| Straw is an important renewable resource,which can be used for feed,fuel,base material,fertilizer and raw material.Its resource utilization is of vital importance to alleviating the energy crisis,developing related industries,and reducing resource waste and environmental pollution.Straw is widely distributed and loose,which affects transportation,storage and subsequent utilization.Briquetting/baling is the most direct and simple method to increase the density of incompact straw.However,the current briquetting/baling theory is still imperfect.There are fatal problems such as low molding density,high energy consumption and poor quality,which restrict the utilization of straw as a resource and the development of related industries.Aiming at the closed compression rheological properties of straw and the technology of bundling,this paper adopts a combination of experiment and theory,taking crushed corn stalks as the research object,and assessing the resilience characteristics of the straw block,the process of restraining resilience,the bundling performance and automatic wrapping research on a series of key technologies,with the purpose of providing a basis for the optimization of straw briquetting/baling process and equipment,and promote the utilization of straw resources and the development of related industries.Summarizing the full text,the main contents are as follows:A straw compression and resilience test platform was built to study the resilience laws of straw blocks in various directions,and determine the compressive strain of straw is composed of reversible strain and irreversible strain and residual stressis viscoelastic force and elastic force.The laws of direct rebound,pressure retention and shape retention of straw under different compression conditions were compared and explored.On this basis,with the help of mechanical elements,a constitutive model of rebound is established as the Kelvin model under compression,and the accuracy of the model was verified,which got a reasonable explanation for the rebound phenomenon of straw blocks.The degree of resilience of various factors to the straw block after constant-speed pressing was analyzed,the results show that the rebound rate of straw block is greater than 18%,which will provide the basis and direction for the research necessity and follow-up research content of this article.With the help of the classical model of viscoelastic material creep and stress relaxation,It is determined that the constitutive models of the straw block at the pressure and shape retention stage are Burgers and Wiechert B models,respectively,and the pressure and shape retention phenomena were reasonably explained,and the moisture content,maximum compressive stress and the influence of input on model parameters are studied.Under different compression conditions,the changes of stress and strain of contant speed compression and pressure retention(CCP)and contant speed compression and shape retention(CCS)process at each stage were compared and analyzed,and then the nature of the pressure-holding/shape-holding restraining the rebound of the straw block was revealed,and the effect of restraining the rebound was compared and analyzed.The results show that the mechanism of pressure retention to suppress springback:suppress the springback of the compressed straw from two aspects:increasing the compression displacement and reducing the rebound displacement,thereby increasing the compression dimensional stability coefficient of the compressed straw.The mechanism of shape retention to suppress springback:reducing the viscoelastic resilience in the straw block,thereby reducing the springback and increasing the compressive dimensional stability coefficient of the straw block.Under the same compression conditions,the effect of restraining rebound of the shape retention is better than that of the pressure retention.The influence of the holding pressure/holding time on the stalk compression dimensional stability coefficient was explored,and the mathematical relationship between the compression dimensional stability coefficient and the stable time was established,which can be expressed by exponential function and provides a basis for the optimization of the straw compression process.A stable process combining constant compact of pressure and shape retention(CCPS)was proposed,and the constitutive model of shape retention and stabble effect in the process was verified,The results show that the Wiechert B model can describe and explain the shape retention phenomenon well;compared with CCS,under the same shape retention time,the stress relaxation rate in CCPS is smaller.The stability of various compression processes was compared and analyzed,and the results showed that after 150s of stability,the compression dimensional stability coefficient of straw under the CCPS process was the largest,followed by CCS and CCP.Using the Box-Behnken test method and taking the ratio of holding pressure and stabilization time as one of the factors,a regression model for the relaxation density of straw blocks,compression dimensional stability coefficient and specific energy consumption was established,and the fit and significance test of each regression model were performed.The influence degree of each factor and interaction on each index was analyzed,and the influence law of significant interaction on each index was studied.On this basis,through comprehensive optimization,the process parameters of crushed corn stalk compression were determined which shows thatthe relaxation density of the block is 145.63kg/m~3,the dimensional stability coefficient is 86.89%,the specific energy consumption is 245.78J/kg,and the error between the test and the predicted value is less than 2%under the condition of moisture content 13.63%,ratio of holding pressure time to stabilization time 0.38(pressure retentiontime 22.8s,shape retention 37.2s),maximum compressive stress 109.58k Pa,raw material feed volume 3.5kg.This provides a basis for the design of straw compression equipment and the selection of process parameters.A comparative study of the bundling performance of the commonly used Square bundleclosed balers for bagging and automatic net wrapping was made,and the problems of the balers were pointed out.The tensile mechanical properties of the net rope were studied,and the tensile mechanical parameters of the net rope were obtained.Aiming at the insufficiency of the netting system,a reverse net-putting pre-tensioned netting mechanism was designed,and the netting process was analyzed through dynamics,the motion equation of the netting was established,and the installation angle between the guide net tube and the net roll and the pre-tensioned spring were determined.Structural parameters.The regression equations of density,volume stability coefficient,net breakage rate and size difference were established through the experimental study of twisted net performance,and the fit and significance test of each regression model were carried out;various factors and interactions were studied.The degree of influence of the function on the index and the law of the influence of the significant interaction on the index were studied;the process parameters of the wrapping net were comprehensively optimized,concluded as the straw mass is 26kg,the net number of layers in the middle is 2,the pre-tightening force is 39N,the density of the optimized straw bale is 198.45kg/m~3,the volume stability coefficient is85.31%,and the size difference is 7.1 mm,which provides a reference for the application and promotion of the baler machine. |
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