Table of Contents


    • Synthesis of machine – tool racking using a genetic-morphological approach

      pg(s) 3-9

      A fundamentally new methodological approach to the creation of progressive machine-tool equipment is proposed when considering a material point as a carrier of genetic information in the synthesis of technical systems of the “object” type. The main attention is paid to the search for new technical solutions with the use of tangential clamping, which allows one movement to simultaneously clamp several cutting tools offset from the axis of rotation, for example, in the form of carbide non-regrowth inserts.

    • Efficiencies and losses comparison of three steam turbines – from conventional, nuclear and marine power plant

      pg(s) 10-14

      This paper presents an analysis and comparison of three steam turbines and its cylinders: from the conventional steam power plant, from nuclear power plant and from the marine propulsion plant. The best parameters for the comparison of whole turbines and its cylinders are: energy loss per unit of produced mechanical power, exergy destruction per unit of produced mechanical power, energy efficiency and exergy efficiency. Steam turbine from marine propulsion plant shows the worst performance, regardless if observing each cylinder or the whole turbine – it has the highest losses per unit of produced mechanical power and the lowest efficiencies (both energy and exergy). Such results can be explained by a fact that marine steam turbine must be much more dynamic in operation in comparison to other two turbines. Also, marine steam turbine analyzed in this paper did not possess steam reheating between the cylinders as the other two observed steam turbines, what has a dominant impact on the obtained results.

    • Analysis of sinking of GRP pipe string DN 1600

      pg(s) 15-21

      The aim of this research it was the installation of a discharge sea water pipeline DN 1600 of GRP (glass-reinforced plastic) material in Vlore Bay. The analysis of the sinking of the pipe string has been carried out by using CAESAR II software and considering different load cases. The calculation was carried out for static condition (sustained load) and transient condition (occasional load). In consideration were taken the allowable stress due to bending for pipe and allowable stress for joint subjected to freezing. From the calculation it was evident that the most critical effect on the GRP pipe has done by the position of Concentrated Force due to the presence of sledge (approx.. 2 tons), not disassembled from the string after moving in the position from the shore. In these cases, where the central crane has been maintained fixed or moved downward, the maximum bending stress on the pipe was 12.03 MPa. According to the verification carried out for pipe wall in the transient condition (occasional load) the stability was good and for the joint, was shown, in the worst scenario, a bending stress 158% of the allowable one. In this case it is possible to have the crack of the resin used for the freezing of the joint but not the failure of the system joint + pipe that can withstand without, failure, a stress 3 times greater than the allowable stress for pipe according to EN1796.


    • Modeling and experimental evaluation of the possibility of using a radial-shear rolling mill for recycling bar scrap of ferrous metals

      pg(s) 22-24

      This work is devoted to the study of the use of radial-shear rolling mills for recycling bar scrap and some metal products from ferrous and non-ferrous metals that have served their service life to obtain a ready-made commercial product. In particular, the paper presents the results of computer modeling and experimental research of the process of scrap metal rolling in the form of rebar on a radialshear rolling mill into a round cross-section bar, which prove that some metal products that have served their service life after recycling using the proposed technology into finished commercial products in the form of bars can find further use without remelting.

    • Alternative possibilities for application of foamed silicate materials

      pg(s) 25-27

      In summary form, some trends in the production and application of foamed silicate materials obtained from recycled waste materials are presented. The existing possibilities for the use of different fractions of foam glass granules for the preparation of various products (lightweight concrete, colored decorative panels, etc.) are considered. Experimental samples are prepared in which the average value of the thermal conductivity coefficient =0.24±0.13 W/m. K was established. The main technological factors determining the operational characteristics of the material and the existing potential prospects for their optimization are analyzed.

    • Thermodynamic analysis of a 500 MW ultra-supercritical pulverized coal power plant

      pg(s) 28-31

      This paper analyses the performance of a future planned 500 MW ultra-supercritical pulverized coal power plant. The steam cycle configuration comprises a single-stage reheat, four high pressure feedwater heaters, three low pressure feedwater heaters and the deaerator. The electricity generation unit consists of a high pressure turbine, an intermediate pressure turbine, two double-flow low pressure turbines and the electric generator. The analysis is carried out for live steam temperature of 600 °C and pressure of 300 bar while th e reheat steam temperature is 610 °C and the pressure is 50 bar. The condenser pressure is 0.039 bar. The analysis revealed that the ultra-supercritical power plant achieves a gross thermal efficiency of 47.39% and a net thermal efficiency of 45.14%. The specific CO2 emissions per unit of generated electricity are 733.4 kg/MWh. Relatively to existing subcritical units, the analyzed ultra-supercritical power plant achieves a net efficiency gain of 9%-pts. and a CO2 emission reduction of around 20%.


    • Modeling of the process of ultrasonic flaw detection of materials with internal microdefects of different origin

      pg(s) 32-33

      Miniaturization of technical products is one of the driving forces for the development of high-tech systems. The article considers the most well-known method of determining microdefects of microwelded joints – the method of ultrasonic flaw detection. It is known that microdefects weaken the cross-section of the micro-seam, reduce its strength and are stress concentrators. A dynamic computer model of ultrasound propagation in microwelded welds of metal containing defects of micrometric size of various shapes filled with gas (most often, air) was created. For ultrasonic control, oscillations with a frequency of 0.5 MHz and a direct transducer emitting longitudinal waves perpendicular to the contact surface into the welded joint were used. On the basis of results of computer modeling the regularity of sensitivity of measurement of microdefects from parameters of the ultrasonic microdefectoscope which with a high degree correlates with experimentally received data is revealed.

    • Influence of the pressing force on the strength properties of sintered materials based on water-dispersed iron powders alloyed with copper

      pg(s) 34-37

      In this publication we study the influence of the pressing force on the strength characteristics of sintered materials based on water – dispersed iron powders alloyed with copper. Three brands of iron powders were studied – AHC 100.29, ASC 100.29 and ABC 100.30, to which 2 and 4% electrolytic copper were added. After pressing with a force of 300 ÷ 800 MPa, they were sintered at a temperature of 1150 ° C for 1 h. Experiments were performed to determine three strength characteristics – tensile strength, yield strength, elongation. In determining the mechanical characteristics in order to prevent the influence of porosity, five measurements were made for each type of samples, and in the graphical interpretation of the results the arithmetic mean values were used.

    • Preparation and study of new class SeO2 based glass obtained at high oxygen pressure

      pg(s) 38-41

      In recent years, scientists have turned their attention to the synthesis of a new class of amorphous materials – glass with the participation of SeO2 (selenite glass), and to the study of their structure. Among the established centers for systematic research on these materials are the Institute of Metal Science, Equipment and Technologies with Center for Hydro- and Aerodynamics “Acad. A. Balevski” at the Bulgarian Academy of Sciences (IMSETHC – BAS) – Sofia, Bulgaria and the Department of Silicate Technology at the University of Chemical Technology and Metallurgy (UCTM) – Sofia, Bulgaria. These types of glass have specific properties such as high permeability in the visible and the near infrared regions of the spectrum, high refractive index, and low melting point. On the other hand, the amorphous materials in this class of can serve as model compositions. The obtained structural information can be used to form generalizations about the vitreous state and the possibility to modify the structure and properties of glass in order to improve the technological parameters.