Design and experiment of pneumatic-typed precision centralized metering device for rapeseed

Abstract: To improve mechanical direct seeding level, a kind of precision centralized metering device for rapeseed with a reliable performance was designed, applying for high speed and broad width. The wheel type metering device with holes had a simple structure, low rape seeds of uniform granularity, and good spherical degree which could be better utilized, thus easily realizing a centralized seeding operation; otherwise, it had a high damage rate, and therefore thus would affect seeding performance. To solve the problem of the wheel type metering device with holes because of the difficulty of precisely controlling the seeding rate on rape seeding, the seeding type holes were punched in a pyramidal shape. The device used a combination of air clearing seed and air pressure protecting seed, so the device was a kind of pneumatic-typed precision centralized metering device for rapeseed. This subject introduced the working principle of a pneumatic-typed centralized metering device. It determined the main parameters of the centralized metering device, and established the mechanical model of clearing an area and protecting an area. The tests on the influences of clearing pressure and protecting pressure and seeding metering rotating speed were carried out. For seeding performance, the evaluation indexes were stability variability coefficient of the full seeding quantity, the apiece row consistency, variability coefficient of seeding quantity, and damage rate of the rapeseed. Results showed that under the condition that the seeding cylinder diameter was 100 mm, the hole shape was punched in a pyramid shape, the number of holes were 27, while the clearing pressure was 250 Pa, the protecting pressure was 150 Pa, the seed layer thickness was 49.4 mm, the clearing seed angle was 53°, and the protecting seed angle was 90°, the rotating speed varied from 20 to 70 r/min. The whole index and damage rate increased with the rise of the rotating speed of the cylinder. When the speed was not more than 40 r/min, the index changed into good range and had not much variation. When it was from 40 to 50 r/min, the damage rate of the rapeseed rarely changed, while the stability of the full seeding quantity and the apiece row consistency of seeding quantity obviously had a rising trend. If was no less than 50 r/min, the seeding performance was obviously getting worse. Thus, a seeding cylinder speed of 20-40 r/min was much better. For the stability variability coefficient of the full seeding, quantity was less than 2%, The apiece row consistency variability coefficient of seeding quantity was not more than 2%, and the damage rate was less than 0.3%. The field experiment showed that in conditions of clearing pressure 100 Pa, protecting pressure 300 Pa and seeding roller speed 26 r/min, the rape seed field seeding uniformity coefficient variation of the collecting seeding system was 38.76%, and the average emergence distance was 75 mm which satisfied agronomy planting requirements. This seeding method is suitable for small seed metering, and provides a basis for research on the design of this type metering device.