砍切式玉米秸秆还田机的设计与试验

针对中国北方一年两熟区玉米收获后地表秸秆量大,甩刀式秸秆还田机粉碎长度合格率低,影响后续小麦少免耕播种等问题,基于四连杆机构往复运动原理,利用地表作为支撑,提出了利用砍切对秸秆切段还田的思路,进而研发出一种砍切式玉米秸秆还田机。为避免后续小麦播种时出现拥堵现象,设计秸秆切断长度不超过小麦窄行行距的一半(6 cm);通过理论计算和动力学仿真分析,优化了切刀的运动轨迹并确定切秆装置各杆件尺寸并分析了机具切割功耗为28.39 kW;利用ANSYS软件对切刀进行有限元静力分析,切刀力学性能满足设计要求。田间对比试验结果表明,在玉米收获后秸秆全量保留的条件下,与甩刀式秸秆还田机相比,砍切式秸秆还田机粉碎后秸秆平均长度短0.73 cm,秸秆长度不合格率小5个百分点,秸秆长度变异系数小0.218;机具运行平稳性试验表明砍切式玉米秸秆还田机振动略大于甩刀式玉米秸秆还田机,但差异不显著,该机平稳性满足作业要求;切刀入土平均深度为7.71 cm,可明显降低0~10 cm土层土壤容重;后续播种试验试验表明在砍切式秸秆还田机作业后地表进行播种时,播种机无拥堵现象且播种深度合格率比甩刀式大2.3个百分点。该文研究成果能够为中国北方一年两熟区玉米秸秆还田提供一种新型装备,有利于促进秸秆还田技术的推广。

Design and experiment of chopping-type maize straw returning machine

Abstract: In annual double cropping areas in northern China, the straw is directly returned to the field after maize harvest, and the wheat is sown by no-tillage planter. However, the high water content and strong toughness of maize straw result in the low qualification rate of traditional rotary flail knife type returning machine, which can easily lead to straw blocking and thereby affect wheat sowing quality. To address the above problems, in this paper, a chopping method based on the principle of four-bar linkage mechanism was put forward. The maize straw was chopped using ground as the support. A chopping-type straw returning machine, composed of the frame, pressure roller, transmission device and straw cutting device, was developed. The pressure roller was located at the front of the machine, and was designed to press the standing or lying straws forward in the direction of machine movement. The cutting device was at the back of the roller, and was designed to cut the lying parallel straw into segments. To avoid straw blocking, maize straw was chopped into segments with the length less than 6 cm, and the length was half of the narrow row spacing of wheat. Based on theoretical calculation and motion simulation, the size of 4-link mechanism of cutting device was designed and the cutters'' movement trajectory was optimized. In 4-link mechanism, the minimum transmission angle was 70°, the maximum swing angle of rocker was 20°, the eccentric distance of eccentric wheel was 80 mm, and the lengths of cutter holder (connecting rod) and rocker were 267.375 and 460.702 mm, respectively. The distance between the rotation center of eccentric wheel and the hinge point of rocker on frame was 526.627 mm. According to the finite element static analysis by using ANSYS software, the maximum stress of the cutter was calculated as 162 MPa generated near the bolt holes on both sides, which met the design requirements. The field performance experiment was conducted in Hebei Province to compare the chopping-type straw returning machine and traditional flail knife type machine. The comparison and research objects included the unqualified rate of straw length, working stability, soil physical property and the subsequent sowing operation effect. The experiment results showed that the average length of the straw with the designed machine was 4.8 cm, the unqualified rate was 6% and the coefficient of variation was 0.209, which were all superior to the traditional machine. The vibration of the designed one was slightly larger than that of traditional one with no significant difference, and both of the machines worked stably. The cutting depth of new cutter reached 7.71 cm averagely, and soil bulk density in 0-10 cm depth decreased obviously. The subsequent wheat seeding experiments were carried out, and the results showed that there was no straw blocking during seeding when the seeder operated on the surface on which the chop-cutting straw returning machine worked, and the coefficient of sowing depth was 92.5% and it was significantly higher than another one. This study provides a new equipment for the maize straw returning in the double cropping areas in northern China, and it is also conducive to the popularization of straw returning technology.