| The rice straw insulation blocks made of rice straw are compounded with concrete hollow blocks to form the self-insulation composite blocks.This composite can not only promote the utilization of straw resources according to local conditions but also improve the thermal insulation performance of concrete hollow blocks,which is of practical significance for cost-saving and environmental protection,and energy-saving.The previous researches of our group were in the laboratory stage.To promote the production of this self-insulating composite block,this paper studied the production process of straw-concrete composite blocks in the factory.The optimal process parameters for the factory preparation of the straw-concrete composite block were determined through experiments.And the performance of the self-insulating composite blocks prepared by parameters was tested.Then the feeding equipment of the rice straw mixture was optimized by discrete element analysis.The details are as follows:(1)According to the factory investigation and data review,the production process of the straw-concrete composite block factory was determined.Firstly,the process flow of five steps of straw cutting,mechanical stirring and transportation,hopper feeding and unloading,rectangular frame feeding and pressing,and batch curing was obtained.It was found that there were problems to solve in the factory production of rice straw insulation blocks.One was determining the optimal process parameters for factory preparation of rice straw insulation blocks,the other was improving the uneven feeding of the straw mixture during the mechanical pressing process.And then,the batch curing under suitable conditions of rice straw insulation blocks pressed and formed mechanically was determined,and the blocks were stored intensively after the curing.Finally,the concrete hollow block,whose size was determined to be 320 mm×190 mm×150 mm and the minimum strength level should reach MU5,was produced by the production technology of the conventional ordinary concrete small block.And a mechanical automatic assembly production device,which was to compound the rice straw insulation block and the concrete hollow block,was designed.(2)The optimal process parameters for mechanical pressing and forming of rice straw insulation blocks and the process parameters for batch curing and storage of rice straw insulation blocks were determined.Firstly,the influence of the mixing amount of industrial slaked lime and the degree of compaction on the formation of the rice straw insulation block was studied,and a single factor experiment was designed to determine the range of the ratio of slaked lime to rice straw was 0.3～0.9,and the range of compaction degree was 20%～40%.A controlled experiment was designed to study the effect of the combined length of the rice straw sections on the forming of the rice straw insulation block,and it was determined that the rice straw section treated by the grass crusher was beneficial to the forming of the rice straw insulation block.And then,three-level factors of the forming process were selected as the amount of straw per unit volume(A),the ratio of slaked lime to rice straw(B),and the degree of compaction(C)were designed using the Design Expert 12(DE12)software according to the design of the center combination test,and the response surface simulation analysis was carried out,and the optimal molding process was finally determined as the amount of straw per unit volume is 0.191g/cm~3,the ratio of slaked lime to rice straw is 0.4,and the compaction degree is 38.6%;Finally,the batch curing and storage process parameters of rice straw insulation blocks are determined as follows:curing for 30 d under the curing conditions with a temperature range of 15～30°C and a relative humidity range of 40%～75%,the spacing of the straw insulation blocks is 150 mm at the initial stage of curing.On the 7th day,the spacing of the rice straw insulation blocks was reduced to 75 mm,and the layer height was 150～180mm.After 30 days,the straw insulation blocks were intensively stored;The moisture content of the rice straw insulation blocks is less than 15%and there is no mildew phenomenon.(3)The application form of the rice straw insulation block was to form a self-insulation composite block by compounding with the concrete hollow block.Therefore,the strength properties,thermal properties,and hygroscopicity of the self-insulation composite blocks were tested.Firstly,the compressive strength and softening coefficient of self-insulation composite blocks were tested according to the standard"Test Methods for Concrete Blocks and Bricks"(GB/T 4111-2013),which was 5.21 MPa and 0.96,respectively,all of which meet the requirements of the specification.And then,the equivalent thermal conductivity and equivalent heat storage coefficient of the straw-concrete composite block were measured according to the test method of the specification"Self-Insulation Composite Block"(JG/T 407-2013),which were 0.393 W/(m·K)and1.093 W/(m~2·K),respectively,which meet the requirements of the specification.Finally,a simplified experimental study on the hygroscopicity of the rice straw insulation blocks inside the walls of different floors was carried out,and the results showed that the rice straw insulation block absorbed moisture slowly and the moisture content does not exceed17%,which meets the specification requirements;(4)To solve the problem of uneven forming of rice straw insulation blocks when pressed by mechanical in the factory,the discrete element analysis method was used to simulate and explore the feeding process of the factory machinery.Firstly,the contact model of"Hertz-Mindlin with JKR"was selected according to the physical properties of the rice straw mixture.The interaction force between rice straw particles was characterized by surface energy,and the particle model of rice straw was constructed.The surface energy between the rice straw particles was calibrated by the stacking angle test and the simulation test,and the value of the surface energy was determined to be 0.5 J/m~2.And then,the three-dimensional model of the factory’s mechanized production equipment was drawn by Solidworks three-dimensional software.After that,the process of unloading,rectangular frame feeding,and mold frame feeding of rice straw mixture were simulated and analyzed by EDEM software.The results showed that the rice straw particles on both sides were more and in the middle part of the mold frame were less.The maximum difference of the rice straw particles between each area of A was 25731,and the maximum difference of the rice straw particles between each area of B was 33464.The particles in A which was near the side of the rectangular frame were significantly more than that of B,and the maximum difference between the rice straw particles in the corresponding areas of A and B was 44221.Finally,the improved measures for machinery equipment of feeding were proposed:one was the nails were added to the length and width of the rectangular frame respectively,the other was the lower edge of the rectangular frame was cut by 2 cm along the height direction.The feeding process was simulated again.The results showed the maximum difference of the rice straw particles between each area of A was 5684,which was about 77.9%smaller than before the improvement of mechanical equipment,and the maximum difference of the rice straw particles between each area of B was 2059,which was about 93.8%smaller than before the improvement of mechanical equipment.There was little difference between the heights of the bar graphs in A and B,the maximum difference between the rice straw particles in the corresponding areas of A and B was 5330,which was about 87.9%smaller than before.That showed that the optimization measures of mechanical equipment could effectively improve the uniform distribution of straw particles. |
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