Structural Optimization Of The Cleaning Screen For Maize Grain Harvester

Maize which is one of the three grain crop is wildly planted in our country, so there is great practical significance to develop mechanized harvest of maize. Maize grain harvester is able to obtain maize grain directly by combine operation, which has advantages of saving procedure, shortening harvest period and reducing labor intensity. Therefore it attracts more attention in recent years. The cross air-and-screen cleaning device is widely used in maize harvester due to its advantages of low loss rate and strong adaptability.Vibrating screen is a main working part of cross air-and-screen cleaning device, and the structure of vibrating screen has important effects on cross air-and-screen cleaning device. In order to improve cleaning performance of cross air-and-screen cleaning device in maize harvester, the field test was conducted to compare the screening performance of woven screen and shell screen. And the structure of shell screen was selected as the main object of study in this paper. Experiment and simulation were combined to optimize the structure of shell screen. The main research contents are as follows:(1)The screening performance of woven screen and shell screen were compared in the field test. The results show that shell screen performs better as the upper screen of maize harvester. And the cleaning effects of cross air-and-screen cleaning device under different air velocities were investigated by adjusting the rotating speed of fan in the maize harvester.(2)Tests of maize distribution under the shell screen were conducted on the cross air-and-screen cleaning laboratory bench to obtain the distribution regularities of length and density of maize. The results show that the maize average length tends to increase along the area in length direction, meanwhile the maize average density increases first and then decreases.(3)Computational fluid dynamics and discrete element method(CFD-DEM) were coupled in the simulation test. And the results of simulation were compared with that of field test, which shows substantially coincident with each other. The screening regularities were obtained through analyzing the simulation process of maize on shell screen in the simulation test. And the results were validated by the high speed camera test.(4)Single factor simulation test was conducted to obtain the influence of the structure parameters of shell screen on objective indexes. Simulation results show that the screening efficiency falls with the length of screen holes increasing, rises with the height of screen holes increasing, and falls with the space between screen holes increasing; The cleaning rate of grain rises with the length of screen holes increasing, falls with the height of screen holes increasing, and rises with the space between screen holes increasing.(5)In the quadratic orthogonal rotational combinational simulation tests, the objective indexes were screening efficiency and the cleaning rate of grain, the factors were the length, the height of screen hole and the space between screen holes. The test data were analyzed by the response surface method, and the results show that height of screen holes has the most significant effect on the indexes, followed by the space between screen holes, then the length of screen holes. Furthermore, the regression mathematical models were multi-objective optimized by using Design-Expert software. The results of verified test were that screening efficiency is increased by 8.12% and the cleaning rate of grain is increased to 97.28%, which were consistent with the simulated results. The performance of the cleaning device is enhanced.