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Corrosion resistance of cementing steel X19NiCrMo4 in medium of 5 % NaOH and 5 % H2SO4
No full textThis paper presents the results of testing the corrosion behavior of X19NiCrMo4 cementing steel in 5 % NaOH and 5 % H2SO4 solution. Electrochemical measurements were performed by measuring the open circuit potential, determining the corrosion parameters using electrochemical impedance spectroscopy (EIS) and Tafel extrapolation. The corrosion rate, which was determined by Tafel extrapolation method, was lower in 5 % NaOH solution than that in 5 % H2SO4 solution. The obtained results were confirmed by the method of electrochemical impedance spectroscopy, which showed a higher value of charge transfer resistance of the tested steel in an alkaline medium, which proves higher corrosion resistance. Metallographic analysis were performed on a sample previously etched in nital and on a sample after polarization measurements. Images of the electrode surface after polarization measurements in 5 % H2SO4 medium showed a completely corroded steel surface indicating dissolution of the oxide layer due to acid exposure. No changes were observed on the sample surface in the alkaline medium
Intermetallic bonding between a ring carrier and an aluminum piston alloy
No full textThis paper presents an analysis of the intermetallic bond between a ring carrier and an aluminum piston alloy. An optical microscope combined with the SEM / EDS analysis has been used to metallographically analyze the quality of the intermetallic bonding layer. The obtained results show that can be established intermetallic bond between two materials of different qualities
Utjecaj temperature žarenja na mikrostrukturu i tvrdoću AlSi10Mg dijelovaproizvedenih SLM aditivnim postupkom
No full textSLM proizvodnja Co-Cr dentalnih legura je relativno novo područje inženjerstva materijala. Utjecaj pojedinih parametara SLM postupka na strukturu i svojstva konsolidiranih Co-Cr dentalnih legura i njihova interakcija predstavlja važno područje za istraživanje. Preliminarna istraživanja koja su provedena na proporcionalnim uzorcima izrađenima od istog komercijalnog praha Co-Cr legure SLM postupkom na strojevima različitih proizvođača koristeći preporučene parametre postupka pokazala su velike razlike u mikrostrukturi dobivenih uzoraka te značajna rasipanja vrijednosti mehaničkih svojstava konsolidiranog materijala (vlačna i savojna čvrstoća, istezanje i žilavost). Rasipanja rezultata nisu uočena samo između uzoraka izrađenih na različitim strojevima, već i između uzoraka različitih šarži na istom stroju. Dobiveni rezultati preliminarnih istraživanja pokazuju da u samoj proizvodnji Co-Cr legura SLM postupkom dolazi do utjecaja pojedinih parametara koji značajno utječu na kvalitetu dobivenog proizvoda. Ta povezanost glavnih tehnoloških parametara SLM proizvodnje sa strukturom i svojstvima proizvoda i njihova interakcija je velikim dijelom nepoznato područje i predstavlja veliki znanstveno istraživački potencijal, gdje rezultati istraživanja mogu doprinijeti optimizaciji strukture i svojstava dentalnih Co-Cr legura. U ovom istraživanju planira se napraviti ispitivanje utjecaja pojedinih parametara DSLM postupka, i to snage lasera te brzine taljenja na mehanička svojstva (vlačnu, tlačnu i savojnu čvrstoću) Co-Cr legure za dentalnu namjenu. Također će se napraviti i analiza mikrostrukture kojom će se utvrditi utjecaj pojedinih parametara na ispitivana mehanička svojstva.SLM production of Co-Cr dental alloys is a relatively new field of materials engineering. The influence of individual parameters of the SLM procedure on the structure and properties of consolidated Co-Cr dental alloys and their interaction is an important area for research. Preliminary studies conducted on proportional samples made of the same commercial powder Co-Cr alloy SLM process on machines of different manufacturers using the recommended process parameters showed large differences in the microstructure of the obtained samples and significant differences in mechanical properties of consolidated material (tensile and flexural strength, elongation and toughness). Scattering of the results was observed not only between samples made on different machines, but also between samples of different batches on the same machine. The obtained results of preliminary research show that in the production of Co-Cr alloys by SLM process there is an influence of certain parameters that significantly affect the quality of the obtained product. This connection of the main technological parameters of SLM production with the structure and properties of products and their interaction is largely an unknown area and represents great scientific research potential, where research results can contribute to optimizing the structure and properties of dental Co-Cr alloys. In this research, it is planned to examine the influence of certain parameters of the DSLM procedure, namely laser power and melting rate on the mechanical properties (tensile, compressive and flexural strength) of Co-Cr alloy for dental purposes. A microstructure analysis will also be performed to determine the influence of individual parameters on the examined mechanical properties
Microstructure and hardness of welded low-carbon steel
No full textZavarivanje je interdisciplinarna tehnologija spajanja istovrsnih ili raznovrsnih materijala, taljenjem ili pritiskom, sa ili bez dodavanja dodatnog materijala. Cilj provođenja zavarivanja je da se dobije homogen zavareni spoj. Postupci elektrolučnog zavarivanja su bili među prvim postupcima koji su se razvili u 20. stoljeću. U ovom radu provedeno je proučavanje literature koja opisuje teorijske osnove različitih postupaka zavarivanja. Posebna pažnja je posvećena detaljnom proučavanju postupka zavarivanja netaljivom elektrodom pod zaštitom plina (TIG). U eksperimentalnom dijelu rada samostalno je provedeno zavarivanje niskougljičnog čelika st 35.8 (Č.1214, DIN17175, W. Nr. 1.0305, EN-P235GH) TIG postupkom. Nakon zavarivanja provedena je analiza mikrostrukture optičkim mikroskopom. Mikrostrukturna analiza je provedena na osnovnom materijalu, zoni utjecaja topline i zoni taljenja. Uočeno je da osnovni materijal imaferitno-perlitnu mikrostrukturu, dok je u zoni utjecaja topline prisutna također feritno-perlitna mikrostruktura s mjestimično prisutnim Widmanstattenovim feritom. U zoni taljenja zamijećena je lijevana mikrostruktura koja se sastoji od ferita i bainita. Zona taljenja je pokazala najveće vrijednosti tvrdoće (228,7 HV10).Welding is an interdisciplinary technology of joining identical or diverse materials, by melting or pressing, with or without the addition of additional material. The aim of process welding is to obtain a homogeneous welded joint. Arc welding processes were among the first processes to be developed in the 20th century. In this thesis, a study of the literature describing the theoretical foundations of different welding procedures was obtained. Special attention is paid to the detailed study of the process of welding with a non-fusible electrode under gas protection (TIG). In the experimental part of the work, low-carbon steel st 35.8 (Č.1214, DIN17175, W. Nr. 1.0305, EN-P235GH) was independently welded by TIG process. After welding, microstructure analysis was performed with an optical microscope. Microstructural analysis was performed on the base material, the heat affected zone and the melting zone. It was observed that the base material has a ferrite-perlite microstructure, while in the heat affected zone a ferrite-perlite microstructure with Widmanstatten ferrite is also present in places. A cast microstructure consisting of ferrite and bainite was observed in the melting zone. The melting zone showed the highest hardness values (228.7 HV10)
Optimiranje uljevnog sustava numeričkom simulacijom
No full textSuvremena proizvodnja odljevaka nezamisliva je bez implementacije novih strategija i koncepcija. U ljevačkoj industriji najviše se ističu koncepcije: “Near net shape castings” – odljevci s gotovo konačnim dimenzijama, kod kojih nije potrebno provesti strojnu obradu nakon lijevanja ili je ona minimalna i “Right for the first time” – ispravno već po prvi puta, tj. koncepcija kvalitativnog managementa u smislu prevencije grešaka pretpostavljenom detekciji i eliminaciji grešaka. Jedan od osnovnih ciljeva ovih postupaka je visoka iskoristivost materijala, uz što manji broj primijenjenih operacija u procesu oblikovanja. U ovoj je inovaciji fokus usmjeren na tehnologije CAD - Computer Aided Design, računalom podržano projektiranje procesa razvoja proizvoda i konstrukcijske pripreme proizvodnje, te CAE – Computer Aided Engineering, računalom potpomognuto inženjerstvo i razrada procesa lijevanja i skrućivanja, te predviđanje grešaka.
Ovom je inovacijom provedena optimizacija uljevnog sustava pomoću numeričke simulacije lijevanja i skrućivanja odljevka koji čini sklopni dio peći na kruta goriva, s ciljem postizanja laminarnog punjenja kalupne šupljine, usmjerenog skrućivanja, te uklanjanja greške površinske hrapavosti. Dobiveni rezultati su visoke točnosti, koji vizualno kvalitativno i kvantitativno prikazuju tijek lijevanja i proces skrućivanja prije i poslije optimizacije
Testing of X19NiCrMo4 tool steel on resistance to local corrosion in different media
No full textU ovom radu provedeno je ispitivanje otpornosti alatnog čelika X19NiCrMo4 prema lokalnoj
koroziji elektrokemijskim i metalografskim metodama. Provedena je ciklička anodna
polarizacija navedenog čelika u različitim medijima u svrhu definiranja parametara lokalne
korozije. Ispitivanje se provodilo u četiri medija: 3,5 % NaCl, umjetna kiša, otopina emulzije
Lenox Band-Ade i vode te voda.
Elektrokemijska ispitivanja pokazala su kako je alatni čelik oznake X19NiCrMo4 najotporniji
prema lokalnoj koroziji u mediju emulzije Lenox Band-Ade, dok je najpodložniji lokalnoj
koroziji u mediju 3,5 % NaCl. Naime, jedino u kloridnom mediju je došlo do pojave pitting
korozije pri čemu je registriran piting potencijal, dok u ostalim medijima u referentnom
intervalu elektrodnog potencijala nije zabilježena pojava piting lokalne korozije.
Rezultate elektrokemijskih ispitivanja potvrdila su metalografska ispitivanja gdje se uočava
kako je cijela površina čelika nakon ispitivanja u mediju 3,5 % NaCl prekrivena korozijskim
produktima, dok je nakon ispitivanja u mediju emulzije Lenox Band-Ade površina čelika ista
kao i prije ispitivanja.In this paper, the resistance of tool steel X19NiCrMo4 to local corrosion by electrochemical
and metallographic methods was tested. Cyclic anodic polarization of said steel in different
media was performed in order to define local corrosion parameters. The test was performed in
four media: 3.5% NaCl, artificial rain, water solution of Lenox Band-Ade emulsion and water.
Electrochemical tests have shown that X19NiCrMo4 tool steel is the most resistant to local
corrosion in water solution of Lenox Band-Ade emulsion medium, while it is most susceptible
to local corrosion in 3.5% NaCl medium. Namely, pitting corrosion occurred only in the
chloride medium and pitting potential was registered, while in other media, the occurrence of
pitting local corrosion was not recorded in the reference interval of the electrode potential.
The results of electrochemical tests were confirmed by metallographic tests where it is
observed that the entire steel surface after testing in 3.5% NaCl medium is covered with
corrosion products, while after testing in water solution of Lenox Band-Ade emulsion
medium the steel surface is the same as before testing
Kontrola zavara pri izradi distributora izmjenjivača topline nedestruktivnim metodama ispitivanja
No full textIzmjenjivači topline su uređaji u kojima se toplinska energija jednog fluida koji struji
kroz izmjenjivač prenosi na drugi fluid koji struji kroz izmjenjivač bez njihovog međusobnog
miješanja. Ovisno o izvedbi, često puta se provodi reparacija postojećih izmjenjivača. Primjer
reparacije postojećeg izmjenjivača topline opisan je u ovom završnom radu. Za reparaciju je
bilo potrebno izraditi novi distributor. Pri konstrukciji i izradi novog distributora korišteni su
tehnički nacrti postojećeg distributora kojeg je bilo potrebno zamijeniti. Pri konstrukciji
korišteni su različiti tipovi zavara, koji su naknadno ispitivani razornim i nerazornim metodama
ispitivanja. U ovom završnom radu dan je opis izmjenjivača topline i njihovih elemenata, kao i
opis uobičajenih metoda ispitivanja bez razaranja. Promatrana je konstrukcija jednog
distributora izmjenjivača topline i praćena su NDT ispitivanja kontrole kvalitete zavarenih
spojeva. Kako se radi o složenoj konstrukciji bilo je potrebno provesti više metoda ispitivanja.
Zaključak kontrole kvalitete je kako su svi zavareni spojevi zadovoljili normom propisane
vrijednosti, te je distributor bio spreman za ugradnju na postojeći izmjenjivač topline.Heat exchangers are instruments in which thermal energy of one fluid, which flows
through exchanger, is transferred to second one that flows through exchanger, without mixing
up two of them. The existing exchangers often need reparation, depending on their performance.
The example of reparation of the one heat exchanger is described in this paper. For reparation,
it was necessary to build a new distributor. In the process of construction and making of new
distributor, technical designs of existing one that needed to be replaced were used. In the process
of construction, different types of welds were used, which were later tested with destructive and
non-destructive methods. In this paper, a description of heat exchangers and their elements are
given, as well as the description of usual non-destructive testing methods. The construction of
new heat exchanger distributor was observed and afterward the NDT quality control test of
welded compounds were monitored. As it was a complex structure, it was necessary to carry
out several testing methods. The conclusion of quality control is that all welded joints meet the
all requirement prescribed by used standards, and the distributor is ready for installation on the
existing heat exchanger
Modelling the biomass updraft gasification process using the combination of a pyrolysis kinetic model and a thermodynamic equilibrium model
No full textConversion of biomass into gas suitable for further exploitation is one of the valuable renewable energy pathways due to the wide distribution and availability of raw materials. Biomass gasification is a thermochemical process of partial combustion in a reduced oxygen environment that aims to produce hydrogen-enriched syngas. Updraft gasifier design, with its advantages of high efficiency, produces syngas with higher hydrogen yield compared to other gasifier designs. The main drawback of the updraft gasifier is high yield of tars in the outflow gas decreasing its lower heating value. Recently, significant research efforts have focused on the optimization of the updraft gasifiers operating conditions, especially by developing numerical models as a complementary approach to experiments. The simplest modelling approach for predicting biomass gasification behaviour is the thermodynamic equilibrium model. When describing the behaviour of an updraft gasifier, special focus needs to be given to the pyrolysis stage, since in this type of reactor pyrolysis products directly outflow from the gasifier. In this work, a pilot-scale biomass gasifier was modelled using a combination of a pyrolysis kinetic model with a thermodynamic equilibrium model. To describe the pyrolysis behaviour, the CRECK-S-BIO and two secondary gas-phase mechanisms with distinct levels of complexity were used. The gasification and oxidation of char were modelled using a thermodynamic equilibrium model through the minimization of Gibbs free energy approach. The predicted results of dry clean syngas were compared to the experimental data considering eleven different operating conditions. The model combination that used the detailed secondary gas-phase mechanism achieved generally lower average prediction errors. Although some discrepancies were observed in the predictions, these preliminary results show that the model approach considered in this study represents a good basis for future development of the model
Nucleation and graphite growth in nodular cast iron – an overeview
No full textThe term nodular iron cast refers to a group of iron alloys with a maximum carbon content of 4 wt. % and silicon from 1.7 wt. % to 2.8 wt. %. This type of cast iron is characterized by the presence of carbon in the spherical or nodular form of graphite in a ferrite, pearlite or ferrite-pearlite matrix. Due to its better mechanical properties in relation to the other iron cast groups, it is widely used in production of gearboxes, crankshafts, turbine rotors, tanks, transportation industries, etc. Generally, size, distribution and shape of graphite nodules ensure a good toughness, high value of elongation and yield strength, castability and machinability. The course of solidification and each parameter of the production and solidification process has a certain impact on the mechanical properties and microstructure of the final product. However, solidification and graphite growth mechanisms in nodular cast iron have not been fully explained in despite to a large amount of research on the subject. Different experiments have led to the creation of different theories about the solidification process which aim to enable the creation of models for predicting the solidification process and the growth of graphite nodules. Predicting the development of microstructure and defining optimal parameters of the production process could prevent casting and microstructural defects thus ensuring desired properties of the casting. This paper provides an overview of several studies regarding the nucleation and graphite growth mechanism theories and experiments
Application of waste materials for removal of acetic acid from aqueous solutions
No full textOnečišćenje vode je jedan od gorućih problema s kojom se čovječanstvo danas suočava,
nažalost prvenstveno zbog neodgovornog ponašanja te nepropisnog zbrinjavanja otpada. U
vodene sustave dnevno se ispuštaju velike količine različitih otpadnih tvari kao što su
organski, anorganski i radioaktivni otpad. Različiti oblici onečišćenja vode štetno djeluju
na eko – sustav, te posljedično na ljudsko zdravlje. Zbog kontaminacije, otpadne vode
zahtijevaju dodatno pročišćavanje prije ulaska u sustave ribnjaka, potoka ili rijeka. Postoje
različiti stupnjevi i metode pročišćavanja otpadnih voda, a najefikasnija je adsorpcija. Cilj
ovog rada je usmjeren na adsorpciju octene kiseline iz vodenih otopina primjenom
otpadnih materijala kao što su troska, anodna prašina, ljuske jajeta, talog kave i aktivni
ugljen.Water pollution is one of the burning problems that humanity is facing today,
unfortunately, mainly due to irresponsible behavior and improper waste disposal. Large
amounts of various waste materials such as organic, inorganic and radioactive waste are
released daily into water systems. Various forms of water pollution have a detrimental
effect on the ecosystem, and consequently on human health. Due to contamination,
wastewater requires additional treatment before entering the systems of ponds, streams or
rivers. There are varying degrees and methods of wastewater treatment, and the most
effective is adsorption. The aim of this paper is focused on adsorption of acetic acid from
aqueous solutions using waste materials such as slag, anode dust, egg shells, coffee
grounds and activated coal