| Water caltrop is an annual herbaceous aquatic plant of trapaceaeone.It is one of the characteristic aquatic vegetables in China.It is mainly grown in the Lower-and-Middle Section of Yangtze River and the Pearl River Delta region.It has high nutritional value and medicinal value.Water caltrop kernel can be further processed after it is obtained by shelling,so as to significantly improve the added value of its products.However,due to its irregular shape,hard shell and uneven surface,there is no special shelling machinery at home and abroad,so water caltrop shelling completely depends on manual operation.Manual shelling has the disadvantages of high labor intensity,low production efficiency,high labor cost and high damage rate of water caltrop kernel,which has become the bottleneck restricting the development of water caltrop industry.With the increase of planting area and output of water caltrop in China year by year,it is of great significance to study the shelling mechanism and its mechanized production technology.In view of the above problems,this paper took water caltrop produced in Hubei Province as the object of research.The physical and biomechanical properties were measured,and the shelling process was mainly analyzed.The technical scheme of mechanical shelling was designed.Based on the analysis of shelling mechanism,the water caltrop sheller was trial produced,and the shelling performance test was carried out.The main research contents and results are as follows:(1)The physical parameters of fresh water caltrop and the SEM test of the microstructure of water caltrop shell were carried out.The average moisture content of whole water caltrop,water caltrop kernel and water caltrop shell were 74.31%,70.44%and 79.53%,respectively.The average length,thickness and height of water caltrop were76.01 mm,24.48 mm and 34.63 mm,respectively.The average thicknesses of umbilicus,pedicle,upper epidermis,lower epidermis and inner side of the corner were 3.2 mm,3.4mm,1.7 mm,2.4 mm and 8.4 mm,respectively.The average single seed weight and average density of water caltrop were 18.76 g and 1.09 g/cm~3,respectively.The density ranges of crispy matured,waxy matured and fully matured water caltrop were<0.92 g/cm~3,1.00g/cm~3～1.09 g/cm~3 and>1.10 g/cm~3,respectively.The average static friction coefficients of water caltrop with PU,cast stainless steel and rubber were 0.48,0.45 and 0.52,respectively,and the average dynamic friction coefficients with the three materials were 0.39,0.36 and0.44,respectively.The SEM test of water caltrop shell microstructure was carried out.The results of electron microscope scanning test conjectured that it is relatively easy to cut the shell from the umbilicus of water caltrop under the same conditions,and the shell of crispy water caltrop is easier to remove than that of fully matured.(2)The mechanical properties of water caltrop were studied.The failure load,deformation,compressive strength and elastic modulus of three mature water caltrop under two compression directions were obtained,and the failure load,deformation,shear strength and shear modulus of three mature water caltrop under two shear directions were obtained.The test showed that the maturity has a significant effect on all the test indexes of compression and shear of water caltrop,and the loading direction only has a significant effect on the deformation,elastic modulus and shear modulus.The crack formation and propagation law of the sample during the test were analyzed.The crack of water caltrop vertical compression was generated from the umbilicus and runs through the pedicle from top to bottom.With the increase of water caltrop maturity,the width of the crack increases,and the crack propagation has a certain direction as a whole.The crack of horizontal compression was generated from the water caltrop pedicle and propagates around,and the crack propagation has a certain randomness.The crack propagation along both sides of the shear stress point during the shear of water caltrop had a certain directionality,and there was no significant difference in the crack width between the samples with different maturity.The stress-strain nephogram of water caltrop under load was obtained through the finite element simulation results,which verified the inference of the crack generation and propagation law of water caltrop under stress by the mechanical characteristic test,and proved that water caltrop were anisotropic in compression and shear.(3)An innovative scheme of mechanical shelling of fresh water caltrop combining cutting and grinding was proposed.According to the test data of physical parameters and mechanical properties of water caltrop,the shelling bench was designed and the bench test was carried out.On the basis of the feedback of bench test,three shelling technical schemes were put forward,and the shelling mode of combining shear and extrusion rubbing and tearing was determined.The overall scheme included grading-shell cutting machine and clamping shelling machine.The grading-shell cutting machine of water caltrop was designed,and its key components such as grading drum,conveyor belt,baffle group,pressing device and shell cutting blade were designed and analyzed.The clamping shelling machine was designed,and the structure design and stress analysis of the clamping plate,elastic pressing device,corner cutting blade and shelling device were carried out.Using EDEM and Solid Works motion,the dynamic simulation of the grading mechanism,shell cutting mechanism,the corner cutting mechanism and sheller mechanism were carried out.The results showed that there is no interference between the main mechanisms and the operation is stable.(4)The formation and propagation mechanism of shelling crack of fresh water caltrop was studied innovatively.The equilibrium differential equation,geometric equation and physical equation of water caltrop shell under the external force of the cutter were established based on the Boundary Element Theory.Combined with the fracture mechanics theory of linear elastic materials,the formation mechanism of the surface crack of the water caltrop shell during shelling was analyzed.The crack propagation conditions of water caltrop shell were analyzed.Combined with the measured data of physical parameters and mechanical property test data of water caltrop,the average critical stress and critical external force of water caltrop shell crack propagation were 0.17 MPa and 6.22 N,respectively.ANSYS Explicit Dynamics module was used to simulate the shelling process of water caltrop,and the variation laws of force,deformation and energy in the shelling process were explored.(5)The prototype of water caltrop sheller was trial produced,and the grading conveying test,longitudinal cutting test,transversal cutting test and shelling test were carried out in turn.The grading test showed that the optimal working parameters are the drum speed of 55 r/min and the feeding amount of 0.04 kg/s.The parameter verification showed that the average grading accuracy is 92.87%and the average grading efficiency is46.32 kg/h.The conveying test showed that the optimal working parameters are the conveying speed of 0.1 m/s and the distance difference of guide baffle of 200 mm.Under this parameter,the average conveying success rate was 93.21%.The longitudinal cutting test showed that the optimal working parameters are crisp matured,conveying speed of 0.1m/s and blade speed of 900 r/min.It is verified that the average shell cutting rate is 72.23%and the average damage rate of kernel is 10.85%.The transversal cutting test showed that the optimal working parameters are crisp matured,conveying speed of 0.1 m/s and blade speed of 1000 r/min.The verification showed that the average shell cutting rate is 79.41%and the average kernel loss rate is 9.82%.The shelling test showed that the optimal working parameters are crisp matured,slow roll speed of 59 r/min and linear speed ratio of 1.5.It is verified that the average shelling rate is 66.52%and the average damage rate of kernel is12.83%. |
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