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Effect of dielectric barrier discharge plasma on film cooling performance
No full textTo improve film cooling effectiveness of a gas turbine blade, a kind of
plasma actuator is introduced on the blade surface. The effect of three
arrangements of plasma actuators on flow characteristics and film cooling
performance is numerically investigated by a verified turbulence model.
Results show that the coolant air under plasma is pulled down to the wall,
and the near-wall air is sped up to promote the film cooling effectiveness
downstream the wall. It is discovered that the plasma actuators near the
film hole show weaker aerodynamic actuation than that downstream the wall.
Compared with the plasma actuators off case, the maximum improvement in the
wall-averaged film cooling effectiveness of the case with up plasma
actuators is 11.7% under low blowing ratios. The wall-averaged film cooling
effectivenesses of the cases with down plasma actuators and up-down plasma
actuators increase by 138.3% and 122.9% under the blowing ratio of 1.5..
Vortex structures are broken up, and vortex is separated by two jets
induced by aerodynamic actuation. The maximum wall pressure difference
reaches 1.89% when plasma actuator is arranged downstream the wall
Microstructural and hardness analyses of welded joined by mig procedure
No full textU ovom završnom radu napravljen je teorijski pregled i to elektrolučnog postupka
zavarivanja s detaljnim opisom postupaka zavarivanja MIG metodom te pregled
metoda mjerenja tvrdoće s detaljnim opisom Vickersove metode mjerenja. Ploče
debljine 15 mm od konstrukcijskog čelika S235JR zavarene su sučeono K zavarom
primjenom MIG metode. Zavareni spojevi hlađeni su nakon zavarivanja na različite
načine, jedan je hlađen na zraku, a drugi u vodi. U eksperimentalnom dijelu završnog
rada na sučeono zavarenim pločama nakon pripreme najprije je napravljena
metalografska analiza mikrostrukture zavarenih spojeva, a zatim je izmjerena njihova
tvrdoća Vickersovom metodom. Provedenim metalografskim ispitivanjima zaključilo
se da zona utjecaja topline ima sitnozrnatu strukturu, a zona taljenja lijevanu strukturu.
Nakon mjerenja tvrdoće vidljivo je da vrijednosti tvrdoća rastu od korijena prema licu
zavara kako u zoni taljenja tako i u zoni utjecaja topline.In this final paper, a theoretical overview of the electric arc welding process with a
detailed description of the MIG welding process and an overview of hardness
measurement methods with a detailed description of the Vickers measurement method
was made. The 15 mm thick plates made of structural steel S235JR are butt-welded
with K welding using the MIG method. Welded joints were cooled after welding in
different ways, one was cooled in air and the other in water. In the experimental part of
the final work on the butt-welded plates after preparation, a metallographic analysis of
the microstructure of the welded joints was first made, and then their hardness was
measured using the Vickers method. The conducted metallographic tests concluded that
the heat-affected zone has a fine-grained structure, and the melting zone has a cast
structure. After measuring the hardness, it is evident that the hardness values increase
from the root to the face of the weld, both in the melting zone and in the heat-affected
zone
The solidification sequence and microstructure development of secondary EN AC 46100 alloy
No full textThe main challenges in the production and utilization of secondary aluminum alloys are achieving the targeted chemical composition and controlling the level of impurity elements. Those challenges originate from the accumulation of trump elements such as silicone, magnesium, nickel, zinc, lead, chromium, iron, copper, vanadium, and manganese during recycling. The inability to achieve targeted chemical composition negatively impacts the secondary alloy properties and hinders its use in the safety-critical applications. Despite the fact that there are a variety of solutions to lower the negative impact of trump elements, each of them represents a trade-off between the coast and the recycling potential. The research was performed to estimate the influence of excess Mg and Zn on solidification sequence and microstructure development of secondary EN AC 46100 alloy. The investigation comprehended determination of chemical composition, equilibrium and non- equilibrium solidification sequence using Thermo- Calc software support as well as metallographic analysis. Based on the obtained results, it was concluded that the excess amounts of magnesium and zing led to the solidification and precipitation of complex phases, mainly Q-Al5Cu2Mg8Si7, π- Al8FeMg3Si6 and Al5(Cu, Zn)6Mg2 that are not characteristic for EN AC 46100 type alloy
Željezo
No full textOpisane su glavne karakteristike tehničkog željeza i čelika. Prikazan je razvoj tehnologija dobivanja željeznih materijala od prapovijesti do suvremene proizvodnje u svijetu i na tlu Republike Hrvatske
Aluminij
No full textOpisan je aluminij i aluminijske legure s njihovim svojstvima, postupak proizvodnje primarnog aluminija, razvoj industrije aluminija i RH te značajne tvrtke u RH
Risk assessment of physical hazards in foundries
No full textFizikalne štetnosti obuhvaćaju zvuk, buku, vibracije, svjetlost, rasvjetu, zračenje i mikroklimatske uvjete prostora, koji predstavljaju potencijalni rizik za zdravlje i sigurnost radnika, ali i za okoliš. U današnje vrijeme polažu se veliki napori kako bi se smanjio rizik od fizikalnih štetnosti i njihovih posljedica, međutim postoje djelatnosti u kojima je nemoguće ukloniti sve rizike. Ljevaonice su, u pravilu, zatvoreni prostori u kojima dolazi do isparavanja, dima, prašine, buke, povišene temperature, radnici rade u prisilnom položaju tijela, manipuliraju velikim i teškim predmetima, rastaljenim metalom, stoga posljedično dolazi do velikog naprezanja organizma.
Nažalost, radna mjesta u ljevaonicama zbog prirode samog procesa imaju nepovoljne uvjete rada i svrstavaju se u poslove s posebnim uvjetima rada. Zaposlenici raspoređeni na radna mjesta s posebnim uvjetima rada u potencijalnom su riziku od razvoja profesionalne bolesti bez obzira na korištenje osobne zaštitne opreme.
U ovom radu pobliže će se obraditi fizikalne štetnosti koje nastaju tijekom radnih procesa u ljevaonicama uz osvrt i na druge opasnosti, štetnosti i napore s kojima se susreću zaposlenici tijekom metaloprerađivačkog procesa.Physical hazards include sound, noise, vibrations, light, lighting, radiation and microclimatic conditions and can pose a potential risk to the health and safety of workers, but also to the environment. Nowadays, great efforts are made to reduce the risk of physical hazards and their consequences, but there are activities in which it is impossible to eliminate all risks. Foundries are closed spaces where evaporation, smoke, dust, noise, elevated temperatures occurred, workers work in a forced body position, manipulate with large and heavy objects, molten metal, which is resulting in great stress to the body.
Unfortunately, jobs in foundries, due to the nature of the process itself, have unfavourable working conditions and are classified as jobs with special working conditions. Employees assigned to jobs with special working conditions are at potential risk of developing an occupational disease regardless of the use of personal protective equipment.
In this paper the physical hazards that occur during work processes in foundries, with reference to other dangers, hazards and efforts encountered by employees during the metalworking process are discussed
Stable and semi-stable systems for extinguishing tanks in an oil refinery
No full textSpremnici zapaljivih tekućina u rafinerijama nafte sadrže različite zapaljive tekućine počevši od sirove nafte do poluproizvoda, proizvoda i raznih aditiva. Aditivi se namješavaju u gotove proizvode da bi im se poboljšala svojstva pod određenim uvjetima kao što je zimsko vrijeme pa se smanjuje točka smrzavanja ili se dodaje aditiv za bolji oktanski ili cetanski broj za bolju eksplozivnost kod benzinskih goriva, a kod novijih goriva se nadomješavaju i aditivi na biološkoj bazi te tako dobivamo goriva koja su ekološki prihvatljivija.
Cilj ovog rada je da se prikaže kako se štite spremnici zapaljivih tekućina u rafineriji nafte, kojim zakonskim i podzakonskim aktima se regulira to područje, koje vrste zapaljivih tekućina postoje, koje vrste spremnika i na koji način se takvi spremnici štite, te kakve vrste zaštita se još mogu upotrijebiti i koji problemi se mogu dogoditi.Tanks of flammable liquids in oil refineries contain from crude oil to semi-products, products and various additives that are mixed into finished products in order to improve their properties under certain conditions, such as when it is winter, so the freezing point is reduced or an additive is added for better octane or cetane number for better explosiveness with gasoline fuels, and with newer fuels, additives on a biological basis are added, and thus we get fuels that are more environmentally friendly.
The goal of this paper is to show how such tanks are protected in an oil refinery. What legal and by-laws regulate that area, what types of flammable liquids we have, what types of tanks and how such tanks are protected, and what types of protection can still be used and what problems can occur
Migration of heavy metals from steel dishes due to preparation and storage of food
No full textIzrada i primjena posuđa od metala, posebno čelika, omogućila je bržu i jednostavniju pripremu
hrane. Međutim, pri pripremi hrane posuđe je izloženo visokim temperaturama. Osim toga,
hrana zbog kiselog ili lužnatog pH također utječe na posuđe. Budući da se posuđu od čelika pri
proizvodnji dodaju određeni elementi radi poboljšavanja svojstava gotovog proizvoda, postoji
mogućnost migracije navedenih elemenata u hranu.
U ovom radu praćena je migracija teških metala (As, Cd, Cr, Ni, Pb i Zn) u ovisnosti o
temperaturi i vremenu kontakta s hranom. Za ispitivanje su korištene dvije modelne otopine
koje su predstavljale kiselu i lužnatu hranu. Također su korištene i dvije vrste posuđa: posuđe
od nehrđajućeg čelika i posuđe od ugljičnog nelegiranog čelika s prevlakom od emajla.
Dobiveni rezultati su pokazali da uslijed kontakta posuđa s hranom dolazi do migracije
ispitivanih elemenata. Koncentracija migriranih elemenata ovisi o vremenu kontakta posuđa s
hranom, pH vrijednosti hrane, temperaturi i starosti posuđa.The production and use of dishes made of metal, especially steel, enabled faster and simpler
food preparation. However, dishes are exposed to high temperatures when preparing food. In
addition, food due to acidic or alkaline pH also affects dishes. Since certain elements are added
during the production of steel dishes in order to improve the properties of the finished product,
there is a possibility of migration of these elements into food.
In this graduate thesis, the migration of heavy metals (As, Cd, Cr, Ni, Pb and Zn) depending
on the temperature and time of contact with food was monitored. Two model solutions
representing acidic and alkaline foods were used for the research. Two types of dishes were
also used: stainless steel dishes and enamel-coated carbon steel dishes. The obtained results
showed that there is a migration of the analysed elements due to the contact of dishes with
food. The concentration of migrated elements depends on the time of contact of the dishes with
food, the pH value of the food, the temperature, and the age of the dishes
Hazards at the production of titanium alloys in the electric arc furnace
No full textOvaj rad opisuje metal titan, njegove karakteristike i svojstva te vrste legura titana obzirom na njegovu mikrostrukturu. Opisani su postupci proizvodnje čistog titana. Također su opisani postupci proizvodnje odnosno postupci taljenja i lijevanja legura titana. Fokus je stavljen na proizvodnju legura titana elektrolučnim postupkom te su ujedno opisane i moguće opasnosti u proizvodnji titana u elektrolučnim pećima. Prikazane su i odgovarajuće mjere zaštite koje je u slučaju određene opasnosti potrebno poduzeti. S obzirom na pojavu mogućih nesreća u proizvodnji titana prikazana je i računska obrada koja prikazuje koliko je potrebno uložiti u zaštitu od potencijalnih nesreća, a da se pritom maksimizira profit. Na kraju je prikazana primjena i postupak lijevanja legura titana u dentalnoj medicini.This paper describes the titanium metal, its characteristics and properties as well as types of titanium alloys regarding its microstructure. Processes for the production of pure titanium are described. Also, the processes of production, that is, the processes of melting and casting of titanium alloys are described. The focus is on the production of titanium alloys by the electric arc process, and possible dangers in the production of titanium in electric arc furnaces are also described. Appropriate protective measures that must be taken in the event of a certain danger are also shown. With regard to the occurrence of possible accidents in the production of titanium, a calculation is also presented that shows how much it is necessary to invest in protection against potential accidents, while maximizing profit. Finally, the application and casting process of titanium alloys in dental medicine is presented
Technological development of the casting process for the thin-walled gray cast iron
No full textThe research was performed to optimize the casting process and geometry of the fireplace door frame casting to increase productivity and prevent the appearance of the surface casting defects. The ProCAST software support was used to optimize the vents and casting temperature. Although, the proposed optimization reduced casting time and the mass of the casting, the increase in the hot spot had a negative impact on the appearance of the burn-on. The simulation results indicated that the appearance of the surface defect could be avoided by lowering the casting temperature of the optimized version