Abstract:
Aiming at the problem that the multiple compression and impact of the air-assisted centralized seed metering device on rice seeds during high-speed sowing (≥12 km/h) can easily lead to seed damage and affect the emergence rate, the damage law of rice seeds under single and multiple mechanical compression was studied based on the damage accumulation theory. The fitting equations of seed impact damage characteristics and compression characteristics were clarified. The matching range of the stirring speed and the conveying airflow parameters during high-speed seeding for the air-assisted centralized seed metering device has been clarified. By analyzing the working process of the air-assisted centralized seed metering device, it was determined that the main link where seed damaged during high-speed seeding is the repeated compression of seeds by the seeding device during the seed maxing process, and the multiple impacts of airflow during transportation and distribution. The single compression test on hybrid rice and conventional rice varieties was carried out to construct an elastic plastic model suitable for rice seeds, and analyzed the critical value of elastic-plastic deformation. The multiple equal displacement compression tests were carried out to determine the process of damage to rice seeds under multiple compressions, and determined the critical deformation of rice seeds under multiple compressions. Combined with the seed germination rate test, the correctness of the critical deformation of damage was verified. On this basis, based on the law of conservation of energy, the critical speed at which rice seeds are compressed and damaged by the stirring device was constructed. Combined with the fitting equation of impact damage and compression characteristics, the speed of seed airflow impact damage was analyzed. The results of the single compression test of rice seeds showed that the single compression crushing force of conventional rice and hybrid rice seeds were 118.4N±35.6N and 113.2N±39.9N, respectively, the deformation during crushing was 0.59 mm±0.07 mm and 0.63 mm±0.11 mm, respectively, and the average critical deformation of elastic plasticity was 0.4mm and 0.44 mm, respectively. The results of multiple compression tests on rice seeds show that when the compression distance is less than the elastic-plastic average critical deformation, the maximum compression force of the seeds remains consistent during multiple compression processes; When the compression distance is greater than the critical elastoplastic deformation, the maximum compressive force on the seed gradually decreases. The results of multiple compression tests on rice seeds and germination rate verification tests show that the critical deformation of hybrid rice seeds that causes damage is 0.44 mm. When the deformation of compressed seeds is less than 0.44 mm, there is no significant difference in germination rate between compressed and uncompressed seeds after multiple compressions; When the compression deformation of the seeds is greater than 0.44 mm, the germination rate of rice seeds decreases after multiple cycles of compression. In the process of matching the operating parameters of the air-assisted centralized seed metering device, the deformation of rice seeds after being loaded should be avoided to be greater than 0.44 mm. After calculation, the rotation speed range of the stirring device should be lower than 125 r/min and the seed transport speed should be lower than 8.5 m/s to reduce the compression and impact damage of the air-assisted centralized seed metering device on rice seeds. This study can provide a theoretical basis and parameter range for the matching of operating parameters during rice high-speed sowing.