Structural design and test of seed-suction hole of air-sucking seed-metering device for millet

Abstract: Millet is the main crop in China. At present, due to the lower mechanization level of millet cultivation in China, it is easy to damage seeds and clog suction holes when sowing. In view of the problem of poor hole formation, precision sowing has become a modern technological means to improve grain yield. In order to realize precision sowing, the mechanical and physical properties of three domestic typical millets were firstly studied by measuring size, sphericity degree and the maximum coefficient of static friction between the millet and the steel plate. And to make our design of the suction hole have a good adaptability, the comparative analysis was performed in the Jingu 21 millet. According to the physical characteristics of the millet, air -sucking seeding disc was designed, and Q235 cold-rolled steel plate was selected as the material for making the seed plate. There were 18 holes evenly distributed in the circumferential direction of the seed plate, and the range of pore size was from 1.04 to 1.17 mm. Four kinds of structure of seed suction holes were designed, including cylindrical hole, chamfered truncated cone hole, truncated cone hole and four-prism hole. In order to test the seeding effect, the millet seeding experiment was carried out by using the JPS-12 seeding device performance test rig. The relevant national standard of the planter was cited and six test indices were selected: the average grains number per hill, the qualified rate of grains number per hole, the average hill distance, the qualified rate of hill distance, the single grain rate, and the average seed's quantity per hill. Three kinds of hole geometry on the seeding disc, such as cylindrical hole, chamfered truncated cone hole, truncated cone hole, were selected to test the seed selection efficiency, and the results showed that truncated cone hole was the best in the 3 kinds of adsorption pore structures, which could effectively reduce all kinds of plugging holes, so truncated cone hole was chosen to continue to compare. Two kinds of seed suction hole structures, such asthe truncated cone hole and four frustum pyramid, were selected to conduct the comparative experiment on the seeding efficiency. The results showed the optimal structure of seed suction hole was four-prism hole structure on the seeding disc, which had the best effect on seed sowing and solved the problems of serious seed damage, suction hole plugging, and cavitation. Through the millet seeding effect comparison test, the design scheme of the suction hole was ultimately determined as four-prism hole structure. The millet seeding performance test of this suction hole structure was carried out to determine the best seeding index. The seeding performance indices were the average number of seeds per hill of 3.3, the qualified rate of seeds per hill of 89%, and the qualified rate of hill space of 94%, and the average hole distance was 1.24 cm. Through the seeding performance test, the best working parameters of the seeder were determined: Vacuum degree was -2 kPa, and the rotation speed was 28 r/min. Precision hole sowing of millet seed was preliminarily realized by the use of air-suction seed-metering device in this study. The test results will provide a theoretical reference for the design and related research of millet precision seeding device.