Structure Design And Optimization Of PVC Blown Film Die

PVC material is the second largest industry in the plastic system,with low price,flame retardant,abrasion resistance,chemical resistance,high mechanical strength and good electrical insulation.However,domestic PVC is overcapacity and its advantages cannot be fully applied.Therefore,it is urgent to research the processing and forming of PVC materials.The use of PVC film is extremely broad,and it can be used as a nursery film,a greenhouse film or the like in agriculture,and can also be used as a moisture-proof,waterproof cover film and packaging film in industry.This topic takes PVC film as the research object,and conducts targeted research on PVC film from two aspects of blown equipment and material formula proportion,and provides a certain research basis for the future development of PVC blown die.The specific work is as follows:1.Aiming at the factory existing PVC blown film die structure,numerical simulation was conducted to analyze the melt pressure field,velocity field and shear rate filed in the die.The results show that the distribution of the exit velocity of the existing die is not uniform,and the main reason for this phenomenon is the unreasonable die structure.2.Based on the existing die model,the structure of the diverging section of die was improved,and the influence of the number and size of the blocks on the melt flow filed was discussed.The results show that when the number of flow block is 8 and the width is 16mm,the outlet flow velocity is the most uniform.Based on this,orthogonal design is used to optimize the lengths of the four main parts of the flow path in the die.The objective is to minimize the standard deviation of the outlet flow velocity,and to optimize the maximum pressure show that the optimal geometry of the die channel is:the length of the diverting section is 66mm,the length of the transition section is 60mm,the length of the compression section is 25mm,and the length of the shaping section is 50mm.3.Rheological tests were performed on formulations with different additive contents to study the relationship between additive content and viscosity.Simultaneously,the effects of viscosity and inlet flow on the flow field of the melt in the flow path of the die were simulated.The results show that the more plasticizer,stabilizer and lubricant content,the smaller the melt viscosity.On the contrary,when the content of processing aid increases,the melt viscosity increases;when the viscosity coefficient increases,the pressure drop of the die increasing,the maximum shear rate of the melt decreases,and the outlet flow rate does not change significantly;the inlet pressure and outlet flow rate of the die increase with the increase of the inlet flow rate,and the distribution uniformity of the outlet flow velocity does not change.4.Using the optimized die,the performance of the PVC film obtained by different formulas was experimentally studied.The results showed that the optimized die can obtain the PVC film that meets the requirements.And,as the content of processing aids and lubricants increases,the transverse tensile strength of PVC film increases;the greater the addition amount of plasticizer and processing aid,the greater the longitudinal tensile strength of the film;and the plasticizer and increasing the stabilizer content increases the elongation at break of the film.After a short period of UV light aging,the tensile strength of the film showed an increasing trend.With the aging time increasing,the tensile strength and elongation at break decreased.This result has certain guiding significance for the design of the actual formula.