Browsing by Author "Bobek, Jiří"

Now showing 1 - 9 of 9
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    Aplikace tepelné trubice ve fázi chlazení procesu vstřikování polypropylenu
    (Technická Univerzita v Liberci, 2007-01-01) Bobek, Jiří; Běhálek, Luboš
    Thermal relations during plastic injection molding affects end-use performance of injection molded parts significantly. These relations are indirectly related with end price of products. This diploma work evaluates aspects of heat pipe application as temperature control system, especcially in concerning with thermal zone in injection mould and mechanical properties and is rationalizing these effects on the bassis of arised microstructure. Heat pipe expectations shot cycle shortening are solved, too.
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    Dýchací maska se společným nádechovým a výdechovým otvorem - výrobní proces v poloprovozním režimu
    (Technická Univerzita v Liberci, 2014-01-01) Běhálek, Luboš; Bobek, Jiří; Habr, Jiří; Lenfeld, Petr; Seidl, Martin; Katedra strojírenské technologie - oddělení tváření plastů
    Tato zpráva se zabývá popisem výrobního procesu dýchací masky se společným nádechovým a výdechovým otvorem v poloprovozním režimu. Tato dýchací maska se skládá z pružné a tuhé části a je navržena pro dvě tvarové varianty vyměnitelných filtrů – kruhový a obdélníkový. Pružná část dýchací masky je současně navržena ve dvou materiálových variantách – silikon a termoplastický elastomer.
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    Influence of different coupling agent type on processibility and applicability of polymer composites
    (Trans Tech Publications Ltd, 2016-01-01) Seidl, Martin; Habr, Jiří; Běhálek, Luboš; Šafka, Jiří; Ackermann, Michal; Bobek, Jiří
    The contribution deals with the processibility and applicability of polymer composite systems based on polypropylene matrix. The composites were filled with vegetable fibres (particularly the cotton fibres, coir fibres, hemp fibres and jute fibres) and the interface between the polymeric matrix and the natural fibres was modified using two types of coupling agents (the organosilane coupling agent and maleic anhydride grafted polypropylene). For evaluation of the final impact of all three phases presence on the processibility of the polymer composite the melt flow behaviour was analyzed (MFI analysis according to ISO 1133) for the filler concentration of 10, 20 and 30 wt. %. This study involves also the natural fibre surface profile analyses (based on SEM observation) and the applicability of created composite materials was determined using the heat deflection temperature (HDT analysis according to ISO 75). © 2016 Trans Tech Publications, Switzerland.
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    Prototyp – Dýchací maska se společným nádechovým a výdechovým otvorem
    (Technická univerzita v Liberci, 2014-01-01) Běhálek, Luboš; Bobek, Jiří; Habr, Jiří; Lenfeld, Petr; Seidl, Martin; Katedra strojírenské technologie - oddělení tváření plastů
    Tato výzkumná zpráva se zabývá návrhem konstrukce a výrobního postupu výroby prototypu ochranné dýchací polomasky s filtrační vložkou vyměnitelného kruhového a obdélníkového filtru.
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    Selective laser melting technology and individual ti-6al-4v implants
    (MM publishing Ltd., 2019-06-01) Ackermann, Michal; Šafka, Jiří; Čapek, Lukáš; Bobek, Jiří; Mendřický, Jaromír
    This paper deals with the use of additive manufacturing from Ti-6Al-4V metal powder in the field of individual implants. Additive technologies such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM) enable the manufacturers to design the implants precisely with respect to actual anatomy of each patient. In this paper, two major properties of the printed parts are studied. In the first part, monotonic mechanical properties of the material in as-built and heat treated condition are evaluated. In the second part of the work, shape accuracy is evaluated on the model of individual cranial implant. For this study, the cranial implant was once built as a fully dense part and once using lightweight structure. Both parts were submitted to optical 3D scanning to evaluate the nominal deflections from CAD model. Uniaxial tests show full usability of additively manufactured Ti-6Al-4V parts. Basic material constants are comparable to those evaluated on conventional bulk material. Apart from shortening the build time, lightweight structures also significantly reduce deflections of the model.
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    Solid and microcellular polylactide nucleated with PLA stereocomplex and cellulose nanocrystals
    (SPRINGER, VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS, 2020-03-01) Borůvka, Martin; Běhálek, Luboš; Lenfeld, Petr; Brdlík, Pavel; Habr, Jiří; Wongmanee, Sorasak; Bobek, Jiří; Pechočiaková, Miroslava
    Blending polylactide (PLA) with poly(d-lactide) (PDLA) and cellulose nanocrystals (CNC)-based stereocomplex (SC) nanohybrids presents practical approach to produce fully biobased blends and nanocomposites with enhanced properties. This paper investigated the nucleation effect of PLA/PDLA and PLA/PDLA-g-MAH/CNC nanohybrids at low loading levels on the non-isothermal crystallization, morphology, as well as thermal and thermo-mechanical properties of PLA-based samples. Neat PLA, blends and nanocomposites were produced by conventional and microcellular injection molding. Nitrogen (N-2) in a supercritical state was used as the physical blowing agent for preparation of microcellular samples. CNC-based SC showed superior nucleating efficiency compared to SC nucleating agents. However, low mold temperature resulted in relatively low degree of crystallinity (similar to 15%). In addition, decrease in cell size and increase in cell density of microcellular samples have been observed after introduction of both nucleating agents. Slight increase in mechanical properties of nucleated samples compared to neat PLA has been ascribed to the higher degree of crystallinity. Despite these, decrease in all mechanical properties of microcellular samples has been noticed when compared to solid counterparts. Furthermore, dynamic mechanical analysis (DMA) reveals subsequent foaming and dramatic decrease in dimensional stability of microcellular samples above glass transition temperature (T-g). The storage modulus in a glassy region has been improved in both solid blends and nanocomposites. In addition, shift of T-g due to restricted chain mobility of PLA due to retarded relaxation of amorphous regions due to SC interactions has been observed.
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    Use of composite materials for FDM 3D print technology
    (Trans Tech Publications Ltd, 2016-01-01) Šafka, Jiří; Ackermann, Michal; Bobek, Jiří; Seidl, Martin; Habr, Jiří; Běhálek, Luboš
    This article deals with specific polymer composites modified for the Fused Deposition Modeling (FDM) which is a 3D print technology. These two phase systems involve thermoplastic matrix filled with natural fibres. The crucial demand of this progressive technology is put on the accuracy of the semi-product formed into the filament shape. To reach the smooth production of 3D prototypes the filament should have a constant diameter. In the article, individual steps of the polymer composite pelletization and following pre-processing and processing activities are described. Among these steps the extrusion of the filaments belongs and subsequent print test on “RepRap” device accompanied by optimization of building parameters. Tensile specimens were chosen for print with regard to maps mechanical properties of this newly developed material which was the final stage of this work. Tensile test curves were then compared with those graphs which can be found for the material produced by conventional technologies such as injection moulding. © 2016 Trans Tech Publications, Switzerland.
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