Study On The Crystallization And Shrinkage Of Injection Molded Products Under Multiple Fields

Crystallization behavior of polymer in injection molding is compounded by temperature field and shear field,which is more complicated than static crystallization,and causes complex shrinkage behavior of polymer,so it is more prone to shrink marks or dimensional instability and other defects.Therefore,this paper studies the relationship between the crystallization of injection molded products and their shrinkage.The main work of this paper is as follows:(1)Propose a polymer in the multi-field composite crystallization model.According to the theory of non-isothermal and shear crystallization,the crystallization behavior of the polymer is decomposed into several continuous isothermal crystallization processes,and the effect of the shear field on the crystal behavior of polymer is introduced in each isothermal stage.The crystallization model of the polymer under the multi-field was established.(2)The crystallization model of the polymer under the multi-field compound condition was used to calculate the crystallinity of the polymer in the injection molding,and the calculated results were verified by experiment.The products were got by traditional injection molding and rapid heat cycle injection molding.The multilayer structure of products was obtained by polarized light microscopy.Based on the simulation analysis,the temperature history and shear history of the polymer during injection molding were obtained,and the crystallinity of the different layers in the multilayered structure was calculated.Based on the XRD we analyzed the crystallinity of each layer in the multilayer structure,the feasibility of the method calculated the crystallinity of products under the multi-field compound process was verified.(3)The relationship between the crystallization and shrinkage of the polymer was analyzed,and the shrinkage of the injection molded product under the multi-field compound was studied.Designed isothermal thermal experiments to prepare polymer samples with different crystallization,and the crystallinity and shrinkage of samples were observed by polarizing microscope,the relationship between crystal morphology and crystallinity was discussed.The relationship between the crystallinity and shrinkage of the polymer was studied,the quantitative relationship between the crystallinity and shrinkage of the product was analyzed based on the results of multi-field composite crystallization,and the relationship between crystal morphology and the degree of crystallinity and shrinkage of product was established.In this paper,a multi-field composite crystallization model was proposed,and the method can be applied to calculate the crystallinity of injection molded products.The results show that the model and method were effective and correct.The relationship between crystal morphology and crystallinity of the polymer and the crystallization and shrinkage of the product was studied.The relationship between the crystalline morphology and crystallinity of the polymer molded product was established.These contents provided a theoretical basis for the prediction and control of crystallization and shrinkage of injection molded products.