Machines. Technologies. Materials.
Vol. 18 (2024), Issue 1

Table of Contents

  • MACHINES

    • Exergy analysis of a complex three-cylinder steam turbine at various loads

      pg(s) 3-6

      Exergy analysis results for the Whole observed steam Turbine and each of her cylinders at three loads are presented in this paper.
      Observation of all cylinders shows that LPC (Low Pressure Cylinder) is the dominant mechanical power producer at the highest observed load, while at partial loads the dominant mechanical power producer is IPC (Intermediate Pressure Cylinder). At Load 100% Whole Turbine produces mechanical power equal to 341.11 MW. IPC is the cylinder with the lowest exergy destruction and the highest exergy efficiency (higher than 95%) at all observed loads. The exergy efficiency of the Whole Turbine (WT) continuously increases during the increase in turbine load (WT exergy efficiency is the lowest at Load 50% and equal to 91.36%, while at the Load 100% WT exergy efficiency is the highest and equal to 92.93%). Analyzed turbine is projected to operate dominantly on the Load 100% because at that load the exergy efficiencies of all cylinders and Whole Turbine are higher than 91%.

  • TECHNOLOGIES

    • Development of copper wire deformation technology

      pg(s) 7-9

      The paper studies the evolution of microstructure and mechanical properties of copper wire during a new combined deformation process. The essence of the technological process is deformation of wire in a rotating equal-channel step matrix and subsequent drawing. The matrix rotates around the wire axis and thereby creates stress due to equal-channel angular drawing and twisting in the matrix. The deformed copper wire was investigated by transmission electron microscopy and EBSD analysis, as well as tensile tests and microhardness determination. The deformation resulted in an ultrafine-grained gradient microstructure having a high component of high-angle grain
      boundaries. The tensile strength of the deformed copper wire compared to the undeformed one increases more than twice from 302 to 635 MPa, and the yield strength increases from 196 to 306 MPa, an increase of 56%. The use of such hardened copper wire in construction will reduce the weight of the structure by reducing the diameter.

    • Charge activity of silicon-containing nanophase particles intended for modification of polymer matrices

      pg(s) 10-12

      The article considers the influence of various technological methods for obtaining nanosized silicate-containing particles. Each of the methods has its advantages and disadvantages, none of them is universal. It is shown that, depending on the methods of formation of particles, their activity changes. Silicon carbide particles obtained as a result of the thermolysis process with preliminary chemical treatment from natural raw materials of organic origin are of interest for further research. These particles have an increased charge activity in relation to other studied classes of charged particles.

    • Processes for wire and arc additive manufacturing (overview)

      pg(s) 13-16

      Wire and arc additive manufacturing is a rapidly developing technology for the production of metal parts used in various industries such us space, automotive, shipbuilding, etc. Today, it is a potential alternative to traditional manufacturing processes due to its shorter lead time, low material losses and cost-effectiveness. In recent decades, this technology has been used to produce components from various materials. This overview examines the methods of realization, the specifics of the technological process, the process parameters and their influence on the formation of the layers and typical.

    • Use of gamma irradiation processing for decomposition of aflatoxins in wheat flour

      pg(s) 17-20

      The article presents the effects of different doses of gamma irradiation on the degradation of aflatoxins B1, B2, G1 and G2 in wheat flour. The experiment was conducted after contamination of wheat flour samples with mixture of aflatoxins with concentrations from 3 μg/kg to 12 μg/kg using reference material. Irradiation of flour aliquots with absorbed doses from 5.8 kGy to 27 kGy was carried out in an industrial gamma irradiation facility BULGAMMA. The concentrations of the aflatoxins before and after the radiation processing were measured by HPLC. The results showed that gamma irradiation with 27 kGy caused the highest degree of destruction of aflatoxins B2 (82 %) and G2 (81 %), followed by aflatoxin G1 (65 %) and to the lowest extend of aflatoxin B1 (59 %). Gamma irradiation with the maximum allowable dose for commercial food irradiation of 10 kGy was not sufficient to destroy the studied aflatoxins to the maximum permissible concentrations in wheat flour.

    • Technological characteristics of composite mixtures for the preparation of thermal insulation structural elements

      pg(s) 21-24

      The technological characteristics of suspensions used in the development of new thermal insulation composite structural elements based on foam materials and inorganic binders (Portland cement) are investigated. The role of the components of the compositions, the parameters of the technological regime and other factors in ensuring adequate workability of the prepared cementitious solutions is considered. Determination of the necessary technological characteristics of composite mixtures ensures their effective distribution in the formwork moulds when forming the specimens, cost-effective performance at production stage and obtaining products with the planned
      functional properties. The existing opportunities for potential application in modern construction of the developed composite elements are analyzed.

    • Cathodic protection for cooling water system

      pg(s) 25-28

      The aim of this research was the installation of a cathodic protection system for the inlet and outlet steel sea water pipeline respectively DN 1800 and DN 1600 mm in Adriatic Sea. It is extremely important to maintain the integrity of metallic structures in contact with aggressive effluents for both economic and environmental reasons. The proper design of cathodic protection system can help maintain this integrity and increase the useful service life of metallic structures. All cathodic protection systems should be installed with the intent of conducting uninterrupted, safe operations. When cathodic protection is applied, it should be operated continuously to maintain polarization for this purpose were calculated the protection current density, coating breakdown, protection current demand, sacrificial material weight, anode contact resistances, anode current outputs and number of anodes to be installed.

  • MATERIALS

    • The influence of aging parameters on thermal, mechanical and structural properties of the EN AW-6060 aluminum alloy

      pg(s) 29-32

      This paper investigates the influence of aging parameters (temperature and time) on thermal, mechanical and structural properties of the EN AW-6060 aluminum alloy. Thermal diffusivity and hardness were measured after applied heat treatments followed by investigation on scanning electron and transmission electron microscopes. Heat treatments included: solutionizing at 550°C for 1 hour followed by quenching in ice water; after quenching samples were aged at two separate temperatures of 180°C and 200°C for 1-8 hours. The results show that hardness gradually increases with aging time achieving peak value of 95 HV10 after aging at 180°C for 5 hours. Thermal
      diffusivity also increases with both aging time and temperature achieving peak values after aging at 200°C for 4 hours. SEM/EDS analysis show the existence of finely distributed precipitates containing Mg, Si and Fe. TEM investigation confirms the existence of rod-shaped precipitates several nanometers in length.

    • Experimental coatings for photovoltaic panels obtained by the sol-gel method based on compositions with the participation of Y2O3 and ZrO2

      pg(s) 33-36

      A summary study of the development of solar energy and the main factors determining the productivity of photovoltaic systems has been carried out. The predominant surface contaminants of solar panels, reducing the efficiency of photovoltaic installations, and the existing different design types of cleaning systems for their effective removal are examined. The main trends in the development of singlelayer and multi-layer hydrophobic and other oxide coatings with diverse performance indicators suitable for solar panels are traced. In laboratory conditions, experimental self-cleaning coatings (based on compositions with the participation of Y2O3 and ZrO2) deposited by the sol-gel method on vitreous samples were obtained. The structure and morphology of the prepared thin films and the technological conditions for the deposition of nanoscale layers with different functional characteristics were investigated. The experimental results represent a prerequisite for the development of a series of additional compositions and a detailed technological regime for obtaining various modifications of resistant, long-lasting self-cleaning coatings, potentially applicable to photovoltaic panels.

  • TECHNOLOGIES

    • Cathodic protection for cooling water system

      pg(s) 52-28

      The aim of this research was the installation of a cathodic protection system for the inlet and outlet steel sea water pipeline respectively DN 1800 and DN 1600 mm in Adriatic Sea. It is extremely important to maintain the integrity of metallic structures in contact with aggressive effluents for both economic and environmental reasons. The proper design of cathodic protection system can help maintain this integrity and increase the useful service life of metallic structures. All cathodic protection systems should be installed with the intent of conducting uninterrupted, safe operations. When cathodic protection is applied, it should be operated continuously to maintain polarization for this purpose were calculated the protection current density, coating breakdown, protection current demand, sacrificial material weight, anode contact resistances, anode current outputs and number of anodes to be installed.