Optimization and experiments of the drum longitudinal axial threshing cylinder with rod tooth for rice

Rice is the second most important cereal in the world after wheat. Threshing is one of the most essential steps in the rice harvesting process. Previously, the drum rod toothed longitudinal axial-flow threshing device has been designed to reduce the blockage of the thresher and threshing power consumption. Specifically, the power consumption of the drum-shaped threshing cylinder can be reduced by 5% to 15% on average, compared with the traditional cylindrical one. Previous work has focused on the structural design of drum-shaped threshing cylinders. But it is still lacking in the uniformity of axial loads on the drum-shaped threshing cylinder. At the same time, the current rice combine harvester threshing and separating devices are focused mostly on the structural improvement and optimization of working parameters, with respect to the performance indicators, such as threshing power consumption, harvesting yield, entrainment loss, unthreshing rate, and crushing rate. The threshing power consumption is mostly measured directly by the power consumption detector during the bench test. Only a few studies have been reported to measure the threshing power consumption, where the axial load uniformity of the drum has been quantified to optimize the rod tooth and drum structure form. In this study, the rod teeth of a drum-shaped threshing cylinder were optimized to improve the axial load uniformity of the drum-shaped threshing cylinder for a higher reduction in power consumption. The impact mechanics model of rod tooth and rice grain was established to determine the structural parameters of the rod teeth that affected the axial load uniformity of the drum, including the diameter of the rod tooth and the threshing gap. Theoretical analysis was implemented to clarify the influence of rod tooth diameter and length on the threshing power consumption. The bending angle of the elbow rod tooth and closed bow tooth was calculated to be set at 45° for better consistency of the threshing gap. The structural parameters were determined for the axial load uniformity of drum rollers, including the rod tooth diameter (7-16 mm), and threshing gap (15-30 mm). The optimal structural parameters were determined with the smallest coefficient of variation in the axial load uniformity as an indicator. A series of simulation tests were conducted to investigate the influence of rod tooth diameter and threshing gap on the axial load uniformity of cylindrical rod tooth, elbow rod tooth, and closed bow tooth drum. The results showed that the axial load trend of the drum roller with the elbow rod tooth was more uniform than that of the cylindrical rod tooth and closed bow tooth. The optimal structural parameters of the rod teeth were 10 mm rod tooth diameter, and 25 mm threshing gap. A three-factor, three-level Box-Behnken response surface bench test was conducted with the feed rate, threshing cylinder speed, and rod tooth shape as the factors, while the threshing power as the indexes, in order to reduce the threshing power consumption. A regression model was established to optimize the working parameters for the threshing power consumption. The bench test showed that the optimal working parameters of the cylindrical rod teeth drum were achieved in the feeding rate of 1.1 kg/s, and the speed of cylinder 900 r/min under the optimal structure parameters, where the lowest power consumption was 4.61 kW. The optimal working parameters of the elbow rad tooth drum were the feeding rate of 0.95 kg/s, and the speed of cylinder 935 r/min, where the power consumption was 3.58 kW. The parameters of closed arch tooth drum were no longer optimized, due to the weak ability to transport stalks easily for the blockage. The rod tooth of the drum was optimized for the shape of the tooth of the elbow rod. The drum simulation and bench tests were carried out to verify the structure and working parameters before and after the optimization of the cylindrical and elbow rod tooth. The variation coefficient of axial load uniformity of the optimized elbow rod tooth drum was 10.34% lower than that of the cylindrical rod tooth drum. The power consumption was reduced by 7.15%, indicating that the optimized elbow rod tooth effectively reduced the threshing power consumption of the drum for the better performance of the drum. This finding can provide a strong reference to optimize the performance of small longitudinal axial flow harvesters in the hilly mountainous areas in China.