The Influence of Gas Heating on Material Properties of P92 Steel During Boiler Tube Alignment

The pipes and the pipe walls are of the utmost importance to all power plant facilities. Under exploitation, they are subjected to effects of aggressive media, high temperature corrosion and possible mechanical damage. Consequently, special attention is paid to the control of material properties during the power plant construction in order to minimize the risk of flaws or failures. In this paper, the influence of gas heating on the structure and properties of P 92 martensite steel is examined, as occurring during tube alignment. The experiments have been performed on the polished and shot – blasted surfaces, and the obtained results have been compared with the values of specimens with the same surface treatment, but without heat treatment

Acoustic emission as tool wear monitoring

U radu je opisana brza Fouriova transformacija te njena primjena na praćenje trošenja alata. Opisana je transformacija prikupljenog signala tijekom rezanja iz vremenske domene u frekvencijsku. U uvodu je opisana diskretna Fouriova transformacija, nedostatak DFT se primjećuje kod većeg broja uzoraka. Stoga svoju primjenu u ovim slučajevima nalazi brza Fouriova transformacija. Kao primjer opisana je indirektna metoda za praćenje stanja alata koja se temelji na mjerenju vrijednosti procesnih varijabli (akustična emisija), na koje utječe vrijednost istrošenja alata.Praćenje trošenja alata je težak zadatak, jer mnogi obradni procesi su nelinearni vremenski promjenljivi sustavi, te se kao takvi ne mogu modelirati i ti signali dobiveni iz senzora ovise o nizu drugih čimbenika, kao što su uvjeti strojne obrade.This paper describes a fast Fourier transformation and its application to monitoring tool wear. It describes the transformation of the collected signal during cutting from the time domain to the frequency. The introduction describes the discrete Fourier transform, DFT deficiency observed in a large number of samples. Therefore, its use in this case is fast Fourier transform. As an example, an indirect method for monitoring tool wear is shown, based on the measurement values of process variables (acoustic emission) and the relationship between tool wear and these values. Tool wear monitoring is a difficult task because many machining processes are non-linear time-variant systems, which makes them difficult to model and the signals obtained from sensors are dependent on a number of other factors, such as machining conditions

Održivi proces obrade – mit ili stvarnost

The industry is under increasing pressure of the financial crisis, global competition, stricter environmental legislation and supply-chain demand. To tackle these issues, a sustainable development trend has to be assured synergetically on all the levels/fields, including machining processes. This paper promotes sustainable production via an improvement of machining technologies through an alternative cryogenic machining process. Presented are comparative experimental results of cryogenic machining performances in accordance with conventional processes, through the analysis of: cutting forces, tool-wear, temperatures and costs. This work proves that the cryogenic machining technology has a high potential to cut costs and improve competitiveness by reducing resource consumption therefore, creating less waste, and has less of an environmental and social impact. The results of this work confirm that alternative sustainable cryogenic machining offers conditions for fulfilling the sustainability pillars: the economical, social and environmental one, over conventional machining processesIndustrija je pod sve većim pritiskom financijske krize, globalne konkurencije, strožih zakona o zaštiti okoliša, lanaca ponude i potražnje. Da rješavajući ova pitanja, održivi trend razvoja mora osigurati sinergiju na svim razinama / poljima, uključujući i obrade. Ovaj rad promovira održivu proizvodnju putem suvremene tehnologije u vidu alternativnog kriogenog procesa obrade. Prikazani su eksperimentalni rezultati komparativne kriogene obrade u odnosu na konvencionalne procese, kroz analizu: sila rezanja, trošenja alata, temperature i troškove. Ovaj rad dokazuje da kriogene tehnologije imaju visok potencijal za smanjenje troškova i poboljšanje konkurentnosti smanjenjem potrošnje resursa, dakle, omogućuje manje otpada, a ima manji ekološki i društveni utjecaj. Rezultati ovog rada potvrđuju da alternativna održiva kriogena obrada omogućava ispunjenje uvjeta za održivost: ekonomsku, socijalnu i ekološku, u odnosu na konvencionalnu obradu

Application of Tribometer Measurements for Evaluation of Machinability

Investigation of machinability of materials is continuously faced with new demands, new principles and new achievements. The outcome of evaluation of machinability presented in this paper resulted out from observation of two tribological parameters: friction factor and width of the wear area on contact between two sliding bodies, blocks and discs. Measurements are performed on tribometer in condition of wet sliding while one body is sliding over the other. A block is made of material which is usually used for cutting tool, and a disc is made of material which is used as a material of workpiece. Achieved contact condition (normal loading and sliding speed) meets real machining-cutting condition. The aim of the tests performed on tribometer “Block on Disc” is to evaluate the opportunity of investigation of materials machinability by tribological parameters (friction factor and width of wear area on the block). Comparison of experimental results obtained during real cutting condition setup and tribological setup show a good correlation between wear values and cutting forces. For certain conditions, it is possible to acquire machinability indexes obtained on a tribometer with respect to friction factor and wear on the block as relevant and representative for real cutting condition

Usporedba utjecaja različitih tehnologija rezanja materijala na kvalitetu reza konstrukcijskih čelika

The paper deals with a comparison of the most frequently used thermal cutting technologies applied to the structural, low carbon steel EN S355J0 in engineering enterprises with a focus on experimental measurement and evaluation of characteristics of the heat affected zone. It gives a mutual comparison of these technologies in terms of the achieved heat affected zone. The goal of this paper was to use the property changes in the used material (affected by laser, plasma arc and oxygen cutting) as the quality indicator of the cutting process.U radu se daje usporedba najčešće korištenih toplinskih postupaka rezanja, koje koriste proizvodne tvrtke, u primijeni na konstrukcijskom, nisko ugljičnom čeliku EN S355J0 s naglaskom na eksperimentalna mjerenja i vrednovanje svojstava zone utjecaja topline. Rad prikazuje usporedbu tih tehnologija u kontekstu dobivene zone utjecaja topline. Cilj ovog rada je korištenje spoznaje o promjenama svojstava korištenog materijala na površini reza (dobivene laserom, plazmom i plinskim rezanjem) kao pokazatelja kvalitete procesa rezanja

Optimization of Machining Parameters Using the Taguchi and ANOVA Analysis in the Face Milling of Aluminum Alloys AL7075

This paper examines the influence of the cutting parameters on the cutting forces and the surface roughness at the face milling process when machining aluminum alloy 7075 is obtained by the new SSM casting process. The parameters of the milling process are the cutting speed, the feed per tooth and the depth of cut. The experiments were performed according to the Taguchi method according to the L9 plan and the factors varied at three levels. For analysis of the effects of these parameters S/N ratio is used. In addition, ANOVA analysis was performed, i.e. analysis of the variance of the selected parameters. The analysis of the results shows that the optimal combination for the cutting force is the choice of a minimum level for all tested parameters. In contrast, for average arithmetic roughness, the optimal processing regime is achieved with minimum values for cutting speed and feed per tooth, whilst it is preferable to choose the cutting depth at the median level for the observed range. In addition, the study shows that the Taguchi method is suitable for solving the problem, where the research was carried out with a minimum number of tests compared to a full factorial experimental plan

Optimization of cutting process of AISI 316 L corrosion resistant steel with hydro abrasive jet

Suvremeni tehnološki razvoj karakterizira pronalazak velikog broja novih i naprednih materijala za koje je obrada standardnim postupcima koji trenutno prevladavaju u industriji s tehničkog i ekonomskog stajališta često teško izvodiva. Zbog nemogućnosti ispunjavanja svih zahtjeva suvremene tehnologije sve je značajnija primjena nekonvencionalnih postupaka obrade poput hidro abrazivnog rezanja. Članak se fokusira na provjeru teze mogu li se standardni postupci poput glodanja zamijeniti nekonvencionalnim postupkom hidro abrazivnog rezanja uz zadržavanje zahtijevane kvalitete obrađivane površine. Ukoliko se teza prihvaća, potrebno je odrediti maksimalnu dubinu rezanja do koje je moguće ostvariti traženu kvalitetu površine uz minimalni utrošak resursa.Modern technological development is characterized by discovering a large number of new and advanced materials for which the standard machining processing that currently prevails in industry from technical and economic point of view is often difficult to achieve. Due to the inability of fulfilling all the requirements of modern technology, application of non-conventional machining processes such as hydro abrasive cutting is more significant. The paper focuses on the verification of the thesis whether the standard operations such as milling could be replaced by non-conventional machining process of hydro abrasive cutting while maintaining the required quality of the processed surface. If the thesis is accepted, it is necessary to specify the maximum cutting depth to which to achieve the required quality of surface material machining is possible with minimal consumption of resources

Uloga kriogenika u postupcima strojne obrade

The purpose of this work is to present some guidelines in the sustainable machining processes, using cryogenic conditions and gaining higher performances, lower environmental and health influences, increased safety, etc. The study presents the details about cryogenic fluids and their use in machining processes as an alternative to oil-based emulsions. The details of liquid nitrogen and the ways of their application in the machining processes, known as cryogenic machining process, are given. The research is upgraded with experimental case study on high temperature alloy machining – tungsten, and so presenting an important scientific and sustainability contribution in production processes. Experimental and analytical results are proving that the cryogenic machining technology has a high potential to cut costs and improve competitiveness, by reducing resource consumption and creating less waste and have less of an environmental and social impact, fulfilling the sustainability pillars: economical, social and environmental one, over conventional machining processes.Cilj je ovog rada dati prikaz smjernica u ostvarenju održive proizvodnje stvaranjem kriogenih uvjeta radi postizanja viših perfomansi u obradi, manjeg utjecaja na okolinu i ljude, povećanja sigurnosti itd. Istraživanjem se prikazuju pojedinosti o kriogenim fluidima i njihovoj upotrebi u postupcima strojne obrade kao alternativno sredstvo emulzijama na bazi ulja. U radu su dane pojedinosti o tekućem dušiku i načinima njegove primjene u strojnoj obradi, poznatim kao kriogeni procesi strojne obrade. Istraživanje je provedeno eksperimentalno pri obradi legura za rad na visokim temeperama na bazi volframa i na taj način dan značajan znanstveni doprinos u postupcima održive proizvodnje. Eksperimentalni i analitički rezultati potvrđuju da kriogena tehnologija strojne obrade ima dobar potencijal za smanjenje troškova i poboljšanje konkurentnosti, smanjenje potrošnje sirovina, smanjenje otpada, manji utjecaj na okolinu i ljude, ispunjavajući uvjete održivosti: ekonomske, socijalne i okoliš u odnosu na konvencionalne postupke strojne obrade