中央集排气送式玉米精量排种器设计与试验

该文提出降低充种阻力的新型气流结构，结合集中排种与气送投种的特点设计了一种中央集排气送式玉米精量排种器，阐述了工作原理并确定了关键结构参数。以漏播指数、重播指数、合格指数为试验指标，对充种型孔直径、作业速度进行了双因素等重复试验。结果表明：4 mm孔径漏播指数较高；作业速度为4～10 km/h，孔径为4.5 mm时平均合格指数最高为97.9%，其次为5 mm孔径（97.2%）、5.5 mm孔径（96.3%）；作业速度超过12 km/h后，4.5 mm孔径漏播严重，漏播指数达到8.47%，5和5.5 mm孔径漏播指数为2%左右。

Design and experiment of centralized pneumatic seed metering device for maize

Abstract: Research showed that the moving resistances between seeds have an adverse effect on the seed-filling of pneumatic metering devices. The moving resistances between corn seeds are relatively high as they have large weights and irregular shapes. To attain good performance of the corn precision metering devices, a new airflow structure that could effectively reduce the moving resistances was utilized. In the airflow structure, compressed air could flow through a perforated seedbed and blow the seeds in a "boiling" movement. Based on the airflow structure, a centralized pneumatic metering device for maize was designed. The working principle was expounded here, and the key structural parameters were confirmed. The centralized pneumatic metering device presented in this paper consists of a centre drum and a positive press system. It can distribute seeds to four sowing rows, and this function makes it more efficient than a conventional one which can accomplish only one row's sowing. A pneumatic conveying system was applied to throwing seeds. Under the system, seeds were "shot" through long pipes full of positive pressure into the furrow. The system enabled the separation of the metering device from the placement system and obviously reduced the vibration of the metering device.The performance of the centralized pneumatic metering device was investigated under laboratory conditions to optimize the design and operating parameters. Double factors equal repeated trials were carried out on a metering device test-bed PS-12 to evaluate the influences of filling hole diameter and working speed on the miss rate multiple rate and single rate. The filling hole diameter was varied from 4 to 4.5 mm, and the working speed varied from 4 to 12 km/h. Other conditions were constant, the pressure in the air chamber was 3.5 kPa, and the seed spacing was 247 mm.The test results showed that: the miss rate increased while the multiple rates reduced with the rise of the working speed. The miss rate reduced while the multiple rate increased with the rise of the filling hole diameter, and the miss rate was high when the filling hole diameter was 4 mm. As the working speed was between 4 to 10 km/h, the average single rate of the filling hole in a 4.5 mm diameter was 97.9%, in a 5 mm diameter it was 97.2%, and in a 5.5 mm diameter, it was 96.2%. When the working speed was over 12 km/h, the miss rate of the filling hole in a 4.5 mm diameter became as higher as 8.47%, and the miss rate of the filling hole in a 5 mm or a 5.5 mm diameter was around 2%. As stated above, the filling hole diameter should not be less than 4.5 mm. The centralized pneumatic metering device showed a good performance even at a high working speed.