Study on Performance of Concentric Threshing Device with Multi-Threshing Gaps for Rice Combines.

S concentric threshing device can improve rice crop separation and transportation capabilities. As one of the main factors affecting the threshing performance of rice combine harvesters, the threshing gap can influence the grain unthreshed rate and the grain damage rate directly. However, the clearance between any threshing cylinder tooth and the concave grid is constant for the traditional threshing device, named the single threshing gap in this paper, resulting in a consistently high total loss rate (the sum of unthreshed and damaged grains). Therefore, multi-threshing gaps are proposed in this paper for the concentric threshing device to solve the above problem. To compare the threshing performance between the single threshing gap and the multi-threshing gaps, the movement process of rice mixture (grain, short straw, and long straw) was simulated using the discrete element method (DEM). The simulation results showed that the separation and transportation abilities of the multi-threshing gaps were not decreased, but the distribution of threshed output mixture was more even for the multi-threshing gaps. Furthermore, a field experiment was also carried out on a combine harvester to compare the total loss rate. The experiment results showed that the total loss rate of the concentric threshing device with multi-threshing gaps was reduced by 0.0593%, which was 5.77% less than the total loss rate of the concentric threshing device with a single threshing gap. [ABSTRACT FROM AUTHOR]