The Effect Of Extrusion Pre-forming On Foaming Quality Of Molded Sheet Of Recycled Plastics

Recycled plastics reuse is one of the important ways of resource recycling,which plays an important role in resource saving and environmental protection.The compression molding foaming sheet of recycled plastics is one of the products which can be produced by recycling plastics.At present,the production process of recycled plastics compression molding foaming sheet in the factory is as follows: mixing with internal mixer → thight roll preforming with three two-roll open mills → sheet cooling→laminating → foaming with compression molding machine → slicing.However,the method of sheet preforming with two-roll open mill is low efficiency,complex process and laborious operation.However,the extrusion method for preforming sheet with melt extruder can effectively overcome the defects of the above procedures,but there are still some quality problems in final compression molding forming products,such as hard particles,low rate of foaming and uneven cell size.It can be inferred that the poor dispersive mixing effect of the screw configuration of the melt extruder is the main reason for the quality defects of the foamed sheet.Therefore,it is of great significance to design a new type of screw which meets the requirements of high dispersion and strong mixing for producing high quality foamed sheet and improving the production efficiency of recycled plastics extrusion preforming sheet.The research contents and results are as follows:(1)Through the theoretical analysis,a new type of screw is designed based on the original screw configuration.By combining the elongational mixing mechanism with the barrier screw,a mixing section with a strong elongational flow field is added between the feeding section and the extrusion section,which solves the problem that the high molecular weight polymer fractions in the recycled plastics are difficult to melt and improves the dispersion effect of fillers in the mixture.(2)The finite element analysis software POLYFLOW is used to conduct numerical simulation analysis of the two kinds of screw.The results show that,compared with the original screw,the elongational and shear mixing effect of the new screw is greater,the increase of mixing index is closer to 1.(3)By designing the experimental formula of different recycled plastics(PE)content,the new screw and the original screw were experimentally compared and studied.The experimental results show that the dispersive mixing and melting capacity of the new screw is obviously higher than that of the original screw,and the aggregation of gels and fillers in the preformed sheet is significantly reduced;After molding and foaming the preformed plate,the appearance and quality of the foamed plate obtained by the new screw are obviously improved,and 100% recycled material can be foamed normally;The extrusion capacity of the new screw is about 3.6% higher than that of the original screw.The extrusion temperature of the new screw is about1.7% higher than that of the original screw.The power consumption of the new screw is about 10% higher than that of the original screw.