Optimization design and test of the key components of crawler-type sorghum harvester

Sorghum cultivation has expanded in recent years, due to ever-increasing demand for raw materials in specific industries. It is often required for the highly efficient, low-loss mechanical harvesting of sorghum in industry. Conventional harvesting equipment has been modified from standard grain combined harvesters. However, mechanical harvesting has been confined to the “prone to clogging, high losses, and incomplete threshing” bottlenecks, when operating on tall, easily lodging sorghum: The header inlet is prone to clogging, resulting in low operational continuity; Uncontrolled lodging direction of the stalks can lead to severe grain loss at the header; And the threshing system can suffer from the contradiction of incomplete threshing and high mechanical damage to grains, with the overall performance falling far short of ideal levels. This study aims to optimize and design the key components in a tracked harvester prototype for sorghum, with emphasis on the header and threshing modules. In the header, the collaborative flow-guiding mechanism was designed with straw-diverting and gathering bars, according to the theory of enveloping cylinders, the inclined plane sliding, and the cantilever bending models. The angle between the adjustable stalk-separating bar and the horizontal plane was determined as 14.36° after calculations, while the minimum effective working length was not less than 1 475.6 mm. As such, the stalks slid smoothly along the bar rather than being entangled. The mechanism also covered the entire height range of sorghum plants (as measured height of 1 806.2-2 105.4 mm). Additionally, the gathering rods were added on both sides of the header, according to the sliding-cutting principle; Their 60°-inclined guide surfaces generated the lateral guiding forces, thus restricting the lateral movement path of the cut stalks. Furthermore, the layout of the stalk-diverting chains was significantly optimized according to the torque balance in mechanics. The two outer rows of chains on the header’s exterior were arranged in a staggered “outer high, inner low” configuration. The application points of the chain teeth were altered at different heights. The resultant torque on the straw bundles was systematically adjusted to redirect the stem lodging from outward (away from the header) to inward (toward the header), thus effectively reducing grain loss. In threshing, multiparameter optimization was performed on the axial-flow threshing drum. The number of threshing elements was determined to be 114 using a material throughput model; Six tooth plates and a three-head spiral layout were adopted for uniform loading, thereby preventing straw blockages. The optimal drum was a diameter of 620 mm and a length of 1 880 mm. A variable-aperture concave plate was integrated with a front-dense, rear-sparse configuration. The large apertures on the concave plate's front section worked together with the dense tooth spacing (90 mm) at the threshing drum inlet. Efficient threshing was achieved to rapidly separate grains, while the smaller apertures on the rear section were matched with the wider tooth spacing (180 mm) in the outlet section, suitable for the gradual reduction of material volume in the threshing chamber. The rearward conveyance of straw was promoted to reduce the load on the subsequent cleaning. There was a gradient variation in the threshing intensity from strong to weak. A high threshing efficiency was obtained to minimize the risk of grain breakage. Field trials also validated the effectiveness of synergistic optimization. The optimal prototype demonstrated excellent and stable performance in a range of cutting heights of 300~600 mm and forward speeds of 0.6-1.2 m/s: The total loss rate was controlled between 1.25% and 1.71%, the grain breakage rate was 0.48%-0.72%, and the impurity rate was 0.72%-1.06%, at grain and stalk moisture contents of 20.12% and 67.69%, respectively. All key performance indicators met the requirements of national standards, such as the “Technical Specifications for Full-Feed Combine Harvesters.” The prototype operated smoothly without any blockages. In summary, the better performance was achieved for the header’s “orderly flow guidance and anti-clogging” and the threshing system’s “high-efficiency, low-loss separation”. The research findings can provide a technical solution and practical reference to develop the specialized, high-efficiency, low-loss harvesting equipment suitable for major sorghum-producing regions.