| High moisture content maize threshing technology has become a bottleneck restricting the development of maize grain harvesting methods in Huang-Huai-Hai area.At present,the maize grain harvesting machinery introduced in this stage has the problems of high grain breakage rate,high non-desquamation rate and difficult to improve the ear feeding rate when facing the high moisture content ear of maize,which greatly affects the harvesting effect of maize.Therefore,improving the threshing effect of high moisture content maize and the working efficiency of threshing device become the research topic of maize grain harvesting machinery.In this paper,maize ears with high moisture content were studied.The mechanical properties of maize ears and grains were studied.A longitudinal-axial flow threshing test-bed was designed,in which the key technical parameters could be adjusted quickly.The single factor experiment and orthogonal experiment were used to optimize the working parameters of maize ear in different water content areas.The mechanism of maize ear threshing was analyzed by high-speed photography.The main research work and conclusions of this paper are as follows:?1?Static compression tests and shear tests were carried out on maize grains with different water content ranges.The results showed that the minimum breaking load of the side,top and ventral surface of maize grains decreased with the increase of water content,and the minimum breaking load of the top of maize grains was lower than the minimum breaking load of the side and ventral surface of maize grains in this range.The minimum rupture load decreases with the increase of water content.The minimum rupture load increases first and then decreases with the increase of water content when shearing the top of maize grain.When shearing the ventral surface of maize grain,the minimum rupture load increases gradually with the increase of water content.With the increase of water content,the grain compressive strength decreases gradually,but the grain surface toughness changes with the change of water content,resulting in the phenomenon that the minimum breaking load increases with the increase of water content when shearing the top and ventral surface of maize grain.?2?The threshing compression and bending tests of maize ears under different constraints were carried out.The results showed that the axial and tangential bending strength of maize grains was smaller,the longitudinal and lateral compressive strength was larger,and the longitudinal compressive strength was greater than the lateral compressive strength.The vertical and tangential force acting on maize grain is the main factor to ensure maize threshing.?3?The threshing method and threshing device were studied,and a threshing test-bed was designed,in which the feed amount of ear,the clearance of concave plate and the rotational speed of drum could be adjusted rapidly.?4?A single factor experiment was conducted on maize ears with 26-28%and28-31%moisture content in the range of grain breakage rate and non-desquamation rate as evaluation indicators,and with ear feeding rate,concave clearance and drum speed as investigation factors.The results showed that with the increase of ear feeding,the breakage rate of maize grains first decreased and then increased,and the non-desquamation rate gradually increased.The lowest grain breakage rate was3.13%and 4.51%when the ear feeding rate was 8 Kg S-1 in 26-28%and 28-31%water content ranges.With the increase of the concave gap,the breakage rate and undegraded rate of maize grains decreased first and then increased.The corn ear with26-28%moisture content reached the lowest grain breakage rate of 2.97%when the gap between concave plates was 29 mm;the ear with 28-31%moisture content reached the lowest grain breakage rate of 4.83%when the gap between concave plates was 31 mm;with the increase of the rotational speed of drum,the corn grain breakage rate first decreased,then increased,and the non-degrading rate gradually decreased.The corn ear with 26-28%moisture content reached the lowest grain breakage rate of3.51%when the drum speed was 510 r2min-1,and the corn ear with 28-31%moisture content reached the lowest grain breakage rate of 4.72%when the drum speed was495 r2min-1.?5?Orthogonal experiment was carried out on the basis of single factor experiment.The optimum parameters of threshing device with longitudinal axial flow were analyzed by variance analysis and GLM analysis.Through data analysis,the main and secondary order of technical parameters affecting maize grain breakage rate in single longitudinal axial flow toothed threshing device is:drum speed>concave clearance>ear feeding quantity;and the primary and secondary order of technical parameters affecting undefined rate is concave clearance>drum speed>ear feeding quantity.According to the results of variance analysis and significance test,the optimum parameters of single longitudinal axial flow threshing device for maize ear with water content of 26-28%are as follows:cylinder speed 525 r2min-1,concave clearance 31 mm,ear feeding 13 Kg2s-1;and single longitudinal axial flow threshing device for maize ear with water content of 28-31%is as follows:cylinder speed 530 R min-1,concave plate speed 530 r2min-1.The gap was 38 mm,and the amount of ear feeding was 11 Kg2s-1.?6?The movement of maize ear during threshing was analyzed by high-speed photography,and the threshing mechanism was analyzed based on the stress of maize ear in threshing drum and the mechanical characteristics of maize ear and grain.The results showed that the threshing process of the ear was mainly concentrated in the first third of the threshing drum.The ear moved to the rear of the drum in the direction of helix on the whole inside the threshing drum.The head and tail grains of the ear of maize which entered the inner part of the threshing drum were first impacted and threshed.The remaining grains were attacked by pin teeth,and between the ear and the ear,the ear and the core axle.The threshing was realized by the collision between the ear and the concave sieve,and between the ear and the grid fixed plate of the concave sieve.The phenomenon of grain breakage mainly occurs in the process of rubbing and collision between ear and concave plate and the impact of nail teeth on grain. |
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