Papers by János Dobránszky
Coronary stents are thin-walled and mesh-structured metallic implants, which are made generally b... more Coronary stents are thin-walled and mesh-structured metallic implants, which are made generally by laser beam cutting of high-precision tubes of 90-120 micrometer thickness. The tube material can be 316L stainless steel or L605 type cobalt-chromium alloy. The paper present how laser settings influence geometry and surface quality of the kerf and residual stresses, which play very important role in the precision of stent strut homogeneity. Hungarian Tentaur stent was developed 15 years ago. This coil stent made of 145 micrometers thick stainless steel wire contains 9-25 joints produced by electric resistance projection welding. Developments were bringing out for increasing flexibility of Tentaur stent, and a new design and a new technology was elaborated, which's based on laser beam mi-crowelding. TentaFlex stent also is constructed from austenitic stainless steel wire, but it does not contain any wire-crossing joint, because stent struts are configured from sinusoidal helix. Stent contains only two welded joints at its ends. Laser welding experiences of these joints are presented in the paper. A Trumpf PowerWeld Nd:YAG laser work station was used for welding, and after optimization of laser settings joints can't produces from only one side of the coiled stent.
Biomechanica Hungarica, Apr 1, 2010
Az Amerikai Egyesült Államokban az FDA (Food and Drug Administration) gyorsított eljárással két i... more Az Amerikai Egyesült Államokban az FDA (Food and Drug Administration) gyorsított eljárással két ilyen típusú sztentet engedélyezett, Investigation of the polymer coatings of drug eluting coronary stents from the aspect of drug absorbing and eluting Abstract Coronary stents are the most important materials in our day's cardiology. The rate of restenosis can be decreased by the usage of drug eluting stents compared to bare metal stents. The aim of this work was to optimize polymer coatings for medical applications and the examination of drug absorbing and releasing properties of these coatings. The examined medical grade polymers were Chronofl ex ® , Carbothane ® and Tecothane®. Control groups were bare metal stent models (316 LVM type austenitic stainless steel tube slices). The three medical grade polyurethane granules were applied onto the stent surface. In this paper different techniques were used to cover the samples by polyurethanes then topcoated with heparin. The heparin was injected into the coatings by soaking. The polyurethane coating is an appropriate passive coating. It is expedient to add pharmaceutical agent as a topcoating to prevent the infl ammatory reactions and to obtain other pharmaceutical effects. All of the applied polyurethanes were able to bind the heparin, but in different ways depending on their properties. The most bound heparin was found at the three-layer Chronofl ex ® coating, by 48-hour soaking. Tecothane ® coating bound the least heparin, but this coating had the longest elution time. Based on these results it can be concluded that the applied coatings were swelling and it is possible to set an optimum recovery time and concentration of the solution where the maximum amount of heparin can be dissolved in the coatings.
DyTh Műszaki Tanácsadó Bt., 2018
Biomechanica Hungarica, 2010
Az Amerikai Egyesült Államokban az FDA (Food and Drug Administration) gyorsított eljárással két i... more Az Amerikai Egyesült Államokban az FDA (Food and Drug Administration) gyorsított eljárással két ilyen típusú sztentet engedélyezett, Investigation of the polymer coatings of drug eluting coronary stents from the aspect of drug absorbing and eluting Abstract Coronary stents are the most important materials in our day's cardiology. The rate of restenosis can be decreased by the usage of drug eluting stents compared to bare metal stents. The aim of this work was to optimize polymer coatings for medical applications and the examination of drug absorbing and releasing properties of these coatings. The examined medical grade polymers were Chronofl ex ® , Carbothane ® and Tecothane®. Control groups were bare metal stent models (316 LVM type austenitic stainless steel tube slices). The three medical grade polyurethane granules were applied onto the stent surface. In this paper different techniques were used to cover the samples by polyurethanes then topcoated with heparin. The heparin was injected into the coatings by soaking. The polyurethane coating is an appropriate passive coating. It is expedient to add pharmaceutical agent as a topcoating to prevent the infl ammatory reactions and to obtain other pharmaceutical effects. All of the applied polyurethanes were able to bind the heparin, but in different ways depending on their properties. The most bound heparin was found at the three-layer Chronofl ex ® coating, by 48-hour soaking. Tecothane ® coating bound the least heparin, but this coating had the longest elution time. Based on these results it can be concluded that the applied coatings were swelling and it is possible to set an optimum recovery time and concentration of the solution where the maximum amount of heparin can be dissolved in the coatings.
Increasing demand for advanced steels with outstanding mechanical properties appeared in the mode... more Increasing demand for advanced steels with outstanding mechanical properties appeared in the modern vehicle manufacturing. These materials are used mainly in the automotive industry as parts for high loads (i.e. car body, chassis). The application of multi-phase steels, i.e. TRIP steels is an obvious solution in the automotive industry. Car body elements assembled of several pieces by various technological solutions (spot welding, bonding). One of the most widely used methods is the resistance spot welding. By this method the welded joint prepared in seconds that is significant in the automotive mass production. During the welding of TRIP steels cracks could appears around the nugget.
This paper presents those experimental results, which were obtained in many years research that f... more This paper presents those experimental results, which were obtained in many years research that focused to the increasing of productivity of the tungsten inert gas (TIG) welding. We focused on two directions. One of these – the gas mixture shielded and the pulsed TIG welding – is widely applied in the industry. The second one was the activated TIG (ATIG) welding which is a less known and rarely applied process variant of the TIG welding. Regarding to the attainable weld penetration depth values resulted by various shielding gases, we demonstrated that some of them may facilitate to achieve ATIG welding-like deep penetration. Concerning the 2nd objective, we established an overview on the proper technological characteristics of the silica powder using ATIG welding of stainless steels and on the consequences in the weld bead geometry of the welding parameters.
The increasing productivity in industrial applications gets more and more into the focus of atten... more The increasing productivity in industrial applications gets more and more into the focus of attention during the last decades. This intention is also present at the developments of welding technologies. TIG welding developments have also been parallel to the really heavy-duty welding processes (like MIG/MAG, SAW, Beam Weldings, etc.). Several TIG welding variants were developed due to these researches. In spite of the fact that a very wide literature of TIG welding process is well known, the number of those publications which write down exact equations between the different parameters is very low. The situation is even worse for the new TIG variants. Three TIG variant (using pure Argon, furthermore 70% Ar + 30% He as shielding gas, finally Activated TIG welding) are investigated and compared together in this paper. The comparison is executed from the penetration depth (D), the bead width (W), the penetration profile (D/W) and the weld bead cross section (A) point of view. This work ...
Műszaki Tudományos Közlemények, 2016
Additive manufacturing (AM) as a rethinking of build-up welding, growing use itself in several fi... more Additive manufacturing (AM) as a rethinking of build-up welding, growing use itself in several fields of mechanical engineering. Using AM, optional geometry can be build, which is limited by the volumetric resolution of the applied process. In industrial application, laser-based AM processes are most popular with integrated five-axis machining centers. The use of metal active gas welding for AM is less honed but perfectly suitable for robotisation. The application of AM can produce spectacular results in the world of arts ("printed" bridges), but its technical use has many challenges. The background of the research is a need that came up at an industrial partner of Flexman Robotics Ltd. Compared to the traditional build-up welding, the robotized MAG-AM can assure a clear cost-effectiveness when repair large forging tools; because of much less welding consumable consumption and posterior fashioning, thanks to very precise following of the tool geometry during the welding process.
Műszaki Tudományos Közlemények, 2015
Increasing demand for advanced steels with outstanding mechanical properties appeared in the mode... more Increasing demand for advanced steels with outstanding mechanical properties appeared in the modern vehicle manufacturing. These materials are used mainly in the automotive industry as parts for high loads (i.e. car body, chassis). The application of multi-phase steels, i.e. TRIP steels is an obvious solution in the automotive industry. Car body elements assembled of several pieces by various technological solutions (spot welding, bonding). One of the most widely used methods is the resistance spot welding. By this method the welded joint prepared in seconds that is significant in the automotive mass production. During the welding of TRIP steels cracks could appears around the nugget.
Műszaki Tudományos Közlemények, 2015
Duplex stainless steels (DSS) are one of the modern stainless steels. Their name comes from their... more Duplex stainless steels (DSS) are one of the modern stainless steels. Their name comes from their duplex microstructure, which contains about equal proportion of austenite and δ-ferrite. DSS are typically alloyed with chromium, nickel, manganese, molybdenum and nitrogen and contain low carbon. Their excellent corrosion resistance and mechanical properties make them proper base material for almost any task, that is why it is important to have a suitable welding technology for these materials. They are hard to weld because of their duplex microstructure and high alloy content, which, together, make sensitive these alloys to undesirable precipitations. The heat input, the shielding gas and the welding consumable must be chosen wisely. Thick (10 mm) plate just like in this experiment, are harder to handle. Careless handling of the welding parameters can cause problems in the ferrite-austenite phase balance and because of that the mechanical properties and corrosion resistance cannot fulfil the requirements. This experiments aims to compare a few possible welding procedure designs according for the previous details.
Ausztenites acél vékony lemezekből hengerített hengerpalástok hosszvarratainak és körvarratainak ... more Ausztenites acél vékony lemezekből hengerített hengerpalástok hosszvarratainak és körvarratainak hegesztése impulzusívű plazmasugaras hegesztéssel történhet hegesztőanyag adagolásával vagy a nélkül. A technológiai jellemzőket értékeljük a varrathibák képződésének szemszögéből, különös tekintettel a volfrámelektródára.
A vékony (közelebbről: s ≤ 2 mm) acéllemezek hegesztése meglehetősen gyakori feladat. A feladat v... more A vékony (közelebbről: s ≤ 2 mm) acéllemezek hegesztése meglehetősen gyakori feladat. A feladat végrehajtására tipikusan alkalmazott eljárás a védőgázos, fogyóelektródás ívhegesztés (MIG/MAG), az AVI (TIG) hegesztés, illetve gyakran az ellenállás ponthegesztés. Rögtön hozzá kell azonban tenni, hogy az ilyen vékony lemezek anyaga az esetek döntő többségében ötvözetlen acél, austenites korrózióálló acél, ritkábban mikroötvözött vagy gyengén ötvözött acél. Ezekben az esetekben az acél karbontartalma olyan kis értékű, hogy ezt valamint a további ötvözők csekély mértékét és a kis falvastagságot is figyelembe véve nem csak a hidegrepedési veszély, de más hegeszthetőségi probléma sem vetődik fel.
Materials Science Forum, Jun 1, 2008
Investigations of microstructural differences of tempered eutectoid steel strips are presented. T... more Investigations of microstructural differences of tempered eutectoid steel strips are presented. The constituent phases-fine mixture of ferrite and cementite and a small amount of retained austenite-considerably affect the mechanical properties, especially the resistance to high cycle fatigue. The amount of retained austenite was determined by XRD and EBSD analysis. Thermoelectric power (TEP) measurements were performed for 270 different batches of C75S type eutectoid steel strips. TEP measurement shows characteristically the fine microstructural differences. The TEP of the investigated samples varied between 5650 and 7030 nV/°C. The amount of retained austenite can be significantly higher at the surface (20 %) than at the internal part (0-5 %). The sensitivity of XRD analysis was reduced because of the presence of coarse cementite particles. Using Cu anode, the measurements were more successful than in case of using Co anode. The EBSD analysis showed that also samples immeasurable with XRD contain retained austenite, but its detectability with XRD analysis declines with the coarsening of cementite.
Woodworking industry uses in mass band-saw blades. Their material is mainly unaloyed eutectoide s... more Woodworking industry uses in mass band-saw blades. Their material is mainly unaloyed eutectoide steel. The load characteristics are followed by the presentation of the typical failures. The first significant failure type is concentrated to the weld and the heat-affected zone, where the welding heat process causes the decreasing of toughness. The second but much frequently affected part, where cracking may apear is the gullet, because it raises the stress intensity factor. Following 15 year's experiences and researches it was developed an expertise system for failure analysis of band-saw blades. This expertise system is demonstrated by case studies.
A sztentek olyan hálós szerkezetű implantátumok, amelyek az érfal kitámasztásáról gondoskodnak a ... more A sztentek olyan hálós szerkezetű implantátumok, amelyek az érfal kitámasztásáról gondoskodnak a ballonkatéterrel tágított érszakaszon. A sztentek rendeltetése, hogy meggátolják az ér visszaszűkülését. Dolgozatunkban összefoglaljuk a napjainkban alkalmazott koszorúérsztentek anyagait és gyártástechnológiáit. Ismertetjük a sztentek felületi, illetve geometriai tulajdonságainak vizsgálati lehetőségeit (sztereomikroszkópos, mérőmikroszkópos, fémmikroszkópos, energiadiszperzív röntgendetektorral felszerelt pásztázó elektronmikroszkópos és atomerő mikroszkópos vizsgálatok). Bemutatunk különböző módszereket a tágulási jellemzők (elsősorban a radiális visszarugózás és tágulási rövidülés) meghatározására. Ismertetjük a koszorúérsztentek különböző mechanikai tulajdonságaira irányuló, preklinikai vizsgálati módszereket és azok eredményeit különböző, forgalomban levő koszorúérsztentek esetén.
TIG welding experiments have been used for the welded joints of the austenitic stainless steel an... more TIG welding experiments have been used for the welded joints of the austenitic stainless steel and molybdenum. The aim of the experiments was to find the optimal welding parameters. The problems that occurred throughout the welding process were due to the very high melting point of the Mo. Also, using optical microscopy and scanning electron microscopy have performed a proper testing in parallel with the experiments. Regarding to the wear of electrode, there have been determined the tip angle, the tapering and the effect of the electrode's material composition. The latter parameter was investigated for thorium-oxide and lanthanum-oxide alloyed electrodes
A duplex acélok hegesztett kötéseiben a hegesztés során bevitt hő és a nagy hűlési sebesség hatás... more A duplex acélok hegesztett kötéseiben a hegesztés során bevitt hő és a nagy hűlési sebesség hatására a ferrit-ausztenit arány jelentősen eltérhet az alapanyag fázisarányától. Az eltérő fázisarány miatt a hegesztett kötések korrózióval szembeni ellenállása és mechanikai tulajdonságai elmaradnak az alapanyag jellemzőitől, ezért kívánatos a megfelelő fázisarány kialakítása a hegesztett kötésekben. Jelen dolgozatban az LDX2101 és a 2205 típusú duplex acélok lézersugaras, illetve volfrámelektródás, védőgázos hegesztési kísérleteit és a varratok metallográfiai vizsgálatát ismertetjük, különös tekintettel az ausztenit mennyiségének meghatározására. Az eredmények alapján következtetéseket vonunk le az ausztenit mennyiségét leginkább befolyásoló hegesztéstechnológiai tényezőkre vonatkozóan.
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Papers by János Dobránszky