| 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. |
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