Letteratura scientifica selezionata sul tema "Rotomoulées"

Rotational moulding or rotomoulding is a manufacturing process best suited for producing one-piece, hollow plastic products. The raw materials can be in powder or liquid form with linear polyethylene of varying densities being dominant worldwide. Due to the modest material properties of polyethylene, reinforcement in various forms have been incorporated within the rotomoulded components to improve the performance of these products. With the abundance and eco-friendliness of natural fibre resources, this study has focused on the use of sisal and woodfibres along with linear medium density polyethylene (LMDPE) powder to produce rotomoulded composite components. Tensile and impact properties of the rotomoulded natural fibre-reinforced composites have been determined as a function of fibre content.

Warpage and poor dimensional stability of rotomoulded products are two of the main obstacles to the use of this technique in the production of engineering parts. The knowledge of the effect of the processing conditions on the shrinkage of rotomoulded parts will allow overcoming some of the restrictions of this process. In the present work the influence of the processing conditions on the development of shrinkage and warpage of rotomoulded parts was studied. The moulding of the parts was performed using a rotational moulding machine build at the University of Minho. The shrinkage and the warpage of the moulded parts were assessed using 3D MMC (3D measuring Machine Control) equipment, and understanding the microstructural development.

Rotational moulding (rotomoulding) is one of the fastest growing plastics manufacturing processes using linear polyethylenes dominantly as raw materials. However, due to their modest mechanical properties, rotational moulders worldwide are keen to develop stronger and stiffer materials. In the present study, an attempt was undertaken to apply the concept of microfibril reinforced composites (MFCs) for improving the material performance. Melt blended and subsequently cold drawn and undrawn linear medium density polyethylene (LMDPE) with either poly(ethylene terephthalate) or poly(ethylene naphthalate) possessing MFC structure were mixed with neat LMDPE and thereafter processed via rotational moulding. The rotomoulded samples were characterised morphologically and tested mechanically. The obtained unsatisfactory mechanical characteristics led to the subsequent morphological study which revealed some interesting phenomena for the rotomoulded products containing MFC blends.

This paper describes the development of a new processing technology for rotational moulding of wollastonite microfibre (WE) reinforced polyethylene (PE). Manufacturing wollastonite-polyethylene composites involved blending, compounding by extrusion, and granulating prior to rotational moulding. The properties of the resulting composites were characterised by tensile and impact strength measurements. The results show that tensile strength increases monotonically with the addition of wollastonite fibres, but impact strength is decreased. In addition, the processability is also decreased after adding more than 12 vol% WE because of increased viscosity. The effects of a coupling agent, maleated polyethylene (MAPE), on the mechanical performance and processability were also investigated. SEM analysis reveals good adhesion between the fibre reinforcements and polyethylene matrix at the fracture surface with the addition of MAPE. It is proposed that fillers with small particles with high aspect ratio (such as wollastonite) provide a large interfacial area between the filler and the polymer matrix, and may influence the mobility of the molecular chains.

In day-to-day life, usage of plastics is numerous. It offers variety of benefits compared to other materials in various sectors like house hold applications, agricultural industry, and packaging, etc. There are numerous methods for processing plastics. These include: blow moulding, injection moulding, rotational moulding, transfer moulding and thermoforming. Rotational moulding is a competitive alternative to other plastic manufacturing process, since it offers designers an opportunity to achieve an economic production of stress free products. Many products made by rotational moulding process using linear low density polyethylene (LLDPE) are widely used in outdoor applications such as boats, over head tanks, and car body parts etc. In such applications, fracture properties are considered to be critical from the quality characterization point of view. Selection of appropriate cooling medium plays vital role to enhance the quality of rotomolded products. In this paper, an attempt has been made to investigate the effect of cooling medium on fracture toughness of the rotationally moulded products. Fracture tests are carried out on a compact tension (CT) test specimens prepared as per the ASTM D 6068 (2012). The tests are performed on a universal testing machine. R-curve method is used to determine the fracture toughness (JIC) of rotomoulded products. From the experimental results it is found that rapid cooling method favours better fracture toughness of rotomoulded products. Therefore, it is recommended to use faster cooling aids like water cooling in rotational moulding process to achieve highest fracture toughness.

This research focus on the characterization of banana and abaca reinforced composites obtained by rotational molding process. These composites were fully characterized by means of DSC and mechanical tests (tensile, flexural, impact and DMA), as well as by optical microscopy. Tests presented in this paper aim to the observation of failures occurred in composites, in comparison with those observed in pure polyethylene. This equipment consists in a microtensile tester, equipped with an optical microscope, a camera and specific software for images capture. Tests have been carried out with test samples obtained from rotomoulded parts, at a rate of 1000 μm/min. Differences between both types of fiber have been observed, showing different compatibility of these fibers with the polymeric matrix; treated fiber also shows different failure process. Banana and treated abaca fibers break in the PE matrix, while pull-out effect was observed for abaca fiber.

La thèse traite du suivi du comportement viscoélastique des polymères, notamment le polyuréthane, au cours du processus de rotomoulage réactif, avec pour objectif l’optimisation de la fabrication de réservoirs de type IV pour le stockage d’hydrogène. Un des défis principaux a été la mise au point d’une méthode de suivi en temps réel à l’aide de la technologie ultrasonore, afin de contrôler la viscosité du matériau pendant la polymérisation. Cette technique garantit une répartition homogène et une polymérisation complète du polymère, deux conditions essentielles pour la qualité des pièces produites.L’innovation majeure de cette recherche repose sur l’utilisation des ultrasons, offrant un suivi plus précis de l’évolution des propriétés mécaniques du polyuréthane comparé aux méthodes classiques basées sur la température. Des techniques complémentaires, telles que la rhéométrie, la DMA (analyse dynamique mécanique) et la DSC (calorimétrie différentielle à balayage), ont approfondi la compréhension des propriétés thermomécaniques du matériau, apportant une vision plus détaillée du processus de polymérisation.Cependant, l’intégration de capteurs ultrasonores dans un moule rotatif, qui tourne sur deux axes simultanément, a présenté des défis en raison des contraintes liées à la chaleur et aux vibrations inhérentes au processus de rotomoulage. L’optimisation de cette intégration reste un défi pour une application industrielle. Les objectifs de la thèse ont été partiellement atteints, notamment en démontrant une corrélation claire entre les mesures ultrasonores et les propriétés rhéologiques du polyuréthane. Cette approche permet aussi une meilleure maîtrise des paramètres de production, tels que la température et le temps, réduisant ainsi les coûts tout en améliorant la fiabilité du processus.Néanmoins, des pistes d’amélioration existent. L’intégration des capteurs dans un environnement industriel demeure complexe, nécessitant des recherches supplémentaires pour optimiser leur positionnement et leur résistance aux conditions de production. Il est aussi suggéré de développer des capteurs multiparamétriques capables de mesurer simultanément la viscosité, la température et les modules élastiques pour un suivi encore plus complet du matériau.En conclusion, cette thèse a montré le potentiel significatif de l’utilisation des ultrasons pour améliorer le contrôle et la qualité des produits dans le rotomoulage réactif. Ces avancées ouvrent des perspectives prometteuses pour la production de polymères et de composites de haute performance
The study focuses on monitoring the viscoelastic behaviour of polymers, particularly polyurethane, during the reactive rotational moulding process, with the aim of optimising the production of Type IV tanks for hydrogen storage. One of the main challenges was the development of a real-time monitoring method using ultrasonic technology to control the viscosity of the material during polymerisation. This technique ensures a homogeneous distribution of the polymer and complete polymerisation, both essential for guaranteeing the quality of the produced parts.The innovative aspect of this research lies in the use of ultrasound, which provides more precise monitoring of the evolution of the mechanical properties of polyurethane compared to traditional temperature-based methods. Complementary techniques such as rheometry, DMA (dynamic mechanical analysis), and DSC (differential scanning calorimetry) allowed for a deeper understanding of the thermomechanical properties of the material, offering a more comprehensive view of the polymerisation process.However, integrating ultrasonic sensors into a rotating mould, which revolves simultaneously on two axes, posed challenges due to the heat and vibrations inherent in the moulding process. Optimising this integration remains a critical challenge for industrial applications. The thesis objectives were partially met, notably by demonstrating a clear correlation between ultrasonic measurements and the rheological properties of polyurethane. This approach also allows for better control of production parameters, such as temperature and time, thereby reducing costs and improving process reliability.Nonetheless, areas for improvement remain. Integrating sensors into an industrial environment is still complex, requiring further studies to optimise their positioning and resistance to production conditions. It is also suggested to develop multiparametric sensors capable of simultaneously measuring viscosity, temperature, and elastic moduli to provide more comprehensive material monitoring.In conclusion, this thesis has demonstrated the significant potential of using ultrasound to improve the control and quality of products in reactive rotational moulding, paving the way for advancements in the production of high-performance polymers and composites

Aujourd’hui, la fabrication des turbomachines est conditionnée par des normes de plus en plus restrictives. L'enjeu industriel pour les chercheurs est d'envisager des solutions optimales visant à réduire les sources de perte d'énergie, d'instabilité et du bruit, en particulier l'écoulement de jeu (débit de fuite). Des actions préliminaires ont été élaborées à Arts & Métiers ParisTech sur le rotomoulage du ventilateur axial de refroidissement d'automobile. L'idée de ce travail est d'utiliser la forme creuse induite par le rotomoulage afin de l'exploiter dans le controle de l'écoulement de jeu radial par soufflage rotatif. Pour cela, la virole comporte des trous d'injection orientés de façon à réduire simultanément le débit de fuite et le couple. Dans ce travail, trois parties ont été traité. La première concerne la réalisation du ventilateur par rotomoulage. La deuxième concerne l'étude expérimentale menée dans le banc d'essai ISO 5801. Cette étude comporte la réalisation d'un montage dédié au contrôle par soufflage rotatif, la métrologie menée pour la détermination des performances globales et la caractérisation de la vitesse axiale du sillage proche. La troisième partie traite la modélisation numérique des conditions expérimentales rentables ensuite l'extrapolation du travail vers des taux d'injection importants. Pour ce dernier, on arrive à annuler le débit de fuite avec un gain considérable du couple mettant ainsi le ventilateur en autorotation
Nowadays, the manufacture of turbomachinery is conditioned by more and more restrictive rules. The industrial challenge for researchers has to consider optimal solutions to reduce sources of energy loss, instability and noise, particularly the tip clearance flow (leakage flow rate). Preliminary actions have been developed at Arts & ParisTech on rotational molding process used for the automobile cooling axial fan. The idea of this work is to use the hollow shape induced by rotational molding process in order to exploit it in the control of tip clearance flow through rotary steady air injection. For this, the shroud ring is composed of injection holes oriented in such away to reduce both of leakage flow rate and the torque. In this work, the thesis focuses on three parts. The first concerns the build of the fan by rotational molding process. The second concerns the experimental study carried out in the ISO 5801 test bench. This study involves the realization of drive system dedicated to rotary steady air injection, metrology for performance determination and the characterization of the near wake axial velocity. The third part deals with the numerical modeling of efficient experimental conditions, then the extrapolation of work towards high injection rates. For this latter, it is possible to cancel leakage flow rate with a considerable gain of the torque thus putting the fan in autorotation

An experimental investigation on the aerodynamic performances of thick blades axial-flow fans was carried out in this study. Two fans are considered, the first one is rotomoulded (in plastic) and the second one is milled (in aluminium). Both have exactly the same shape, except that the rotomoulded fan has hollow blades. They were designed from an existing fan (manufactured by plastic injection process) used in the cooling system of an automotive vehicle power unit. As far as shape is concerned, the only difference between the two first fans and the traditional injected fan is the blade thickness, whereas as far as rigidity is concerned, the only difference between the rotomoulded and the milled fans is the ability of the rotomoulded fan to be deformed easier than the milled fan. The aim of this study is to determine on the one hand the influence of the blade thickness and on the other hand the way the deformation of the hollow blades may affect the global and the local performances. The global performances of the fans were measured in a test bench designed according to the ISO 5801 standards. The curve of the aerodynamics characteristics (pressure head versus flow rate) and of the global efficiency are slightly lower for the roto-moulded fan. The wall pressure fluctuations were also investigated for three flow rates: one corresponding to the maximum efficiencies of both fans and the two others corresponding to an under-flow and an over-flow rate. The power spectral density (PSD) levels, are between six and nine times higher for the roto-moulded fan at nominal flow rate. At partial flow rate, however, the PSD levels are close for both fans.

Rotomoulded plastic parts have no internal stresses, as it is a process carried out at lower temperatures than injection moulding and no pressure is applied. The main disadvantage is the high cycle times needed. This paper focuses on reducing this cycle time and in producing a mould using standardized parts. For cycle time reducing, it is proposed to heat the mould by thermal fluid in continuous circulation; heat transfer processes have been studied for over 20 different configurations of the oil’s inlet – outlet, obtaining acceptable results with a manifold with 25 perforations in the front and rear faces. This configuration has been optimized by computational fluids dynamics, allowing reducing heating and cooling time and improving the energetic efficiency and the uniformity of heating. Design, simulations and testing of a 100 mm3 cube have been carried out in order to produce a standardized mould; this mould consists in some standardized parts and a nickel shell, obtained by rapid prototyping and electroforming process. This shell can be removed from the rest of elements in the mould, allowing thus to obtain parts with any other geometry just by changing the nickel shell. An experimental machine for testing has been developed as well.