| Gas-assisted extrusion molding technology is a promising technology developed on the basis of the conventional extrusion molding technology since it can form a thin air cushion film between the polymer melt and the inner wall to reduce the die swell during the extrusion process,therefore it has attracted the attention of scholars and industries.Throughout the gas-assisted extrusion molding study,the former investigations gave more attention to study the shape of the die or control the process of parameters on how it will affect the sizes and cushion stability,rather to the angle of gas intake.This dissertation,mainly focus on the polymer sheet,Through the theoretical analysis and experimental study of gas assisted extrusion molding to reveal how gas intake angle would affect plastic sheet gas-assisted extrusion process,furthermore,have a better understanding of how different polymer material would adapt to different air intake angle.And finally,come up with adequate principles on how to choose gas intake angle when it comes to different material,in order to make a piece of reliable scientific evidence on how to make a better-quality product.The main contents of this dissertation are as follows:(1)The brief story of polymer extrusion molding,its development and improvement.Including the study on the die of gas-assisted extrusion and how it works.As well as the discussion of Rheological theory and experimental model.(2)Conduct a study towards plastic sheet and build a three-dimensional coupled finite element model on sheet gas-assisted extrusion.And divide the model into threephase: port airless auxiliary section,port with gas-assisted section and free-expansion section,and list air as a sole simulation factor;by comparing its change,to prove how the usage of air would improve the traditional method.By building an examination platform,conduct experiment on air and air-free auxiliary extrusion separately,by comparing its result with the control group,to prove the validity and reliability of the Three-dimensional finite element model.(3)To study the effect of the ejection angle,build up six different angle(0°,15°,30°,45°,60°,90°)and apply them into the model,use Polypropylene as examine material and simulate the performs under six different injection angle,analysis the change in pressure,speed and shear rate during the entire process,to find the pattern on how the change of injection angle would play a part in plastic sheet molding result.When the angle is 15°,it would have best perform in reducing the shear rate and eliminate the impact from air to polymer melt.Based on examination of six different angles,and observation of the appearance of the samples,so we can confirm that 15°is the best angle for injection which consists with the result,and furthermore it verifies the correctness of finite element simulation.(4)To further explore the adaptability of different polymer materials to the intake angle,based on six different angles experimental platform,use high-density polyethene as raw material,found out that only when it's 30° can eliminate the die swell of highdensity polyethene,and minimize the shear rate,also improve the quality of polymer products.By comparing these two experiments,come up with the result that in the same experimental condition,polymer products with higher density would need a bigger air intake angle to reduce the expansion. |
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