Design and experiment of oriented seed churning device on pneumatic seed metering device for rice

Due to high tilling capacity and preventing the risk of low seedling emergence rate in the field, generally 3-4 seeds are required for each hole when hybrid pregnant rice seeds were direct seeded to the field by drilling machine. Even though the seeds sprouted and their bud length were less than 3 mm with high moisture content, they were low in liquidity and had irregular shapes making it quite difficult to meet the requirement. In order to solve the problem, a novel pneumatic metering device was designed with group sucking holes plate in a seed metering device, by which 3-4 seeds can be sucked and dropped at the same time. Existing experiments were conducted to investigate the suck characteristic of the group holes on the sucking plate under vacuum, diameter of the holes, and seed-clearing device. The results showed the optimal parameter combination was vacuum at 3.2 kPa and the diameter of the hole at 1.5 mm. The results: the <2 sucked seeds per hill, the (3-4) sucked seeds per hill, and the ≤5 sucked seeds per hill were 8.27%, 81.87%, and 9.86% while the sucking plate rotating speed was 8 rpm. In order to improve the device performance, the group sucking holes on the plate were increased from eight to ten, its circular distribution was replaced by a linear distribution, and a kind of oriented churning device that consisted of two churning teeth was set on the plate. The single factor experiments and combination factor contrast experiments were conducted to investigate the suck characteristics of the sucking plate under vacuum, diameter of the holes, and oriented churning device. The experimental equipment consisted of a pneumatic metering device with group holes, a U-shaped manometer, a positive and negative pressure air pipeline, a cut-off valve, and a vortex pump. In the experiments, the rotating speed of the sucking plate was 30 rpm and its diameter was 165 mm, the distance between 3 sucking holes were 6.5 mm and 11.5 mm while the distance was 65 mm between the middle hole and the center of the plate. A fingerlike clearing device was set on the plate while the distance was 118mm between it and the center of the plate; its length was 38mm and its installation angle was 25°. Rice varieties were Indic hybrid, Peizataifeng, and Y-Liangyou 1 pregnant rice seed. Their moisture content (wet basis) were 11.6%-11.9% and 23.93%, their 1000-grain were 22g and 25.2g, and their overall dimensions (length × width × thickness) were 8.94mm × 2.30 mm × 1.94 mm and 9.11 mm × 2.30 mm × 1.87 mm. The experimental results showed the metering device performance was obviously improved after installing the oriented churning device, by which its rotating speed was significantly increased and its air vacuum requirements were reduced on the same precision. To suck Y-Liangyou 1 pregnant rice seed, the optimal parameter combination was the vacuum with 2.0kPa, the rotating speed of the plate at 30 rpm, the wedge angle of the churning tooth at 60°, the thickness of the churning tooth at 2 mm, the installation angle of the inner-churning tooth at 90°, the installation angle of the outer-churning tooth at 60°, and the diameter of the hole at 6 mm. The (3~4) sucked seeds per hill of the pneumatic seed metering device, <2 sucked seeds per hill, and the ≤5 sucked seeds per hill were 59.48%, 15.03%, and 25.49%. The results showed that the seeds were separated, oriented, rubbed, and pushed by churning device that has a good influence to the precision of the pneumatic seed-metering device.