Numerical Investigation of Viscoelastic Flow and Swell Behaviors of Polymer Melts in the Hollow Profile Extrusion Process

Mu, Yao; Zhao, Guo Qun; Zhang, Cheng Rui

doi:10.4028/www.scientific.net/amr.97-101.209

Cited by 6 publications

(4 citation statements)

References 8 publications

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“…The viscoelastic stress tensor can be described in terms of the conformation tensor c 𝝉 = G(c − I) ( 5 ) with G is the modulus, which is assumed to be temperature independent. Note that the polymer viscosity 𝜂 p (T) and the relaxation time 𝜆(T) are temperature dependent, that is, G = 𝜂 p (T)∕𝜆(T)…”

Section: Constitutive Equationsmentioning

confidence: 99%

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Numerical Study of Residual Stresses Due to External Cooling in Extruded Polymer Profiles

Spanjaards

Hulsen

Anderson

2022

Macro Theory & Simulations

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Profile extrusion is a production technique to make polymer profiles and hollow tubes. At a certain distance after the die exit the polymer extrudate is guided into a cooling chamber, where the polymer is cooled extensively to set the part dimensions. Uniform cooling in the cooling chamber is required to avoid warpage and twisting of the extrudate due to differential shrinkage. The effect of extrudate cooling on the shape of the extrudate and the residual stresses in the final extrudate product are numerically studied. Two different cases are studied: a 2D axisymmetric problem of a viscoelastic fluid exiting an annular die and a 3D problem of a hollow square shaped die. The extrudate is extensively cooled from a distance L c from the die exit. Extrudate cooling is modeled by subjecting the extrudate to heat loss via convection. For L die < z ≤ L c the Nusselt number Nu is fixed to 1 to represent the part of the extrudate in between the die exit and the entrance of the cooling chamber. For z > L c the Nusselt number is varied to mimic different cooling speeds. The Weissenberg number Wi, the Nusselt number and L c are varied in this work. Results show that for high values of Wi a significant skin-effect of high residual stresses appear near the extrudate edges for high Nusselt numbers and small values of L c . It is also shown that for high Weissenberg numbers the shape of the extrudate is significantly altered due to extrudate swell, when the extrudate is cooled slower. For fast cooling and small values of L c , the polymer does not have time to relax and the elastic stresses are "frozen in." This leads to less extrudate swell but large residual stresses near the extrudate edges.

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Section: Constitutive Equationsmentioning

confidence: 99%

“…The swell behavior and physical properties of polymer melts emerging from a 3D hollow extrusion die is numerically studied by Mu et al, [5][6][7][8] using a multi-mode differential Phan-Thien Tanner (PTT) model. Zhang et al [9] proposed an inverse design method for thin-walled hollow profile extrusion dies.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Residual Stresses Due to External Cooling in Extruded Polymer Profiles

Spanjaards

Hulsen

Anderson

2022

Macro Theory & Simulations

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“…A relatively coarse mesh containing 1536 elements was used in a study of the effects of energy partitioning, flowrate, and convergence angle. The work was extended to include extrudate swell in the same geometry [130], and comparison with experimentally measured velocity fields in a planar step contraction flow [131] at Weissenberg numbers up to 1.39. Reference [132] deals with transient 3D simulation of the flow of a KBKZ fluid using a Lagrangian kinematics formulation with a temperature-dependent pseudotime based on the assumption of a thermo-rheologically simple material.…”

Section: Viscoelastic Flow Simulationsmentioning

confidence: 99%

Computer-aided design and optimization of profile extrusion dies for thermoplastics and rubber: a review

Pittman

2011

Proceedings of the Institution of Mechanical Engineers, Part E:

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A review is provided of issues and techniques in design and optimization of profile extrusion dies for thermoplastics and rubber, with particular emphasis on unplasticized polyvinyl chloride and rubber compounds. Traditional profile die design methods are contrasted with computer-based ones, with respect to efficiency and economic benefits. The main types of die construction are outlined. Physical phenomena relevant to the design and performance of dies are summarized, including: rheology and kinematics of the flow, wall slip, extrusion instabilities, residence time and degradation, extrudate swell, draw-down, and thermal effects. Approaches and strategies for die design are explained, including: flow balancing – with guidance from analytic flow results, the Avoid-Cross-Flow strategy, use of flow separators, and designing for extrudate swell. Published computer simulations of die flow used to assist with design are reviewed. Introducing automatic die design, the structure and elements of a computerized design optimization environment are set out. Key components and options within this are described, including: objective functions, constraints, design variables, optimization algorithms, design parameterization and flow domain meshing, and optimization strategies. Published implementations of computerized profile die design optimization are described. Automatic design optimization is compared with the work of a designer assisted by flow simulations in the industrial environment, showing how substantial reductions in demands on the designer's time are possible. The nature and potential of robust design is outlined, with techniques for its implementation. Conclusions are drawn as to the present state of the art in computer-assisted profile die design and optimization, and potential advances.

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“…Deng [10,11] explored the influence of the length of the micro-tube forming section on the processing. Nevertheless, the conventional molding process for extrusion involves the elastic restoration of the melt in the die by wall shear, which may result in defects such as deformation, extrusion swelling, and melt cracking [20][21][22][23]. Although analysis of the traditional extrusion process can improve the quality of the extrusion product to a certain extent, it is still difficult to solve the above defects.…”

Section: Introductionmentioning

confidence: 99%

Influence of Gas Inlet Slit Width on Gas-Assisted Plastic Micro-Tube Extrusion

et al. 2023

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In the process of the double-layer gas-assisted extrusion of plastic micro-tubes, the external size and surface quality of the micro-tubes are greatly affected by the size of the assisting gas inlet slit inside the mold. Therefore, in this experiment, a two-phase flow model was established based on a compressible gas and a non-compressible melt. The Polyflow finite element solution software module was used to solve the velocity field, temperature field, pressure field, and section size of the melt under the condition of double-layer gas-assisted extrusion in a mold under different gas inlet slit widths. The results show that, with an increase in the width of the gas inlet slit, the melt outlet velocity increases, the surface temperature increases, wall thickness shrinkage increases, and interior diameter expansion increases. In the process of gas-assisted extrusion, the thickness of the air cushion is affected by adjusting the size of the gas inlet slit, and, hence, changes the shape and size of the plastic micro-tubes.

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Numerical Investigation of Viscoelastic Flow and Swell Behaviors of Polymer Melts in the Hollow Profile Extrusion Process

Cited by 6 publications

References 8 publications

Numerical Study of Residual Stresses Due to External Cooling in Extruded Polymer Profiles

Numerical Study of Residual Stresses Due to External Cooling in Extruded Polymer Profiles

Computer-aided design and optimization of profile extrusion dies for thermoplastics and rubber: a review

Influence of Gas Inlet Slit Width on Gas-Assisted Plastic Micro-Tube Extrusion

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