Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Stances on the Xylella fastidiosa bacterium and the coronavirus in the public discourse
No full textThe paper deals with the stances on the Xylella fastidiosa (Xf) bacterium and the
coronavirus in the public discourse. Relying on Hyland’s stance model (2005), we
seek to identify the linguistic devices (hedges, boosters, attitude markers and selfmentions), used in both contexts, which helped the authors express their opinions.
The corpus comprises articles on Xf and the coronavirus collected from the internet
sources in English. The findings indicate that the most frequent stance markers
in both subcorpora include hedges and boosters. There are slight differences in
the marker frequencies, depending on the disease in question. The conclusion
discusses the role of stance markers in impacting attitudes while reporting on these
two important issues and their use in communicating tentativeness or certaint
Simulation of a three-axis mechanism with parallel kinematics based on Chebyshev’s linkage
No full textU okviru ovog rada će biti prikazan konceptualni dizajn mehanizma sa paralelnom kinematikom koji poseduje tri stepena slobode kretanja. Novina u konstrukciji razmatranog mehanizma je primena Čebiševljevog mehanizma kao pasivnog translatorno-obrtnog zgloba. Razmatrani mehanizam kao predstavnik mehanizama sa paralelnom kinematikom je sačinjen od velikog broja spojki međusobno povezanih pasivnim zglobovima, te kao takav predstavlja kompleksnu konstrukciju sa velikim brojem posledičnih kretanja unutar konstrukcije. Kako bi se došlo do zaključaka po pitanju mobilnosti konstrukcije, nameće se potreba za simulacijom razmatranog mehanizma u nekom virtuelnom okruženju. U okviru ovog rada biće prikazana simulacija
razmatranog mehanizma u softverskom paketu PTC Creo Parametric.This paper presents the conceptual design of a mechanism with parallel kinematic capable to achieve three degrees of freedom. A novel feature of the proposed mechanism is the application of the Chebyshev's linkage as a passive translational-rotary joint. As a representative of parallel kinematic mechanisms, the proposed design consists of numerous linkages connected with passive joints, resulting in a complex structure with a high number of dependent motions within the system. To gain insights into the mobility and overall performance of the mechanism, a simulation of the design in a virtual environment is required. This paper includes a simulation of the mechanism using the PTC Creo Parametric software package.Za izdavača: Dekan, dr Vladimir Popović, red. prof.
Tehnički urednici:
Prof. dr Saša Živanović, Doc. dr Miloš Pjević , Doc. dr Dušan Nedeljković, Lazar Matijašević, mast. inž. maš.
Štampa: Planeta prin
Concept of a complex redundant machine tool intended for the wire-cutting process
No full textU okviru rada je prikazan koncept jedne mašine alatke koja predstavlja unapređenje prethodno već izgrađene kompleksne mašine MOMA-W. Predložena mašina, namenjena za proces obrade sečenja žicom, sačinjena je od dva mehanizma sa paralelnom kinematikom. Svaki od mehanizama poseduje po tri stepena slobode, što ukupno čini šest stepeni slobode koje poseduje predložena mašina. Kako je za proces obrade sečenja žicom neophodno da mašina poseduje četiri stepena slobode, kojima se obezbeđuje željena pozicija i orijentacija žice, dodatna dva stepena slobode predloženu mašinu čini redudantnom. Kako bi bilo moguće rešiti kinematičke probleme uvode se dodatni uslovi za rešavanje kinematičkih problema kojima se sam proces obrade poboljšava.This paper presents the machine tool concept, which improves the previously built complex machine MOMA W. The proposed machine, intended for wire-cutting, consists of two mechanisms with parallel kinematics. Each of the mechanisms has three degrees of freedom, which makes a total of six degrees of freedom possessed by the proposed machine. Since the wire-cutting process requires the machine to have four degrees of freedom, which ensures the desired position and orientation of the wire, the additional two degrees of freedom make the proposed machine redundant. To solve kinematic problems, additional conditions are presented, that in principle improve the machining process.Za izdavača: Dekan, dr Vladimir Popović, red. prof.
Tehnički urednici:
Prof. dr Saša Živanović, Doc. dr Miloš Pjević, Doc. dr Dušan Nedeljković, Lazar Matijašević, mast. inž. maš.
Štampa: Planeta print
Cavitation resistance of chromium-nickel tool steels obtained by hot isostatic pressing
No full textThe paper presents the results of research into the cavitation resistance of tool steels obtained by
the process of hot isostatic pressing. The compositions of the powder mixture for pressing, as
well as the parameters of the HIP process, primarily temperature and pressure, were investigated.
The pressing temperature ranged from 1000-1150°C, the pressing pressure was 100 to 300 MPa,
and time was 3-4 hours. These steels are used for the production of equipment parts in
metallurgy, mechanical engineering and mining. The cavitation resistance of three series of steels
with different nickel and chromium content was tested using the ultrasonic vibration method with
a stationary sample according to the ASTM G32 standard. The reduction of the nickel content in
the composition of the steel has a favorable effect on the development of the martensitic
transformation and the increase in the hardness of the steel. The presence of chromium improves
the mechanical properties and chemical stability of steel. The obtained cavitation speeds below
0,11mg/min indicate a good cavitation resistance of the samples and the possibility of application
in conditions of exploitation where the presence of cavitation, corrosion and wear is expected
A comparative analysis of algorithms for the determination of resonant-affected zones for surface mining and bulk material handling machines
No full textUsing two different approaches, identification of the resonant-affected zones
was performed over the domains of two variable parameters of the
superstructure of a stacker machine that was in the design stage – the
inclination angle of the discharge boom and the velocity of the belt conveyor,
which is the key parameter of the variable periodic excitation load caused
by the eccentricity of the discharge pulley of the conveyor. The first method
varies the velocity of the belt over the entire domain in fixed step increments,
whereas the second method searches for the boundaries of the resonantaffected zones around the resonant velocities of the belt by adaptively
varying the step size. In the first approach, the fixed step size was divided by
10 in each subsequent analysis until all zones were fully defined and the
results satisfied the predefined criterion of precision. Quality of the results
obtained by the two methods were compared with regards to precision and
time-to-completion. Although both methods have produced satisfactory
results, the step size needed to obtain the required degree of precision using
the fixed step approach has resulted in excessive computation times, with
debatable feasibility for practical application of such an approach
WHO USES BIM INFORMATION?
No full textMost of the current efforts in the BIM sector are focused on the proper and complete structuring of all data on AECO (Architecture, Engineering, Construction, and Operations) projects in order to provide all the necessary information. The ISO 19650-1 and ISO 7817 (Level of information need) standards state that attention should be paid to who, when, why and to what extent will use information. In doing so, only information relevant to the AECO sector is taken into account, while broader social needs are neglected. This problem has become more pronounced recently with the need to include in BIM models information that warns future users of possible dangers, as well as information relevant to regulatory bodies.
The paper outlines current initiatives to include information of importance to the wider community such as Golden thread of information and Regulatory Information Requirements. Existing studies on the possibility of including information on the ways of use and users of facilities in the BIM model are presented. These researches refer to areas such as building performance analysis and representation of the building use. Finally, new technologies such as IDS and ICDD are presented. The IDS is developed for the specification and verification of information requirements, and ICDD to support effortless access to archived documents. Both rely on metadata to define ways of using information. However, as both use natural language text for this purpose, the paper advocates the formalization of metadata that describes ways of using information
Analysis of Service Problems of Caustic Tanks Installed in Oil and Gas Plants
No full textThe paper deals with the one of the most general classifications of atmospheric tanks according to their roof type in oil and gas plants. An overview of recommended periods of inspection of storage tanks is given, together with their structural characteristics. Upon irregularities in the process of water purification, the caustic soda tank is prematurely open for inspection. Visual inspection of the major elements, ultrasonic thickness measurements, penetrant tests of welded joints, and checking the functionalities: cathodic protection system, level controller, electric heater, are performed on the tank. On that occasion, it is noticed that the electric heater is found distorted and inoperative. The damaged heater made of Incoloy 800 is carefully removed from its holder and a new heater is welded to the holder by GTAW procedure. The necessary NDE is performed and required electric parameters after repair welding are confirmed
Ball bearing life assessment depending on lubricant contamination level
No full textThis paper investigates deep groove ball bearing rating life, focusing on the systems approach to service life calculation according to the ISO 281 standard. The schematic presentation of the systems approach factor (also known as life modification factor) aISO, depending on bearing size and operating conditions is shown in the figure below. Lubricant contamination can accelerate damages and fatigue on the bearing contact surfaces, reducing bearing service life. The paper analyzes the impact of lubricant contamination on bearing rating life, using empirical data and standard formulas. The analytically derived diagrams are presented, illustrating the dependence of the rating life on bearing size and various operating conditions, such as lubricant viscosity, sealing quality, and load intensity. The research results provide a more accurate understanding of ball bearing rating life assessment under real operating conditions
Structural integrity assessment of the exit convective steam collector superheater
No full textStructural integrity assessment of parts of the boiler pipe system that are exposed to highpressureduring the working life requires primarily determining the nature of the load, with not only the theworkingpressure and temperature, but also all external loads that should be taken into account. Accordingtotheaforementioned facts, the quality of the basic and additional material used for the manufacture of pressurevessel equipment were of great importance as a final confirmation of conducted methodology. Inthespecific case, the integrity assessment of one of the output collectors of the convective steamsuperheater1at Block 1 of the "REK Bitola" thermal power plant, which was the subject of fabrication and replacementdue to increased durability due to operation for over 40 years, is shown. Proof of the structural integrityofthe newly manufactured outlet collector was proven by microstructural material testing, non-destructiveand destructive material testing and hydrotesting. All of the above was used with the aimof provingtheintegrity of the collector that was manufactured, and all with the aim of making the newpressurizedequipment safe for operation
The effect of build orientations and raster angles on impact toughness of PET-G FDM material
No full textPolyethylene terephthalate glycol (PET-G) material is used in additive manufacturing (AM) for the
production of moderately loaded polyester-based parts. Scientific papers show that build orientation and printing direction angle substantially influence the mechanical properties of additively manufactured specimens. This paper explores the effect of build orientations (flat, on edge and upright) and raster angles (0° and 90°) on the impact toughness. In this study, a low-energy instrumented Charpy Instron Ceast 9050 (Figure 1.) test was used as an experimental method to evaluate the impact behavior of PET-G material. An experimental evaluation of impact toughness in the case of AM impact specimens fabricated with different build orientations and printing angles was performed. The impact tests were carried out on five specimens per batch (a total of 30 specimens). The results obtained from an instrumented pendulum were compared between different specimen groups to gain insight into the influence of build orientations and raster angles on PET-G material impact specimens. It was confirmed that different build orientations and raster angles have a strong influence on the final mechanical properties of this material