Experimental research on the influence of threshing roller structures on the quality of mechanically-harvested soybeans

Abstract: Grain threshing and separation are the main stages that cause grain breakage in the process of mechanized soybean harvesting. The harvest quality of soybean depends mainly on the configuration of threshing parts, particularly on the structural and performance parameters. In this study, a feasible threshing roller with replaceable components was proposed to investigate the influence of various factors in the mechanical process on the harvest quality of soybean. Lindou 11 was selected as the test material with a moisture content ranging from 10.2% -20.0% in the Linyi area. The impact of soybean machine harvest quality provided in-kind support. The arch tooth, rasp rod, and rod tooth were selected as the typical threshing components. The threshing roller with replaceable components was characterized by a unique roller spindle assembled by the replacing threshing bar unit and the adding fixed plate, as well as the roller shell in turn. Three types were obtained, including the rod-tooth, combined rasp bar-rod tooth, and closed arch tooth threshing roller. Experimental factors were selected as the forward speed, rotate speed of roller, threshing gap, and angle of deflector. The evaluation indices of soybean were set as the seed crushing rate and unthreshing rate, according to the characteristics of soybean plants. A single factor test was designed to obtain the optimal working parameters of each influencing factor. Four factors were gained for the best roller structure and the optimal combination of operating parameters. A three-level orthogonal test was conducted to determine the significance of the influence of each influencing factor on the evaluation index. An evaluation test was designed to verify the accuracy of obtained data from the field test. The test results show that the forward speed and rotate speed of roller had a greater influence on the crushing rate, whereas, the rotate speed of roller and threshing gasp had a greater influence on the unthreshing rate. There was generally high threshing quality in the combined rasp bar-rod tooth threshing roller when the moisture content of soybean was 10.2% and 15.2%.The influencing factors on the grain crushing rate were ranked in a descending order: the rotate speed of roller, forward speed, threshing gasp, and angle of deflector. The primary and secondary orders on the unthreshing rate were the rotate speed of roller, threshing gasp, angle of deflector, and forward speed. The threshing quality in the closed arch tooth threshing roller was relatively high 20.0% moisture content. The influencing factors on the grain crushing rate were as follows, the rotate speed of roller, forward speed, angle of deflector, and threshing gasp, where those on the unthreshing rate were in the order of threshing gasp, rotate speed of roller, angle of deflector, and forward speed. When the moisture content of soybean was 13.1%, the combined rasp bar-rod tooth threshing roller was at a forward speed of 4 km/h, a rotate speed of roller of 600 r/min, a threshing gasp of 30 mm, and the angle of deflector of 70°, where the crushing rate and unthreshing rate were the lowest, 0.90% and 0.18%, respectively. When the moisture content was 19.3%, the closed arch tooth threshing roller had a forward speed of 3 km/h, the rotate speed of roller of 600 r/min, the threshing gasp of 25 mm, and the angle of deflector of 75°, where the crushing rate and unthreshing rate were the lowest, 1.20% and 0.23% respectively, indicating an excellent harvest quality. The findings can provide a potential reference to design the promising threshing roller in a grain harvester.