Multi-scale Mechanical Analysis And Parameter Optimization Of Alfalfa Densification Molding

Alfalfa is a kind of forage with high nutritional value,but due to its loose and low density,it is inconvenient to store and transport,resulting in uneven distribution and waste of forage resources.Compressing loose alfalfa into regular and stable products can effectively solve the above problems.However,at present,the compression equipment has problems such as high energy consumption,poor molding quality,low stability and serious wear of key components.In order to solve these problems,the research team introduced vibration as an auxiliary process into the biomass compression molding process,and verified that vibration can reduce compression energy consumption and improve the density of molding products through experiments.In order to further study the effect mechanism of vibration on the compression process and molding products,this thesis studies the stress distribution and stress transfer during the alfalfa compression process from the macro,micro and micro perspectives;The compression process parameters were optimized with molding pressure,die density,stable density and relaxation ratio as evaluation indexes.The specific research contents are as follows:1.Using the biomass vibration compression test bench,taking the moisture content of alfalfa,vibration frequency,molding time and feeding amount as the test factors,and taking the molding pressure and stable density as the evaluation indicators,the single factor test was carried out.According to the results of four groups of single factor tests,on the basis of ensuring the molding density,the appropriate vibration force field can effectively reduce the molding pressure;Proper moisture content can ensure good molding quality and reduce processing energy consumption;The feed rate has little effect on the molding pressure and molding density;The suitable retention time can improve the stable density of the molded products.2.According to the arc-shaped boundary formed during the compression of crushed alfalfa,the adhesive force between materials is judged,the put-off force in the discrete element simulation model of alfalfa straw is calibrated,and the discrete element simulation model of open compression alfalfa straw under the action of vibration force field is constructed.3.Taking vibration frequency as the experimental factor,the simulation analysis of alfalfa open vibration compression process was conducted,and the stress distribution and transfer laws were analyzed from the perspectives of macro particle average compression force,micro force chain,micro porosity,and coordination number.The results are as follows:(1)When there is no vibration compression,the particle average compression force gradually decreases from top to bottom;Under the action of vibration force field,the average compression force of particles in the compression chamber tends to be consistent,which indicates that vibration can promote the material flow in the mold and the material stress is uniform.(2)When there is no vibration compression,the strength of the force chain decreases gradually from top to bottom,and the force chain is concentrated near the compression piston;During vibration compression,the strength of the internal force chain in the compression chamber tends to be consistent,indicating that vibration can effectively solve the internal stress concentration.(3)Without vibration compression,the porosity of the material increases gradually from top to bottom,and the coordination number decreases gradually from top to bottom;During vibration compression,the porosity distribution and coordination number of alfalfa particles in the compression cavity tend to be consistent,which indicates that vibration can promote the density homogenization of formed products,thus improving the stability of formed products.Taking molding pressure,porosity and coordination number as evaluation indexes,the optimum vibration frequency range of alfalfa open compression is 10Hz～15Hz.4.Taking moisture content,vibration frequency and shape retention time as test factors,and alfalfa compression molding block molding pressure,mold density,stable density and relaxation ratio as evaluation indicators,response surface tests under different working conditions were carried out on the biomass vibration test bench.The process parameters were optimized in the test,and the values were as follows: water content18%～20%,vibration frequency 10Hz～15Hz,retention time 1s～8s.