Study On The Mechanism Of Screw Conveying Theory For Rubbing And Breaking Corn Straw

Screw conveyor is widely used in the harvest and processing of agricultural fiber materials because of its simple structure, reliable work, low cost, easy operation management, good seal, and less pollution to the environment and so on. However, some undesired problems such as low productivity, high power consumption, and easily jammed also exist in the process of conveying the agricultural fiber materials, because the theoretical study of the screw conveying process of fiber material is not enough depth, and conveying mechanism is not clear, which seriously affect the harvest and post-processing effect, and restrict the agricultural fiber material screw conveyor’s application and extension. In order to solve these problems, the theoretical study and conveying performance experiment of the screw conveying of the rubbing and breaking corn straw as the breakthrough point, screw conveying mechanism, productivity, power consumption and specific power consumption of screw conveyor of the rubbing and breaking corn straw are researched. Screw conveying test-bed is developed. By the theoretical analysis, the force distribution of screw blade and casing, axial thrust, productivity, power consumption, and specific power consumption during conveying are researched by experiment. The effect of pitch, rotational speed, feeding quantity, and the moisture content of materials on screw conveying performance of the rubbing and breaking corn straw is analyzed. The main research work is as follows:The rubbing and breaking corn straw is assumed compressible continuously moving body, which variation of density, speed, axial and normal stress are only along the direction of movement of materials. And the density is a function of the pressure. Ignore the influence of curvature of screw blade and the gap between screw blade and casing. In the above hypothetical premise, the pressure-bearing surface and the back of screw blade are seen as two blocks infinite and inclined parallel steel plate, and the material group enclosed with the pressure-bearing surface, the back and the central axis is seen as an infinite multilayer compressible micro-unit. Screw conveying model is found, which is taking micro-unit of spiral blade at any radius in the material group and took into account compressibility, mechanical property of rubbing and breaking corn straw, and centrifugal force of screw axis.Plug flow theory, non-plug solid conveying theory and Triaminic non-plug conveying theory used for reference, motion and stress analysis of rubbing and breaking corn straw micro-unit is made in the screw groove. Continuity equation and kinematics equation are developed and then solved. The model of pressure on material and velocity model under different working conditions are found. On the basis, the productivity model and power consumption model are built. The variation of pressure on the material, movement speed, productivity and power consumption with the structural, movement and characteristics parameters of material is analyzed, and provided the theoretical basis for the analysis and calculation of pitch, rotational speed, and feeding quantity.The rubbing and breaking corn straw parameter determination test stand is developed and the characteristic parameters of material are researched by experiment. The experimental platform of screw conveyor is developed, which rotational speed is adjustable, feeding quantity is controllable, pressure on blade and screw groove, axial thrust, productivity, and power consumption can accurate on-line measurement and experimental study on the conveying process. The main conclusions are as follows:The conveying performance of material is influenced by moisture content, density, sliding friction coefficient, internal friction coefficient and compressible coefficient of rubbing and breaking corn straw. And there is a certain relationship between each other. The characteristic parameters of rubbing and breaking corn straw are researched by experiment. The effect rule of moisture content and density on friction coefficient, and the relationship between moisture content with internal friction coefficient, density, and compressible coefficient are found and can provide the basis for the analysis of rubbing and breaking corn straw conveying mechanism.Using the CX402 thin-film pressure sensor to test the pressure of each part on screw blade and casing under different working conditions, variation rule of pressure distribution of the surface on the screw blade and casing is gained. The results show that pressure distribution on the screw blade and casing is influenced by conveying length, blade radius, pitch, rotational speed, feeding quantity and so on. With the conveying length, blade radius, pitch, rotational speed and feeding quantity increasing, the pressure on each part of the blade increased; as the pitch increased, the pressure on different parts of the casing decreased, and with the conveying length, blade radius, rotational speed and feeding quantity increasing, the pressure on each part of the blade increased.Using the LDCZL-FK loop force-measuring sensor system to test the axial thrust of screw conveyor under different working conditions, the results show that the theoretical and experimental results are accordant by the comparison between them. Under the tested range of the parameters, the axial thrust decreased with the pitch increasing, and the axial thrust increased with the rotational speed and feeding quantity increasing. On the condition of other parameters unchanged, with moisture content of material higher, the axial thrust during the conveying is smaller. Theoretical model of pressure is corrected by the axial thrust experiment data.The experiment studied the impact of pitch, rotational speed, feeding quantity, and the moisture content of material on productivity. The results show that the theoretical and experimental results are accordant by the comparison between them. Under the tested range of the parameters, with the pitch and feeding quantity increasing, the productivity increased and when the speed within the scope of the 28～117 r/min, as the speed increased, the productivity increased. Under the experimental condition of this paper, 117r/min is the critical speed of screw conveyor. With the moisture content of material increasing, the productivity increased when the other parameters were invariant.The experiment studied the impact rule of pitch, rotational speed, feeding quantity, and the moisture content of material on power consumption. The results show that the theoretical and experimental results are accordant by the comparison between them. Under the tested range of the parameters, with the speed and feeding quantity increasing, the power consumption increased. As the pitch increased, the power consumption first increased and then decreased. With the moisture content of material increasing, the power consumption decreased when the other parameters were invariant.Mathematical model of specific power consumption is developed, and the model is corrected by corresponding experimental data. On the basis, parametric level is optimized based on the principle of the specific power consumption smaller the conveying performance better. Orthogonal experiment is designed by using specific power consumption and axial thrust as experimental index, and the order and the better level of various factors on target index is confirmed. The results show that the order of impacted factors on specific power consumption of screw conveyor is rotational speed, pitch and feeding quantity. And the combination of the better level is that the pitch is 300mm, the rotational speed is 87r/min and the feeding quantity is 30kg/min. The order of impacted factors on axial thrust of screw conveyor is pitch, rotational speed and feeding quantity. And the combination of the better level is that the pitch is 300mm, the rotational speed is 58r/min and the feeding quantity is lOkg/min.Generally speaking, all the preliminary research achievements can provide relatively exact theoretical basis for design and optimize of screw conveyor, which suitable for conveying agricultural fiber material. At the same time, it can also provide the reference to design and research for screw conveyor of other agricultural fiber material.