Table of Contents


    • Synthesis and design of hyperboloid gear drives: Methodology and aspects

      pg(s) 285-290

      The high current requirements for the characteristics determining the accuracy, reliability and efficient manufacturing of modern machines, apparatus and devices applicable in various fields of industry and transport in a big extend dictate the applied scientific methodology to the technological synthesis, design and production of gears. In the processes of synthesis and design of the different types of gear transmissions, the designer faces an extremely complex set of questions to solve, which together define the desired optimal construction.
      In this case, an optimal design means a gear transmission that is capable of delivering preliminary defined kinematic and / or strength requirements at minimum design, production and operation costs (including the repair costs during their exploitation). This work presents a review of the methodology, developed by the authors, oriented towards the synthesis and design of spatial gear mechanisms (hyperboloid gear drives), realizing rotations transformation between crossed shafts. The main principles, on which the construction of adequate software programs are based for the synthesis of treated transmissions, are presented.


    • Processing of bimetals in the electrolyte plasma

      pg(s) 291-293

      Electrolyte plasma processing is environment-friendly and high-effective method to treat surfaces of metals and alloys and can be used for heat or thermochemical treatment as well as for cleaning or polishing of metal surfaces. Modes of processes in the electrolytic cell for different metals can partially overlap. So it is possible to perform the same or different processing for different metals (including components of bimetal) simultaneously. This article describes modes to be established at the active electrode during the anodic process, and application of these modes to various types of treatment of bimetals. It is shown that there exists an option of separate or simultaneous heat or thermochemical treatment, as well as polishing of one or both surfaces of bimetals.

    • Development and research of characteristics of two-layer diamond plates for drilling tools

      pg(s) 294-297

      Two-layer diamond-hard alloy plate is the cutting element of the drill bit and consists of a layer of polycrystalline diamond compact (PDC) binded with the superhard alloy substrate (WC-Co).
      In PDC cutter developed in FSBI TISNCM the plate of PDC, 2-3 mm thick and up to 18 mm in diameter, is bonded with a substrate of
      WC-Co, forming the working element of the drill bit. PDC consists of a diamond frame with grains of 20-10 microns impregnated with a binder metal Co. The ratio of the diamond fraction and the binder metal, as well as the size of the diamond grains vary, depending on the specifications. The entire PDC cutter is manufactured using high pressure and high temperature technology. The surface of the PDC plate is ground and polished to the required values.
      Full-scale tests of PDC cutters showed that their impact strength and wear resistance are determined by the quality of the contactlayer between the PDC and the substrate.
      The paper presents the results of the study of the mechanical characteristics of PDC cutters, as well as the microstructure, element and phase composition and defects of the contact layer of PDC with substrate.

    • Investigation and analysis of electrochemical machining of 321-Stainless Steel based on response surface methodology

      pg(s) 298-301

      Electrochemical machining (ECM) is prevalent and competitive manufacturing process which uses for machining of hard and tough materials in high tech industries. Hence, experimental investigations on ECM of different materials play essential role to effectively utilize this process. This paper demonstrates a systematic approach for achieving comprehensive mathematical models in order to investigate the effect of machining parameters on the process responses of 321-Stainless-Steel and analysis of machining performance based on the response surface methodology (RSM). Machining voltage, tool feed rate, electrolyte flow rate and concentration of NaNO3 solution were considered as the machining parameters while material removal rate (MRR) and surface roughness (Ra) were considered as the process responses. Experimental plan was performed by a central composite design (CCD), and the proposed mathematical models statistically have been evaluated by analysis of variance (ANOVA). Analysis shows that the RSM method has been appointed properly as the design of experiments (DOE) method for resolving curvature in ECM process responses. Also, the results show that the machining performance is greatly influenced by machining parameters. Especially the voltage and electrolyte concentration are the most important parameters.

    • Desalination by flue gas humidification-dehumidification using two different flue gas compositions

      pg(s) 302-305

      The objective of the work is to utilize waste heat from power stations’ flue gases in desalination of seawater by humidificationdehumidification. Two power station fuels namely fuel oil and natural gas are considered. The two fuels differ in composition, calorific value, and usage of percent excess air requirements. In order to achieve the same electric power production, the composition (moisture content and specific heat) and amount of flue gases ensuing from combustion of the above two fuels will be different. One humidificationdehumidification desalination scheme is generated and results are compared with respect to the anticipated cost of produced water versus
      the source of flue gases. Cost is calculated on the basis of energy balance and design equations. The scheme includes: preheating of seawater using hot flue gas, humidification of an air stream by direct contact with seawater, and dehumidification of the same stream by indirect cooling in a condenser. In case of fuel oil combustion, desulphurization of the flue gas by seawater is also included. The cost of produced fresh water includes the fixed cost of heat exchangers, condensers, humidifiers, packing, pumps and fans based on the cost index of 2018, and the operating cost is based on the current electricity cost. The results show that the total cost of the produced water is much less in the case of using flue gases ensuing from natural gas fueled power stations. This happens because the flue gases in this case have a very high humidity ratio which will result in the condensation of a significant amount of water on cooling. As a result, the total amount of fresh water produced is greater than in the case of fuel oil flue gases.

    • Automated 2D laser scanning systems for investigations of solid surfaces

      pg(s) 306-309

      Automated optical scanning systems for analysis of solid surfaces are presented in this work. The prototypes are capable of detecting various parameters and irregularities related to the surfaces of solid bodies by measuring the amplitude of modulated signals of the Electromagnetic Echo Effect. The systems allow various sizes of all kinds of surfaces to be scanned and the results to be visualized on a computer screen. The aim of this work is to present two prototype versions (which use analogue and digital measuring devices) and to show their capabilities. Their general purpose is to scan different areas of specimens and visualize their sensitivity to the Electromagnetic Echo
      Effect onto a plot of coordinates but they are also capable of providing valuable information about structural, mechanical and electrical surface parameters.

    • Calculation of the parameters on output current in full-bridge serial resonant power converter

      pg(s) 310-313

      In this paper for full─bridge serial resonant converter, exact general equations for dependencies of phase angle, the maximum voltage of the capacitor and the maximum value of the output current are derived. Mathematical analysis of the this dependence on the resonant circuit dumping frequency when it is excited with pulse voltage with a different frequency than the resonant one is made. This dependences derived in wide a band around the resonant frequency.

    • Analasys of opportunities for development of Bulgarian industrial manufacturing

      pg(s) 314-317

      This publication analyses opportunities for development of Bulgarian industrial manufacturing in conditions of dynamic selfchanging competitive environment during the period 2015 – 2018. A comparative analysis is done for different industrial sectors with purpose to determine the trends in their development and to identify the opportunities for improvement of their production activity. Actual statistical data are used and different methods for the existing information analysis. The specific of development in the leading sectors in Bulgarian economy are identified. In addition, a comparative analysis is implemented as well as a classification of different industrial sectors on the base of Index of industrial production is created. The results show that the realized production of Bulgarian industrial enterprises during the considered period increase. This is a reason to search favourable opportunities for their further sustainable development and competitive location on the internal and external markets. Some fundamental problems and barriers in the industrial enterprises are considered, that obstruct the fast temps of their developments and are presented some appropriate decisions. The current publication put the beginning of a more depth investigation of the effectiveness of the industrial enterprises, their capacity utilization, as well as the development and introduction of different types of innovation decisions that will be implemented during the next two years in the range of a doctoral thesis in the field of the same problematics and researching analogical problems in the more comprehensive aspect.

    • Improving the classification of strategy of innovative activity of the enterprise

      pg(s) 318-320

      The classifications of innovation strategy of industrial enterprises are investigated: their advantages and disadvantages are determined. Classifications of innovation strategy of industrial enterprises are improved. Classification features, types of strategies of innovation activity of industrial enterprises are characterized. The expediency of using a certain innovation strategy of industrial enterprises is substantiated.


    • Al matrix FGM having 5, 15 and 25 % B4Cp reinforced layers

      pg(s) 321-323

      Functionally graded materials (FGM) containing different amounts of B4C particles within 4 layers in an aluminum matrix were produced and characterized. The layers contained B4C particles at amounts of 0, 5, 15 and 25 volume %. In order to form the composite structure, pure aluminum (<10 microns), copper (1 micron) and B4C powders (<10 microns) were utilized. After mixing, functionally graded materials were compacted and shaped in a rectangular cross sectional geometry, having 6.4 mm thickness, 12 mm width and 33 mm length, by cold pressing at 600 MPa pressure. The parts were pressureless sintered at 610 oC for 30 min in high purity nitrogen atmosphere. The properties of the FGM sample were compared with those of the sample which did not contain B4C particles, and which contained 25% B4C particles throughout the whole sample.
      Microstructural examinations were performed by an optical microscope. 3- point bending tests were conducted by a universal testing machine. The sample that did not contain B4C particles presented a 3-point bending strength of 380 MPa, whereas the sample that contained 25 % B4C had a bending strength of 140 MPa. The FGM sample had a bending strength of 190 MPa. However, the failure of the FGM sample was composed of steps. The stepwise failure of the FGM sample was due to delamination and fracture of the layers containing 15 and 25 % B4C. Microhardness values of each layer the samples were determined by Vickers micro hardness measurements.

    • Features of wear of railway wheels tread

      pg(s) 324-327

      Causes of wear particles formation on railway wheels tread were investigated. Structural factors connecting with plastic deformation, formation of “white layer”, and also with non-metallic inclusions and corrosive products of wheel steel, defining wear of railway wheels tread during operation were fixed. Repeating heat-mechanical action on railway wheel tread by interaction between wheel and rail promotes incandescence of stresses and defects (microcracks, separations) that promote wear particles formation having different shape, source and mechanism of nucleation. Results of analysis of microcracks, spalles and wear particles and also of mechanisms of their formation was shown that wear of railway wheel tread is very composite phenomenon. It passes by few mechanisms (fatigue, adsorbtional, corrosive, under friction) and is multifactors process.

    • The phenomenon of reversion in aging magnesium alloys with the rare-earth metals

      pg(s) 328-330

      The reversion in magnesium binary alloys with rare-earth metals (Nd, Sm, Y, Gd, Tb, Dy, Ho) at a temperature of 300ºC has been studied. The phenomenon of the reverse dissolution of rare-earth metals in solid magnesium has been established to begin in all alloys under study already after short-term annealing at 300°C for 15 min. As the annealing time at 300°C further increases, the reverse dissolution of rare-earth metals in solid magnesium first continues and then the magnesium solid solution becomes again depleted of rareearth metals because of their precipitation. The degree of reversion has been found to generally increase with an increase in the atomic
      number of the yttrium-group rare-earth metal in accordance with its position in the lanthanum row: Gd, Tb, Dy, and Ho. The degree of reversion in the alloys with cerium-group metals (Nd, Sm) with atomic numbers below those of Gd, Tb, Dy, and Ho is substantially smaller than that is in the alloys with yttrium-group metals.