| In recent years,due to the damage of industrial waste and agrochemical residues,the cultivated soil in some areas of our country has various environmental problems such as soil acidification and heavy metal pollution,which need to be solved urgently.Practice shows that the application of quicklime powder can effectively improve the quality of cultivated land.At present,the domestic researches on lime spreading machinery is still relatively small,and the market demand is increasing.Therefore,it is of great practical significance to carry out the research on the key technology of lime spreading mechanization.This paper takes the spiral circulation lime spreader as the research object,and based on the discrete element method,the spreading performance of the spreading device is deeply studied.The main research work is as follows:(1)In order to establish the quicklime particle model,the particle size distribution,bulk density and static angle of repose of agricultural quicklime powder were measured by sieving method,measuring cylinder method and funnel injection method respectively.The measurement results are as follows:about 88%of the particle size of quicklime powder is concentrated in 80～300 mesh,and corresponding particle size is 0.054～0.2mm.The average particle size that calculated on the basis of mass is 0.126mm,and the bulk density is 1.127g/cm3,and the static angle of repose is 48.76°.(2)On the basis of introducing the structural composition and working principle of the lime spreader,the mechanics and kinematics analysis of the quicklime powder in the conveying process were carried out,and the motion equations were obtained.Afterwards,a theoretical analysis was carried out on the spreading process of quicklime,and from the mass flow function of quicklime,it was known that the number and opening size of the discharge holes,the rotational speed of the spreading screw shaft were proportional to the lime spreading amount.The screw pitch,and the diameter of the helical blade was quadratically related to the spreading rate.(3)Aimed at the problem that when the discrete element simulation of materials with small particle size such as quicklime powder was performed,the simulation calculation couldn’t be performed due to the large number of model particles.The method of artificially scaling the particle size was used for analysis.After magnifying the quicklime particles,the discrete element simulation parameters were calibrated with the static angle of repose as the response value.Through the design and result analysis of the Plackett-Burman test,the steepest climbing test and the Box-Benhnken test,a set of optimal parameters was obtained.Used this set of parameters for simulation verification,the relative error between the simulation result and the actual angle of repose was 0.76%,which shown that the accumulation characteristics of quicklime powder could be well represented.(4)The EDEM software was used to simulate the spreading process of quicklime,and the distribution coefficient of variation and the amount of spreading were used as evaluation indicators to carry out a positive analysis of factors such as the opening width of the discharge hole,the rotational speed of the spreading screw shaft and the forward speed of the machine.The test results show that the order of magnitude affecting the distribution coefficient of variation is:opening width,rotational speed,and forward speed;and the order of magnitude affecting the amount of spreading is:opening width,forward speed,and rotational speed.Taken different spreading requirements as the goal,the obtained regression model was optimized and solved,and the optimal working parameter combination was obtained.Finally,compared the simulation results with the field test results,the average relative error of the two was 9.51%,which could prove the credibility of the simulation model. |
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