In order to solve the problem of high broken rate and impurity rate in the direct harvesting of corn kernels in China, a flexible threshing element with variable stiffness consisting of a conical spring and rasp bar was developed on the basis of the existing horizontal axial-flow flow corn threshing cylinder structure to achieve low loss harvesting of corn kernels. Through mechanical analysis of the key components of the threshing element, its structure and operating parameters were determined. Then, orthogonal tests were carried out using the feed amount, threshing clearance and cylinder speed as the test factors, and the broken rate and impurity rate of the corn kernels as the test indicators. The results showed that the feed amount, threshing clearance and cylinder speed had a significant effect on the broken rate and impurity rate of corn kernels; the optimum parameters for the corn variable stiffness flexible threshing device were feed amount 6.1 kg•s−1, threshing clearance 40 mm and cylinder speed 392 r•min−1. The broken rate of corn kernels was 1.67% and impurity rate 1.03%. The test results fully met the requirements of the national standards for corn harvesting operations. This study provides a technical basis for the application of the axial flow corn flexible threshing device in the corn direct harvesting combine.
Based on the mechanical test (shear test, compression test), the bond model of corn kernel and straw was established to explore the rolling and crushing effect of different crushing rollers. The type of crushing roller is different. The material crushing process by the force (extrusion and kneading) is different. The mechanical analysis of the crushing process reveals that the disc crushing roller (DCR) has the characteristics of large unit-length kneading area; the spiral-notched serrated crushing roller (SNSCR) has transverse shearing effect on the material; and they affect the crushing effect of the material. By means of discrete element method and simulation test, multiple regression method and variance analysis method are used to systematically analyze the data. The optimal working parameters of each roll (crushing roll speed, crushing clearance, differential ratio) were obtained. The simulation test and bench test of the crushing process of materials with different roll shapes were carried out under the optimal working parameters. The crushing effect was evaluated with a Binzhou screen and a corn silage grain-crushing score screen. The crushed materials of corn kernel can be divided into three categories according to the size (broken grains passed through 2 mm sieve; broken grains passed through 4.75 mm sieve; and broken grains that cannot pass through 4.75 mm sieve), and the crushed materials of corn stalk can be divided into four categories according to the size and thickness (broken straw through 4 mm sieve; broken straw through 8 mm sieve; broken straw through 19 mm sieve; and broken straw that cannot pass 19 mm sieve). The crushing effect and crushing classification of the simulation test and bench test were basically consistent. The results showed that the disc crushing roller group had the highest comprehensive score with straw rolling rate of 89.1% and grain crushing rate of 87.7%, which was the most suitable for harvesting whole-plant silage maize (WSM).
Studies on the operational adaptability of slope corn harvesters on hilly slopes are of great significance to improve the performance and safety of the whole machine, but there are few studies on this aspect at the present. Therefore, this paper takes a self-developed small sloping land crawler corn harvester as the object combined with the special topography of the hilly sloping land and the technology adopted by the machine to make a mathematical analysis of its operational adaptability on the sloping land. Through the field test, the forward speed of the corn harvester, track wheel spacing and slope angle are used as the test factors, and the harvest loss rate of the corn ear is used as the assessment index to carry out the orthogonal test on the slope land. The analysis of the results based on the Design-expert response surface was completed. The results show that the ear loss rate of the experiment under different conditions is less than 5% of the national standard. The corn harvester has good adaptability to sloped land, which can realize the mechanized operation of corn on the hilly and sloped land, and has good agricultural production application value.
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