| The development of modern light industry in China is getting faster and faster,which also makes our country pay more attention to it gradually.In the field of bulk material conveying,screw conveyor with simple structure can ensure the conveying process of bulk materials continuous and stable.It has been widely used in powder packaging,chemical industry,medicine,construction industry and so on.Nowadays,however,in the context of devoting in the green environmental protection production,there are still many problems in powder spiral transportation,such as large gas content of powder,as well serious pollution to the working space,which poses a new challenge to powder spiral transportation.Taking the horizontal pipe screw conveyor as the research object,this paper carries on the structure design to its dense section and the parameter optimization based on the genetic algorithm.Its main contents are as follows:(1)Directed against these problems in the process of screw conveyor,including higher air content,serious dust pollution,lower packing efficiency and precision,inconvenience to the follow-up of storage and transportation,etc.,the TMS-Pro type structure instrument is used to conduct powder compression experiment;the Gas-volumetric method is applied to determine the powder material compaction density;the spiral conveying flow-formula is combined to calculate the smallest pitch which could achieve compaction density;the structure of the dense section with variable pitch is designed on the basis of the arithmetic principle of equal difference;Adding micro negative pressure vacuum chamber to the powder compaction section is to further compact degassing the powder material in the conveying process by applying micro negative pressure environment,which not only improves the degassing efficiency,degassing effect,and the density of the material,but also reduces the mass flow fluctuation and the dust pollution.(2)For the design of the powder compact degassing spiral conveyer,based on multi-objective genetic algorithm,aiming to get the minimum of helicoid quality and the maximum of conveying flow,at one time,with pitch,diameter of spiral vane,screw shaft diameter and inner shaft diameter as variables,the key parameters of the spirochete are optimized to obtain the optimal parameter combination;through the secondary optimization design of helix,the optimal parameter combination in the degassing section is obtained.The both provide a reference for the design of the confidential degassing device of helix feeding and also a good foundation for the follow-up research.(3)For starch materials,in order to make the discrete element simulation more accurate,it is necessary to calibrate the parameters of the discrete element simulation.The actual angle of repose of starch is measured to be 57.78°by BT-1000 powder tester.A 3D model of Angle of repose for module tests is established by Solid Works,and the EDEM discrete element simulation software is imported.The contact parameters of starch particles are calibrated by using the Edinburgh Elasto-Plastic Adhesion contact model with Angle of repose as the response value.The 3D model of spiral feeding dense degassing device is imported into EDEM to detect parameters such as starch density,mass flow rate and stability in the dense section.Taking the material density as an index,by detecting the degassing degree of materials in the process of spiral feeding,we conclude that:the average density of materials in the normal equidistant spiral feeding process is 746.41kg/m~3,while that in the variable pitch spiral feeding process designed in the paper is 778.49kg/m~3;after adding the micro-negative pressure degassing device,the former is 810.63kg/m~3 while the latter is 889.3kg/m~3.Compared with the conventional equidistance screw of the same size,it is concluded that the designed screw feeding device has higher material density,better conveying stability and feeding accuracy.(4)In order to verify the rationality of the designed screw feeding dense conveying device,the machining prototype is tested according to the adjusted parameters,and the conveying mass flow rate and conveying stability are both measured in the test.Under the same spiral speed,the average feeding flow rate of the equidistance screw is 0.769kg/s,and the flow fluctuation is between0.685kg/s and 0.847kg/s,and the fluctuation percentage was±12.92%;while for the variable pitch screw designed in the paper,the first number is 0.831kg/s,and the second is between 0.783kg/s and0.883kg/s,and the third one is±6.26%.Through the dust concentration measurement test,the dust concentration of the conventional equidistance screw and the designed screw in the filling process are compared and detected.When the rotating speed reaches 100 r/min,the maximum dust degree at the discharge outlet is reduced by about 36.35%;and when the rotating speed reaches120 r/min,the average dust degree is reduced by about 30.68%.It can be seen from the experimental results that the density of starch conveying after compaction of micro-negative pressure degassing device is higher than that of conventional equidistance screw,and the degassing effect is better.In short,this design improves the mass flow of screw feeding device and reduces the fluctuation of flow,providing a reference for solving the problem of compaction degassing of screw conveyor. |
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