| In recent years,with the development and research on the comprehensive utilization of straw,the utilization of straw for building materials has become an effective way to make use of straw and increase the added value of agricultural waste.Currently,the production process of straw board calls for an industrial-scale mixing device for the mixing of straw and binder,which is an indispensable step in the production of straw board and directly affects its compressive strength,seismic performance,etc.Therefore,based on the parameter and characteristics of straw fibers,this paper designs and analyzes a mixing device for large-scale mixing of straw materials and binders.The device uses lifting blades and a rotating drum to rotate the straw and mix the materials thoroughly.The main research findings of this paper are as follows:(1)Through experimental measurements of the mechanical and flow properties of straw fibers,I find that straw has low material density,agglomerates easily,and shows poor ability to flow.The particle size of straw is between 25 to 40mm,accounting for56.36%of the total particle volume of straw fragments.The diameter of straw particles is relatively uniform,generally ranging from 3 to 5mm,with few wide flakes and long rod-shaped particles.The static friction coefficient between straw and steel is 0.20,and the static friction coefficient between straw and straw is 0.39.The rolling friction coefficient between straw and steel is 0.10,and the rolling friction coefficient between straw and straw is 0.19.The restitution coefficient between straw and steel is 0.30,and the restitution coefficient between straw and straw is 0.28.The average shear modulus of straw is G=6.26 MPa,the average elastic modulus is E=16.9 MPa,and the Poisson’s ratio is found to be v=0.35.The average bulk density of straw material is 47.9 kg/m~3;the average compacted density is 60.4 kg/m~3;the average compression ratio is 22.31%;the average dispersity is 6.23%;the average static angle of repose is 44.3°;the average dynamic angle of repose is 26.5°;the average porosity is 81.2%.(2)Based on the physical properties of straw fibers and the requirement for continuous production,I focus on a rotary mixer to study the trajectory of straw fibers inside the rotating drum in relation to the type,length,and bending angle of lifting blades.Formulas were derived to calculate the blade holding capacity,curtain density,and retention time,providing recommendations for the diameter and length of the drum,the inclination angle of the blades inside the drum,and the number of blades.The research results show that a two-section bending type of lifting blades is more suitable for mixing straw and adhesive materials.The length of the blade’s section near the drum wall(section a)has a minimal effect on the holding capacity and scattering effect,while the length of the section farther from the drum wall(section b)is positively correlated with the holding capacity of the blades but has a minimal impact.As the bending angle increases,the discharge angle decreases.When the bending angle is 120°,the curtain effect formed by the straw material inside the mixing drum is better,and the scattered material covers almost the entire cross-section of the rotating drum,meeting the requirements of straw mixing.Considering factors including predetermined production capacity and retention time,it is recommended to set the inner diameter of the rotating drum at 2500mm,the length at 6000mm,and the ratio of diameter to length at 0.373.The inclination angle of the lifting blades with respect to the axis directly influences the axial transport of straw.As the inclination angle of the lifting blades increases,the retention time gradually decreases,so an appropriate blade inclination angle of 15°to 20°is recommended.The more lifting blades there are in the circumferential direction,the lower the curtain density,indicating a more uniform scattering of materials.Once the diameter of the rotating drum is set,using 18 lifting blades yields better mixing effects.(3)I conducted a static mechanical analysis of the lifting blades with Ansys to verify if the material strength meets the requirements for use.I further performed a discrete element method(DEM)simulation analysis on the mixing process with EDEM.On one hand,the simulation validated the curtain density for different numbers of lifting blades.On the other hand,it verified the feasibility of mixing straw and adhesive materials.The simulation results showed that the maximum stress experienced by the equipment is below the allowable stress of the material,and the deformation and displacement of the equipment meet the requirements for experimental production.The relationship curve between the number of blades and scattering effect was obtained through EDEM.Furthermore,from the velocity and mass characteristic vectors of the two types of particles,it can be observed that under the action of lifting blades’scattering and gravity,uniform mixing of straw and adhesive can be achieved,which suggests a reasonable design.(4)I optimize the stirring process of the rotary straw mixer,manipulating the following factors:material filling rate,rotary drum speed,and stirring duration.After conducting single-factor experiments on the aforementioned parameters,the optimal range of mixing parameters was obtained.A three-factor,three-level orthogonal combination experimental design was performed with the Design-Expert 10.0 software.The experimental results showed that the factors influencing mixing uniformity in the stirring process,ranked from high to low based on their effect,were material filling rate,stirring duration,and rotary drum speed.The factors affecting machine energy consumption in the stirring process,ranked from high to low based on their effect,were stirring duration,rotary drum speed,and material filling rate.The optimal stirring parameters were determined using response surface methodology,with a straw filling rate of 36%,a rotary drum speed of 7.5 r·min-1,and a stirring time of 357 seconds.Experimental verification was conducted with these parameters,and under the specified stirring conditions,the mixing uniformity of straw and adhesive reached 91.5%,while the energy consumption of the experimental prototype was 0.594 kW·h. |
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