Research And Experiment On The Stripping Mechanism Of Concave Combs And Increasing Flow Header For Stripping Prior To Cutting

Rice is one of the most important food crops in the world,and also one of the four major food crops in China.Rice has the characteristics of high and stable yield,and has grain and economic attributes.Its stable production is of great significance to ensuring world food security and economic stability.At present,mechanized rice harvesting is the main way in rice production.Stripping prior to cutting is a method of threshing first and then cutting.Compared with full-feed and half-feed combined harvesting,it has the advantages of high harvesting efficiency,low power,seizing agricultural time,and complete stalks after harvest.The way of stripping prior to cutting is of great significance for improving rice harvest efficiency,saving cost and increasing efficiency.There are many advantages of stripping prior to cutting,but its popularization and development are limited by a large number of header losses,that is,there are a large number of uncombed losses,splash losses and return losses in the harvesting process.In addition,the material is thrown close to the header,which is easy to cause the material that has been stripped to accumulate and block at the screw conveyor.Therefore,it is an urgent scientific and engineering problem to explore the loss mechanism and develop new key components to reduce the losses in the stripping prior to cutting process.On the basis of summarizing the research status of combined harvesting methods and threshing equipment at home and abroad,this study this study systematically explored the relevant stripping theory and loss characteristics by combining several methods such as rice basic parameter measurement,key component design,discrete element model establishment,fluid-structure coupling analysis,high-speed camera technology and bench comparative test.This study provides ideas for the innovative design of the key components of the stripping prior to cutting combine harvester and the promotion of the development of the Stripping prior to cutting harvesting mode,and also provides a reference for the exploration of the rice and wheat harvesting loss reduction mode and mechanism.The main research contents are as follows:(1)Determination of material characteristics of whole plant rice and establishment of discrete element model at harvest stageThe "Longjing 29" rice variety widely planted in Northeast China was selected as the test sample,and its physical parameters were measured by dividing it into main stems,primary stems,secondary stems and grains.Their typical geometric characteristics,moisture content and density were measured.The static friction coefficient and rolling friction coefficient were measured by the self-developed friction coefficient measurement test bench and high-speed camera technology.The elastic modulus of the whole rice was measured based on the compression test and shear test.The impact recovery coefficient of various rice grains was accurately measured by impact method.Through Plackett-Burman screening test,the steepest climbing test and Box-Behnken optimization test,the parameters of the discrete element model of the whole vertical rice cluster were reasonably optimized.The research in this chapter provides an effective solution for the exploration of the loss mechanism and the mechanical response of the whole plant of rice during the stripping prior to cutting harvesting operation.(2)Design and analysis of concave comb increasing flow header for stripping prior to cuttingAccording to the design requirements of the key components of stripping prior to cutting harvesting mode and the structural profile characteristics of the tongue surface,a concave comb was developed,and the blowing mechanism with uniform air volume was designed and analyzed.The overall structure parameters were determined,and the working principle of the overall structure was analyzed.The optimum structural parameters of the arc radius,the magnification ratio of the filamentous papilla and the concave angle of the concave comb were determined through experimental analysis.According to the principle of air jet and the structural characteristics of combs,the adaptive design of uniform air volume for the branch air duct and main air duct of the blowing mechanism which can improve the throwing distance and reduce the return loss was carried out.The research in this chapter provides equipment support and theoretical basis for the subsequent analysis of stripping mechanism and bench performance test.(3)Study on the flow field characteristics of the concave comb increased flow header for stripping prior to cutting Taking the speed of the stripping drum,the key factor affecting the flow field,as the main factor,the characteristics of the header flow field were analyzed theoretically.The CFD method was used to establish the fluid simulation models of flat combs,concave combs,blowing mechanism and other related components,and set the boundary conditions.The characteristic evolution of header flow field,the effect of flat combs and concave combs steady flow field,the flow field in different sections of the blowing mechanism and the internal flow field of the concave combs increased flow header(concave comb+blowing mechanism)were analyzed.The characteristic evolution of header flow field was clarified.In the radial direction,the closer to the center of rotation,the lower the pressure.Before reaching the steady flow field,the air flow produces "bottom bounce" and "eddy current" and other phenomena.The average velocity of the air flow generated by the concave combs at the entrance of the spike head was greater than that of the flat combs,and the "flow around" phenomenon was lower than that of the flat combs.The flow field generated by the concave combs was better than that generated by the flat combs.The taper of the main air duct and the length of the branch air duct affected the uniformity of the air flow of the blowing mechanism,and the maximum velocity deviation ratio was 21.55%.The air flow velocity of concave comb increased greatly at different rotational speeds.With rotating speed increasing,the velocity deviation in the flow field gradually decreased,and the maximum value was 6.69%.The research in this chapter provides reliable data support and method reference for improving the flow field characteristics inside the header.(4)Analysis and numerical simulation of stripping mechanism of concave combs and increasing flow header for stripping prior to cuttingThis chapter further deepens the research on the internal flow field characteristics of the concave combs and increasing flow header.Through theoretical analysis and calculation,the mechanism of the combs movement,the related bending,feeding,and extraction of rice during the header operation was deeply explored.Based on the CFD-DEM coupling simulation method,the virtual posture,throwing characteristics and loss characteristics of the whole rice were analyzed.The stripping process mainly included bending,feeding and extraction.The number of stripping times was inversely proportional to the forward speed and directly proportional to the speed of the stripping drum.With e the speed of the stripping drum increasing,the impact force of the combs on the rice grain became larger,resulting in the increase of the number of bonding bond broken,and it was easier to strip the rice grain off.The average resultant velocity of rice grains increased gradually with the speed of the stripping drum increasing in the three regions.The deviation in the X direction(i.e.transverse direction)was small,and the average speed in the Z direction increased with the rotation speed increasing.Splash losses can be reduced by increasing the stripping height,reducing its forward speed or selecting a suitable speed of the stripping drum.Uncombed losses can be reduced by increasing the impact force and frequency of the stripping process,reducing the forward speed of the machine or increasing the stripping height.The blowing mechanism added in this study can effectively reduce the return losses.The research in this chapter provides a strong basis for the selection of factors and levels of the later bench test.(5)Comparison test of performance of concave combs and increasing flow header for stripping prior to cuttingThe test bench was designed systematically,and the throwing characteristics of different drum speeds,different forward speeds and different stripping heights were studied based on high-speed camera technology.The operation effects of two kinds of rice materials thrown by combs in horizontal and vertical distribution were compared and analyzed.Taking the falling grain loss rate and the uncombed loss rate as the test indicators,the loss characteristics of the effect of flat comb and concave comb(equipped with blowing mechanism)under the conditions of drum speed,forward speed and stripping height were investigated through single factor test.The interaction between the relevant test factors and the influence on the test indexes are explored through the orthogonal rotation combination test factors of three factors and five levels,and the performance of the concave combs and increasing flow header for stripping prior to cutting was comprehensively evaluated according to the best parameter combination.Under the conditions of different drum speeds,different forward speeds and different stripping heights,the throwing performance,horizontal distribution of throwing distance and throwing stability of concave combs(equipped with blowing mechanism)were better than those of flat combs.The stability of the vertical distribution of the material thrown by the flat combs was better than that of the concave combs.The uncombed loss rate,falling grain loss rate and total loss rate of concave combs were lower than those of falt combs.The best parameter combination was that when the drum speed was635 r/min,the forward speed was 0.71 m/s,and the stripping height was 845 mm,the falling grain loss rate was 0.75%,the uncombed loss rate was 1.03%,and the total loss rate was 1.78%,which met the requirements of rice harvesting.The research in this chapter provides the experimental scheme and theoretical reference for the research on the reduction of rice combined harvest.