Research On Combined Type Of Spiral Bar Tooth Threshing Mechanism For Seed Corn

Threshing is a key issue in the process of seed corn harvesting and processing, itperformance decides the damage rate of seed corn. After the seed corn is damaged, its seedviability is decreased, which will influence the germination rate of seed and growth. For thisreason, it is a crucial issue to reduce the rate of damage in the process of mechanicalthreshing.This paper takes seed corn as the object of study, it researches on the mechanical damagemechanism of seed corn by means of a series of research methods including finite elementanalysis, simulation study and experimental analysis based on carrying out the researchtechnique on biomechanics characteristics for seed corn, thus the biomechanics characteristicsof seed corn is taken as the theoretical basis, the combined type of spiral bar tooth seed cornthresher with variable radius and space is developed and manufactured, thus it studies on thestructural parameters of seed corn thresher, the optimization of running parameters as well asthe performance test on the whole machine.The main researches and conclusions in this paper can be summarized as follows:(1) The biomechanics characteristics of seed corn is proposed to be the theoretical basisfor the schematic design of threshing, this paper researches on the threshing technology andmechanism which can make the damage rate of seed low and determine the combined type ofspiral bar tooth threshing mechanism for seed corn.(2) It conducts a statistical study on the three-axis sizes and weight of seed corn as wellas the cross sectional area of carpopodium at the base of seed by means of measurement, theresults show that the three-axis size distribution of seed corn is primarily in normaldistribution and its basic sizes can be determined as10.86mm long,7.22mm wide and4.08mm thick.(3) It carries out compression test and shearing test on seed corn. In this paper,compression test and bending test is conducted for0~3support line seeds per corn ear, theoverall compression test is carried out on corn ear, while compression test and bending test isdone for corn cob, finally the mechanical properties of seed corn and the threshing mechanicalproperties of seed under different constraint conditions are obtained.(4) The process of elastic modulus measurement is conducted for seed coat and keratinendosperm, embryo, farinaceous endosperm of seed corn on the universal material testing machine controlled by the common PC with the help of sharp-tip-indentation load–depthcurve, Poisson’s ratio of corn kernel is conducted, and the basic datas are provided for thefinite-element analysis on seed corn.(5) Based on establishing the combined model for seed corn, the disrupture force underpressure of seed corn coat and keratin endosperm, embryo, farinaceous endosperm whenpressure is exerted on the top, ventral and side faces have been measured by testingrespectively, thus the finite element model of seed corn under three kinds of loading methodscan be obtained, and therefore the optimal position of force application and the best way offorce application for the low rate of damage are known.(6) The combined type of spiral bar tooth roller with variable radius and space isdesigned to make the axis of corn ear is approximately consistent with the principal axis ofthreshing, therefore the damage rate of seed corn can be reduced. The spiral flat bar tooth andcoronary bar tooth with variable space are adopted for the principal axis. From the forepart tothe posterior segment of principal axis, the space width of coronary bar tooth is increase whilethat of flat bar tooth is decreased, and the diameters of both are increased. At the beginning ofthreshing, the times of contact between the spiral coronary bar tooth and corn ear can beincreased, seed corns are threshed away from the whole corn cob, and the times of contactbetween the spiral flat bar tooth and corn ear can be increased at the later period of threshingso as to maintain the low damage rate of seed corn. The new-type spiral bar tooth threshingmechanism not only ensures the threshing performance of corn ear but also reduce the rate ofdamage for corn ear.(7) The pressure plate mechanism with variable stiffness at the outlet of corn cob isdesigned. When corn cob is discharged by the corn thresher, the variable stiffness spring canshut down the outlet of corn cob rapidly so that the scope of pressure fluctuation within thethreshing mechanism can be reduced, which can effectively improve the threshingperformance for corn ear.(8) Feed quantity, rotational speed of threshing axis, spiral angle of bar tooth andpressure of plate at the outlet of corn cob are regarded as the independent variables, damagerate of seed, threshing rate and kernel impurity rate are taken as the response value, thereforethe mathematical model between various factors and damage rate, threshing rate and kernelimpurity rate of seed are established. From the analysis on the test data, it can be seen that thefour factors influencing the damage rate, threshing rate and kernel impurity rate of seed arelisted in a descending order as: spiral angle of bar tooth, rotational speed of threshing axis,feed quantity and pressure of plate at the outlet of corn cob (min). Meanwhile, the optimalrunning parameters indicate feed quantity2.80~2.91kg/s, rotational speed of threshing axis 225~241r/min, spiral angle of bar tooth8.25~9.00°and pressure of plate at the outlet of corncob40~48N, under this condition, by comparison with that before the optimization ofparameters, the threshing rate of seed is99.86%, which is reduced by0.15~0.38%, the kernelimpurity rate is3.26%, which is reduced by0.97~1.70%, the damage rate is0.366%, which isreduced by0.084~0.274%.(9) Test report on5TYJ-10A type seed corn thresher released by Dry FarmingAgricultural Implements Quality Supervision&Inspection Testing Center of AgricultureDepartment show that the quality indicators of this inspected sample machine accord with therequirements of Technical Specifications for Seed Corn Rubbing Thresher, the threshingperformance, percentage of damage and percentage of trash content of this sample machineare99.6%,0.4%and3.2%respectively under the condition when the seed moisture content is19%.