Research On Working Mechanism And Optimization Analysis Of Chaffer Sieve Cleaning Device In Corn Grain Harvester

Corn is the most widely produced crop in China and has a vital role in guaranteeing national food security.With an increasing plantation area and the development requirement of mechanization,the corn grain combine harvester is now widely used in corn harvesting.In corn combine harvesting,cleaning is an important procedure.However,there is the high loss rate and impurity rate,which seriously restricts the quality of corn grain harvesting.Therefore,this paper proposed to combine the theoretical analysis with the numerical simulation coupled bench test,and to carry out the research.The air flow distribution and the motion of corn mixture material in the cleaning device were investigated.The mechanism of corn kernels sifting and corn cobs plugging would be clarified.In order to reduce the high impurity rate and loss rate,a new type with low loss and high cleaning sieve was developed.The research in more detail including:(1)The physical characteristics of each component in the corn mixture material were studied.The geometric size,moisture content,density,suspension velocity,elastic modulus,friction coefficient and collision recovery coefficient of were measured.The discrete element models of particles were established.The Multiple ball filling method was used to establish the granular models of corn kernel,corn cob,and corn stalk.Based on the calibration test,the optimal parameters were determined.And the accuracy and reliability of the discrete element model for each component were verified.(2)The mass distribution of corn mixture material was carried out.And the actual measurement and numerical simulation of the airflow in the cleaning device were carried out.The results showed that the mass distribution of kernel,cob,stalk and bract presented "sliding trapezoid","concave","concave" and “stacking distribution patterns in the lower left”,respectively.It can provide the data basis for the subsequent research on reducing cleaning load and the gas-solid two-phase flow coupling simulation.The airflow velocity of multiple measuring points inside the cleaning device was determined by using a hand-held anemometer.The affects of the fan speed,vibrational frequency,and screen opening on the airflow velocity were explored.The mechanism of the airflow loss caused by eddy current generated at the substrate of the chaffer sieve was revealed.The airflow resistance model was constructed,which provided a theoretical basis for the design and optimization of the cleaning screen.(3)The movement mechanism of material particles in cleaning device was studied.The motion of material particles during the cleaning process were analyzed based on the chaffer sieve.Therewith,based on the special structure and spatial shape,the sifting models of corn kernels with sliding and collision were constructed.Moreover,we analyzed and established the plugging model of the corn cob-chaffer sieve.The results showed that corn cobs were easily blocked at the arc screen hole of the adjacent screen.Besides,the internal structure of corn cob was an important factor for the congestion.The results provided a theoretical basis for the design and optimization of the cleaning sieve.(4)The gas-solid two-phase flow simulation analysis of corn cleaning was carried out.The spatial distribution of the material layer above the chaffer sieve and the sifting of the material particles under the sieve were studied.The dynamic motion mechanism about stratificationdispersion-migration-screening of the kernels,cobs,and stalks was clarified.And the effects of the air velocity,vibration frequency,and screen opening on the velocity,particle dispersion,and comprehensive cleaning performance were investigated.(5)In view of the advantages of high efficiency of the chaffer sieve to meet the needs of large feeding cleaning,a new type of corn cleaning screen was designed and optimized.The structural parameters were determined by theoretical analysis.And the smooth transition screen structure effectively reduced the vortex resistance loss of the air flow.The interleaved spatial structure greatly decreased the quality of blocking corn cobs on screen surface.Based on the uneven distribution of air flow in the front and back sections of the chaffer sieve,a two-stage combined opening adjustment scheme was proposed.The test results showed that keeping a unified large opening in the front and middle section could promote the full screening.Keeping a small opening in the back section could block the corn cob,Resulting the cleaning performance improvement.Multi-factor response surface method was used to study the synergistic effects.The experimental factors include: fan speed,vibration frequency,and screen opening.The collaborative optimization of working parameters of the new cleaning screen was carried out,and the optimal parameters were determined as follows: fan speed 1085 r/min,vibration frequency 6.0 Hz,screen opening of chaffer screen in the front middle section 22 mm,and screen opening of chaffer screen in the back section 20 mm.The field experimental results showed that the impurity rate was1.15%,the loss rate was 1.06%,and the corn cob blockage rate was less than 0.1%,which met the performance requirements of the corn grain combined harvester.Compared with the traditional chaffer screen,the new chaffer sieve not only retained the advantages of high efficiency,but also maked up for the shortcomings of high impurity rate and blocking rate,with effectively improving the cleaning performance.