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气辅挤出作为一种新型的聚合物材料成型工艺，通过在熔体和口模内壁之间形成一层气体辅助层，使熔体以完全滑移非粘着的方式挤出成型，可有效减小挤出胀大，在精密挤出成型方面有着潜在的应用价值。国内外的研究者在气辅挤出成型方面开展了多年的研究工作，利用数值模拟技术对其成型机理进行了探讨，并搭建了实验系统，取得了颇有成效的研究成果。但是要实现气辅挤出的工业化应用，还必须在以下三方面展开进一步的研究：1）气辅挤出工艺研究；2）气辅挤出口模结构优化设计研究；3）不同物性材料的气辅挤出特性研究。围绕上述三个问题，本文对气辅挤出成型进行了理论和实验研究。 测试了HDPE、PP和ABS的松弛时间及粘流活化能，通过实验研究了气体压力、气体温度、气体流量以及熔体温度对气辅挤出制品质量的影响。实验结果表明，气体压力与熔体压力大致相等是实现稳定气辅挤出的前提条件。当气体压力过大时，气体会穿透熔体，在熔体内部形成气泡，从而对制品质量造成较大影响；反之，则不能形成气辅层。当气体温度低于熔体温度时，粘流活化能大的ABS在气辅挤出中容易出现半固态熔膜现象，堵塞熔体通道，导致挤出缩小；提高气体温度使之等于熔体温度，可在根本上消除半固态熔膜引起的挤出缩小现象。气体流量对实现稳定气辅挤出非常重要，大流量容易引起气体紊流，使挤出物表面产生波纹形状。 利用数值模拟方法研究气辅挤出口模结构优化设计问题。首先采用有限体积法和Navier壁面滑移方程，建立气辅口模内熔体流动的数学模型。然后对熔体在直角形、圆锥形、圆弧形、反向相切形和三次插值形五种入口口模中的流动情况进行对比研究，使用EVSS/SUPG混合有限元技术和汤普森转换考察各口模中压力场、速度场、应力场及挤出胀大的特点，为口模入口设计提供理论指导。最后对熔体在不同滑移段长度口模内的流动进行研究，使用渐变法考察剪切速率、松弛时间对挤出胀大的影响，讨论熔体在滑移段中停留时间、材料松弛时间与挤出胀大比之间的关系，在此基础上，通过理论分析气辅挤出的机理，为滑移段长度设计提供依据。 以HDPE、PP、ABS三种热塑性塑料作为实验材料，对其进行气辅挤出实验研究。使用传统挤出胀大比的实验数据，同时结合数值模拟提出的方程，对气辅挤出制品径向尺寸进行预测，并与气辅挤出实验值进行比较。结果表明，理论计算值与实测值之间非常吻合，证明文中所提出的气辅口模优化设计是有效的。实验中还考察了螺杆转速和熔体温度对挤出制品表面质量及压力降的影响，表明气辅挤出可提高制品表面光滑度和光泽度，降低能耗。 [ Last edited by gyf_2672 on 2008-12-1 at 09:33 ] |
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7楼2008-12-02 08:00:52
lhzt007
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Des out of gas as a new type of polymer material molding process, and melt through the die to form a wall between the gas-assisted, so as to completely melt adhesive non-slip way out of shape, can effectively reduce Swell out of small, precision in the extrusion has a potential value. Researchers at home and abroad in the gas-assisted extrusion carried out many years of research, the use of numerical simulation technology to its forming mechanism was discussed, and set up the experimental system, and achieved fruitful results. But to achieve out of the gas-assisted industrial applications, it is also necessary in the following three areas for further study: 1) out of gas-assisted process; 2) gas-assisted optimization of the structure of extrusion die design; 3) different physical properties of materials, gas Des extrusion characteristics. Focus on these three issues, this article on gas-assisted molding out of the theoretical and experimental research. Tested HDPE, PP and ABS relaxation of the time and energy flow through the experimental study of the gas pressure, gas temperature, gas flow and the temperature of the gas-assisted melt extrusion products quality. The results showed that the gas pressure and melt pressure is roughly equal to achieve stability in the gas-assisted out of a prerequisite. When the gas pressure, gas will penetrate the melt, melt in the formation of air bubbles in-house, which have a greater impact on the quality of products; On the other hand, can not form a gas-assisted layer. When the gas temperature below the melt temperature, the large flow of energy in the gas-assisted ABS out in the semi-solid prone to the phenomenon of membrane fusion, blocking access melt, leading to reduce crowding; raise the temperature of gas to make it equal to melt temperature Can eliminate the semi-solid membrane caused by the melt extrusion to reduce the phenomenon. Gas flow to the realization of stability in the gas-assisted out is very important, the easy flow of gas caused by turbulence, so that out-of corrugated shape of the surface. The use of numerical simulation of gas-assisted method of extrusion die design of structural optimization. First of all, finite volume method and the Navier wall slip equation, the establishment of gas-assisted die melt flow within the mathematical model. Then melt at the right angle-shaped, conical, arc-shaped, reverse-tangent and interpolation of three-five die in the entrance of the flow of comparative studies, the use of EVSS / SUPG mixed finite element technology and Thompson conversion study Die in the pressure field, velocity field, stress field and swell out of the characteristics of the entrance to die design theory. Finally, melt at different length slip die within the flow study investigated the use of gradual rate cut, swollen out of time to relax, discuss melt in the slip paragraph stay, materials relaxation time And swell out of the relationship between the ratio on this basis, through the theoretical analysis of the gas-assisted out of the mechanism for the slip length based on the design. To HDPE, PP, ABS three types of thermoplastics as experimental materials, gas-assisted out of their experimental study. Out of the use of traditional swollen than the experimental data, combined with numerical simulation of the proposed equation, the gas-assisted radial extrusion products to predict the size and gas-assisted out of the experimental values. The results show that the theoretical value and actual value is between the line that the text proposed by the gas-assisted die design optimization is effective. Experiments also inspected the screw speed and temperature of melt extrusion products and the quality of the surface pressure drop, showed that out of gas-assisted products to improve the surface smoothness and gloss, to reduce energy consumption. |
3楼2008-12-01 21:43:05
lhzt007
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4楼2008-12-01 21:49:58
ghx2156
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| Use HDPE, PP and ABS three kinds of hot Su plasticses as to test material, as to it's carry on spirit to assist to extrude an experiment research.Use tradition extrusion the bulge greatly compare of experiment data, combine the equation that number emulation puts forward in the meantime, assist extrusion product path to carry on an estimate to the size to the spirit, and assist with spirit to extrude experiment value to carry on a comparison.Express as a result that the theories computes a value and actually measures an of value to fit together very much and prove a text that assisting a people's mold in the spirit put forward is excellent to turn a design is effective.In the experiment still investigated a Luo pole to turn soon and Rong body temperature degree to extrude product surface the quality and pressure declines of influence, the enunciation spirit assists extrusion to raise the product surface smooth degree and water, lowering can consume. |
5楼2008-12-01 22:08:42