Design And Experiment Of Vehicle-Mounted Horizontal Straw Unbundling-Spreading Device

The popularisation of dwarf anvil dense cultivation technology has placed new and higher demands on soil moisture and organic matter content of orchards in the Loess Plateau region.Straw mulching combines the effects of land fertility enhancement,water and moisture storage and comprehensive use of agricultural waste resources,which is important for improving the quality of the eco-environment and promoting the economic and environmental sustainability of fruit cultivation in the dry northwest of China.For the orchard soil management and straw utilisation equipment,lack of doors broken,and no machine available,the group created the first straw mulching equipment for orchards,achieving a breakthrough in mechanised straw mulching technology dwarf anvil dense cultivation orchards.However,there are problems such as large and fluctuating resistance torque,material leakage and blockage at the discharge port,and poor uniformity of material spreading during the operation of the vertical unbundling-spreading device on the straw mulching machine.In response to the above problems,this article carries out the design and experimental research of a vehicle-mounted horizontal straw unbundling-spreading device.Through theoretical analysis and performance tests,the defective mechanism of action of the vertical unbundling-spreading device was revealed;on this basis,the bottom unbundling-spreading operation method was proposed to form the design of the horizontal unbundling-spreading device,and the design of the key component structure and the the modular assembly scheme of the device were carried out.Based on the single straw model,a discrete element method（DEM）based straw block modelling and parameter calibration method was proposed to optimise the straw bale simulation modelling process,and a numerical simulation of the straw unbundling process was carried out;the structure and operating parameters of the horizontal unbundling-spreading device were optimised by means of simulation and testing.The experiments showed that the horizontal unbundling-spreading device met the design requirements,improving the overall operating effect.The main results of the study are as follows:（1）Analysis of the defects in the vertical unbundling-spreading device.The way in which the knife teeth break the bale by forcibly scraping,compressing,cutting and combing from the top of the straw bale is the fundamental reason for the high resistance torque of the vertical unbundling-spreading device;the large bale-tooth contact area and the straw block tilting forward and folding when disturbed by the knife-teeth cause a large amount of straw to feed into the discharge opening instantaneously,while the untimely discharge of straw resulting in stagnant blockage is the root cause of large fluctuations in the resistance moment;The excessive fluctuations in the resistance torque are the direct and essential cause of straw blockage at the discharge opening;at the same time,the wedge-shaped triangle formed during the unbale operation exacerbates the blockage at the discharge opening;and the arrangement style of the scraper conveyor and the unbundling-spreading device causes leakage of granular organic fertiliser at the discharge opening.The addition of the anti-blocking device reduces the fluctuation of the resistance moment to a certain extent but does not essentially change the bale-tooth contact method.The risk of blockage still exists,and the problem of organic fertiliser leakage is not solved.（2）The proposal of the bottom unbundling method and design and analysis of a vehicle-mounted horizontal unbundling and spreading device.Three structural design options were proposed:spiral-toothed roller type,counter roller type and horizontal toothed belt type;the horizontal toothed belt unbundling device was determined to be the optimal design option.The overall structure and key components of the horizontal unbundling-spreading device are designed and analyzed,and a modular assembly solution is proposed for the vertical and horizontal unbundling-spreading device.（3）Discrete element model construction for square wheat straw bales.Based on the distribution characteristics of single straw in straw bales,the single flexible wheat straw model of 6×20 mm was constructed using the parallel bonding key of the Bonding V2 model in the EDEM software,and the bonding parameters were calibrated by mechanical properties tests;the basic component unit of the straw bale,the straw block,was used as the object of study,and the compression stressσ₁₀ was used as the compression test indicator for the straw block.The EEPA（Edinburgh elasto-plastic adhesion）contact model is used to characterise the visco-elastic-plastic properties of straw blocks during compression,and a discrete element modelling and parameter calibration method for straw blocks based on uniaxial compression tests is proposed.The coefficient of determination R² of the model between the compressive stressσ₁₀ and the discrete element parameters is 0.9973.The parameters with significant effects on the compressive stressσ₁₀ and their optimal combinations are selected and optimised by PBD,steepest climb and BBD tests:straw-straw rolling friction coefficient of 0.015,surface energy of 5.194 J/m² and The relative errors of the compression stressσ₁₀ were 1.04%,3.89%and 2.60%for the compression verification tests with different thicknesses of straw blocks.The straw blocks in compression were arranged in the direction of their thickness to construct a discrete element model of the bales with the same size as the actual size.（4）Numerical simulation analysis of the straw unbundling process and optimisation of the parameters of the horizontal unbundling-spreading device.The straw unbundling performance simulation found that the horizontal unbundling-spreading device eliminated the high-pressure area of the straw at the discharge opening in the generation of the vertical unbundling-spreading device,avoiding the occurrence of blockage.The standard deviation of the resistance of the knife teeth and the standard deviation of the mass flow rate of straw at the discharge opening were used as indicators for the simulation tests to initially determine the optimum operating angle of the horizontal unbundling-spreading device.The height of the discharge opening is defined to meet the straw cover requirements of the orchard.The optimum sliding angle of the teeth was determined to be 30°based on the scraping efficiencyη;the optimum operating parameters for the horizontal unbundling-spreading device were determined based on the straw cover uniformityεand the standard deviation of the scraping resistance of the horizontal unbundling-spreading device Ω:the height of the teeth was 4 cm,the lateral distance between the teeth was 9 cm,and the distance between the teeth base was 21 cm.In a comparison test of vertical and horizontal unbundling-spreading device with optimum parameters,the average working resistance of the horizontal unbundling-spreading device was reduced by 39.92%,the scraping efficiency was increased by 35.54%,and the standard deviation of the resistance at the same discharge volume was reduced by 8.12%.（5）Horizontal unbundling-spreading device processing and unbundling-spreading operational performance test.Taking the standard deviation of the resistance moment of the unbundling-spreading device σ_T and the coefficient of variation of the thickness of the straw mulch on the ground CV_h as the test index,the optimal practical operating parameters of the horizontal unbundling-spreading device were obtained through single-factor,orthogonal tests as follows:the rotational speed of the horizontal unbundling-spreading device was 256.97r/min,the tilt angle of the horizontal unbundling-spreading device was 37.5°,and the driving speed of the mulching machine was 0.96 km/h;a comprehensive comparison test between the vertical and The results show that there is no straw blockage during the operation of the horizontal unbundling-spreading device,the average and peak resistance torque is reduced by 35.30%and 38.11%respectively compared to the vertical unbundling-spreading device,the standard deviation of resistance torque is reduced by 8%,the coefficient of variation of straw mulching thickness is reduced to 10.94%,the organic fertiliser leakage phenomenon is improved and the overall operation effect is improved.