聚合物气体辅助挤出成型工艺及数值模拟
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摘要
挤出成型是塑料成型加工的重要成型方法之一,但由于聚合物熔体的高粘性、粘弹性,传统挤出成型时存在易出现挤出胀大、挤出口模压降大、挤出物表面缺陷等缺点。以上三大难题严重影响了挤出制品精度、限制挤出速度提升、导致挤出能耗高。气辅挤出是一种新型的挤出成型技术,它是通过气体辅助控制系统和气体辅助挤出口模,使挤出时在挤出口模壁面形成一层稳定的气垫膜层,挤出由非滑移粘着剪切口模挤出方式转换为完全滑移非粘着剪切口模挤出方式,从而将口模壁面对挤出熔体的阻力降到较低限度。
首先,本文归纳总结出气体辅助挤出成型机理和工艺设计的基本原则。针对气辅完全滑移挤出成型过程和特点,基于流变学和流体动力学理论,经合理假设,建立了描述气辅完全滑移挤出成型过程的全三维稳态等温粘性理论数学模型。
其次,通过UG、GAMBIT等三维造型软件进行几何建模和网格划分,以壁面剪切应力为零的边界条件代替气垫膜层作用,自由表面采用三维网格优化法,利用CFD有限元软件POLYFLOW分别对工型材口模和钢骨架塑料复合管口模的气辅挤出过程进行了数值模拟,得到气辅挤出成型口模内外的速度场、压力场和剪切速率的分布,并和传统挤出过程进行了对比。
结果表明,气辅挤出技术可基本消除挤出成型中的挤出胀大和变形,减小压降。因此,气辅挤出技术不仅可实现挤出制品尺寸的精确控制,而且还起到节能降耗的效果。为挤出的高速化生产实现提供了技术前提条件。
Extrusion is one of the basic methods in polymer poreessing. However, in normal extrusion, several problems appear. Firstly, due to the high viscosity and viscoelasticty of polymer melts, appears in extrusion the die swell which makes it more difficult to enhance the precision of extruded products. The next is the lagre pressure drop which leads to high energy consumption and the third is the appearing of surface disfigurement, which astricts the efficiency of extrusion. Gas-assited extrusion is a new type of technology on polymer extrusion. It provides a gas layer between the melt and die wall, so the flow boundary of extruded melt changes to full slip in the die and the friction between the melt and die wall is thereby reduced greatly.
Firstly, this paper, summarizes the gas-assisted extrusion mechanism and the basic principles of process design based on the process and characteristics of gas-assisted full slip extrusion molding and the theories of rheology and hydrokinetics etc., under reasonable assumptions, a full three dimension steady isothermal viscoe theoretical model of describing gas-assisted extrusion molding proeess is established.
Secondly, by UG, GAMBIT and other three-dimensional modeling software for geometric modeling and meshing. Taking the boundary condition of non shear stress as the effect of the gas layer, optimizing the free surface with three dimensional lattice method, the gas-assisted extrusion process numerical simulation of I-type die extrusion and steel framed polyethylene plastic pipe extrusion die was performed by using the POLYFLOW, a kind of CFD finite element software. The velocity field, pressure field and shear rate distributions inside and outside the die were worked out and compared with those simulation results worked out for the conventional extrusion.
The research results showed that the gas-assisted full slip extrusion molding process can almost eliminate extrusion die swell and distort. Therefore, the gas-assisted full slip extrusion molding process can not only implement the automatic and accurate control of production dimention, but also can save energy. And the gas-assisted full slip extrusion molding paves the way to implement the high speed produetion.
首先,本文归纳总结出气体辅助挤出成型机理和工艺设计的基本原则。针对气辅完全滑移挤出成型过程和特点,基于流变学和流体动力学理论,经合理假设,建立了描述气辅完全滑移挤出成型过程的全三维稳态等温粘性理论数学模型。
其次,通过UG、GAMBIT等三维造型软件进行几何建模和网格划分,以壁面剪切应力为零的边界条件代替气垫膜层作用,自由表面采用三维网格优化法,利用CFD有限元软件POLYFLOW分别对工型材口模和钢骨架塑料复合管口模的气辅挤出过程进行了数值模拟,得到气辅挤出成型口模内外的速度场、压力场和剪切速率的分布,并和传统挤出过程进行了对比。
结果表明,气辅挤出技术可基本消除挤出成型中的挤出胀大和变形,减小压降。因此,气辅挤出技术不仅可实现挤出制品尺寸的精确控制,而且还起到节能降耗的效果。为挤出的高速化生产实现提供了技术前提条件。
Extrusion is one of the basic methods in polymer poreessing. However, in normal extrusion, several problems appear. Firstly, due to the high viscosity and viscoelasticty of polymer melts, appears in extrusion the die swell which makes it more difficult to enhance the precision of extruded products. The next is the lagre pressure drop which leads to high energy consumption and the third is the appearing of surface disfigurement, which astricts the efficiency of extrusion. Gas-assited extrusion is a new type of technology on polymer extrusion. It provides a gas layer between the melt and die wall, so the flow boundary of extruded melt changes to full slip in the die and the friction between the melt and die wall is thereby reduced greatly.
Firstly, this paper, summarizes the gas-assisted extrusion mechanism and the basic principles of process design based on the process and characteristics of gas-assisted full slip extrusion molding and the theories of rheology and hydrokinetics etc., under reasonable assumptions, a full three dimension steady isothermal viscoe theoretical model of describing gas-assisted extrusion molding proeess is established.
Secondly, by UG, GAMBIT and other three-dimensional modeling software for geometric modeling and meshing. Taking the boundary condition of non shear stress as the effect of the gas layer, optimizing the free surface with three dimensional lattice method, the gas-assisted extrusion process numerical simulation of I-type die extrusion and steel framed polyethylene plastic pipe extrusion die was performed by using the POLYFLOW, a kind of CFD finite element software. The velocity field, pressure field and shear rate distributions inside and outside the die were worked out and compared with those simulation results worked out for the conventional extrusion.
The research results showed that the gas-assisted full slip extrusion molding process can almost eliminate extrusion die swell and distort. Therefore, the gas-assisted full slip extrusion molding process can not only implement the automatic and accurate control of production dimention, but also can save energy. And the gas-assisted full slip extrusion molding paves the way to implement the high speed produetion.
引文
[1]赵合素,张丽叶,毛立新.聚合物加工工程[M].北京:中国轻工业出版社, 2001: 1-3.
[2]胡晨章.气辅挤出成型机理三维等温粘弹性数值模拟研究[D].南昌:南昌大学(硕士学位论文), 2006: 3-4.
[3]黄兴元.聚合物气体辅助挤出成型的理论及实验研究[D].南昌:南昌大学(博士学位论文), 2005: 1-2.
[4] QU J P, PENG X F, He H Z. Research on Plastic Beheaviors of LDPE Melt during Capillary Dynamic Extrusion[J]. Journal of South China University of Techonlogy (Natural Science), 1998, 26(11): 1-3.
[5]刘瑞霞.塑料挤出成型[ M].北京:化学工业出版社, 2005: 1-3.
[6]鄢超,柳和生,黄兴元,等.聚合物气体辅助挤出成型[J].中国塑料, 2003, 17(11): 15-18.
[7] LAM Y W, RAO K P, XU W L. Advanced Technology for the Design and Manufacture of 3D Extrusion Dies[J]. Hong Kong Institution of Engineers Transactions, 1994, (8): 49-55.
[8]杨卫民,杨高品,丁玉梅,等.塑料挤出加工新技术[M].北京:化学工业出版社, 2006: 105-108.
[9]胡晨章,周国发,谭志洪,等.气辅口模完全滑移挤出成型过程的三维等温黏弹性数值模拟研究[J].工程塑料应用, 2005, 19(1): 14-15.
[10]黄兴元,柳和生,周国发,等.辅助挤出技术在聚合物挤出加工中的应用[J].工程塑料应用, 2005, 33(3): 2-5.
[11]黄兴元,柳和生,周国发,等.气体辅助挤出中影响气垫层形成及稳定性因素分析[J].塑料工程学报, 2005, 12(5): 5-8.
[12]黄兴元,柳和生,周国发,等.气体辅助挤出的实验研究[J].中国塑料, 2005, 19(3): 1-5.
[13]卢臣,柳和生,黄兴元.气体辅助挤出成型技术在塑料异型材中的应用[J].工程塑料应用, 2006, 34(11): 77-79.
[14] HUANG Y. Analysis and Improvement of Die Design for the Processing of Extruded Plastic Pipes[J]. Materials and Design, 2000, 21(5): 465-475.
[15] BRZOSKOWSKI R, WHITE J L, SZYDLOWSKI W, el al. Air-lubricated Diefor Extrusion of Rubber Compunds[J]. Rubber Chemistry and Techonlogy, 1987, 60: 945-956.
[16] LIANG R F, MACKLEY M R. The Gas-assisted Extruison of Molten Polyethlene[J]. Journal of Rheology, 2001, 45(1): 211-226.
[17] LIANG J Z. Estimation of Melt Shear Modulus from Extrudate Swell Ratio and Exit-pressure Drop Data[J]. THERMOPLAST COMPOS, 2004, 17(16): 545-556.
[18] DAWN R A, MALCOLM R M. Sharkskin Instabilities and the Effect of Slip from Gas-assisted Extrusion[J]. Rheologica Acta, 2005, (44): 252-259.
[19]吴舜英.挤出口模内壁面滑移机理研究[J].轻工机械, 2001, (1): 4-8.
[20] LIANG J Z. Quantitative Characterization of Viseoelastic Properties and Their Relationship during Ectrusion Flow of Polymer Melts[J]. Polymer-Plastics Technology and Engineering, 2006, 45(6): 329-334.
[21]周彦豪.聚合物加工流变学[M].西安:西安交通大学出版社, 1998: 56-58.
[22]尹智龙.聚合物气辅共挤成型数值模拟研究[D].南昌:南昌大学(硕士学位论文), 2007: 3-4.
[23] LIANG J Z. A Relationship between Extrudate Swell Ratio and Entry Stored Elastic Strain Energy during Fie Flow of Tyre Compounds[J]. Poly Testing, 2004, 23: 441-446.
[24]古大治.高分子流体动力学[M].四川:四川教育出版社, 1998: 22-30.
[25]蔡奎,周国发,屈娅嘉,等.气辅共挤成型机理的数值模拟研究[J].中国塑料, 2005, 19(4): 57-61.
[26]匡唐清.气体辅助注射成型注气控制系统研制[D].南昌:南昌大学(博士论文). 2002: 32-34.
[27]吴大鸣,李晓林,刘颖.影响挤出成型精密度的因素[J].塑料, 2003, 1(32): 52-57.
[28]李亮,吴大鸣.精密挤出成型研究的新动向[J].塑料, 2002, 1(31): 110-112.
[29]周持兴,俞炜.聚合物加工理论[M].北京:科学出版社, 2004: 10-38.
[30] TOME M F, MANGIAVACCHI N, CUMINATO J A. A Finite Difference Technique for Simulation Unsteady Viscoelastic Free Surface Flows[J]. Non-Newtonian Fluid Mech, 2002, (106): 61-106.
[31]侯万国,罗迎社.流变学进展[M].山东:山东大学出版社, 2006: 12-18..
[32]马文琦,孙红镱.塑料成型模拟软件技术基础与应用[M].北京:中国铁道出版社, 2006: 147-149.
[33] PENG J, CHENG J N. Numerical Simulation of Polymer Melt Conveying in Co-Rotating Twin Screw Extruder[J]. Journal of Being Institute of Technology, 2002, 11(2): 189-192.
[34]徐佩弦,高聚物流变学及其应用[M].北京:化学工业出版社, 2004: 55-61.
[35] GAREIA-REJON A, DIRADDO R W, RGAN M E. Effect of Die Geometry and Flow Charaeteristics on Viscoelastic Annular Swell[J]. Non-Newtonian Fluid Mech, 1995, (60): 107-128.
[36]钱百年,童玉清,汪传生,等.气膜润滑剪切机头及其在短纤维增强胶管中的应用[J].橡胶工业, 1997, 44(6): 323-326.
[37]金光日.聚合物加工流变学基础[M].北京:化学工业出版社, 1996:35-42.
[38]黄兴元,柳和生,周国发,等.聚合物气辅挤出的挤出胀大研究[J].塑料工业, 2005, 33(7): 32-35.
[39]唐志玉.挤塑模具设计[M].北京:化学工业出版社, 1997: 6-10.
[40]孙红镱,马文琦.钢骨架塑料复合管技术[M].哈尔滨:哈尔滨工业大学出版社, 2003: 4-5.
[41] VISHAL G, KURT W K. Gas-assited Displacement of Viscoelatic Fluid: Flow Dynamics at the Bubble Front[J]. Non-Newtonia Fluid Mch, 1999, 83(3): 183-203.
[2]胡晨章.气辅挤出成型机理三维等温粘弹性数值模拟研究[D].南昌:南昌大学(硕士学位论文), 2006: 3-4.
[3]黄兴元.聚合物气体辅助挤出成型的理论及实验研究[D].南昌:南昌大学(博士学位论文), 2005: 1-2.
[4] QU J P, PENG X F, He H Z. Research on Plastic Beheaviors of LDPE Melt during Capillary Dynamic Extrusion[J]. Journal of South China University of Techonlogy (Natural Science), 1998, 26(11): 1-3.
[5]刘瑞霞.塑料挤出成型[ M].北京:化学工业出版社, 2005: 1-3.
[6]鄢超,柳和生,黄兴元,等.聚合物气体辅助挤出成型[J].中国塑料, 2003, 17(11): 15-18.
[7] LAM Y W, RAO K P, XU W L. Advanced Technology for the Design and Manufacture of 3D Extrusion Dies[J]. Hong Kong Institution of Engineers Transactions, 1994, (8): 49-55.
[8]杨卫民,杨高品,丁玉梅,等.塑料挤出加工新技术[M].北京:化学工业出版社, 2006: 105-108.
[9]胡晨章,周国发,谭志洪,等.气辅口模完全滑移挤出成型过程的三维等温黏弹性数值模拟研究[J].工程塑料应用, 2005, 19(1): 14-15.
[10]黄兴元,柳和生,周国发,等.辅助挤出技术在聚合物挤出加工中的应用[J].工程塑料应用, 2005, 33(3): 2-5.
[11]黄兴元,柳和生,周国发,等.气体辅助挤出中影响气垫层形成及稳定性因素分析[J].塑料工程学报, 2005, 12(5): 5-8.
[12]黄兴元,柳和生,周国发,等.气体辅助挤出的实验研究[J].中国塑料, 2005, 19(3): 1-5.
[13]卢臣,柳和生,黄兴元.气体辅助挤出成型技术在塑料异型材中的应用[J].工程塑料应用, 2006, 34(11): 77-79.
[14] HUANG Y. Analysis and Improvement of Die Design for the Processing of Extruded Plastic Pipes[J]. Materials and Design, 2000, 21(5): 465-475.
[15] BRZOSKOWSKI R, WHITE J L, SZYDLOWSKI W, el al. Air-lubricated Diefor Extrusion of Rubber Compunds[J]. Rubber Chemistry and Techonlogy, 1987, 60: 945-956.
[16] LIANG R F, MACKLEY M R. The Gas-assisted Extruison of Molten Polyethlene[J]. Journal of Rheology, 2001, 45(1): 211-226.
[17] LIANG J Z. Estimation of Melt Shear Modulus from Extrudate Swell Ratio and Exit-pressure Drop Data[J]. THERMOPLAST COMPOS, 2004, 17(16): 545-556.
[18] DAWN R A, MALCOLM R M. Sharkskin Instabilities and the Effect of Slip from Gas-assisted Extrusion[J]. Rheologica Acta, 2005, (44): 252-259.
[19]吴舜英.挤出口模内壁面滑移机理研究[J].轻工机械, 2001, (1): 4-8.
[20] LIANG J Z. Quantitative Characterization of Viseoelastic Properties and Their Relationship during Ectrusion Flow of Polymer Melts[J]. Polymer-Plastics Technology and Engineering, 2006, 45(6): 329-334.
[21]周彦豪.聚合物加工流变学[M].西安:西安交通大学出版社, 1998: 56-58.
[22]尹智龙.聚合物气辅共挤成型数值模拟研究[D].南昌:南昌大学(硕士学位论文), 2007: 3-4.
[23] LIANG J Z. A Relationship between Extrudate Swell Ratio and Entry Stored Elastic Strain Energy during Fie Flow of Tyre Compounds[J]. Poly Testing, 2004, 23: 441-446.
[24]古大治.高分子流体动力学[M].四川:四川教育出版社, 1998: 22-30.
[25]蔡奎,周国发,屈娅嘉,等.气辅共挤成型机理的数值模拟研究[J].中国塑料, 2005, 19(4): 57-61.
[26]匡唐清.气体辅助注射成型注气控制系统研制[D].南昌:南昌大学(博士论文). 2002: 32-34.
[27]吴大鸣,李晓林,刘颖.影响挤出成型精密度的因素[J].塑料, 2003, 1(32): 52-57.
[28]李亮,吴大鸣.精密挤出成型研究的新动向[J].塑料, 2002, 1(31): 110-112.
[29]周持兴,俞炜.聚合物加工理论[M].北京:科学出版社, 2004: 10-38.
[30] TOME M F, MANGIAVACCHI N, CUMINATO J A. A Finite Difference Technique for Simulation Unsteady Viscoelastic Free Surface Flows[J]. Non-Newtonian Fluid Mech, 2002, (106): 61-106.
[31]侯万国,罗迎社.流变学进展[M].山东:山东大学出版社, 2006: 12-18..
[32]马文琦,孙红镱.塑料成型模拟软件技术基础与应用[M].北京:中国铁道出版社, 2006: 147-149.
[33] PENG J, CHENG J N. Numerical Simulation of Polymer Melt Conveying in Co-Rotating Twin Screw Extruder[J]. Journal of Being Institute of Technology, 2002, 11(2): 189-192.
[34]徐佩弦,高聚物流变学及其应用[M].北京:化学工业出版社, 2004: 55-61.
[35] GAREIA-REJON A, DIRADDO R W, RGAN M E. Effect of Die Geometry and Flow Charaeteristics on Viscoelastic Annular Swell[J]. Non-Newtonian Fluid Mech, 1995, (60): 107-128.
[36]钱百年,童玉清,汪传生,等.气膜润滑剪切机头及其在短纤维增强胶管中的应用[J].橡胶工业, 1997, 44(6): 323-326.
[37]金光日.聚合物加工流变学基础[M].北京:化学工业出版社, 1996:35-42.
[38]黄兴元,柳和生,周国发,等.聚合物气辅挤出的挤出胀大研究[J].塑料工业, 2005, 33(7): 32-35.
[39]唐志玉.挤塑模具设计[M].北京:化学工业出版社, 1997: 6-10.
[40]孙红镱,马文琦.钢骨架塑料复合管技术[M].哈尔滨:哈尔滨工业大学出版社, 2003: 4-5.
[41] VISHAL G, KURT W K. Gas-assited Displacement of Viscoelatic Fluid: Flow Dynamics at the Bubble Front[J]. Non-Newtonia Fluid Mch, 1999, 83(3): 183-203.