat,branch,stem and leaf are:4.35-11.01,0.62-1.71,1.62-4.52,1.14-6.28 and 0.91-3.56,respectively.The difference of suspended velocity between all kinds of components of the ejecta was analyzed.The following experiments were carried out to analyze the influence of the moisture content of each component on its suspension velocity.The test results showed that: with the decrease of the moisture content,the suspension velocity gap between the components of the ejected material increased,which was beneficial to the separation by air separation.The suspended velocity increases with the increase of water content.The relationship between water content and suspension velocity is helpful to select proper cleaning wind speed.(3)According to combined harvester characteristics and Agricultural Machinery Design Manual,designed a kind of coarse grain crop out the wind screen type cleaning test device,the frequency of wind speed and direction amplitude can be adjusted,the adjustment range can meet the requirements of mechanical harvest cleaning parameters of millet,buckwheat,oats and other crops,and can monitor the wind speed at the air inlet of the cleaning chamber in real time.(4)D’alembert’s Principle is used to analyze the dynamic characteristics of the separated material in the vibrating screen,and ADMAS software is used to simulate the movement of the separated material on the screen surface.The simulation results are consistent with the theoretical analysis results,proving that the structure and vibration parameters of the vibrating screen are reasonable.FLUENT software was used to carry out simulation analysis on the flow field distribution in the cleaning chamber of the cleaning test device when there was no ejection feeding.The analysis results showed that the flow velocity in the vicinity of the sieve in the cleaning chamber was generally uniform with no vortices and reflux,which proved that the structure design of the cleaning chamber was reasonable.(5)Utilizing the cleaning experimental device,we conducted the single factor experiments,response surface experiments and the optimal level combination verification experiments for the threshed materials of foxtail millet,buckwheat and oat crops.The experimental results showed that,with the increase of cleaning airflow velocity,amplitude and frequency,the 3 kinds of threshed materials’ cleaning loss ratios of the 3 kinds of coarse cereals crops were all increasing,and the impurity content of them were all decreasing.The effects of cleaning airflow velocity,amplitude and frequency on the 2 cleaning indexes of the 3 kinds of threshed materials of 3 kinds of coarse cereals crops were all significant,whereas the effects of cleaning airflow direction on the 2 cleaning indexes of them were not significant.The optimal cleaning working parameters levels combination of the foxtail millet crop’s threshed materials were as follows,the airflow velocity is 4.19 m/s,the airflow direction is 30.28°,the amplitude is 21.86 mm and the frequency is 218.36 r/min.In that cleaning case,the minimum cleaning loss ratio was 1.85 %,and the impurity content was 8.55 %.The optimal cleaning working parameters levels combination of the buckwheat crop’s threshed materials were as follows,the airflow velocity is 5.85 m/s,the airflow direction is 32.22°,the amplitude is 25.91 mm and the frequency is 186.38 r/min.In that cleaning case,the minimum cleaning loss ratio was 5.79 %,and the impurity content was 8.74 %.The optimal cleaning working parameters levels combination of the oat crop’s threshed materials were as follows,the airflow velocity is 4.33 m/s,the airflow direction is 37.48°,the amplitude is 25.10 mm and the frequency is 185.72 r/min.In that cleaning case,the minimum cleaning loss ratio was 5.08 %,and the impurity content was 8.64 %.The results of the optimal cleaning working parameters level combination verification experiments of the 3 kinds of threshed materials of 3 kinds of coarse cereals crops are all close to their predicted results,which certify that their optimal cleaning working parameters level combination are desirable. |
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