【作者】 张居敏；

【导师】 夏俊芳；

【作者基本信息】 华中农业大学 ， 农业机械化工程， 2014， 博士

【摘要】 我国人口在增长,人民生活水平在提高,粮食总量刚性需求越来越大,与粮食总量相对应的农作物秸秆总量也在同步增加。秸秆还田是农业可持续发展的有效途径,既能解决焚烧难题,又能改善土质、提高地力、降低化肥施用量。我国南方地区土地复种指数高,秸秆量大,农时紧迫,雨水多,秸秆当前处理方式以埋覆还田为主。埋覆前先要粉碎,以避免埋覆过程中秸秆缠绕农机具。秸秆粉碎延误农时、增加作业成本,是农民焚烧秸秆的主要原因。为了能够省去秸秆粉碎环节直接埋覆还田,本课题组于2007年开发了1GMC-70型船式旋耕埋草机产品,该产品有一定的市场占有量。本课题主要研究1GMC-70型船式旋耕埋草机刀辊的秸秆埋覆机理,并在此基础上进行结构优化,进一步提高其作业效率和耕作效果。本文首先对该机核心耕作部件即螺旋横刀建立了数学模型,分析了各结构参数对作业性能的影响。研究发现,螺旋横刀刃口的动态滑切角为25.2°±0.1。,近似为常数,耕作过程中刀辊受力平稳,振动小。螺旋横刀的动态滑切角接近秸秆-旋耕刀之间的摩擦角(26°450)下限,它对秸秆既有砍压作用,又有滑切作用,滑切作用可以让横刀本身保持自洁、不缠草,降低其切土阻力；砍压作用可以将秸秆直接压覆入泥。刀辊埋覆秸秆的方式不是将秸秆切碎并与耕层土壤混合,而是由螺旋横刀将秸秆直接压覆入泥。刀辊在作业过程中切断了易碎秸秆,但柔韧性较大的秸秆仍然保持整株状态。刀辊对秸秆的埋覆效果与切碎程度之间没有相关性。刀辊中立刀有34把-36把,数量最多,尺寸最小,焊接难度及焊接工作量等都比较大。立刀辅助螺旋横刀完成作业功能,这种辅助作用对刀辊整体耕作性能至关重要。但是本文通过理论分析发现,立刀没有实现其预期的设计功能,并通过田间对比试验验证了这一观点。立刀对后续螺旋横刀有破茬效应,但破茬量不超过后续螺旋横刀切土节距的32.4%,破茬能力不足；立刀对后续横刀切下的土壤垡条有预先切断效应,但只切割了垡条横截面积的40%左右,没有切断垡条。立刀没有发挥作用,整机作业功能基本上都由螺旋横刀实现,功能过于集中,这是造成1GMC-70型船式旋耕埋草机作业效率偏低的主要原因。秸秆埋覆功能主要由螺旋横刀实现,本文详细分析了螺旋横刀的制造工艺过程。结果表明,现行工艺存在较大的制造误差,该误差对刀辊作业性能有一定影响。螺旋横刀动态滑切角的理论值为25.2。±0.1°,但由于制造工艺误差量较大,耕作过程中螺旋横刀沿刀轴方向按照先后入土顺序,其刃口对地表秸秆的动态滑切角从32.4°逐渐降低至14.70,切削方式由滑切过渡为砍切。砍切方式使螺旋横刀后入土一端丧失了自洁性和不缠草性,这从理论上解释了田间作业过程中螺旋横刀后入土一端经常出现缠草现象的原因。为发挥立刀对后续螺旋横刀的破茬效应,减轻螺旋横刀切土阻力,本文重新设计了立刀：用国家标准旋耕刀IIT245替代立刀。为了最大限度地发挥旋耕刀IIT245对后续螺旋横刀的破茬效应,本文对旋耕刀IIT245的排布方式进行了理论研究,给出了较优的排布方案。在该排布方案中,旋耕刀IIT245对后续螺旋横刀切土节距的增加量(即破茬量)占切土节距的118.0%-122.7%,起到了完全破茬效果,对后续螺旋横刀切下的垡条也起到了预先完全切断作用。旋耕刀IIT245还存在一定的破茬宽度,总的破茬宽度约占整机耕幅的1/3。用标准旋耕刀IIT245替代立刀,有效减轻了后续螺旋横刀的切土阻力。田间试验表明,新刀辊作业效率提高了5-6倍,原刀辊需要两遍作业才能满足农艺要求,新刀辊耕作一遍即可满足农艺要求,耕深及耕深稳定性、秸秆埋覆率、碎土率、耕后地表平整度等各项作业指标都有明显提高。本文研究结果为提高旋耕埋草机三化水平(标准化、系列化和通用化)提供了理论参考依据。更多还原

【Abstract】 With the increasing population and desires for higher living standard in China, more and more grain is needed rigidly. Correspondingly, the total amount of crop straw is increasing too. The arable land yields more grain year after year. How to deal with the crop straw? Straw returning is an effective approach to sustainable agricultural development. It can not only solve the problem of straw burning, but also improve the soil fertility, and reduce the amount of chemical fertilizer usage. In south China, the land cropping index is high. The amount of crop straw is large. The time for tillage is short. The rainfall is high. The straw is buried in field currently. But the straw should be cut to pieces firstly to avoid winding the burying tillage machine. It spends some time and tillage cost to cut straw. So the farmers are inclined to burn straw after harvest. In order to directly bury straw to paddy field without cutting, The Boat tractor rotary tiller named after1GMC-70is developed in2007.This machine is now widely used in south China. It can bury crop stubbles of height under600mm in paddy field. The main objective of this study is to answer the following two questions. What is the straw burying mechanism of1GMC-70? How to optimize the structure of this machine so as to improve tillage performance?Firstly, the spiral blade of this rotary tiller is researched. Through mathematical model and analysis, equations are deduced for edges of spiral blade. Curves of dynamic sliding cutting angle, dynamic cutting angle and dynamic clearance angle versus position angle of rotary tiller are plotted. Parameters of the spiral blade and the traditional rotary blade are compared. The dynamic sliding cutting angle of the spiral blade is approximately constant, which is25.2°0.1°. So the rotary tiller has no vibration theoretically during tillage. The value of25.2°0.1°is close to the lower limit of interval [26°,45°], which is the friction angle range of straw versus rotary blade. So the spiral blade has both sliding cutting effect and chopping effect on crop straw during tillage. The former effect may keep the spiral blade free from being winded by straw, while the latter effect may press the straw into soil directly. The spiral blade buries straw not by the way of cutting straw into pieces, then mixing them with soil, but by the way of pressing straw into soil directly. It is believed that the major function of spiral blade is not soil cutting, but straw burying.Secondly, the design purposes, the functions, and the structure parameters of vertical blade in this machine are analyzed. Mathematic equation of leading edge was built for vertical blade kinematic analysis. Results show that the structure parameters of vertical blade do not match well with their design intents. Vertical blade effective cutting length is less than one-third bite length of helical blade. So its own cutting straw capability and capability of helping helical blade to process straw underground are all weak. The vertical blade can break untilled soil in advance. But the depth of cutting untilled soil is about one-third thickness of soil slice cut by spiral blade. So the untilled soil breaking effect of vertical blade is weak. The vertical blade can break tilled soil behind rotor. But this soil breaking effect is negligible. The vertical blade cuts soil slice cross sectional area about40%. So its soil slice breaking effect is small. The vertical blade arrangement does not increase its own tillage opportunities. Field experiments show that the existence of vertical blade has little impact on paddy field tillage quality. The tillage functions of this machine are realized mainly by spiral blade. Tillage functions are too concentrated, this is the main cause for the low efficiency of the machine.Thirdly, being the core tillage part of this machine, the manufacturing process errors of the spiral blade and their influences were analyzed in detail. Results show that the spiral blade manufacturing process is defective. If the spiral blade had no manufacturing process errors, the two axis of spiral blade and rototiller would coincide. Because of manufacturing process errors, the two axis form spacial straight lines in different planes, whose distance is204.2mm, and space angle28.7°. If the spiral blade had no manufacturing process errors, the parameters of spiral blade leading edge, such as rotary radius, static sliding cutting angle and static cutting angle, would be all constant, which were200.0mm,25.3°and71.7°in sequence. But to the spiral blade made by present manufacturing technology, those parameters are no longer constant. The rotary radii of points on spiral blade leading edge are ranging from189.0mm to200.0mm. The static sliding cutting angle of spiral blade changes from14.7°to32.4°. The static cutting angle of spiral blade varies from70.3°to73.7°. At the end of the spiral blade, the smallest static sliding cutting angle is only14.7°, which belongs to chopping mode. This results in stubble winding. In the last tillage end of spiral blade, the rotary radius and static cutting angle are all largest, which are200.0mm and73.7°in sequence. Those factors may reduce the tillage depth at one time.Fourthly, based on our previous research achievements, a new straw burying rotary tiller is designed. In the new machine the standard rotary tiller blades namely Ⅱ T245are widely used instead of vertical blades. So there are mainly three kinds of cultivating blades in the new machine. They are, respectively, rotary blades IIT245, bent blades and spiral blades. The former two types of blade are used to cut soil, while the latter one to bury straw. The tillage width is2000mm. The rotor speed is still335rev/min. The range of forward speed is0.7m/s-l.lm/s. The tractor power is62.5kw-73.5kw. The three kinds of tillage blades cooperate with each other during tillage. Their interrelationships and interactions were analyzed in detail. An advisable arrangement of rotary blades IIT245fixed on the rotor is provided. Experiments of crop straw burying rotary tillage were conducted repeatedly not only in wet land but also in dry land. The tillage results show that this machine possesses not only the advantages of traditional rotary tiller’s soil tillage, but also the straw burying advantages of1GMC-70. After one time tillage in fields of cone index value under1260kpa for about150mm depth, the tillage qualities could meet the agro-technical requirements in terms of tillage depth, stability of tillage depth, field surface roughness, vegetation coverage rate and soil breakage rate. The values are, respectively,151.2mm-214.5mm,91.6%-94.8%,9.7mm-17.0mm,91.4%-97.0%and64.5%-90.2%.Results of this research provide some useful theoretical references to reduce the energy requirement of straw burying rotary tiller. They are also useful to mass-produce the straw burying rotary tiller.更多还原