Design And Experiment Research On Pneumatic Metering Device For Rice And Wheat

Rice and wheat are important grain crops in China.Compared with the traditional rice seeding transplanting and planting mode,rice direct seeding has the advantages of saving time,labor and water,so the area of rice direct seeding expands year by year.At the same time,the planting area of wheat has also increased year by year,and the mechanized seeding level is 86.52%,but most of them are drill.The seeding season and seeding process of rice and wheat are similar,but there is a lack of research on the general seeding device of rice and wheat,and even less of the machine type put into practical application.Most of today's seed metering devices are mechanical seed metering devices,which may cause problems such as seed injury and poor universality.Modern agriculture requires high speed and high efficiency of seeding operation.If the seeding machines can only be planted in a single row,the whole machine will be bloated,consuming a lot of energy and the seeding efficiency will be low.In response to this situation,this paper designs a kind of universal pneumatic metering device for rice and wheat;study the material characteristics of rice seed and wheat seed;study the distribution of airflow field of main part by ANSYS/CFX software;carried out the performance bench test of metering device to test the working performance of the device,find the best working condition and verify it.The main research contents are as follows:(1)Perform the experiments on material characteristics of rice seeds and wheat seedsThe experimental subjects were Huanghuazhan conventional rice,Peiza Taifeng hybrid rice,Zhengmai 9023 and Xiangmai 25,which are commonly used in the middle and lower reaches of the Yangtze river.The moisture content,triaxial size,1000-grain weight,sliding friction angle,recovery coefficient,stacking angle,suspension characteristics and compression characteristics of the above seeds were measured through experiments,which provided a reference for the structural design and parameter selection of the universal pneumatic metering device for rice and wheat.(2)Characterize the moisture content of rice seeds by EDEM softwareMoisture content has a great influence on the physical characteristics of rice seeds,but there is no moisture content input parameter in the EDEM simulation software.To solve this problem,the stacking angle of rice seed under five kinds of moisture content was measured by cylinder method and square box method,and the relationship curvebetween stack angle and moisture content was obtained.Then,stacking angle was repeatedly measured by EDEM software.The effects of three parameters,elastic modulus,dynamic friction coefficient between seeds and static friction coefficient,on the stacking angle were studied through the single-factor repeated test,and it was found that the influence of static friction between seeds on the stacking angle was similar to that of moisture content on the stacking angle,and the relationship curve of stacking angle and static friction coefficient between seeds was drawn.According to the two relationship diagrams obtained by experiments and simulations,the moisture content was characterized by static friction coefficient between seeds,with the stacking angle as the intervening variable.The characterization results were verified by hopper unloading test,and the corresponding friction coefficient was input in EDEM software for simulation verification.The error of the verification results was less than 5%.(3)Design the structure of the universal pneumatic metering device for rice and wheatBased on the working principle of negative pressure seed suction and positive pressure seed discharge,this paper used the three-dimensional modeling software PRO-E to design and manufacture a kind of universal pneumatic drum seed metering device for rice and wheat which was convenient to replace the core components,and analyzed the working principle of the device.On the basis of the material characteristic experiments of rice and wheat above and the standard of precision seeding,the structure parameters of the core components of the device and the working parameters in the seeding process were designed.Also,the working process of seed suking,seed cleaning,seed carrying and seed arranging was analyzed.4)Airflow field simulation analysis based on ANSYS/CFX softwareANSYS/CFX software was used to simulate the airflow field in the negative pressure suction chamber of rice and wheat seeds.In order to explore the influence of three factors on the adsorption capacity of the suction port: diameter D,suction port diameter D,and negative pressure strength P,the average pressure on the end face of the suction port was taken as the evaluation index to carry out the orthogonal test of three factors and three levels,and the optimal combination of three factors was obtained and verified.Orthogonal test shows that the main and secondary factors affecting the adsorption capacity of the suction hole are: negative pressure P of the air outlet,diameter D of the air outlet,and diameter D of the suction hole.For the negative pressure suction chamber of rice,the optimal combination plan is: suction hole diameter d: 1.8mm,airoutlet diameter d: 25 mm,air outlet pressure P: 4600Pa;For the negative pressure suction chamber of rice,the optimal combination plan is: suction hole diameter d: 2.0mm,air outlet diameter d: 25 mm,air outlet pressure P: 4200 Pa.The combination of the optimal parameters obtained from the orthogonal test was imported into ANSYS/CFX software for verification simulation test.The results showed that under the optimal parameters,the airflow field in the negative pressure suction chamber of rice and wheat seeds was both stable and could generate a large pressure at the suction hole entrance,which was conducive to seed sorter.(5)Test the performance of metering deviceSingle factor test,quadratic regression orthogonal combination rotation test and seed discharge adaptability test were carried out by taking the shape of sockets,drum rotation speed,pressure of negative pressure suction chamber and height of seed layer in seed filling area as experimental factors.The single factor repeated experiments showed that the conical and ellipsoidal socket eyes were suitable for rice seed and wheat seed respectively,and the working parameters of the metering device were obtained preliminarily,which provided a reference for the factor level setting of the quadratic regression orthogonal combination rotation test.By analyzing the results of the rotation test of quadratic regression orthogonal combination,the optimum working parameter combination of the seed metering device is obtained as follows:Rice: drum rotation speed:17 r/min,seed layer height:40 mm,negative pressure suction chamber pressure:4.2kPa.Wheat: drum rotation speed:21 r/min,seed layer height: 40 mm,negative pressure suction chamber pressure: 4.6kPa.The optimum working parameter combination obtained by quadratic regression orthogonal combination rotation test was used to verify the adaptability of seed discharge.The test subjects were Huanghuazhan conventional rice,Peiza Taifeng hybrid rice,Zhengmai 9023 and Xiangmai 25 The test results showed that the performance indicators of the metering device were better.