Research On The Design And Parameter Optimization Of PET Preform Heating Device Based On Microwave Technology

PET is the thermoplastic linear polyester,which is a kind of non-toxic and tasteless food packaging material developed after the United States Food and Drug Administration banned PVC for food and drug packaging.Since its inception in the last century,the application scope,production capacity and output of PET bottles are expanding all the time.The two-step stretch blow molding(SBM)is the main technology of PET bottle manufacturing,in which the heating of bottle blank is the key link.In the heating process of PET preform,not only the expected temperature value of preform is required,but also the reasonable temperature difference between the inner and outer sides of its wall is required to meet the stress demand of bottle blowing,which can effectively improve the bottle making speed and bottle quality.At present,the main way of heating the preform is quartz tube heating with many problems,such as high temperature gradient,high energy consumption,long heating time and so on,thus it is urgent to explore an efficient and energy-saving heating method.As a kind of bulk heating method,microwave heating by use of microwave to directly penetrate the material to generate energy loss and enable the overall temperature of the material to rise rapidly,which can effectively avoid many problems caused by surface heating.Therefore,a new type of heating device based on microwave technology is developed in this subject,which will heat PET preform efficiently,quickly and cheaply.The main contents of the study are as follows:1.Feasibility analysis of PET preform heating based on microwave technology.The heating theory of microwave technology and the material properties of PET preform were analyzed,including its dielectric and thermal properties.According to Maxwell's equations and Poynting theorem,the conversion relationship between microwave energy and heat is deduced,and the feasibility of microwave heating PET bottle is theoretically determined.Microwave heating by use of molecular polarization phenomenon to produce thermal effect,so the microwave heating effect of preform is determined by its dielectric properties;while the thermal properties of PET material determine the heating link of bottle billets in bottle making process,and also clarify the temperature requirements of preform heating.2.The size and structure design of PET preform heating device based on the microwave technology,and its simulation optimization.The main devices of microwave heating system,i.e.resonator and waveguide,are designed.Microwave is mainly used to heat polar materials,such as food,medicine and wood.Although PET is a kind of strong polar polymer,the parameter that determines its heating effect,that is,its dielectric constant is not high enough,and conventional microwave equipment cannot heat it efficiently.Therefore,in this study,based on the theory of electromagnetic field,the mode field component of microwave device is deduced as the basis for the selection and design of resonator and waveguide.And its shape type,resonance mode and corresponding size parameter range are determined by combining with the size and structure of PET bottle.In order to achieve better heating effect,the microwave device is further optimized with the help of COMSOL simulation software,that is,the optimal dimensions and coupling structure of the resonator,waveguide and coupling hole are determined.3.Modeling,simulation and experimental results analysis of the PET preform heating device based on microwave technology.In COMSOL,a parametric model is established for the final design of the heating device to simulate the effect of microwave heating,and the visual results of simulation are analyzed,which is determined that the microwave heating device of this study can meet the requirements of temperature distribution and heating efficiency of the preform in the design.According to the design scheme,the resonator and waveguide are produced,and the electrical components are selected to build the experimental platform.The temperature of the heated preform was measured to verify the correctness of the simulation,and the heated preform was blow tested.The thickness of each part of the blown bottle was reasonable,its transparency was good and there was no deformation,which showed that the actual heating effect of the microwave device met the heating requirements of the PET preform.