Development of the variable amplitude vibration grading device for maize parental seeds

Manual sowing is often used in the early stage of seed breeding. However, the seed quality cannot fully meet the large-scale production in recent years. When sowing in the experimental field, 2-3 seeds are sown in each hole, where the small ones are removed and then the large ones after emergence. The seeds only require simple threshing and packaging. There is no need to clean and grade the seeds. Since 2015, most maize seeds have gradually replaced manual sowing with plot seeders. Small-scale experimental planting can be conducted through single-seed sowing. Therefore, the planting quality can be greatly improved during the experimental stage. The germination rate of seeds can increase for better consistency between seedling emergence and plant growth. It is necessary to grade the seeds, in order to better meet the requirements of single seed precision sowing in the seeder. The graded seeds have similar sizes and shapes, which is beneficial to the sowing qualification rate of the seeder. Maize seed grading before sowing has been one of the most important parts of seed breeding. There is a large demand for seed breeding machinery because seed breeding test has a heavy task, with many kinds and various modes. Therefore, it is necessary to develop the seed grading equipment for the different varieties of seed breeding tests. Efficient screening can be used to maintain an effective screening area, appropriate thickness of material layer, and effective movement. Numerous studies have focused mainly on the screen structure, vibration mode, screen hole shape, parameter optimization, and screening mechanism, in order to improve the screening performance of vibrating screens. However, it is still lacking in the existing grading equipment for seed breeding. The performance of seed breeding needs to be modified for better technical requirements. In this study, the variable-amplitude vibrating screen technology was proposed to improve the efficiency of seed grading and self-purification quality before sowing in seed breeding. A vibrating screen device was also designed for seed grading. Jingke 968 maize seed was taken as the test object. With the qualified rate of grading, operation time, and the number of plugging seeds as the test index, the response surface mathematical model was established by four-factor (feed port height, amplitude, vibration frequency, and screen inclination angle) three-level Box-Behnken test. The verification tests were carried out to optimize the parameters. There were highly significant effects of vibration frequency and screen inclination angle on the qualified rate of grading and operation time. The number of plugging seeds regression model was highly significant, but it was lacking in fitting, indicating the lower fitted regression model. There was no analysis of variance in the number of plugging seeds regression model. The greatest influence of vibration frequency was found on the qualified rate of grading, followed by the screen inclination angle, amplitude, and feed port height. There was the greatest influence of vibration frequency on the operation time, followed by the amplitude, screen inclination angle, and feed port height. The number of plugging seeds on the screen holes increased sharply at the low amplitude and vibration frequency. The very low self-purification was caused by the greater randomness in the number of plugging seeds. The optimal combination of parameters was obtained at the opening height of 19 mm, amplitude of 5 mm, vibration frequency of 8.25 Hz, and screen surface inclination angle of 7°. The validation test under the optimal conditions was 89.55% of the qualified rate of grading and 39 s of the operation time, which was basically consistent with the predicted after optimization. The better self-purification was achieved, where the number of plugging seeds was 8. The grading efficiency of the device was about 0.33 t/h. All the indicators can fully meet the design requirements. The operational performance was better than that of the uniform amplitude vibration grading device. The finding can provide a strong reference to design the seed grading equipment for seed breeding.