| China is a big country in the production and consumption of fruits and vegetables.In recent years,the total output of fruits and vegetables has consistently ranked first in the world.90%of the total amount of fruits and vegetables are packaged by corrugated boxes.During transportation,Corrugated boxes are subject to impact,vibration,drop,sway,static pressure and resulting in cracks,squeezing,loss and other damage.At the same time,the juice leaked from the fruits and vegetables causes the corrugated cardboard box to invade,accelerating the crushing rate of the corrugated box.According to the above phenomenon,the loss rate of fruit and vegetable storage and transportation in China is 25%to 30%.In view of the current fruit,vegetable and food packaging fields,the ordinary corrugated box has low compressive strength,and has poor functions such as waterproof,moisture proof,gas barrier and heat preservation.In this paper,the calcium plastic corrugated core replaces the common corrugated corrugated core to develop a calcium plastic corrugated box.The key technologies and equipment development of the basic elements of calcium plastic corrugated boxes,namely calcium plastic sheet and calcium plastic corrugated board are researched.The main findings are as follows:(1)The key technologies and equipment have been studied for the production of new calcium-plastic corrugated cardboard.A new type of calcium-plastic corrugated board is developed and supported for subsequent experimental research on new materials.According to the requirements of the production line of corrugated board for adhesives,the formulation of polyacrylate adhesive and waterborne polyurethane adhesive is made and optimized.According to the flat compressive strength of calcium-plastic corrugated board under different temperature and production speed conditions,the optimal parameters of the production process are determined to reach 150 ℃ of heating temperature and 5.5 m/min of production speed.The tooth profile parameters of the corrugated sticks,which are the key components of the calcium-plastic corrugated board production line,are optimized,and the mathematical model of the compression coefficient is established.The optimized compression coefficient is reduced by 0.1801 compared with the existing equipment,which reduces the production cost.Meanwhile,some key equipment of the production line is designed with the overall structure,such as heating roller,drying tunnel,gluing machine and electronic control system,hoping to improve the capacity of paperboard and production line,reduce costs,and provide theoretical basis for process design and production.(2)Research on the optimization of calcium plastic sheet formulation,extrusion processing technology and the analysis and modeling of mechanical properties,and the preparation of calcium plastic sheet which satisfies performance and is inexpensive.Through the orthogonal experiment of calcium plastic sheet base material proportioning,content of modifying agent and coupling agent,compatibilizer research,comprehensive consideration of calcium plastic sheet properties such as tensile strength,impact strength and raw material costs,preparation technology and other factors,to obtain the optimal formula for calcium plastic sheet:HDPE5000S:27wt%;HDPE8008:22wt;CaCO3:49wt%;A-174 coupling agent:2 wt%,according to the weight of calcium plastic sheet material;Extruder barrel temperature,mold temperature and rolling speed in the process of calcium plastic sheet as the main influencing factors of constructing orthogonal test,the test influence calcium plastic sheet material mechanical properties of the main index of tensile strength and impact strength.When the barrel melt temperature is 190℃,mold temperature control at 240℃,rolling roller speed of 140 r/min,calcium plastic sheet comprehensive mechanical properties are the best;Through the comparative study and modeling of the main properties of calciumplastic sheet and kraft paper,it is concluded that the tensile strength of calcium plastic sheet is slightly higher than that of kraft paper.calcium plastic material has a relatively stable yield stage,while kraft paper material breaks directly without this stage.The transverse tension of calcium plastic sheet is 1.6 times that of the longitudinal one,showing anisotropy.Both transverse and longitudinal cyclic compressive strength of calcium plastic sheet are higher than that of kraft paper,and the deformation law was basically similar to that of kraft paper.From this,calcium plastic sheet can replace kraft paper as corrugated board core material,and the strength is greater than kraft paper.(3)Through the comparison of static flat pressing,side pressing,bending and dynamic flat pressing,for calcium plastic,three-layer and five-layer corrugated cardboard,the performance of calcium-plastic corrugated cardboard is higher than that of ordinary corrugated cardboard.At the same time,based on the experimental results,the corresponding model is established.The flat pressure test shows that the linear modulus of the calcium-plastic corrugated board is significantly higher than that of the three-layer and five-layer corrugated board,which are 3.69 times and 1.68 times respectively.The maximum load carrying capacity of calcium-plastic corrugated cardboard is 2.58 times and 2.19 times higher than that of three-layer and five-layer cartons,respectively.And a static model of calcium-plastic corrugated cardboard flat pressure is established.The side pressure test shows that the strength of the calcium-plastic corrugated board is 1.34 times and 1.05 times that of the three-layer and five-layer corrugated board respectively,and a static model of the calcium-plastic corrugated board side pressure is established.The bending experiments show that the vertical bending resistance of calcium-plastic corrugated cardboard is 2.25 times and 1.16 times that of three-layer and five-layer corrugated board respectively,and the parallel bending resistance is 1.26 times and 1.07 times respectively.A curved model of calcium plastic corrugated cardboard was established.On the other hand,the bending resistance of calcium-plastic corrugated board in different directions is quite different,and the strength of vertical direction is 3.16 times of the parallel direction,which reflect the excellent carrying capacity of this new packaging material.The dynamic stress-strain curve of calcium-plastic corrugated cardboard is similar to the static stress-strain curve.It is found that the calcium-plastic corrugated board is sensitive to strain rate.There is a phase difference between the elastic modulus under quasi-static and dynamic loads,which is consistent with the nonlinear viscoelastic-plastic model.According to the law of static and dynamic deformation,a dynamic compression model of calcium-plastic corrugated cardboard is established.(4)Based on the mechanical properties of materials and the orthogonal anisotropic constitutive theory,the anisotropic constitutive relationship between calcium plastic materials and paper materials was obtained.Based on the orthotropic constitutive relation of materials,the finite element model of the calcium plastic corrugated structure is established.The deformation mode and post-buckling behavior of the structure under uniform compression are analyzed.The macro stress-strain curve and the corresponding experimental stress-strain curve is in good agreement,which proves the correctness of the finite element model of the calcium plastic corrugated structure. |
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