Machines. Technologies. Materials.
Vol. 14 (2020), Issue 1

Table of Contents

  • MACHINES

    • On intensifying the research processes of regular motions transformation

      pg(s) 3-11

      The study is a review of the scientific and applied content of the research carried out over the years on the topic, both worldwide and by the authors. The research is structured in a way that presents the topic in its active development over the years, which substantially proves its permanent relevance. The development of the researches of the spatial transformation of motions, oriented towards the synthesis and analysis of spatial transmissions with innovative characteristics, at this stage and up to the present moment for Bulgaria are realized exclusively at the Institute of Mechanics at Bulgarian Academy of Sciences (BAS). The content of the researches carried out at the Bulgarian Academy of Sciences clearly determines their market orientation and, therefore, their place of development was in the “Centre of competence MIRACle – Mechatronics, Innovation, Robotics, Automation, Clean Technologies” at the Institute of Mechanics. The above said makes it inexplicable the decision of the former management of the institute, in the face of Prof. Vasil Kavardjikov (Director) and Assoc. Detelina Ignatova (Project Manager), to ignore this topic when designing a project for the creation of the Competence Centre.

    • Exergy analysis of steam condenser at various loads during the ambient temperature change

      pg(s) 12-15

      The paper presents an exergy analysis of steam condenser at three different loads and in the ambient temperature range between 5 °C and 20 °C. An increase in the condenser load and increase in the ambient temperature resulted with an increase in steam condenser exergy destruction (exergy power losses). At low load, condenser exergy destruction is for the order of magnitude lower if compared to middle and high condenser loads. Decrease of the condenser load and decrease of the ambient temperature resulted with an increase in condenser exergy efficiency. The highest steam condenser exergy efficiencies are obtained at the lowest observed ambient temperature of 5 °C and amounts 81.47 % at low condenser load, 76.10 % at middle condenser load and 74.54 % at high condenser load. From the exergy viewpoint, the optimal condenser operating regime is low load and the lowest possible ambient temperature.

    • Investigation on single phase induction motor efficiency and starting capability enhancement by incorporating magnesium alloys rotors

      pg(s) 16-19

      There is an increasing interest in saving energy through improving single phase induction motors (SPIMs) efficiency due to recent environmental concerns and industrial trends. According to the latest efficiency standards the minimum efficiency that the SPIMs have to present is that of IE3 (premium efficiency). Aiming to meet this target, the researchers have focused on the implementation of new manufacturing techniques, the development of effective design methodologies and the incorporation of advanced but also low-cost materials. In the most cases, the SPIMs rotor is constructed of a high-conductivity material, such as the die-cast copper, which benefits the motor’s efficiency, but deteriorates its starting performance. Thus, the aim of this work is to investigate if the use of die-cast magnesium alloys, which present lower electrical conductivity and cost than the corresponding ones of copper, could lead to the development of topologies with enhanced efficiency and starting capability. To make this happen, the authors proceeded to several investigations regarding the rotor slot configuration and the selection of the proper windings turns ratio along with the run-capacitor value. The derived topologies satisfied all the set requirements and have been proven to be advantageous over the die-cast rotor SPIMs by considering several operational characteristics

    • Automated design of proposal for new construction knitting unit consisting of a needle bed, needles and CAM systems for flat knitting automatic machine

      pg(s) 20-22

      The work proposes a new design of a new kind of knitting unit consisting of a needle bed, needles and cam systems that allow selection in operation only with the needles on the needle bed without any other additional details, such as springing or stopping jack. The proposed construction is designed in accordance with the requirements of modern flat knitting machines with the possibility of individual needle selection. Because the structures are interdependent, the braiding systems are designed to work only with the new proposed needles and needle bed construction. The three new construction for needle, needle bed and cam systems are aligned with one another and allow the introduction of a new principle for electromechanical needle selection with a special electromechanical selector operating with negative selection, i.e. turns the needle off when is on. The choice is made by working with needles with three types of butts, short and long, onesidedly rounded, and long two-sidedly rounded, as well as with cam systems divided into two parts. This makes it possible to remove the additional details used in existing methods. Which would lead to a reduction in the depreciation of the machine and, consequently, to a lower maintenance cost. The designs are designed in Solid works environments, providing excellent exploration and dynamic visualization capabilities.

  • TECHNOLOGIES

    • Improving the resolution and accuracy of temperature distribution on the surface of microsystems using thermographic methods

      pg(s) 23-27

      Improvement of thermographic imaging device by using an automatic scanning system as opaque for infrared radiation of a matrix aperture with a window of transparency at the lens of the thermal imaging lens, leads to improvement of the spatial and temporal characteristics of the thermal imager, namely, its separation from the point of view. As a result of the experiments, it was found that the spatial resolution of the improved thermographic method (compared to the standard method of determination) was improved by 15 – 20%, and the spectral resolution by 0.3 – 0.5 μm. According to the results of the analysis of the processed image, the adjusted temperature scale of the thermogram, which, in turn, allowed to increase the accuracy of temperature determination in each accurate image (the temperature distribution error did not exceed 5.5%).

    • “Equal-channel angular pressing-drawing” technology

      pg(s) 28-30

      This article describes the technology of the combined process “equal-channel angular pressing-drawing”. The analysis of the influence of this process on the structure and mechanical properties of aluminum, copper and steel wires is given. The results of the study showed that the proposed combined deformation method “equal-channel angular pressing-drawing” has a significant advantage over the existing technology for the production of high-strength wire. This deformation method due to the combination of two deformations: severe plastic deformation in a matrix with parallel channels and the process of deformation through a drawing die, allows to get a wire with an ultra-fine structure and a high level of mechanical properties, the required size and shape of the cross section in a small number of deformation cycles.

    • Synthesis and application of new nanostructured materials for the degradation of organic pollutants from municipal landfill leachate

      pg(s) 31-33

      The photocatalytic degradation of pharmaceutically active compounds, persistent contaminants in aquatic media, based on advanced oxidation processes was the subject of investigation. The study evaluates application of three different nanopowder mixtures (ZnO/SnO2, ZnO/TiO2 and ZnO/In2O3) for decomposition of diclofenac, naproxen, ibuprofen and ketoprofen, some of frequently detected pharmaceuticals in wastewaters and landfill leachates. The phase morphology, composition, specific surface area, crystalline structure and optical properties of the newly synthesized nanopowders, prepared by three step mechanochemical solid-state treatment, were characterized in detail. Effects of optimization parameters on degradation rate were examined and a set of experiments were performed in order to investigate influence of catalyst concentration (0.10–0.60 mg mL-1), pH values of ambience (5-9) and initial concentration of pharmaceutics (0.002–0.010mg mL-1) for this purpose.

  • MATERIALS

    • Investigation of anticorrosive behavior of zirconia-titanium coatings in NaCl medium

      pg(s) 34-36

      Sol gel TiO2-ZrO2 composite films were dip coated on stainless steel substrates and treated at 300, 400 and 500oC. The morphology and surface features were examined by Scanning electron microscopy (SEM) and X ray photoelectron spectroscopy (XPS). Xray diffraction analyses (XRD) was applied to investigate the phase composition. The corrosion resistances of the coatings were studied by evaluation of the weight loss in NaCl medium. According to XRD while the Zr-Ti composites are amorphous after treatment even at 500oC. The surfaces of the coatings possess typical island structure. The coatings, treated at 500oC ehxibit higher corrosion resistance than the other two type of samples. This could be explained by the amorphous structure of the composites, which lowers ion and electron conduction, high hydrophobicity and lower oxygen content.

    • Alkali and acid activated geopolymers based on iron-silicate fines – by-product from copper industry

      pg(s) 37-39

      Geopolymer based on iron-silicate fines (fayalite slag) were synthesized in alkaline and acidic media using activation solution
      comprised of respectively alkali silicate and phosphoric acid solutions. The raw material consists of fayalite, magnetite and pyroxene which could be a conglomerate in some particles. The alkali activation occurs very slow at room temperature, while acid activation take place very rapid. The acid activated geopolymer binder phase include cracks probably formed by thermal gradient because of the rapid exothermal reaction. The morphology of the alkali activated geopolymers were presented by porous structure.

    • Literature survey of fatigue analysis approaches of vehicle components made of rubber under the influence of temperature

      pg(s) 40-43

      Vehicle components made of rubber usually exhibit large deformations. Cyclic finite deformations generate temperature in hyperelastic materials. Furthermore it is necessary to take into consideration the effects of ambient temperature. The mechanical properties of rubber depend on temperature and temperature changes can accelerate chemical alteration processes which lead to the material deterioration and fatigue processes. Research on fatigue behavior and fatigue properties of rubber has a great significance for predicting fatigue life and improving durability of rubber products. First purpose of this paper is summarizing the influence of temperature and temperature changes on the fatigue behavior of rubber. The second purpose of this study is to provide an overview of the state of the art on the fatigue life prediction of rubber with primary focus on the different methods available for prediction of fatigue life under the influence of temperature and temperature changes.

    • Improving the Linearized stresses resistance by Nano-Coating, Part-2

      pg(s) 44-54

      The part-2 research is a continuation of part-1 of using a simulation of Nano coating effect on linearized stresses resistance using Finite Element Analysis (FEA) software was carried out. The prime focus here was on exposing a thin Aluminum (Al7075-T6) walled spherical vessel to internal pressure before and after coating, this spherical vessel was coated by Nano- layer using two different materials such as Titanium (Ti) and Nickel (Ni) with thicknesses ranging (100 nm, 500 nm, and 900 nm). Then a comparison of the obtained results was made before and after coating. The results showed that the aluminum Al7075-T6 thin walled spherical vessel successfully coated with Titanium and Nickel separately using ANSYS software. In addition, the results have shown that 100,500 and 900 nm thickness Nickel coated aluminum 7075-T6 thin walled spherical vessel has a better improvement in linearized stresses resistance. These improvements in linearized stresses resistance were equal to 42% with Nickel coating in comparison with Titanium coating of thickness (100, 500 1nd 900 nm). The improvement of the linearized stress highest resistance is about 2.5% and 5% for Ti and Ni, respectively.