Table of Contents


    • Improvement of the design of the string extrusion machine based on the modernization of the worm

      pg(s) 171-173

      An option to modernize the worm of the strand extrusion machine is proposed. The technical solution of this worm of the string extrusion machine is the improvement of the mixing section of the extruder worm, which is located in the gap of the screw line in the homogenization zone of the extruder. This design of the mixing section of the worm of the strand extrusion machine allows to intensify the process of dispersion of agglomerates and mixing of the dispersed phase in the dispersed medium and as a result to obtain a homogeneous structure of the polymer, which in turn allows to improve the quality of the final product.


    • Approbation of the process for obtaining highly porous ceramic filter materials using porous shells on removable spherical carriers

      pg(s) 174-176

      On the example of a powder based on mullite, the process of obtaining highly porous ceramic filter materials using porous shells on removable spherical carriers was tested, including the deposition of thin shell coatings from powder based on mullite on spherical granules of expanded polystyrene, pressing the mixture in the form of evenly distributed in the powder of the same composition ( matrix) and sintering. It’s shown that the resulting material is characterized by a good complex of filtering properties and a developed biporous structure.

    • Innovative plasma-deposited nanothin films for oxygen evolution reaction and their prospective application for electro-ozonation

      pg(s) 177-179

      Water recycling plays a prominent role, especially for water-consuming industries. Thus, wastewater purification becomes indispensable to achieve the ideal degree of quality. Electrochemical processes combined with ozonation are chosen as advanced treatments to be studied and developed in this work since they can operate at ambient conditions and are more efficient and compact when compared to other technologies. The plasma-deposited film used as an electrode seems to be a promising and interesting option. The main objective is to investigate the role of synergistic effects between ozone and plasma-deposited thin film electrodes in hybrid electrochemical and ozonation processes of water contaminants degradation. The essence of the process is to find both the active, sustained, and photostable plasmadeposited thin-film electrocatalysts, which enhance the degradation process with the combined action of ozone. Therefore, the chemical stability of developed thin films after contact with ozone is one of the significant requirements for further application.

    • The influence of the composition of the working fluid on the characteristics of high-voltage electric discharge in the “hydrocarbon liquid–Al powder” disperse system

      pg(s) 180-182

      Physical modeling of processes in a layer of Al powder in kerosene and ethyl alcohol during high-voltage electrical discharges in the spark discharge mode was carried out. The regularities of the distribution of plasma formations in the volume of the discharge chamber were studied when using ethyl alcohol and kerosene as working substances with an increase in the number of discharges. It is shown that the use of kerosene as a working fluid leads to an increase in the intensity of the formation of discharges between particles. It has been established that ethyl alcohol as a working fluid makes it possible to relatively stabilize the discharge mode, as well as to increase the number of discharges before the appearance of visual signs of the presence of residual nanocarbon, as a result of which it is possible to achieve greater dispersion of the processed powders. The possibility of synthesis of submicron and ultradisperse particles during highvoltage electric discharge processing of aluminum powder in a hydrocarbon liquid (alcohol or kerosene) due to the electrothermal effect of the discharge plasma on the powder particles has been confirmed.

    • Analysis of strength, microstructure and hardness of the butt-welded K-joint

      pg(s) 183-186

      It is well known that there are several ways to make a butt weld depending on the thickness of the plates to be welded. This paper shows how important it is to prepare the surfaces to be joined by welding. In this paper, the 15 mm thick plates, made of mild steel S235JR, were welded face-to-face with a K-weld using the MIG welding method. The preparation of the plates before welding was not satisfactory, according to empirical instructions, and the resulting weld has defects. Four plates were welded face to face, resulting in two welds. The welds cooled in different ways after welding, one was cooled more slowly in air, and the other was cooled more quickly in water. After welding and cooling the welds, a metallographic analysis of the microstructures of the welds was carried out, and then their hardness was measured using the Vickers method. The conducted metallographic tests concluded that the heat-affected zone has a fine-grained structure, and the melting zone has a cast structure. After the hardness measurement, it can be seen that the hardness values in both the melting zone and the heat-affected zone increase from the root to the surface of the weld. Finally, a strength calculation was performed to determine how much static and dynamic alternating force the realized welded K-joint can withstand compared to the ideal value with good surface preparation

    • Development of diamond-hard alloy plate (D-HAP) manufacturing technology on the GY850 multi-punch press and study of the characteristics of experimental batches of samples

      pg(s) 187-189

      A two-layer, diamond-hard alloy plate (D-HAP) is the cutting element of a drill bit and consists of a layer of polycrystalline diamond compact (PDC) sintered on a superhard alloy (WC-Co) substrate. The entire D-HAP is manufactured using high pressure and high temperature technology. In the FSBI TISNUM the GY850 multi-punch press with a working reaction volume of ≈135 cm3 is used to create high pressure. In one working cycle, sintering takes place from 2 to 12 (depending on the dimension-type) of the D-HAP, consisting of a PDC with grains of 20-10 microns, impregnated with a binder metal and bonded to a hard alloy substrate, forming the working element of
      the drill bit.
      The report describes the manufacturing process of various amounts of D-HAP in one working cycle and the results of the study of the profiled contact layer (interface) of the diamond layer with the substrate and the presence of defects in this layer.

    • Effective shrinkage compensating admixture for joint-less fiber-reinforced concrete industrial floorings

      pg(s) 190-193

      The shrinkage is an inherent characteristic of Portland cement concretes, leading to their volume changes, which potentially create preconditions for the development of different types of cracking – prerequisites for integral decreasing of their durability. The elimination of the negative processes from the development of shrinkage in all its varieties (autogenous, plastic, thermal and carbonization) is based on optimization of complex mix design and technological factors, including the use of innovative chemical products – mainly minimizing and/or compensating the volume changes during setting and hardening of the concrete.
      In recent years, new innovative products have entered the world and Bulgarian practice aimed to compensate the shrinkage by initiating of specific additional hydration interactions. These processes give some attractive possibilities for manageable early age increasing of the concrete volume, leading to partial or complete compensation of the negative effect of later shrinkage.
      The report presents full-range complex results for the effective action of a special shrinkage compensating modifier ShCA KEPTONITE on the strength-deformation characteristics of fiber-reinforced concrete for advanced joint-less industrial flooring systems with different purposes, especially for heavy loaded logistic bases.
      It is concluded that ShCA KEPTONITE demonstrates very good performance in direction to strongly minimize the final shrinkage of the concrete tested. The different dosage rate of the product is an optimal for Bulgarian cement used for testing.

    • 3D Design and Prototyping of a Microfluidic Device for Blood Cells’ Investigations

      pg(s) 194-197

      The present study offers an important technological approach for the development of a disposable microfluidic channel using 3D nanoprinter – Photonic Professional GT2 (Nanoscribe, Germany). This publication aims to present 3D modelling, simulation, and prototype of a 3D nanoprinted microfluidic device for the investigation of blood cells. The design of 3D model of a microchannel is realized by the 3D CAD analysis software – SOLIDWORKS. A suitable laminar flow is generated by using computational fluid dynamics (CFD) software. As a result, the critical points of the pressure, velocity and wall shear stress into the microfluidic channel are obtained. An actual physical prototype of the proposed microfluidic device is developed, using a highly innovative technology of 3D nanoprinting by two-photon polymerization. Experimental studies with dilute erythrocyte suspensions are conducted to test the functionality of the developed real-world prototype of nano 3D printed microchannel.