Optimization of operating parameter and structure for seed thresher device for rape combine harvester

Abstract: Rapeseed germination rate is directly related to rapeseed yield, which is one of the most important indices to evaluate the rapeseed quality. Combine harvesters have greatly improved the harvest efficiency, but rapeseeds would be damaged by the mechanical threshing equipment during harvesting, and mechanical damage extent of rapeseeds was directly correlated to the design characteristics of the threshing apparatus, such as the movement speed of rasp bars, feeding rate, clearance between the drum and the concave. The rapeseed damage caused by mechanized harvest has aroused the concern of scholars, but there is no study on the rape harvest. In order to explore the damage of rapeseed caused by combine harvester during threshing process and the superior parameters of the threshing mechanism, rape combine harvest comprehensive experiment and germination rate experiment were carried out. Germination rate was used as an index to evaluate the damage. The type of rasp bars, the movement speed of rasp bars, the clearance between the drum and the concave and the feeding rate were taken as the influencing factors in the rape combine harvest comprehensive experiment and each factor had 3 levels. The evaluation indices were the germination rate and loss rate, the undamaged rapeseeds grown in the same plots were used as the comparison. The germination of mechanically harvested rapeseeds and hand harvested rapeseeds was tested in the same environment. The parameters of threshing apparatus with the highest germination rate (lower damage rate) were obtained through the comparison of germination rates between undamaged rapeseeds and mechanically harvested rapeseeds. The results showed that the germination rate of hand harvested rapeseeds was 99.8%, and the highest germination rate for mechanically harvested rapeseeds was 97.6% and the lowest was 85.7%. Therefore, mechanized harvest did cause damage to rapeseed and the damage rate was 2.4%-14.3% within the range of parameters selected. Through the range analysis of germination rate experiment, the factors affecting the damage of rapeseed were the threshing component form, the clearance between the drum and the concave, the movement speed of rasp bars and the feeding rate in turn. Through the variance analysis of germination rate experiment, the feeding rate (P=0.727) had no significant effect on the test results, the threshing gap (P=0.004) and threshing component form (P<0.001) had highly significant effect on the results, the drum speed (P=0.012) had a significant effect on the results, and the repeated experiment error (P=0.202) had no significant effect on the test results, and the test results were reliable. The threshing component form had a great influence on the harvest damage of rapeseed. The germination rate was 88.3% when using striped rod and was 97.3% when using full nailed tooth, which had 9 percentage points difference. For the rapeseed, striped rod was more likely to cause threshing damage than nails. Due to the limitation of the number of experiments, the relationship among drum rasp bars speed, clearance between the drum and the concave and rapeseed damage couldn’t be concluded. But the optimal parameters should exist between drum rasp bars speed and clearance between the drum and the concave. It needed further research to clarify the relationship among drum rasp bars speed, clearance between the drum and the concave and rapeseed damage. The effect of feeding rate was not significant. The change range of germination rate was less than 1.1 percentage points under different feeding rates. The optimal combination of threshing parameters was: nailed tooth, threshing drum clearance of 9 mm, drum rasp bars speed of 856 r/min, and feeding rate of 2.2 kg/s, and the damage rate was lower. In order to verify the accuracy of the combination of superior parameters, the artificially harvested rapeseed was threshed by experiment bench and different combinations of parameters were used for the comparison. The germination rate under the optimum parameters combination was 97.4%, which was the highest. Combine harvest damage could be reduced to a very small extent through adjusting the threshing system parameters. The study provides a reference for the design of combine harvester threshing system.