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Spalionice komunalnog otpada su složeni industrijski sustavi koji se koriste za proizvodnju energije, tehničke pare i termičku obradu otpada. Kao i drugi industrijski sustavi, podložni su trošenju, oštećenjima i kvarovima zbog utjecaja raznih faktora poput temperature, tlaka i dimnih plinova tijekom eksploatacije. Izvođenje redovitih remonta je od iznimne važnosti za održavanje optimalne razine performansi i sigurnosti sustava. Takvi remonti mogu produžiti radni vijek opreme, smanjiti rizik od skupih popravaka i dugotrajnih zastoja postrojenja, te osigurati siguran i pouzdan rad. U radu je prikazan primjer mehaniziranog kladiranja površine segmenta ložišta, s naglaskom na probleme koji su redovito prisutni tijekom ovakvih radova te iskustva i perspektivu za daljnji rad. Waste-to-energy plants are complex industrial systems used for generating energy, technical steam, and thermal treatment of waste. Like other industrial systems, they are subjected to wear, tear, damage, and malfunctions due to various factors such as temperature, pressure, and flue gases during operation. Performing regular maintenance is of utmost importance to maintain optimal levels of 12. Međunarodno znanstveno-stručno savjetovanje SBZ 2023 „STROJARSKE TEHNOLOGIJE U IZRADI ZAVARENIH KONSTRUKCIJA I PROIZVODA, SBZ 2023.“ Slavonski Brod, 26. i 27. 04. 2023. i Požega 28. 04. 2023. Društvo za tehniku zavarivanja Slavonski Brod 209 performance and system safety. Such maintenance can extend the equipment's lifespan, reduce the risk of costly repairs and long plant downtimes, and ensure safe and reliable operation. The article presents an example of the automated overlaying of a furnace segment surface, with a focus on the problems that are regularly present during such work, as well as experience and prospects for further work.

In order to test the tribological properties of the high alloy ledeburite steel X210Cr12, test samples were made on which the mass loss was measured before and after the wear test. The test was performed using the “pin on disk” method on the Taber abraser device, with part of the samples tested without lubricant and part with lubricant to compare and present the results. X210Cr12 steel was chosen as the material for the pin sample, while low alloy steel was chosen for the disk sample. In the lubricant test, hemp oil was used and analyzed to show the effects of this oil on the lubrication and wear of the material. During the test, each sample was subjected to a modified load and a modified number of cycles. From the test results, it can be concluded that hemp oil exhibited satisfactory properties over all test cycles, with an approximately constant pattern of mass loss. In addition, hemp oil showed more favorable properties at higher test loads and a greater number of test cycles, so it can be used as a lubricant based on the test results obtained under test conditions such as those that prevailed in this test.

Due to the mechanical properties (toughness, elongation, tensile strength) that characterize ductile iron, its application in foundry technology is becoming more pronounced every day. The chemical composition and heat treatment of ductile iron have a great influence on the required mechanical properties. Given the operating conditions, the main purpose of heat treatment of ductile iron is to change the desired mechanical properties. Since the specific mechanical properties of ductile iron are generally related to the regularity of the mined graphite nodules, the main objective in production is to produce ductile iron with the highest possible percentage of ductility. In the experimental part of the paper, microstructure and hardness tests were carried out on specimens of ductile iron NL 400 and NL 700 before and after heat treatment by soft annealing (ferritization) and improvement. It was found that the type and corresponding parameters of heat treatment significantly affect the microstructure and the achieved hardness values of the ductile iron test specimens.

This research focuses on testing of abrasion resistance of boron- and vanadium-based coatings. Coating of samples with vanadium was completed by classic and duplex procedure with previous carburization. The samples were abraded by applying the ASTM G65-94 method of „dry sand/rubber wheel“. The greatest wear was recorded on boron- based coating, and the least wear was exhibited by the vanadium-based coating with previous carburization. The dominant form of „zero“ abrasion was determined by analyzing the sample wear traces.

Svakim danom svjedoci smo sve primjetnijih i brojnijih klimatskih mijena kao posljedica stoljeća nemara i nebrige za okoliš. Potreba ljudskog roda za energijom danas još uvijek je snažno vezana i uvelike ovisi o fosilnim gorivima. Industrijska revolucija, kolosalna prekretnica u životu čovjeka unijela je napredak u sve sfere ljudskog života. Nerazumnim vrednovanjem tehnološke i industrijske revolucije kao i povećanim stupnjem urbanizacije dolazi do disbalansa ravnoteže u prirodi. Stihijska eksploatacija zaliha rudnih i energetskih resursa fosilnog podrijetla u želji za daljnjim napretkom dovelo je postupno do iscrpljivanja zaliha, ali i do prvih ekoloških katastrofa. Spoznaja o vrlo limitiranoj zalihi fosilnih goriva kao izvora energije te nepovratnoj šteti učinjenoj planeti uzrokovanoj ljudskim utjecajem nagnala je razmatranje o alternativnim izvorima energije koji će doprinijeti smanjenju emisije ugljičnog dioksida. U ovom radu razmatra se uloga bioplina (biometana), jednog od predstavnika obnovljivih izvora energije te njegova implementacija u procesu dekarbonizacije sektora transporta.

U procesu deguminacije sirovog ulja nastaje deguminacijski talog koji se dodaje suncokretovoj pogači kao balast prilikom transporta do hladionika. Talog sadrži fosfatide koji sa suncokretovom pogačom tijekom biološke razgradnje čine masne kiseline. Segmenti lanca čine tribosustav kada na njih djeluju sastojci masnih kiselina iz uljne pogače. Dijelovi lanca (čahure i svornjaci) izrađeni su od austenitnog nehrđajućeg čelika. Glavni uzrok njihovog trošenja je prisustvo masnih kiselina u uljnoj pogači koje na kontaktnim površinama elemenata lanca uzrokuju pojavu tribokorozije. Trošenje se manifestira oštećivanjem spojnog mjesta (lamela-čahura), a kao rezultat toga je povećanje koraka lanca i „naskakanje“ na tjeme zuba lančanika, što uzrokuje pojavu nedopuštenih sila istezanja i kidanja spojnog mjesta lanca.

Biootpad, premda organskog podrijetla također predstavlja ozbiljnu ugrozu za okoliš zbog produkcije metana kao nusproizvoda uslijed raspadanja na odlagalištima koji sudjeluje u emisiji stakleničkih plinova. Zbog sve izraženijeg problema sa zagađenjem okoliša i gubitkom biološke raznolikosti, Vijeće Europske Unije bilo je prinuđeno donijeti Direktivu o odgovornosti za okoliš, kojom se pojedinac ali i zajednica potiče na ekološko odgovorno ponašanje prema okolišu. Kao jedna od alternativa za rješavanje problema biootpada nameće se proces fermentacije ili anaerobna digestacija. Anaerobna digestija definira se kao biokemijski proces razgradnje supstrata organskog podrijetla bez prisutnosti kisika, uz nastanak bioplina i digestatora kao produkata procesa. Proizvodnja bioplina fermentacijom u digestoru predstavlja optimalni način zbrinjavanja i tretiranja organskog otpada biljnog i životinjskog podrijetla kojom se u kontroliranim uvjetima oponašaju mikrobiološki procesi nastanka fosilnih goriva. Uz brojne, za okoliš ekološki prihvatljive učinke, također sa sobom povlači i socio – ekonomsku dobit za zajednicu, kao i za sve uključene u ciklus proizvodnje. Izgradnjom postrojenja za bioplin te njegovom proizvodnjom podiže se standard i osiguravaju radna mjesta naročito u ruralnim predjelima, koja su vezana uglavnom uz djelatnosti primarnog sektora (stočarstvo i poljoprivreda).

Od davnina, izvori energije biološkog podrijetla nastali fotosintezom čovjeku su služili kao hrana i energent. Sve do I. industrijske revolucije i početka intenzivnog korištenja fosilnih goriva, drvo – prvotna biomasa bila je gotovo jedini biološki izvor energije. Energetska kriza 70 – ih godina prošlog stoljeća potaknula je svijet na razmatranje o stanju preostalih zaliha fosilnih goriva nakon nekoliko stoljeća nekontrolirane eksploatacije te njihov utjecaj na okoliš s obzirom na sve izraženije ekološke katastrofe. Poslije stoljeća uporabe energije dobivene iz neobnovljivih izvora, danas se globalna slika pomalo mijenja, a obnovljivi izvori energije poput biomase sve više se ističu kao potencijalno ključni čimbenici budućih strategija razvoja. Upravo je biomasa jedini izvor obnovljive energije koji omogućava proizvodnju plinovitih i tekućih goriva visokog energetskog potencijala. U prometu i toplinarstvu svoju primjenu već su našli, a u bližoj budućnosti očekuje se da će se još više implementirati i ostvariti svoju punu potvrdu. Posebna postrojenja – kogeneracije omogućavaju da sagorijevanjem biomase u ložištu, uz korisnu toplinu proizvodi se i električna energija. U daljnjem tekstu rada opisan je princip rada kogeneracijskog postrojenje, elementi od kojih se sastoji te primjena kogeneracijskih i trigeneracijskih postojenja. Kao jedna od članica Europske Unije a ujedino i potpisnica Kyoto protokola, Republika Hrvatska obavezala se na reduciranje emisija štetnih plinova i zaštitu okoliša. Navedeni ciljevi djelomično su ostvarivi orijentacijom energetskog sektora k obnovljivim izvorima energije poput biomase, koja u zemljama poput Republike Hrvatske imaju veliki potencijal.

U suvremenom svijetu, kotlovska postrojenja svoju primjenu su našla unutar brojnih grana industrije, od kojih se ponajviše ističe energetika. Iako termoenergetska postrojenja predstavljaju efikasan rješavanja problema gomilanja komunalnog otpada u gradovima i dobivanja korisne topline, zbog svog, još uvijek nereguliranog sastava, predstavljaju značajan izvor emisija štetnih plinova i lebdećih čestica, koji prilikom izlaska iz kotla odlaze u atmosferu negativno utječući na okoliš. U vremenu kada se zbog sve strožih zakona o zaštiti okoliša i svijesti o sve manjim zalihama fosilnih goriva koja su nam dostupna, čovjek se sve više okreće ekološki prihvatljivim metodama dobivanja električne energije poput biomase. Unutar jednog kotlovskog postrojenja, izgaranje je vrlo bitan proces, jer predstavlja izvor korisne energije u vidu topline dobivene energetskom transformacijom iz goriva. Opseg i vrsta opreme od koje se ložište kotla sastoji prvenstveno će ovisiti o procesu sagorijevanja ali i o vrsti goriva koja se unutar njega spaljuje. Rešetka predstavlja glavnu opremu ložišta za sagorijevanja u sloju ; na kojoj se odvijaju sve četiri faze procesa sagorijevanja uz mogućnost regulacije njenog kapaciteta i odnosa količine goriva i zraka. Tehnološki proces izrade mehaničke rešetke postrojenja za spaljivanje ostataka iz papirne industrije, pulpe eukaliptusa i šumske drvne biomase u radu će biti detaljno opisan, s posebnim osvrtom na tehnologiju zavarivanja. Tehnologija izgaranja u fluidiziranom mjehurićastom sloju (eng. Bubbling Fluidized - BedB.F.B.) svoju primjenu nalazi u kotlovima manje snage koji koriste gorivo niske energetske vrijednosti i visokim postotkom vlage poput spomenute biomase. Uz opsežan prikaz tehnološkog procesa izrade rešetke, također su opisane metode kontrole kvalitete za ispitivanje zavarenih spojeva te finalne aktivnosti.

Zavarivanje je jedan od najvažnijih proizvodnih postupaka. Isto tako, kontrola zavarenih spojeva izrazito je važna s obzirom da su zavareni spojevi u širokoj uporabi. Upravo iz spomenutih razloga, važno je da zavar bude ispravan te da zadovoljava sve uvjete koji se očekuju u eksploataciji. U svrhu toga se provode razna ispitivanja s ciljem sprječavanja neželjenih oštećenja i pucanja zavara. U radu su provedena laboratorijska ispitivanja na odabranom uzorku zavarenog spoja (poluga kombajna), izrađenom od nelegiranog čelika za poboljšavanje C45E. Cilj ispitivanja bio je pružiti uvid u metalografska i mehanička svojstva, dobivena nakon provedenog postupka zavarivanja, a na osnovu kojih je provedena kontrola zavarenog spoja.

Kod strojnih elementa i dijelova konstrukcija, uslijed djelovanja eksploatacijskih uvjeta, tijekom rada mogu nastati promjene u strukturi i neželjene promjene svojstava. Da bi se utvrdilo dolazi li do strukturnih promjena tijekom eksploatacije i na vrijeme otkrili potencijalni kvarovi, nužno je njihovo praćenje. Većina metalografskih metoda za određivanje strukture metala su metode s razaranjem i zbog toga zahtijevaju izrezivanje uzorka. Kada se radi o strojnim elementima koje je potrebno kontrolirati tijekom eksploatacije, primjena metalografskih metoda s razaranjem često je teško provediva i neprihvatljiva. Metoda ispitivanja strukture primjenom metalografskih replika je razvijena kao nerazorna metoda u okviru metalografskih ispitivanja. Ova metoda ima široku primjenu i često se primjenjuje kod metalografskih ispitivanja dijelova termoelektrana. Kod termoelektrana pojedini konstrukcijski elementi i sklopovi izloženi su djelovanju povišene ili visoke temperature i zbog toga postoji opasnost od pojave neželjenih strukturnih promjena. U ovome radu provedeno je ispitivanje strukture metodom metalografskih replika na pregrijaču komore ekonomajzera izrađenom od čelika 13CrMo4-5. Pored ispitivanja metalografskim replikama provedeno je i ispitivanje tvrdoća. Ispitivanja su provedena na pregrijaču prije puštanja u rad s ciljem utvrđivanja njegove strukture i tvrdoće. Analizom metalografskih replika napravljenih na pregrijaču utvrđena je feritno-perlitna struktura koja odgovara deklariranom materijalu. Izmjerene vrijednosti tvrdoće odgovaraju vrijednostima spomenute strukture.

Concept of modern boiler power plant represents a set of a large number of elements, whose primary function is the transformation of heat energy given by combustion of fuel into mechanical work and heat. From the humble beginnings of „steam boiler “, named by James Watt, there is a constant need for achieving a larger degree of efficiency, what is successful with the development of technology and application of material with better mechanical, chemical and tribology property. During the construction of welded joints and bevels of elements which will be welded in boiler manufacturing, with experimental and/or calculation, also, it is necessary to take into account all relevant technical regulations and standards in order to achieve all safety and technical conditions for normal and continuous work of facility during the period of exploitation. Introduction of this paper describes the term boiler power plant and pressure part of the boiler. The second part of the paper gives a review of standards which stipulates preparation of ends for welding and manufacturing pressure parts according to EN and ASME standards. Taking into account rules defined and conditioned with technical restrains and manufacturing standards, this paper gives a detail description of bevel preparation for membrane and butt welding and also welding nozzles on headers.

In this paper the influence of hemp seed oil on the lubrication of two materials in sliding contact as well as the tribological effects of this oil was analyzed. Tribological examination was performed with help of the method by ball and flat disk on tribometer with alternating motion (eng. ball on flat). Material selected for the ball is AISI E52100 steel, while for the disk sample was selected X210Cr12 steel. The examinations were performed for three different oscillation frequencies: 10, 15 and 20 Hz, whereby for each frequency the loads of 10, 13, 16 and 19 N were changed in duration of 30 minutes for each examination, whereby the final result was shown by measuring the loss of sample mass. During examination, the oil showed a very good physico-chemical and tribological properties at higher loads and lower oscillation frequencies and can therefore be used as a lubricant in industrial applications.

This paper presents some characteristic examples of damage the parts of power plants. The causes of damage from smoke and water side were analyzed. Test methods with and without destruction were applied. On the example of new elements before installation, the importance of applying non-destructive methods was indicated, by taking the imprint of the structure by “replica” method, with measuring the hardness and wall thickness. It was concluded that selecting of “benchmarks” on which the condition of the embedded materials will be monitored, can significantly contribute to improving the efficiency of the power plant and the speed of problem solving.

During the injection molding procedure of plastics, the gear pumps in their work are exposed to the effect of elevated pressure and temperature. On one of these pump there has been frequent downtime due to breakage of the driven gear. Gears which were installed as standard spare parts had stood out in operation for three months. On a sample of a broken gear were perfomed laboratory examinations (metallographic examinations, hardness control on cross-section and surface of the fracture was examined). Conclusion was that it was high quench hardening of a steel of which a part is made, the most likely cause of the fracture of a standard gear. In order to extend the useful life, two test gear are made from steel for cementation 20MnCr5. By applying the appropriate parameters of thermal chemical treatment useful life of the gear is significantly extended, after which the test gears have worked for nine months from the moment of installation.

Primary stage of Burley type tobacco in thresher machines includes separation of fine parts of tobacco leaves from the ribs, the so called “stemming”. Thereby cutting edges of knives are exposed to wear by abrasive particles. Analysis has been performed of the influence of two kinds of protective layers on thresher knives on quality of stemming, depending upon tobacco leaves blend. It has been established that operation with worn knives is most negatively reflected on the most quality tobacco fractions – those having the greatest market value. It has been proved that application of sprayed layer instead of installation of plates made of hard metal, followed by partial exchange of worn knives can tribological losses even up to 6 %.

In the conditions of tribocorrosion wear, extending of parts lifetime could be achieved by using stainless steel, which is hardened to sufficiently high hardness. In the tribosystem bolts/shell/link plate of the elevator transporter conveyor machine, the previously quenched and tempered martensitic stainless steel for bolts is hardened at ≈ 55 HRC and welded with the quenched and tempered high yield carbon steel for bolts. Additional material, based on Cr-Ni-Mo (18/8/6) is used. The microstructure and hardness of welded samples are tested. On the tensile tester, resistance of the welded joint is tested with a simulated experiment. Dimensional control of worn tribosystem elements was performed after six months of service. The analysis of test results shows that with regulated additional material and by applying the recommended welding parameters, the adequate weld properties could be achieved. In the conditions of tensile load that properties could ensure reliability of the joint, with a significant increase of the wear resistance.

During the projected lifespan, most components of the boiler are exposed to increased values of temperature and pressure, flue gasses and variable loads, which are causing significant changes in the structure of the material. Since we live in a time when survival is almost impossible without electricity, halting of the entire power plant in order of taking samples for examination represents enormous expense. Application of metallographic replicas as a method of non-destructive examination of the structure represents a practical and reliable way of detections changes in the layer under the the surface, as well as changes in structure caused by work on elevated temperatures. This method can be used for examination of entire constructions, as well as finished products from the industry. In the experimental part of the work, quality estimation of material used for manufacturing of boiler the headers made of low - alloyed steel 13CrMo4-5 was performed. The aim of the test is a determination of workability of tested components, as well as evaluation of the possibilities for further course of exploitation.

Standard and welded ploughshares were tested. The standard ploughshares are made of steel 50Mn7. The welded ploughshares are made by applying C-Cr-Co-Ni-Si additional material on the same steel. The research was carried out by using two tractors with two four-furrow plough of the same power in a total of 360 working hours, and a total of 180 hours of ploughing with each ploughshare. The average achieved effect of ploughing with standard ploughshares was 0, 85 ha/h with fuel consumption of 29, 70 l/ha. With welded ploughshares was achieved the average effect of 0, 90 ha/h with average fuel consumption of 28, 30 l/ha. Based on these preliminary results of research it was concluded that the welding layer which containing Cr carbides can be affected to increase the efficiency of ploughing.

In this paper the laboratory tests on the selected steel for cementation 20MnCr5 was perfomed. The influence of the contact load resistance to the adhesion wear of high-temperature carbonitrided MnCr steels was analyzed. As a representative example was selected a tribosystem drive/driven gear of reducers in which are expressed high contact loads. For the purposes of these tests, the samples were first high-temperature carbonitrided, and then they are carried to the appropriate chemical and metallographic analysis, control of the surface hardnesses and the resistance to the adhesion wear. The aim of this paper was to observe the representative tribosystem as much possible to define its working parameters in order to determine the optimum conditions for testing the influence of the contact load on resistance to the adhesion wear. The analysis results show that high-temperature carbonitrided steel where the atmosphere of furnace at the beginning of carburizing was enriched with nitrogen, and finally with carbon showed significantly greater resistance to the adhesion wear compared to steel that at the beginning of carburizing had atmosphere of furnace rich in carbon, and finally with nitrogen.

Obradom tla dolazi do abrazijskog trošenja pojedinih radnih dijelova pluga, najviše lemeša. Spomenuto trošenje uzrokuju čestice tla. Međusobno su uspoređivani standardni i navarivani lemeši. Standardni lemeši su izrađeni od manganskog čelika 50Mn7. Navarivani lemeši su izrađeni nanošenjem C-Cr-Co-Ni-Si dodatnog materijala na opći konstrukcijski čelik S355JO. Lemeši su ispitivani na plugu prevrtaču. Istraživanja su obavljena u razdobljima 120, 240 i 360 sati oranja, odnosno 60, 120 i 180 sati rada svakog lemeša. Trošenje lemeša praćeno je kontrolom gubitka mase i promjene dimenzija. Nakon 180 sati rada prosječni gubitak mase navarenih lemeša iznosio je 25, 06 %. Za isto vrijeme oranja prosječni gubitak mase standardnih lemeša iznosio je 26, 29 %. Zaključeno je da se primjenom navarenih lemeša može utjecati na produljenje vijeka lemeša.

The paper describes mechanical testing on specimens made from 13CrMo4-5 boiler steel and numerical analysis based on conducted experiment. During magnetic particle testing (MT) examination of weld on the bottom header of a front wall of boiler large amount of indications (cracks) were noticed. In the experimental part of paper tension test was conducted in order to determine basic mechanical properties of specimens. After that, bend testing was conducted to determine an angle on which cracks occur, and ultimately fracture. In order to compare obtained results with results obtained experimentally, 3D model of specimens was created, and numerical analysis by finite element method (FEM)was carried out. Analysis of results has given guidance for further examinations, assuming that they will ultimately give an answer on type an incurred cracks.

Composite materials are materials obtained by joining two or more different materials with a compatible matrix as a binder for the purpose of obtaining specific properties. Polyester laminates are obtained by various production methods, and in this paper are more detailed described manual and RTM laminating procedure. The advantages and disadvantages of the two most commonly used procedures are shown. An example of boat hull production, techno-economic analysis was made. It is concluded that the RTM procedure is economically more cost-effective in relation to production by manual air extrusion.

Researchs of the influence of the soil particles were perfomed on the powder loamy soil to powder clay texture. Standard and welded ploughshares were tested. The standard ploughshares are made of steel 50Mn7. The welded ploughshares are made by applying C-Cr- Co-Ni-Si additional material on the steel 50Mn7. The ploughshares are tested on the plough roller machine. Researches were perfomed in periods of 120, 240 and 360 hours of ploughing, or 60, 120 and 180 work hours of each ploughshare. After 180 hours of work at least average reduction of the ploughshares lenght was at welded ploughshares and it amounted to 8, 27 % of the initial length. At the same time reduced the average length of the top of the ploughshares with standard ploughshares amounted to 19, 65 % of the initial length. It was concluded that the application of welded ploughshares can contribute to increased of the productivity.

During ploughing the soil particles wear of plougshares plough by abrasion. Standard and welded plougshares were tested. The standard ploughshares are made of manganese steel 50Mn7. The welded ploughshares are made by applying a C-Cr-Co-Ni-Si additional material on the general structural steel S355JO. Ploughing is done using a plough roller machine, on soils silty loam to silty clay texture. Ploughing is done in a period of 120, 240 and 360 hours. Each of ploughshare is ploughing 60, 120 and 180 hours. Ploughshares wear followed by the controlled mass loss and change in dimensions. After 180 hours the average weight loss of welded ploughshares was 25, 06 %. In the same time of ploughing the average weight loss of standard ploughshares was 26, 29 %. Based on these preliminary results of research it was concluded that the welding layer which containing Cr carbides can affect the extension of the life of ploughshares.

The basic requirement which is placed in front of modern thermal power plants is higher degree of utilization rates. As one of possible way of fulfilling the requirement is to increase steam parameters, which is conditioned by application of materials suitable for work on default temperatures and pressures. Materials used in steam boiler production must fulfill quality requirements, which are defined according to terms of exploitation which will be exposed during his lifespan, but also should be appropriate for the manufacturing process. At the same time, with the development of of boiler power plants, development of materials to be installed in boilers has run also. As one of significant representative of materials in boiler power production is also heat resistant low alloy steel 13CrMo4 - 5. Aim of this paper was to present and analyze main causes which led to the occurence and propagation of crack on bottom header front wall of crack. After conducted experiments type of cracks is determined, and after detailed analysis causes of cracks.

U gradu Slavonskom Brodu izvršena je modernizacija kotlovnica. Stari toplovodni kotlovi loženi na mazut zamijenjeni su novim kotlovima loženim na prirodni plin. Dat je prikaz parametara starih i novih kotlova. Praćeno je stanje novih kotlova u petogodišnjem periodu nakon puštanja u pogon 2008. godine. Zaključeno je da automatikom vođen pogon kotla i priprema vode omogućava pouzdan rad kotlovnica, a da primjena prirodnog plina kao gorivo doprinosi smanjenju zagađivanja okoliša. Ovakvim ulaganjem bitno su smanjeni troškovi održavanja, te je postignuto pouzdanije snabdijevanje potrošača toplinskom energijom.

In the production of oil in the oil mill parts of the equipment wear due to contact with seeds which contain microabrasive particles. This wear manifests itself by changing the dimensions and geometry of the screw press. The paper analyzes the influence of tribo-corrosive wear on the workpieces of the screw press. The appearance of wear is most likely due to the action of aggressive media, in this case the oilseeds. In the experimental part of this paper, on samples made of cast steel and austenistic stainless steel, following laboratory tests were performed: electrochemical testing, testing of chemical composition of the base material, wear analysis, microstructure recording and hardness testing. Based on the laboratory testing, conclusion was that the austenistic stainless steels 304L and 316L with nitrated surfaces exhibit better resistance to tribo-corrosion wear in relation to cast steel GS-42CrMo4.

Izvršena je usporedba starih steamblock kotlova loženih mazutom i novih kotlova loženih plinom. Iz starih kotlova bile su izvađene oštećene cijevi. Na temelju ispitivanja utvrđen je tip oštećenja, a nakon analize taloga i uzroci. Zaključeno je da su oštećenja cijevi nastajala kao posljedica prisutnog vanadija u mazutu, ali i neadekvatne pripreme vode. Konstatirano je da je zbog blindiranja oštećenih cijevi kapacitet starih kotlova bio značajno smanjen. Izvršena je usporedba relevantnih parametara rada jednog starog kotla koji je bio ložen mazutom i jednog novog kotla loženog plinom. Zaključeno je da je modernizacijom energetskih postrojenja postignuta pouzdanost snabdijevanja grada toplinskom energijom. Pri tome je zagađenje okoliša svedeno na minimum uz značajne efekte smanjenja troškova održavanja.

Analizirani su iskustveni primjeri uočenih nepravilnosti na plinomjerima i instalacijama. Pokazani su karakteristični primjeri namjerno izazvanih nepravilnosti na plinomjerima. Ispitivanje plinskih instalacija smije vršiti isključivo stručno osposobljeni djelatnik s važećim ovlaštenjem. O izvršenom ispitivanju izdaje se izvješće o ispravnosti. Bez obzira na takvu podjelu odgovornosti, vlasnik/korisnik dužan je prijaviti svaku primjećenu neispravnost – dežurnoj službi distributera plina, kao npr. propuštanje plina i/ili oštećenje plinske instalacije. Poslije svakog periodičkog pregleda plinomjeri se šalju na baždarenje. Na temelju analize primjera iz prakse predlažu se češće kontrole stanja i plinomjera i instalacija.

Mechanical, metallographic and chemical testing of the metallic materials typically are conducted in accredited laboratories, particularly for energy and process equipment. Accreditation according to HRN EN ISO/IEC 17025 is done by the National Institute of Metrology – National Accreditation Service. There are many requirements which a laboratory must satisfy if it wants to be accredited. The functioning of the laboratory in accordance with the requirements of that rule is the organizational challenge, especially with the financial side. Among the advantages highlighted are confidence in the testing of the laboratory and the implementation of testing procedures and the results of test reports. The main disadvantage is really reflected in significantly increased costs of the accredited laboratory maintance.

For the purposes of testing tribological characteristics of the stainless steel X20Cr13 designed for the parts of process industry plants for the production of sunflower oil, test samples were made and heat treatment by improving on different hardnesses was performed. Final machine processing of the samples was performed out by grinding and polishing. This way, the different characteristics of the surface layer and the different surface topography were achieved. The paper presents the results of the impact of the hardness on characteristics of the stainless steel X20Cr13. By examining the resistance to the adhesion wear it was concluded that the higher wear was on the test samples which have been in the raw condition and who were also loaded by higher forces. Therefore, the quality of the surface wear greatly affects the surface roughness and the coefficient of friction.

Razvoj turbopuhala doprinijeo je sve većoj primjeni u automobilskoj industriji. Turbopuhalo predstavlja složen tribološki sustav u kojem pri ekstremnim radnim uvjetima (visoke temperature i brzine vrtnje) treba zadovoljiti projektirani vijek. Prvi pokazatelji oštećenja turbopuhala su povećena potrošnja ulja, a nakon toga i slabljenje motora. Snimanje stanja i rezultati ispitivanja uzoraka turbopuhala ukazuju na to da kod vožnje pri većim brzinama na dužim relacijama može doći do njegovog ekstemnog zagrijavanja. Prestanak podmazivanja, ali i hlađenja nakon gašenja motora jedan je od razloga lokalnog pregrijavanja rotora turbopuhala. Vremenom dolazi do debalansa rotirajućih dijelova. To uzrokuje oštećenja turbinskog rotora i kompresorskog impelera. Kao jedno od rješenja nameće se primjena senzora koji ne bi dopustio gašenje pogonskog agregata sve dok se ne snizi temperatura turbopuhala na prihvatljivu vrijednost.

The results of the examination of the thermal sprayed layers are shown and their most common applications can be found in many industries, with a tendency of increasing their application. Three types of samples were tested for resistance to the rotation: samples with a groove, samples with the rendered surface and samples with the smooth surface without the groove. The analysis of the test results for the resistance to the rotation of the thermal sprayed layers show that the highest resistance to the rotation is provided by the samples with the rendered surface. Conclusion was that the reason for this is in the direction of the grooves of the rendered surface which is perpendicular to the force of rotation of the samples.

Kinetics of boride layers formation on C15 carbon steel has been investigated in this paper. Pack boronizing is carried out at a temperature range of 870 – 970 °C in durations of 4 – 8 h. Average thickness of obtained layers ranges from 65, 3 to 215, 5 µm. Values of frequency factor (3, 02 x 10-4 m2/s) and activation energy (195, 43 kJ/mol) are determined by means of Arrhenius equation. Based on these values, empirical expression showing functional relationship between boride layer thickness and boronizing temperature and duration has been obtained.

This paper examines the possibility of applying polyester laminates with reinforced different layers of glass fibers concearning the mechanical properties. Test plates are made by impregnating reinforcing fibers with resin with the manual extrusion of air bubbles by rollers. Based on the results of strength test (interlayer, tensile and flexural), modulus of elasticity, toughness and share of inorganic matters, it was concluded that the mechanical properties of polyester laminates depend not only on the „composition“, but also cavities presenting themselves as no homogeneity in boundary matrix/reinforcement.

The paper analyzes the impact of the contact load resistance to adhesion wear of high-tem¬pe-rature carbonitrided MnCr steel. As an example there is selected tribosystem drive/driven gear of reducers in which they expressed high contact load. The aim of this paper is observing a rep¬re¬sen¬tative wear systems, as faithfully as possible to define its operating parameters, in order to determine the optimum conditions for inves¬ti¬ga¬ting the impact of the contact load resistance to adhesion wear. For the purposes of these tests, the samples were first high-temperature carbo¬ni¬trided, and then they are carried to the appr¬o¬pri¬ate chemical and metallographic analysis, con¬trol of the hardness and the resistance to wear. Based on the analysis of the results it was con¬cluded that the increase in contact load, at con¬stant speed occurs an increased loss of mass in high-temperature carbonitrided MnCr steel.

Gear pumps for plastic injection are exposed to the effect of elevated pressure and temperature. In one such pump there has been frequent downtime due to breakage of the driven gear. Gears which were installed as standard spare parts had stood out in operation for three months. On a sample of a broken gear were conducted metallographic examinations and hardness control on cross section. Surface of the fracture was examined. Conclusion was that it was high quench hardening of a steel of which a part is made, the most likely cause of the fracture of a standard gear. In order to extend the useful life, two test gear are made from steel for cementation 20MnCr5. By applying the appropriate parameters of thermal chemical treatment useful life of the gear is significantly extended. Test gears have worked for nine months after installation.

U diplomskom radu analiziran je utjecaj kontaktnog opterećenja na otpornost adhezijskom trošenju visoko-temperaturno karbonitriranih MnCr čelika. Kao reprezentantni primjer odabran je tribosustav pogonski/gonjeni zupčanik reduktora u kojem su izražena visoka kontaktna opterećenja. Tribologija je znanstveno-stručna disciplina koja se bavi pojavama i procesima na površinama koje su u međusobnom djelovanju, direktnom ili indirektnom kontaktu i relativnom gibanju. Cilj ovog diplomskog rada bio je promatranjem reprezentantnog tribosustava, što vjernije definirati njegove radne parametre, kako bi se odredilo optimalne uvjete, ispitivanja utjecaja kontaktnog opterećenja na otpornost adhezijskom trošenju visoko-temperaturno karbonitriranih čelika, čija je primjena veoma česta u izradi zupčanika. Za potrebe ovih ispitivanja, uzorci su prvo visoko-temperaturno karbonitrirani, a potom su na njima provedena odgovarajuća kemijska i metalografska analiza te analiza tvrdoća i analiza otpornosti na trošenje. Na temelju analize prikupljenih rezultata ispitivanja, moguće je uočiti da pri porastu kontaktnog opterećenja, uz konstantnu brzinu, dolazi do povećanog gubitka mase kod viskoko-temperaturno karbonitriranih MnCr čelika.

Prikazanim rezultatima obuhvacena su mehanicka i tehnološka svojstva te metalografske pretrage kako na uzorcima izuzetim sa objekta, tako i na samom objektu, uzimanjem otiska strukture – replike, zatim mjerenja debljine stjenke te analiza kemijskog sastava materijala. Na primjeru korozije uslijed zamora materijala, uslijed kausticne krhkosti, korozije na granici faza voda/vodena para i uslijed nepravilnog konzerviranja u izvanpogonskom periodu, ukazano je na specificnosti oblika oštecenja razlicitim korozijskim mehanizmima. Konstatirano je da ce uzroci promjene svojstava i oštecenja osnovnih materijala biti lakše i preciznije utvr"eni uz pomoc podataka, ne samo o ugra"enom-pocetnom stanju, nego i o parametrima rada i njihovim promjenama tijekom uporabe. Zakljuceno je da je za Laboratorij suradnja s ovlaštenim inženjerima i Službom održavanja od neprocjenjive važnosti.

Some characteristic examples, with the components worn by the abrasion and fatigue of the surface layer, were chosen. The analysis of structure, wear marks and hardness measurement were conducted on the components with clad layers. It was found that the abrasion influences on a decrease of installed capacity efficiency as the result of pronounced local damage of components due to wear, and that the fatigue results in seizure of components and losses due to seizure. The possible causes could be in the type and distribution of carbides and the matrix of clad layers. By introducing a dimensional criterion of seizure of components, the preconditions for investigating the possibilities of using the carbonitrided layers were created. Considering the properties of samples achieved by the high temperature carbonitriding with a variable C and N potential, some advantages of its use on the components with the dimensional criterion of seizure up to 0, 2 ev. 0, 3 mm were emphasized. It was concluded that the cladding of protective layers is recommended in the cases where the dimensional criterion of seizure is a few millimetres with the condition that carbides/carbonitrides are distributed as evenly as possible in the tough matrix. The high temperature carbonitriding, with a variable C and N potential, is recommended for the conditions where the dimensional criterion of seizure is up to 0, 3 mm.

High temperature carbonitriding is a process of heat treatment that is used to increase the surface hardness of components, in order to reduce wear. The worm press for production of vegetable oil was chosen as an example of a system in which the high temperature carbonitrided components, made of Mn- Cr steel, are also built in. In exploitation, the extraction cage knife is exposed to a significant influence of the abrasive media, and the fatigue of material. A decrease of installed capacity efficiency is the result of local damages of components due to wear. The determined dimensional criterion of seizure makes the process of high temperature carbonitriding very suitable for the production of components that are used in the given exploitation conditions. The possibility of changing the level of carbon and nitrogen potential, as well as the effect on the possible life of extraction cage knives, were analysed. The use of a different carbon and nitrogen potential at the high temperature carbonitriding of test samples results in an extremely favourable flow of hardness at the crosssection. It can be observed that the achieved course of hardness is an extremely important indicator that had a significant impact on the final decision on the suitability of the observed process of thermochemical treatment for the intended purpose.

U završnom radu analiziran je pojam polimeri, klasifikacija i sistematizacija polimernih materijala, te pojmovi kao što su zavarivanje, lijepljenje i uskočni spojevi. Glavni dio rada odnosi se na postupke spajanja polimernih materijala. Prilikom opisivanja postupaka detaljno su opisana tri postupka spajanja polimernih materijala, a to su zavarivanje, lijepljenje i uskočni spojevi. Za zavarivanje koje je jedno od najprimjenjivanijih i najvažnijih postupaka spajanja opisana je glavna podjela postupka, gdje je detaljno opisana njihova primjena u određenim granama industrije. U poglavlju „Lijepljenje“ opisan je postupak lijepljenja polimernih materijala, njegova podjela, najvažnija ljepila i njihova primjena, te sastavljanje spoja, koja je jedna od najvažnijih točki lijepljenja. Na kraju su opisani uskočni spojevi, njihova podjela i oblici u kojima se najčešće pojavljuju, te proračun spojeva.

Od devedesetih godina do danas mnoge studije su se bavile svojstvima MTA-a. Sastav komercijalno dostupnih vrsta MTA-a je mješavina trikalcij silikata, trikalcij aluminata, dikalcij silikata, kalcij sulfata dihidrata i bizmutova oksida (ProRoot MTA, Dentsply, Tulsa Dental, Tulsa, OK). Zapažena je sličnost MTA cementa i PC-a, osim sastojka bizmutova oksida koji je odgovoran za svojstvo radiokontrasnosti MTA-a. Bez obzira na tu sličnost, uočene su još neke različitosti zbog kojih se PC ne smije koristiti kao jeftinija zamjena za MTA. MTA se u mnogim in vivo i in vitro studijama pokazao kao dobar endodonski materijal. U početku se koristio kao materijal za liječenje korijenskih perforacija, a zatim se masovno počeo koristiti kao materijal za retrogradno punjenje, u terapiji vitalne pulpe za direktno prekrivanje pulpe, pri pulpotomiji s apeksogenezom. Zbog svojega dobrog svojstva brtvljenja počeo se koristiti kao apikalna barijera u liječenju zubi s otvorenim apeksom u slučaju nekrotične pulpe (apeksifiklacija). Sudeći po svim opisanim svojstvima, MTA po svim opisanim svojstvima može okarakterizirati kao idealni reparatorni materijal. On je visoko biokompatibilan, ima sposobnost vezanja na dentin te stimulira cijeljenje i osteogenezu. Također pokazuje antimikrobnu aktivnost, a zbog svoje hidrofilnosti može se koristiti u operativnom polju bez obzira na prisustvo krvi.