| Roof greening has become an important way to improve the quality of natural ecological environment,improve people’s living environment,increase urban green coverage area,and reduce urban waterlogging and heat island effect.At present,it is difficult to get soil for roof greening,and the construction difficulty and high cost of granular matrix cultivation are higher due to the light particle dispersion.Straw and other agricultural and forestry waste resources are rich,and its matrix utilization is one of the effective means to realize the comprehensive utilization of agricultural and forestry waste.Discard the agriculture,forestry and preparation of cultivation matrix block,after pretreatment of compression molding can effectively fixed plant,provide sufficient nutrients to plants,but also can reduce pollution of the environment,to reduce the roof greening construction process of the intensity of labor,has a broad application prospect,but the lack of on the market at present can achieve continuous production of matrix block molding machine.Aiming at this situation,this article to tobacco straw rotten material pile and urban sludge fertilizer as matrix material,prior to the matrix block forming feed,key parameters of mixing and compression molding process simulation,and completes the compression molding machine overall structure design of matrix block and the spindle component statics analysis and modal analysis,in order to shape the straw substrate utilization and molding machine to provide theoretical basis for the design.The main research contents and conclusions are as follows:(1)Explore the influence of mixing process parameters on material mixing uniformity in matrix block forming process.The best mixing time was determined by single factor test with material mixing uniformity as the evaluation index.The results showed that the highest mixing uniformity was achieved when the mixing time was 180 s.Taking the mixing parameters(material proportion,material moisture content and mixer speed)as test factors,the three-factor and three-level orthogonal test was carried out,and the comprehensive evaluation of mixing uniformity was carried out by the weighted average of variation coefficient and mixing ratio deviation from the set value.The results showed that:In the range of test level setting,the most significant factor affecting the mixing uniformity is the material proportion,the second factor is the water content,and the last is the mixer speed.When the material ratio is 6:4,the mixer speed is 40 r/min,and the material moisture content is 30%,the mixing uniformity of the mixing process is the best,and the adjustment of the material ratio and the initial moisture content of the material is more conducive to improve the mixing effect.The mixer speed can be coordinated and controlled according to the performance of the machine.(2)To explore the influence of feeding process parameters on material dispersion in matrix block forming process.Taking the mixing uniformity as the evaluation index,taking the feeding parameters(feeding speed,bin Angle,bin height)as the test factors,three factors and four levels orthogonal test was carried out,and the comprehensive evaluation of mixing uniformity was carried out by the weighted average of the variation coefficient and the deviation of the mixing ratio from the set value.The results showed that:In the range of test level setting,the most significant factor affecting the mixing uniformity is the bin Angle,the second factor is the bin height,and the last is the feed speed.When the bin Angle is 75°,the bin height is 110 cm and the feed speed is 0.1 m/s,the material dispersion degree is the lowest,and the best uniformity can be maintained in the feeding process.The control of the bin Angle and the bin height can effectively avoid the material dispersion in the feeding process.The feed rate can be controlled according to the requirements of production capacity without considering its influence on material uniformity.(3)By combining bench experiment and EDEM simulation,the eigenparameters of straw,the contact parameters between straw and straw,and the contact parameters between straw and mold were calibrated.Through the image processing of the material accumulation body,the accumulation Angle of the material is extracted.The relative error value of the simulation test results and the bench test results is taken as the evaluation index,and the coefficient of restitution,static friction and dynamic friction between the straw and the straw and between the straw and the mold are taken as the test factors to carry out the six-factor and five-level orthogonal test.Results show that within the scope of the test level is set,the factors effect on material accumulation is the accuracy of the Angle of significant degree between the size of straw and straw between the static friction coefficient,friction coefficient,straw and mould,recovery coefficient and friction coefficient of recovery coefficient between straw and stalk,straw,and the static friction coefficient between the mould.When the restitution coefficient between tobacco straw and mold was 0.28,the static friction coefficient was 0.572,and the dynamic friction coefficient was 0.128.When the coefficient of restoration of tobacco straw and tobacco straw was 0.21,the coefficient of static friction was 0.413,and the coefficient of dynamic friction was 0.133,the relative error value of the test results was the smallest.At this time,the accumulation Angle of the simulation test is 27.15°,and the accumulation Angle of the bench test is 26.56°.The relative error value of the two is 2.22%,indicating that the discrete element simulation results are credible.(4)The simulation model of tobacco straw compression was established,and the effectiveness of the discrete element model was tested and analyzed through EDEM simulation compression test and physical compression test.The results show that the variation of loading force with compression displacement in simulation test is consistent with that in real test,and the loading force at the same displacement is similar.The density of matrix block is 1.08 g/cm~3 in simulation test and 1.04 g/cm~3 in real test,and the relative error is 3.85%,indicating that the discrete element simulation is effective and reliable.On this basis,the effects of compression forming process parameters(loading force and loading speed)on matrix block density and specific energy consumption during forming were studied.The results showed that:With the increase of loading force,the density of matrix block and the specific energy consumption of compression process gradually increase,while the loading speed has almost no effect on the density of matrix block and the specific energy consumption of forming process,and the matrix block has a slight stratification phenomenon in the circumferential direction after forming.(5)According to the expected matrix block size and capacity requirements of the molding machine,complete the overall structure design of the matrix block compression molding machine and check the spindle parts of the molding machine.The results of static analysis and modal analysis show that the strength and stiffness of each axis meet the requirements,and the structure design is reasonable. |
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