| Cotton stalk scrimber as a new type of artificial plate,made of transversely loose and intertwined cotton stalk beams without axial breakage which obtained after defibering and peeling,was processed through a series of procedures such as drying,sizing,paving,hot pressing and so on.However,peeling of the cotton stalk by manual operation seriously restricts the mechanization level of the cotton stalk scrimber processing.Starting with structures and mechanical properties of cotton stalks,peeling mechanisms were developed on the basis of theoretical analysis and experimental study of peeling.This study can improve the efficiency of production and promote the effective utilization of biomass resources.The main contents and results of this paper were as follows:(1)Modeling and mechanical properties testing of defibering cotton stalks.In order to analyse the morphological changes of defibering cotton stalks in mechanical peeling state and explore peeling mechanisms,the defibering cotton stalks were simplified as rectangular composite materials composed of xylem and phloem.Taking the middle of the cotton stalks as the research object,according to the characteristics of transversely isotropic materials,all elastic parameters of xylem and phloem mechanical models were obtained by radial compression,axial tension,three point bending test and mechanical theory of composite materials.Experimental results of the xylem and phloem showed that,the radial modulus of elasticity were 118.07 MPa and 127.71 MPa,respectively;the axial modulus of elasticity were 1921.36 MPa and 1964.53 MPa,respectively;isotropic plane Poisson's ratios were all 0.3;isotropic plane shear modulus were 45.41 MPa and 49.12 MPa,respectively;specific surface bending shear modulus were 33.09 MPa and 29.66 MPa,respectively;specific surface Poisson's ratios were less than 0.0793 and 0.0839.(2)Experimental study on peeling and shearing mechanical performance test of cotton stalks in extrusion state.In order to determine reasonable mechanical peeling method and provide the basis for the design of peeling machine,axial and tangential peeling shear strength of cotton stalks was determined using homemade test-bench.Regression model was established between water content,sampling position,loading pressure and peeling shear strength.And the peeling shear strength of different skin attachment lengths was determined.Besides,peeling shear strength after water softening cotton stalk and fresh cotton stalk was compared.The results presented that the sampling location and the loading pressure had significant influence(p < 0.01)on axial and tangential peeling shear strength;the effect of water content on axial and tangential peeling shear strength was not significant(p > 0.05);the interaction between the three factors was not marked(p > 0.05);tangential peeling was better than axial peeling;the peeling shear strength of fresh cotton stalk was small,so the effect was better right after harvesting.It has good effect for mechanical peeling by pressing and rubbing.(3)Design and dynamic simulation of pressing and rubbing machine.In order to make the peeling mechanism exert tangential reciprocating rubbing pressure,a curved groove ball bearing was developed.Taking this as the critical component,pressing and rubbing machine was constructed to realize radial extrusion and swinging and rubbing of cotton stalk from upper and lower work rolls.The motion simulation of the pressing and rubbing mechanism in ADAMS was carried out.The simulation results indicated that the operation speed of the upper and the lower work roller was the same,but the rotation direction was opposite.Moreover,the lower work roll could carry out reciprocating rectilinear motion while rotating.Overall,the design intention was achieved.In order to study the cotton stalk separation principle between xylem and phloem from the pressing and rubbing machine,finite element model of defibering cotton stalks and the designed mechanism was established in ANSYS Workbench.Explicit dynamic analysis has been conducted using LS—DYNA solver.The dynamic peeling process of defibering cotton stalks was simulated.The results showed that the maximum shearing stress on the interface of xylem and phloem in the process of peeling was 3.7207 MPa,which could achieve better separation.(4)Trial-manufacture and carrying capacity analysis of the curved groove ball bearing as the key part of pressing and rubbing machine.The structural performance of the curved groove ball bearing has a decisive influence on the running stability,the accuracy of the rubbing stroke and the reliability during the operation of the pressing and rubbing machine.In order to explore the effect of structural characteristics of curved groove ball bearing on its performance,five positions from the peak to the bottom of the valley in the outer raceway were marked as the research objects.Contact stress was calculated in this five positions between rolling body and the outer ring raceway under different loading force.The contact stress between the rolling element and the outer ring was reduced from peak to bottom but increased along with the loads.Temperature adjustment and vibration characteristic tests were conducted using the self-made curved groove ball bearing bench.The results manifested that the temperature rised along with the increase of loads when the axial force and radial force were between 50 N and 250 N.And the temperature rising curve tended to be gentle and basically reached the thermal equilibrium state after 10 min.In addition,the increase of axial force would cause the stronger vibration of the curved groove ball bearing;and the influence of radial force on vibration was the same as that of axial force,but the effect is not significant.In the range of 40 r/min to 80 r/min,the increase of rotational speed would cause the rapidly strong vibration.(5)Experimental study on the performance of peeling machine.In order to get the best peeling effectiveness,pressing and rubbing machine was trial-produced,which was installed on the fluffer II.It was made as the cotton stalk peeling fluffer with the function of pressing and rubbing.And then,the performance test of this equipment was carried out.In this experiment,the moisture content,feed quantity,spring pressure,peeling roller speed were the experimental factors.The peeling rate and width expansion rate were the test evaluation indexes.Regression model between influence factors and evaluation indexes was obtained using the response surface method.After parameter optimization,the optimal working parameters of the designed pressing and rubbing machine were as follows: moisture content of 93.88%,feeding volume with 2 PCS,compaction spring pressure of 160 N and peeling roller speed of 46.76 r/min.Finally,the peeling rate and the width expansion rate was 81.77% and122.69%,respectively. |
PDF Full Text Request