Research On Test Method And Equipment Of PVT Relationship Of Typical Special Engineering Plastics

With the development of plastic synthesis modification technology,material performance has been greatly improved.Plastics are widely used in many fields."Replacing wood with plastic","Replacing steel with plastic",and "Weight reduction and noise reduction" have become popular trends in the development of international materials.Compared with general plastics,the comprehensive performance of special engineering plastics is more superior.Most of its application environment is relatively special,and it has higher requirements for molding accuracy.The prerequisite for obtaining high-precision qualified products is a clear understanding of the basic characteristics of the material.The PVT relationship of the polymer describes the change of the specific volume of the material with pressure and temperature,and is an important basis for injection molding flow analysis,mold cavity design,process control and process analysis.However,special engineering plastics have a high melting point and a large temperature span,making it difficult to test the PVT relationship of materials.The special testing equipment is required.Aiming at the problems of small amount,low precision,narrow range,and inaccurate data collection and processing of existing PVT relationship testing equipment,this subject innovatively develops a special engineering plastic PVT relationship testing equipment that uses non-toxic low-temperature alloys as the confining-fluid.Use Labview to develop data acquisition software to test and collect PVT data of special engineering plastics under different temperature and pressure conditions.The mathematical model parameters describing the PVT relationship curve are fitted by multiple nonlinear regression analysis.Calculate and improve the material PVT database,and optimize the processing technology through computer simulation technology.The main research results are as follows:1.Contrast and analyze the two test methods and the characteristics of the existing equipment,innovatively propose to use a non-toxic low-temperature alloy as the confining-fluid,and develop a set of equipment that can test the PVT relationship of special engineering plastics under extreme conditions.The upper limit of the pressure test of this equipment is 120MPa,and the temperature range is from room temperature to 400?.Use the equipment to test two types of typical special engineering plastics PPS and PEEK.The PVT measurement results are compared with the DSC test results,and the phase transition temperature ranges of the two correspond well,which proves that the device has high test accuracy.2.Develop and design PVT data collection software through Labview,including three important modules of setting,testing and historical records,which can realize real-time collection,storage and reading of test data.The collection software can obtain the temperature of the heater and the confining-fluid at the same time,combined with the thermal conductivity,to accurately calculate the actual temperature of the sample.For the constant pressure mode commonly used in testing,the software reserves a pressure fluctuation port.By setting the corresponding upper and lower pressure limits,the pressure value during the test is maintained within a reasonable interval,and the accuracy of the test data is improved.In addition,in order to facilitate the collection and observation of test data,according to the different test materials and test needs,we can choose the appropriate test mode,sampling frequency,coordinate indexing,etc.The PVT relationship obtained by the test can lay a foundation for the construction of the domestic polymer material database and the optimization of the material information of mold flow analysis software,making the analysis results more in line with actual production and processing.3.The PVT relationship of the polymer can be expressed quantitatively by mathematical models.The accuracy of the model directly affects the actual application effect of PVT data.The author uses the Tait model and Renner model to fit the test date,and compares with the calculated results in the three temperature zones.Taking RMSE and MAE as measurement indicators,it is verified that the two types of models have good fitting accuracy for PVT curves.Among them,the Renner model is better for the expression of crystalline polymers in the melting range,and the PVT curve fitted by the Renner model can better reflect the true properties of the material.The study of PVT model fitting accuracy can provide a theoretical basis for polymer injection mold flow analysis and molding control,and provide a reference for technicians to select models.4.Special engineering plastics have higher processing difficulty than general plastics.The PVT relationship of the polymer can be related to the injection molding process,which is conducive to achieving high quality and high repeatability of processing production.The author combines the PVT characteristics of special engineering plastics and uses Moldflow to optimize the injection molding holding pressure process.A constant volume pressure holding scheme is proposed,which is combined with the melt temperature to adjust the pressure holding pressure.Compared with the traditional constant pressure holding pressure,the volume shrinkage and warpage deformation are improved by nearly 50%,which effectively reduces the occurrence of defects such as sink marks and shrink holes,and realizes the precise injection processing of polymer products.