Effect of concentric and non-concentric threshing gaps on damage of rice straw during threshing for combine harvester

Abstract

During threshing rice straw is broken, it becomes mixed with the grains, but it is separated from the grains in the subsequent cleaning process. Reducing broken rice straw can thus help improve cleaning performance. The effect of concentric and non-concentric threshing gaps on threshing performance is different. In this paper, rigid short and flexible long rice straw models were established using discrete element method (DEM) and the flexible model was verified by a three-point bending test. Threshing simulations using the developed straw models and a bench test were conducted to analyse the effects of concentric and non-concentric threshing gaps on rice straw damage. The simulation results showed that comparing concentric with non-concentric gaps the average compressive force on rice straw fluctuated less and the bonds of flexible long rice straw had a lower break proportion. Bench test results showed that the mass fraction of material other than grain (MOG) in threshing outputs with the concentric threshing gap was 4.3% lower than with the non-concentric gap, and the damage level of rice straw was also lower. • Rigid short and flexible long straw models using DEM were established. • The average compressive force on straw was analyzed by threshing simulation. • The weight percentage of MOG in threshing outputs under concentric gap was lower. • The damage level of straw under concentric gap was lower than non-concentric one.