Study On The Operation Process Of The Corn Straw Kneading Machine Based On Discrete Element Method

The operation process of 9FH-40 type of straw kneading machine was divided into two parts:straw kneading and material discharging.Straw kneading and material discharging were crucial to the straw operation.Because of complex operation process,numerical simulation was not deeper studied.The development of discrete element method provided a theoretical basis for studying the mechanical properties of granular materials,and the coupling with multi-body dynamics?MBD?and computational fluid dynamics?CFD?successful made the application field of the discrete element method more widen.Based on the theory of DEM?MBD and CFD,this paper used corn straw as the processed material.Through numerical simulation,the process of the corn straw kneading and material discharging were studied.It provided a theoretical reference for the visual dynamic research and the improvement of the equipment structure for 9FH-40 type of straw kneading machine.The main work of this paper were as follows:?1?The model of 9FH-40 type of straw kneading machine was drawn by 3D modeling software SolidWorks,and the bimodal distribution model of corn straw was established based on DEM.The compression and shear mechanical experiment of Nin Dan 19 corn straw?25mm diameter,50 mm length,water content 87.8%?was carried out,which at the harvest period with different loading velocities.The maximum critical load of radial compression was 160 N,the minimum critical load was 70 N,the maximum critical load of axial compression was 2 260 N,and the minimum critical load was 1 240N.In the shear experiment,the maximum critical shear force was less affected by the loading velocities,and the shear force was approximately linear with the change of the displacement at the same loading velocity.The BPM?Bonded Particle Model?parameters of corn straw were checked by reference experiment results and relevant scholars.The BPM parameters were 9.60×10⁶N/m?Normal stiffness coefficient??6.80×10⁶ N/m?Tangential stiffness coefficient??8.72 MPa?Critical normal stress??7.50 MPa?Critical tangential stress?ultimately,which could represent the physical characteristics of corn straw.?2?The coupling principle and realization process of RecurDyn?MBD?and EDEM?DEM?were explained,4 bimodal distribution models were simulated by MBD-DEM coupling.The number of bonding in the straw model could be divided into 3 stages:reduction rapidly,reduction stable and no change.After crushing,the material existed in 4 kinds of shapes:short,standard,long and incomplete.The data of the force changed process of the hammer was extracted from RecurDyn.When the velocity were 1 500,2 000,2 500 and 3 000 r/min,the maximum impact force between hammer and corn straw were 553.98,627.54,598.96 and 593.08 N respectively.The maximum impact force would not be affected by the velocity,but the average impact force would increase with the velocities.?3?The numerical simulation for kneading machine was carried out at different spindle velocities,which based on the CFD-DEM gas-solid coupling method and used the RNG K-?turbulence model and Euler-Lagrange coupling algorithm.The numerical simulation content contained the distribution of air flow velocity in internal flow field,the distribution of coupling force that air flow acted on the materials,and the movement process of materials at different parts when the fan spindle velocity reached to 3 000 r/min.The simulated results showed that:in the rated velocity of 3200 r/min,with the increase of velocity,the number of discharging was increased,and the discharging performance was improved accordingly.The average velocity of materials in different zones formed a gradient distribution,from big to small were materials outlet zone?10.00 m/s?,fan rotation zone?6.00 m/s?,materials inlet zone?0.87 m/s?.The rotation velocity of the fan had less effect to the coupling force at inlet zone,the coupling force maintained at 2.5×10^-4 N basically?small fluctuation in it?.The average velocity of the airflow in the fan rotation area was 30 m/s?peak value was 50.00 m/s?,the turbulence intensity was the highest in the fan rotation zone,and the material could be accelerated to 10 m/s after entering this zone.The air velocity reached to 40 m/s at the edge of the fan in the radial direction,and this zone also had the strongest coupling force for the materials.The airflow velocity and the coupling force of the material increased with the raise of velocity,and the volatility was aggravated.The increase of turbulence intensity resulted in more vortices in the fan rotation zone,while the loss of airflow energy was aggravated.There would be a small amount of agglomeration in the outlet zone.The coupling force in the zone would fluctuate at the same velocity,but it would be less affected by different velocities.At the end of simulation,quantity of materials were the maximum with a small accumulation in the inlet zone.There was no backflow phenomenon in the outlet zone.?4?The structure improvement of 9FH-40 type of straw kneading machine was suggested:In the process of kneading,the space coverage of the hammer on the pin shaft would be improved,the size and position distribution of the sieve hole would be optimized so as to reduce the leakage of the incomplete broken material from the sieve hole.In the process of discharging,the shell structure of the material inlet zone would be changed to improve the coupling force,short the time of the material entered the fan rotation zone from the inlet zone,and avoid the material accumulation.When the rotating velocity of the main shaft was improved,the number of vortex in the field and the loss of the energy of the air flow would be suppressed.The material outlet zone would reduce the amplitude of the coupling force fluctuation,change the shape of the shell to better guide the flow of air,and make the discharging process more smooth.