No description available.

In this work is developed a proposal for extrusion head for extruding plastic wires of small diameter. There is a new conceptual design of cooling, which allows shape extruded products already in the extrusion head and thereby eliminates the need for large cooling tanks. To determine the optimal design is used software named Virtual Extrusion Laboratory, which is used in practice for the simulation of the extrusion process. Then it is experimentally determined behavior of plastic material, when the temperature of the melt in the extrusion head is reduced.

This work is concerned with the processing of pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The processing methods used are injection molding, sheet extrusion, and extrusion blow molding. The TLCPs used are HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties observed for in situ composites in which the TLCP fibrils are generated in elongational flow fields that occur during processing. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors considered include the effect of in situ composite strand properties on the properties of the injection molded composite, the melt temperature used in injection molding, TLCP concentration, and the melt temperature of the TLCP. It was found in this work that microcomposites can be processed by means of injection molding, sheet extrusion, and extrusion blow molding. It was necessary to process the materials at low temperatures to maintain the TLCP fibrils. However, HX6000, the higher melting TLCP allowed higher processing temperatures than Vectra A. When the TLCP fibrils were maintained, the properties of the TLCP reinforced composites did show reduced anisotropy as compared to an in situ composite. The tensile strength of the composites produced by all three methods was about equal. The modulus of the injection molded composites was slightly higher than that of the composite sheets, but the composite sheets showed a lower degree of anisotropy. In all three processing methods the modulus of the TLCP reinforced composite was a function of the modulus of the in situ composite strand used to produce the microcomposite. Therefore, it is recommended that to improve the properties of the microcomposites the properties of the in situ composite strands should be improved. Furthermore, the mechanical properties of the composites increased with increasing TLCP composition. To provide a basis of comparison the properties of the extruded sheets and the injection molded composites were compared to both the predictions of composite theory and the properties of glass reinforced composites. It was found that the modulus of the 10 wt% composites approached the predictions of composite theory, but at higher TLCP loadings the modulus showed negative deviations from the predictions of composite theory. This is believed to be the result of a reduction of fiber aspect ratio due to poor fiber distribution and fiber breakup. The modulus of the TLCP reinforced composites was about the same as the modulus of the glass reinforced composites produced by both sheet extrusion and injection molding. The tensile strengths were slightly lower than that of the glass reinforced composites. It is expected that as the modulus and strength of the reinforcing TLCP fibrils are improved the properties of the TLCP reinforced composites should exceed those of glass reinforced composites. It was concluded that the processing of microcomposites is a viable means of producing composites based on TLCPs and thermoplastics with good mechanical properties and low degrees of mechanical anisotropy. / Ph. D.

The overall objectives of this work were to improve a dual extrusion process (DEP) which is used to blend thermotropic liquid crystalline polymers (TLCPs) with thermoplastics, determine the mechanism by which TLCP morphology is developed in the DEP and to determine the optimal properties possible in composite materials generated from the blends. The DEP consists of two single screw extruders within which the TLCP and matrix material are plasticated separately. The two continuous polymer streams are joined and then mixed in a series of static mixing elements. Composite materials were formed from pelletized pregenerated strands by processing at temperatures below the melting point of the TLCP. The DEP was improved by the addition of a gear pump to the TLCP stream, a multiple port phase distribution system, static mixing design, minimization of residence time, die design, and introduction of thermal control over the entire strand production process. The TLCP material was introduced into the matrix phase by means of a multiple port phase distribution system which injected 12 individual TLCP streams parallel to the flow direction of the matrix stream. This design resulted in improvements in the axial continuity of the TLCP phase during mixing and improved radial mixing as compared with a simple T-injection system. Both Kenics and Koch static mixer designs were evaluated in this investigation and it was found that the use of either could produce similar mechanical property enhancement in the resulting blends provided that an excessive number of elements were not used. Furthermore, it was found that the most stable strand materials were formed when the die was designed with respect to the flow exiting the static mixer elements. For example, a dual strand die with each capillary having an L/D ratio of 1 produced the most stable strands when used with the Kenics mixing elements. Finally, it was found that drawing the molten blend strand in a vertical drawing chimney provided a favorable thermal environment and resulted in much higher draw ratios and high mechanical properties of the strand. The other objectives of this work including the development of morphology and composite materials produced from pregenerated strands is presented in two manuscripts formatted for submission to appropriate journals. Detailed abstracts dealing with these two topics are included therein. / Master of Science

No description available.

CAPES / Um dos processos de manufatura aditiva mais popularesse baseia na fusão e deposição do material. O princípio de funcionamento aplicado nestes equipamentos restringe o fornecimento de matéria-prima, principalmente no mercado nacional, e a gama de materiais aplicáveis. O desenvolvimento de um equipamento capaz de processar o material na forma granulada contribuiria para a popularização do processo e para a ampliação da gama de materiais disponíveis a serem utilizados. Este trabalho descreve o desenvolvimento de um cabeçote de extrusão capaz de processar polipropileno granulado e extrudá-lo em forma de filamento contínuo e controlado. Este foi projetado de forma a reduzir o efeito da degradação sobre o material. Experimentos foram conduzidos a fim de caracterizar o comportamento dimensional dos filamentos gerados e assim permitir o seu melhor controle. A degradação do material no interior do cilindro aquecido foi avaliada por ensaios de espectroscopia no infravermelho e de tração em amostras de filamentos. Os resultados dos experimentos de extrusão mostraram que os filamentos apresentam variação de vazão ao longo do comprimento extrudado, sendo que a sua largura aumenta até atingir um patamar onde estabiliza. Os ensaios de espectroscopia mostram ocorrer degradação dentro do cilindro aquecido, mas os efeitos negativos sobre a resistência mecânica dos filamentos são menos acentuados quando empregando o cabeçote projetado. Concluiu-se que o princípio de extrusão por êmbolo com alimentação granulada é viável, necessitando, no entanto, desenvolver mecanismos de controle da extrusão mais adequados ao processo. / One of the most popular additive manufacturing processes is based on fuseddeposition of the material. The principleapplied to these machines makes difficult to find suppliers of raw materials, especially in brazilian market, and narrow the variety of materials applicable. The development of equipment able to process the material in the granular form will contribute to the process popularization and extension of available material to be used. This work describes the development of an extrusion head capable to process polypropylene granules and extrudeit as continuous and controlled filament. The extrusion head was designed in order to minimize the volume of material to be fused and reduce the effect of material degradation. Experiments were conducted to characterize the dimensional behavior of the filaments generated and thus allow its better control. The material degradation inside the extrusion head was assessed by infrared spectroscopyand its negative effects over filaments strength by tensile tests.The results of the extrusion experiments showed that the filaments have flow variation along the extruded length, following an increasing curve until a value where its average stabilizes. Spectroscopy showed that degradation occurs inside the heated cylinder, but its negative effects on material strength are less intense when using the designed extrusion head. It was concluded that the extrusion plunger principle with granulated feeding is viable for Additive Manufacturing, requiring, however, better control mechanisms of the extrusion to enable the manufacture of uniform and cohesive parts. / 5000

Innerhalb dieser Arbeit wird ein Fertigungsverfahren entwickelt und erprobt, das den additiven Aufbau von großvolumigen faserverstärkten Kunststoffbauteilen in Skelettbauweise erlaubt. Dafür wird ein modifizierter Extruder zusammen mit einer speziellen Kinematik genutzt. Der Fokus liegt auf der Analyse des Einflusses der Steuergrößen auf geometrische und mechanische Eigenschaften, sowie Haftung im Bauteil. Hinsichtlich der geometrischen Eigenschaften wird ein Prozessmodell entwickelt, das die Abhängigkeit der Strangbreite und -höhe von den Steuergrößen darstellt. Durch experimentelle Untersuchungen werden die Prozessgrenzen und an diesen auftretende Effekte ermittelt. Das Verfahren weist hier große Freiräume auf. So können z.B. mit einer 1 mm Düse Strangbreiten von 1,2 bis 3,2mm erzielt werden. Die mechanischen Eigenschaften in Strangrichtung erreichen im 3D-Druck annähernd die Steifigkeit und Festigkeit der Spritzgießreferenz. Prozessbedingt ist eine Porosität im Material nicht ganz vermeidbar, allerdings sind die Fasern stark ausgerichtet und die Faserlänge im Granulat bleibt im Prozess weitestgehend erhalten. Mittels direktem 3D-Drucken auf endlosfaserverstärktes Tape kann mit Vorheizen des Tapes ein guter Haftverbund generiert werden. Ergänzend wurden zwei Komponenten entwickelt, die für eine Industrialisierung des Prozesses entscheidend sind: Zum einen wurde ein neues Düsenkonzept vorgestellt, das eine schnelle Anpassung des Massestroms während des 3D-Druckens ermöglicht. Zum anderen wurde eine Temperierdüse vorgestellt, mit der mittels Konvektion der abgelegte Strang gekühlt bzw. erhitzt werden kann.:1 Einleitung 2 Zielstellung 3 Literaturübersicht 4 Konzeption eines neuartigen 3D-Druck-Verfahrens 5 Analyse der kinematischen Eigenschaften 6 Betrachtung der Haftungsmechanismen 7 Untersuchung der mechanischen Eigenschaften 8 Weiterentwicklung von Anlagenkomponenten 9 Zusammenfassung und Ausblick / In this thesis, a manufacturing process is presented which enables the additive manufacturing of largevolume fibre-reinforced plastic components in skeleton construction by using an extruder together with special kinematics. The focus is on the analysis of the influence of the control variables on geometric and mechanical properties, as well as adhesion in the component. With regard to the geometric properties, a process model is being developed that shows the dependence of the strand width and height on the control variables. Experimental investigations are used to determine the process limits and the effects occurring at these limits. The procedure knows here large free spaces, so e.g. with a 1 mm nozzle strand widths of 1,2 bis 3,2mm can be obtained. The mechanical properties in the strand direction in 3D printing approximate the stiffness and strength of the injection molding reference. Due to the process, porosity in the material cannot be completely avoided, however, the fibers are strongly oriented and the fiber length in the granulate is largely retained in the process. Direct 3D printing on continuous fiber-reinforced tape can be used to generate a good adhesive bond by preheating the tape. In addition, two components were developed that are decisive for industrializing the process: On the one hand, a new nozzle concept was introduced that enables rapid adjustment of the mass flow during 3D printing. On the other hand, a nozzle was presented with which the deposited strand can be cooled or heated by convection.:1 Einleitung 2 Zielstellung 3 Literaturübersicht 4 Konzeption eines neuartigen 3D-Druck-Verfahrens 5 Analyse der kinematischen Eigenschaften 6 Betrachtung der Haftungsmechanismen 7 Untersuchung der mechanischen Eigenschaften 8 Weiterentwicklung von Anlagenkomponenten 9 Zusammenfassung und Ausblick