| The Inner Mongolia Autonomous Region has rich grass resources.The harvesting and baling equipment of grass resources facilitates the transportation and storage of loose grass materials,and becomes an important equipment to facilitate the commercialization and circulation of grass products.During the baling process of round baler,the compression force transfer of steel roller to the inner bales gradually decreases,which is an important factor affecting the performance of round baler and the radial density distribution characteristics of formed bales.With the continuous development of relevant theories and the continuous enrichment of research methods,It is of great significance for the development of round baler to further study the radial pressure transfer characteristics and the radial density distribution characteristics of bales in the baling process by means of combining and complementing various theoretical and practical means.Based on the systematic study of the physical and mechanical characteristics of alfalfa,a common baling and pressing object in Inner Mongolia,this thesis uses theoretical analysis,high-speed photography,simulation research and experimental research to explore the baling process of materials,the radial pressure transfer characteristics and the radial density distribution characteristics of bales,and establishes a baling model to represent the relationship between the compression stress of materials and the bale density.The hypothesis of the outer structure of the entangled high density annular columnar shell straw bale was put forward and its forming conditions were analyzed.Based on the damage effect of shell structure non-roundness parameters on its own structural strength in the crushing theory,a spiral forming bin round baler was designed to study the effects of different steel rollers layout parameters on the radial pressure transfer characteristics of bales,the radial density distribution characteristics of bales and the baling process of alfalfa from the perspective of practical experiments and simulation,so as to reveal the formation mechanism of the radial density distribution characteristics of bales.And optimize the layout structure of steel roller in round baler chamber.The specific research content and results are as follows:(1)The physical and mechanical characteristics of alfalfa were studied,and the physical parameters of alfalfa,such as basic dimensions,water content,volume density,absolute density,porosity,static friction coefficient,rolling friction coefficient,collision recovery coefficient,repose angle and shear modulus,were determined,which provided basic data for the subsequent discrete element model establishment and simulation parameter setting of rotary compression process of alfalfa.(2)Theoretical analysis and high-speed photography were carried out on the rotary compression process of materials,and the pressure model and kinematic equation of materials were established to clarify the stress state and movement characteristics of materials at different stages.The radial density distribution characteristics of straw bales were studied by means of layer-cutting test method,and the formation mechanism of density distribution characteristics and its influence on the performance of round baler were systematically analyzed.Based on the compression theory,the rotary compression model of round bales was established to clarify the functional relationship between the compression force and the compression degree of materials in the baling process,and the physical significance of each parameter in the model was calibrated.The results show that the loss of steel roller pressure transfer within the bales is the fundamental cause of the radial density difference of the bales.(3)Based on the hypothesis of entangled high density annular columnar shell bales outer structure and the destruction of the structural strength of the shell caused by the non-roundness parameter of the annular columnar shell in the crushing theory,the9YQ-710 round baler was transformed,and the steel roller position adjustment mechanism of the baler was designed and installed.The design method and principle of spiral chamber structure are described in detail and the parameters and range of steel roller layout of spiral chamber are determined.The hardware installation and debugging of the whole structure of the data acquisition test platform are completed.Completed the hardware selection and installation of the control system and data acquisition system and the design of related software.The completed data acquisition test platform of round baler has realized the automation control requirements,and has functions of monitoring the working status of the test platform and recording test data,which effectively enhances the working efficiency of the test and the accuracy of the test data acquisition.(4)Based on the EDEM discrete element simulation technology,a rotary compression model was established to analyze the pressure distribution characteristics of steel rollers.The results of simulation experiments are supplemented to the results of theoretical calculation.Based on the calculation results of the limit value of the adjustment range of the steel roller layout pitch parameters of the spiral chamber,the simulation study of the baling process of the limit pitch adjustment value is carried out.The results show that the maximum limit pitch value can successfully complete the baling simulation is 125 mm,and according to this conclusion,the adjustment range and division level of the steel roller pitch value are determined.The simulation tests of the baling process with different horizontal pitch values show that the compression pressure of all materials in the bales increases exponentially with the increase of the compression ratio of the bales.The change of the layout of steel roller can effectively change the baling pressure required for baling.(5)Taking the pitch value of steel roller layout parameters of spiral chamber,feeding speed and steel roller rotation speed as test factors,the radial pressure transfer loss of bale,average compression pressure of steel roller and baling energy consumption as the performance evaluation indexes of round baler,and the standard deviation of radial density of bale as the quality evaluation indexes.Box-Behnken response surface test method was used to carry out orthogonal test,and a regression model between each index and each experimental factor was established.The influence law of each factor and their interaction on the performance of round baler and the quality of bales was analyzed,and the key parameters of significant influence were determined.The optimal combination of structural parameters and working parameters of round baler with spiral chamber was determined as follows: Pitch 60 mm,feed speed 0.13kg/s,roller rotary speed 280 rpm.Based on the optimization results,the test results show that baling energy consumption is reduced by 11.46%,the radial density uniformity of bale is increased by 28.51%,the radial pressure transfer loss of baling is reduced by 15.58%,and the average compression pressure of steel roller is reduced by 17.02%.The optimized spiral chamber significantly improves the comprehensive performance of the round baler and improves the alfalfa bales quality.The research results of this thesis can provide theoretical basis and realization method for improving the performance of round baler and improving the quality of alfalfa bales by optimizing the steel roller layout,and also provide reference for the research on the density distribution characteristics of fibre agricultural and animal husbandry materials rotary compression in other fields. |
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