Evaluation of a model describing the advancing flow front in injection moulding / F. Pisciotti in INTERNATIONAL POLYMER PROCESSING, Vol. XVII, N° 2 (06/2002)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XVII, N° 2 (06/2002) . - p. 133-145 Titre : Evaluation of a model describing the advancing flow front in injection moulding Type de document : texte imprimé Auteurs : F. Pisciotti, Auteur ; A. Boldizar, Auteur ; M. Rigdahl, Auteur ; G. Aronsson, Auteur ; M. Rigdahl Année de publication : 2002 Article en page(s) : p. 133-145 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : The simulation of the advancing flow front during mould filling in the injection moulding cycle is important as a way of anticipating manufacturing defects, particularly different types of welds, air traps, cold spots and hot spots. The purpose of the present work was to evaluate a model (the distance model) simulating the advancing flow front and predicting potential issues related to the progression of the flow front such as welds and air traps. The distance model is based on a mathematical theory of Hele-Shaw flow for strongly shear-thinning fluids, i. e. fluids with a power-law index, n, equal to 0,3 or preferably less. Two grades of general-purpose polystyrene were selected according to their abilities to shear thin (weakly or moderately strong) at the selected processing temperature and in the typical shear rate range of the injection moulding process. The two grades were injection moulded into twelve mould configurations derived from two similar single-gated moulds. The flow length from the gate to the weld was measured in the mouldings obtained at three distinct rates of filling (conventional, slower and faster) and compared to the flow lengths obtained by the distance model. Good agreement was found between the predicted flow lengths and the experimental flow lengths at the conventional and faster filling conditions. Larger deviations between simulation and experiment were found at the slower filling rate, particularly for the weakly shear-thinning polystyrene grade. Some comparisons were also made with the predictions obtained using the commercial simulation code Moldflow. A comparison between the advancing front predictions of the distance model and experimental short shots of a commercial polypropylene grade in a lure-box type of mould geometry showed that the distance model, despite its simplicity, could probably be used to detect welds and air traps in more complex and practice-related mouldings. Note de contenu : - INTRODUCTION : Manufacturing defects related to mould filling - The distance model - - EXPERIMENTAL : Materials - Mould geometry - Processing - Flow length measurement - RESULTS AND DISCUSSION : Weld detection - The advancing flow front - A practice-related moulding DOI : 10.3139/217.1682 En ligne : https://drive.google.com/file/d/15mW8TQTMJGeBpUZ0EWylo9zGHAYQhFm4/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=15942 [article]

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Extrusion coating with metallocene-catalysed polyethylenes / N. Toft in INTERNATIONAL POLYMER PROCESSING, Vol. XVII, N° 3 (09/2002)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XVII, N° 3 (09/2002) . - p. 244-253 Titre : Extrusion coating with metallocene-catalysed polyethylenes Type de document : texte imprimé Auteurs : N. Toft, Auteur ; M. Rigdahl, Auteur Année de publication : 2002 Article en page(s) : p. 244-253 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : During recent years, the interest in metallocene-catalysed polyethylenes has been steadily increasing. These polymers are generally characterised by a narrow molecular weight distribution and a uniform comonomer distribution. In extrusion coating, the interest in these polymers is mainly related to the enhanced physical performance of the resulting film. However, from the processing point of view, the metallocene-catalysed polyethylenes can present problems. In this study, a number of metallocene-catalysed linear low-density polyethylenes (m-LLDPE) were characterised with regard to their viscous and elastic properties. Conventional grades of LDPE and LLDPE were included as references. The same grades were used in pilot scale extrusion coating experiments. The processability of the polymers was primarily expressed in terms of neck-in (NI), which describes the lateral reduction of the film width as the film is drawn down into the coating nip, and the draw-down ability (DD), which provides a measure of the ability of a thin film to be drawn into the nip at a high machine speed. A lower NI-value, which is desirable, was noted when the polymer melt exhibited a higher elasticity, expressed in terms of the steady state compliance, the extrudate swell and Trouton's ratio. Factors that had a positive effect on the NI-value tended in general to reduce the draw-down ability. A relation between NI and DD was established, which in principle makes it possible to optimise both NI and DD, based on finding the optimal values of the shear and the elongational viscosities. The results obtained indicate that a low shear viscosity and a high Trouton's ratio provide optimal processability with regard to NI and DD. It was noted that m-LLDPE-grades could be chosen to match the processability of more conventional polymers (expressed in terms of NI and DD). Rheology can be an important tool for such a selection. Note de contenu : - Introduction : Extrusion coating process - Aim of the present study - Experimental : Materials - Methods - Capillary viscometer measurements - Dynamic-mechanical analysis - Thermal analysis - Extrusion coating - Results and comments : Thermal analysis - Shear viscosity of the polymer melts - Extensional viscosity of the polymer melts - Extrudate swell behaviour - Dynamic-mechanical properties of the melts - Extrusion coating results DOI : 10.3139/217.1690 En ligne : https://drive.google.com/file/d/11BHcCOoi3xQmnVmkjIA3GTZJ9X_dhFYT/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=16000 [article]

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In situ studies and simulations of mould filling with a model system for PIM / H. Persson in INTERNATIONAL POLYMER PROCESSING, Vol. XXIV, N° 5 (11/2009)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXIV, N° 5 (11/2009) . - p. 406-413 Titre : In situ studies and simulations of mould filling with a model system for PIM Type de document : texte imprimé Auteurs : H. Persson, Auteur ; M. Jenni, Auteur ; L. Nyborg, Auteur ; M. Rigdahl, Auteur Année de publication : 2009 Article en page(s) : p. 406-413 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : The processing conditions and the mould design are important parts of the powder injection moulding (PIM) process. In the present work, the mould filling phase of the process has been studied in situ with a special mould equipped with a sight glass using a high speed camera. Effects of features such as the mould temperature, the melt temperature, the surface roughness of the mould cavity, the gate dimensions, the mould design and the flow rate on the filling behaviour were demonstrated. In particular it was noted that a rougher mould surface to some extent facilitated the filling of the mould. The mould temperature, the nominal melt temperature and the flow rate affected the position of weld lines via the cooling of the feedstock and the corresponding change of the melt viscosity. The experimentally determined weld-line positions were compared with predictions from numerical simulations performed with the commercial software Moldex3D. The agreement between the experiment and the prediction was in most cases quite fair or good. The in situ observation of the mould filling also provided the possibility to study how the gate dimensions and the flow rate influenced the jetting behaviour. DOI : 10.3139/217.2277 En ligne : https://drive.google.com/file/d/1bh8Bw7shoSxGtRs7jQjZK0MmP9ROwB0A/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=6363 [article]

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Injection moulding and mechanical properties of recovered polypropylene / F. Pisciotti in INTERNATIONAL POLYMER PROCESSING, Vol. XX, N° 3 (09/2005)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XX, N° 3 (09/2005) . - p. 257-264 Titre : Injection moulding and mechanical properties of recovered polypropylene Type de document : texte imprimé Auteurs : F. Pisciotti, Auteur ; M. Rigdahl, Auteur ; A. Boldizar, Auteur Année de publication : 2005 Article en page(s) : p. 257-264 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : This work is a part of a study aiming at assessing the processability of recovered polypropylene in relation to the mechanical and aesthetic performance of as-manufactured and heat aged mouldings. The effects of processing and heat ageing on the mechanical properties of injection-moulded recovered polypropylene were studied here. A similar grade of virgin polypropylene was used as a reference. Multipurpose test specimens were manufactured with a two-cavity mould, according to decoupled moulding procedures. The mouldings were aged at 100 °C for 170 h and 340 h. The stiffness, the strength, the elongation at break and the Charpy impact resistance of asmoulded and heat-treated materials were investigated. The results show that the recovered polypropylene could be processed as the analogous virgin grade. Insignificant changes in the measured properties due to the different filling conditions were observed for each polypropylene used. The stiffness and strength of the recycled polypropylene was systematically 20% lower than that of the analogous virgin grade, whereas the impact resistance of the recycled grade was on average 40% higher than that for the virgin grade. There was no significant difference in the elongation at break of the two materials. After the short ageing period, an increase in stiffness and strength of the materials was observed, together with a sharp decrease in the elongation at break and a modest increase in the impact resistance. This was related to re-crystallisation. The long ageing period reduced the stiffness and strength of the materials but there was no significant change in the elongation at break or in the impact resistance. DOI : 10.3139/217.1887 En ligne : https://drive.google.com/file/d/1TV-Z9jY5eCd9DYlxTh6I8Z2746KA0zeu/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=3062 [article]

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Rheological and thermal properties of a model system for PIM / H. Persson in INTERNATIONAL POLYMER PROCESSING, Vol. XXIV, N° 2 (05/2009)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXIV, N° 2 (05/2009) . - p. 206-212 Titre : Rheological and thermal properties of a model system for PIM Type de document : texte imprimé Auteurs : H. Persson, Auteur ; B. Hausnerova, Auteur ; L. Nyborg, Auteur ; M. Rigdahl, Auteur Année de publication : 2009 Article en page(s) : p. 206-212 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : Powder injection moulding (PIM) is an important and accepted industrial technique for net shaping of precision components which can have a rather complex geometry. In order to meet the imposed, often rather strict, requirements with regard to dimensional accuracy, it is important to have an adequate knowledge and control of the rheological behaviour and the related processing properties of the powder/polymer melt (feedstock). Such a knowledge is furthermore of crucial importance in numerical simulations of the PIM-process. In the present work, a model system, consisting of steel powder, poly(ethylene glycol) and wax, is used in order to illustrate how the viscometric properties as well as thermal properties, such as the conductivity and the specific heat, of the system can be related to the corresponding properties of the polymeric binder system. In a similar way, the pvT (pressure-volume-temperature)-behaviour of the model system is analysed and discussed. The pvT-behaviour, which has not been extensively reported on for PIM-feedstocks, is considered to be of significant relevance for controlling the outcome of the injection moulding process. DOI : 10.3139/217.2243 En ligne : https://drive.google.com/file/d/1SBzSGhRN83l7dg6qNTRIYDFr_ompnmHg/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=5253 [article]

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The gloss of injection-moulded recovered polypropylene / F. Pisciotti in INTERNATIONAL POLYMER PROCESSING, Vol. XX, N° 3 (09/2005)  

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