| Straw-curtains woven from rice straw are widely used for greenhouse insulation,edible mushroom production,anti-drying maintenance of building prefabricated parts and so on.With these industries developing,the demand for such Straw-curtains is increasing.However,the current straw-curtain braiding machine has some problems,poor operating environment due to the rice"bundle"structure produced during its natural growth and harvest,low operating efficiency due to the artificial laying of rice straw,and so on.In view of the current lack of Straw-curtain braiding equipment,this paper identified the key factors affecting straws placement by analyzing the structure and instability of rice straw entanglement from the perspective of biology,microstructure and physical properties.Besides,mechanized transportation,selection of operating mechanism and process mode were discussed for the basic requirements of orderly laying and a spreading and raking fascicles device with the existing flat Straw-curtains machine was innovatively designed,with optimized structure and process parameters used in conjunction.The specific research contents and main research results were as follows:(1)The results of biological and physical properties of rice straw samples showed that rice stalks had irregular hollow cylindrical structure under natural drying conditions,the leaves were shorter from the bottom of the straw,leaf curls extended outward along the sheath and there were differences in the moisture content of different parts of rice straw.Not only differences in the stacking angle of rice straw under three different forms and microstructure of three different parts of rice straw,but also the friction angles between rice straw and three different materials were compared.Therefore,the differences in the structure and physical properties of each part were clarified and these showed that branch stems in the panicle,cotyledons on the stalks,especially interspersed windings between the bottom leaves,could cause entanglement between the straws,affecting the flow properties of the material.(2)The shearing,bending,and tensile mechanical properties of the three internodes of the rice straw sample were measured.At the same shear rate,the shear strength of different parts of a single rice straw was:Part I>Part II>Part III,but with the increase in the number of straw bundles,the change in shear strength was:Part III>Part II>Part I.The flexural modulus values of different parts of a single rice straw were measured in the range of 1?6MPa,and its change trend was:part III>part I>part II,but the flexural modulus of each part of the straw bundle will gradually decrease(<1 MPa)as the number of straws increases.The measured maximum tensile strength of a single rice straw was about 134.47 N.The maximum tensile strength and tensile strength were:Part I>Part II>Part III,and the average tensile strength is 48.15 MPa,40.6 MPa and 18.49 MPa respectively.These showed that the mechanical properties of different parts of rice straw were quite different and so were that between single one and bundle straws.(3)As the results of rice straw harvesting process,entanglement structure and instability analysis,the main factors affecting the instability of the rice straw entanglement were the elastic modulus,friction characteristics,external forces of the straw and device structure through the research on the actions of"slap","rolling","shake","pulling"used in the process of manual unbundling and laying,use EDEM for simulation test.For the straw continuous transportation and laying problems that need to be solved for orderly laying,the mechanized process route of"feeding-rubbing-raking"rice straw horizontal spreading with stepwise conveying,bisecting"roller rubbing"spreading and"raking fascicles"separation were achieved by selecting the stepping mechanism and paddle mechanism as the actuator.(4)An automatic spreading and raking fascicles device used with the existing Straw-curtains braiding machine was designed and its parameters were optimized by the simulation and analysis of the operation process of artificially spreading rice straw through ADAMS and other software.Prototype testing were carried out with fascicles rate and leak rate as the evaluation indexes under the conditions of the operating speed of the braiding machine of 90?120 m/h.when the needle frequency(f_z)is 0.8 Hz,weaving speed(v_b)is 90 m/h,and setting the frequencies of the bisecting spreading(f_t)and multi-link raking fascicles(f_p)as 0.8 Hz and1.13 Hz respectively,the fascicles rate(F_s)of the straw was greater than 90%and the leak rate(L_b)was less than 6‰,which showed that the quality of the Straw-curtains woven by this machine meet the requirements of use.Then under the same weaving speed,the device could reduce the labor by 2 to 3 persons compared with the traditional manual feeding method and it could increase the average annual income of the existing knitting machine by nearly 8,000yuan after cost calculation. |
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