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Study on Cutting System for Two Discs Mower Conditioner

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Tutor: FangXianFa;WangDeCheng
School: China Agricultural University
Course: Agricultural Mechanization Engineering
Keywords: Cutting system,Alfalfa,Rotary mower,Knife,CFD
CLC: S817.111
Type: PhD thesis
Year:  2014
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Abstract:
By2010, the cultivated area of alfalfa had been reached4,270,000hm2, but the level of mechanization was fairly low. Developing and manufactureing suitable Alfalfa harvesting machinery for China is necessary. The mower is the main equipment for harvesting, at present, the study on mower is forcused on its structure and the key working parts.such as dynamic analysis of cutting knife and so on. However, the flow field around mower as an important factor to affect the performance of the mower was always neglected. Based on the analyze of Alfalfa mechanical properties,the interaction between alfalfa and cutting tools,and the effect of flow field on the Alfalfa, The article developed a two-disc rotary mower with the special-shaped cutting knife and sloping cutting discs, The main results are as follows:(1) Inorder to desing suitable mower, the physical models of stem and leaf of Alfalfa were built by means of analyzing the morphological character and microstructure, meanwhile,, the apparent volume, surface area, area of contour, apparent density and specific weight were discussed by this model. And then, the mechanical characteristic parameters of alfalfa stem were obtained through experimental collecting. the cutting type impacted on resistance and energy loss in cutting was also discussed. Based on these research, a new cutting method named inclined cutting was proposed in this paper.In order to avoid recutting in working, the conditions meeting to this cutting method were determined, that is a linear velocity greater than30m/s of the cutting knife is needed and the best velocity value is between65m/s to80m/s.(2)The sloping cutting discs and the special-sharped cutting knife were designed to meet the inclined cutting methord. And the torsion angle β of special-shaped cutting knife and the tilt angle a of cutting discs were important parameters which would affect the working performant. Acording to the plural vector theory and the plane vector theory, the best value range of the torsion angle β and the tilt angle α,and the interaction betweenβand a were discussed. Finally, the parameters of the cutter of mower were determined, which were the diameter of the disc was530mm, the rotary speed of the cutters was2170r/min, the length of the cutting knife was60mm, the width of theoretical overlap area was25mm,.he torsion angle β of special-shaped cutting knife was8°,and the range of the tilt angle a of cutting discs was0-8°(3) In order to analyze the effect of cutter rotating airflow on alfalfa,computational fluid dynamics (CFD) was used to simulate the flow around the cutters, the results showed that, the flow had a great impact on the movement of the plants. Specifically, in the flow around the special-shaped cutting knife, the plant obtained the force upward in the bottom and the even load on the whole plant; in the flow around the drum, the plant was lifted along the drum axis derection and bended in the circumference of drum. The pressure field in the flow is expressed by static pressure, dynamic pressure and the total pressure. The range of the static pressure around the drum is-250~100Pa, the dynamic pressure is0-1300Pa and the total pressure is-250~1300Pa. Considering the impact of the flow around the special-shaped cutting knife and drum and optimizing the kinematics and statics model of the plants, analyzing the different motion state by adjusting the parameter in the model. Under the same condition, optimizing the motion model of the special-shaped cutting knife could support the designing of the knives.(4) A rotary mower equipted with designed cutter were used to test its working performance in the field. Comparing with common cutting knife, the rate of broken alfalfa of desigened cutting knife was much lower under the same conditong of victory. Based on this designed cutter, a new rotary mower named9GYZ-1.2machine was designed and manufactured, field testing showed that all indexes of this machine had reached the standard.
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