Weld lines in extrusion: Understanding the role of the flow conditions

Carneiro, O. S.; Ferrás, Luís Jorge Lima; Teixeira, Paulo Francisco; Fernandes, Célio; Nóbrega, J. M.

doi:10.1063/1.4918887

Cited by 6 publications

(9 citation statements)

References 18 publications

(38 reference statements)

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“…The authors compared the performance of the non-linear Simplex method with a trialand-error procedure, but no conclusion about the best method was clearly reported [151]. The optimization results were assessed experimentally [152,153]. Zhang et al [154] applied a gradient method based on a sensitivity analysis of a response surface obtained from 3D numerical modelling relating the objective function with the design variables, to optimize an L-shape profile die.…”

Section: Mandrel Diesmentioning

confidence: 99%

Optimization of Polymer Processing: A Review (Part I- Extrusion)

Gaspar‐Cunha¹,

Sikora²,

Covas³

2021

Preprint

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Given the global economic and societal importance of the polymer industry, the continuous search for improvements in the various processing techniques is of practical primordial importance. This review evaluates the application of optimization methodologies to the main polymer processing operations. The most important characteristics related with the usage of optimization techniques, such as the nature of the objective function, the type of optimization algorithm, the modelling approach used to evaluate the solutions, and the parameters to optimize, are discussed. The aim is to identify the most important features of an optimization system for polymer processing problems, and define the best procedure for each particular practical situation. For this purpose, a state-of-the-art of the optimization methodologies usually employed is first presented, followed by an extensive review of the literature dealing with the major processing techniques, the discussion being completed by considering both the characteristics identified and the available optimization methodologies. This first part of the review focus on extrusion, namely extruders, extrusion dies and calibrators. It is concluded that there is a set of methodologies that can be confidently applied in polymer processing, with a very good performance and without the need of demanding computation requirements.

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Section: Mandrel Diesmentioning

confidence: 99%

Optimization of Polymer Processing: A Review (Part I- Extrusion)

Gaspar‐Cunha¹,

Sikora²,

Covas³

2021

Preprint

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“…Since the FMM has four model parameters, it is expected to provide additional flexibility in fitting a wider range of complex fluid rheology, particularly for complex fluids such as biopolymer gels for which the zero shear viscosity is indeed unbounded. In order to test this, we have performed a fit with a Maxwell model and both FMM and FVF to the experimental data (G and G ) obtained from the rheological characterisation (Small Amplitude Oscillatory Shear at 230 • C) of a polystyrene extrusion grade, Polystyrol 158K from BASF [56], and the experimental data obtained for the xanthan gum with a concentration of 0.25 wt.% [26] (presented before).…”

Section: Infinite Parallel-series Combination Of Springs and Dashpotsmentioning

confidence: 99%

Theoretical and numerical analysis of unsteady fractional viscoelastic flows in simple geometries

et al. 2018

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In this work we discuss the connection between classical and fractional viscoelastic Maxwell models, presenting the basic theory supporting these constitutive equations, and establishing some background on the admissibility of the fractional Maxwell model. We then develop a numerical method for the solution of two coupled fractional differential equations (one for the velocity and the other for the stress), that appear in the pure tangential annular flow of fractional viscoelastic fluids. The numerical method is based on finite differences, with the approximation of fractional derivatives of the velocity and stress being inspired by the method proposed by Sun and Wu for the fractional diffusion-wave equation [ Z.Z. Sun, X. Wu, A fully discrete difference scheme for a diffusion-wave system, Applied Numerical Mathematics 56 (2006) 193-209]. We prove solvability, study numerical convergence of the method, and also discuss the applicability of this method for simulating the rheological response of complex fluids in a real concentric cylinder rheometer. By imposing a torsional step-strain, we observe the different rates of stress relaxation obtained with different values of α and β (the fractional order exponents that regulate the viscoelastic response of the complex fluids).

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“…When melt flow fronts with such 'skin' meet each other and form weld lines, the actual contact part is the 'skin' of the melt flow fronts which have been cooled in some degree and partially solidified, even there may be a portion of the air encapsulated between the contact surfaces. This kind of weld lines greatly reduce the strength of polymer melt joints and seriously affect the mechanical properties of plastic parts [24,25]. In order to understand the influence of weld lines on the mechanical properties of plastic parts and reduce their adverse influence, researchers have done a lot of research through experiments or simulation methods.…”

Section: Introductionmentioning

confidence: 99%

“…In order to understand the influence of weld lines on the mechanical properties of plastic parts and reduce their adverse influence, researchers have done a lot of research through experiments or simulation methods. Carneiro et al [25] simulated and analyzed the flow behavior of polymer melt in extrusion die with splitter bridge during the weld line formation process and studied the flow type of melt and corresponding stress of splitter bridge position by using Giesekus model and the extended version of OpenFOAM under the assumption of isothermal flow of polymer melt during the whole weld line formation process. The results showed that higher temperature and pressure can improve the mechanical properties of extruded polymers with weld lines.…”

Section: Introductionmentioning

confidence: 99%

“…The results showed that the yield strength, yield strain and failure strain of talc filled PP plastic parts with weld lines increase with the increase of melt temperature and holding pressure. In most cases, higher polymer melt temperature and pressure are helpful to improve the mechanical properties of plastic parts with weld lines [25,26,[28][29][30].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A kind of special weld lines with high specific strength and elongation obtained by core-back chemical foam injection molding

Wu¹,

Zhao²,

Wang³

et al. 2019

Express Polym. Lett.

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In this paper, a kind of polypropylene (PP) foam plastic parts with special weld lines were obtained by core-back foam injection molding with chemical blowing agent. A new kind of weld line was found and its formation process was proposed. The unique principle of the weld lines formation in core-back foam injection molding process was revealed. The surface and internal morphologies, fracture morphologies, cell structure, and mechanical properties of the weld line area of the specimens respectively obtained by core-back foam injection molding and conventional foam injection molding were compared and analyzed. The mechanism of core-back foam injection molding in improving the mechanical properties of the weld line was clarified. The results show that the specimens with special weld lines not only have relatively uniform inner cell structure in size and distribution, but also have a special reticular structure in the weld line area. This reticular structure can not only play a role similar to fiber reinforcement itself, but also increases the bonding degree of polymer at weld lines. Under the action of this special weld line structure, the tensile strength and elongation at break of the specimen are significantly improved, and the weight reduction effect is much better under the premise of ensuring certain mechanical properties.

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Weld lines in extrusion: Understanding the role of the flow conditions

Cited by 6 publications

References 18 publications

Optimization of Polymer Processing: A Review (Part I- Extrusion)

Optimization of Polymer Processing: A Review (Part I- Extrusion)

Theoretical and numerical analysis of unsteady fractional viscoelastic flows in simple geometries

A kind of special weld lines with high specific strength and elongation obtained by core-back chemical foam injection molding

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