Machines. Technologies. Materials.
Vol. 18 (2024), Issue 5

Table of Contents

  • MACHINES

  • TECHNOLOGIES

    • Testing of the structural composite panels to determine the design resistance models

      pg(s) 148-152

      Due to intense climate change, the concept of constructing buildings that ensure a reduced carbon footprint is a priority in EU Member States. In EU countries, the construction of new buildings according to the principle of zero energy consumption will be mandatory in the coming years. The use of highly thermally efficient building materials and high product quality is one of the main objectives for green building requirements. The company Tehnoplast profili d.o.o. from Zagreb develops industrially manufactured prefabricated houses with near-zero energy consumption using innovative prefabricated wall/ceiling composite panels. The innovative structural panels consist of an outer gypsum fibreboard, a thin-walled steel panel core and a polyurethane foam in between. In cooperation with the Faculty of Civil Engineering at the University of Rijeka and the company Palijan d.o.o. from Zagreb, several test programmes were carried out, focusing on the definition of design models for the resistance of the innovative composite panels and their connection. Such design models are not provided for in the current EU building regulations. This article presents the testing of the materials of the panel components as well as tests carried out on the panels and their connections with the aim of determining the relevant parameters for the definition of design models for resistance.

    • Increasing the cutting machinability of 18ChGT steel due to increased sulfide content

      pg(s) 153-155

      When machining steel gear blanks for a long time, problems are observed during their turning and machining. Attempts to improve machinability using various heat treatment methods have not been successful. In this regard, the possibility of the influence of changes in the chemical composition of steel on its machinability was analyzed. The goal was set for the machinability of serial steel 18ChGT to be similar to the machinability of automatic steel, without reducing its mechanical properties. The improvement in machinability by cutting automatic steels is due to the presence of inclusions in its structure, which increase the fragility of the chips. These can be chemical compounds of metals (sulfides, phosphides, selenides, etc.), or inclusions of low-strength metals, for example, lead. The analysis of metallurgical processes for steel production led to the conclusion that the use of sulfides is economically feasible. When processing gears made of steel with a high sulfide content, the average resistance of the WNMG080408 pass plate was 214 pieces on the edge, and when processed from serial steel 18ChGT, the average resistance is 180 pcs on the edge, no changes were recorded for the rest of the properties. Also, when processing 18KChGT steel with a high sulfur content, chip formation was improved, and a reduction in lost working time was observed due to a fourfold reduction in the need to replace reusable containers for chips.

    • Use of hollow spheres to create highly porous permeable materials based on fine powders

      pg(s) 156-159

      The possibility of using hollow spheres to create highly porous materials (HPM) based on fine powders is shown. In the process of obtaining HPM, fine powder acts as a matrix, hollow spheres are used as a pore-forming agent. At the same time, in the initial state, hollow spheres are formed in the form of bead-shaped polystyrene granules (PSG) with a coated shell of fine aluminum oxide powder, followed by the removal of PSG during sintering. The shell prevents the integration of spherical voids into a single system of large pores, providing high purification fineness. It is confirmed that this technology provides an increase in throughput at a given fineness of purification.

    • Optimizing Tensile Testing: The Role of Electrochemical In-Situ Charging in Hydrogen- Metal Interaction Research

      pg(s) 160-162

      Steel components often operate in hydrogen-rich environments, where hydrogen dissolves in the steel. This leads to a degradation of mechanical properties, shifting the material behavior under load from plastic to brittle. To investigate these changes in mechanical properties of various pure metals and engineering alloys in the presence of hydrogen, it is crucial to maintain a stable hydrogen concentration in the sample throughout the tensile test. This paper presents the possibilities of the in-situ electrochemical charging technique as an alternative. In this method, the test specimen is placed in a specially designed tensile/hydrogenation electrochemical cell filled with electrolyte, where the specimen acts as the cathode during the mechanical tests. In those conditions, hydrogen forms on the surface of the specimen, and some of it diffuses into its internal structure. This method offers a reliable and practical approach for studying hydrogen embrittlement and its impact on material performance.

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

      pg(s) 163-166

      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.

  • MATERIALS

    • About the problems of low technological plasticity of steel 04H14Т3R1F used in the production of pipes for nuclear energy

      pg(s) 167-170

      The features of the chemical and phase composition, structure and transformations in boride inclusions in the steel 04H14Т3R1F, used for the manufacture of hexagonal pipe covers used during transportation to the place of regeneration and storage of spent fuel assemblies (FA) of nuclear power plants, have been studied. It has been established that steel 04H14Т3R1F contains two types of boride inclusions (Ti,Fe,Cr,V)2B with a shell of (Ti,Cr,V)2B and (Fe,Cr)2B, which have significant chemical heterogeneity. It is shown that in the process of hot deformation the phase and structural transformations occur: a change in the composition of borides due to the redistribution of elements, dynamic diffusion fragmentation and release of “satellite” particles, brittle destruction of borides, boride transformation. The behavior of boride inclusions and their influence on the mechanical properties of 04H14T3R1F steel at different plastic deformation temperatures was studied.

    • Tribological investigation of titanium composite materials used in aviation

      pg(s) 171-175

      Tribological tests were carried out on four Ti-TiC composite samples to investigate the tribological behaviour of this alloy and the influence of sintering parameters on it. The samples were sintered by SPS using a high voltage electrical discharge. The general sintering parameters of the samples are temperature – 1100°C, heating rate – 10 °C/s, heating time – 3 min, initial pulse current – 260 A, maximum pulse current – 500 A. The different parameters are as follows: the number of pulses used for the first and fourth samples is 1000, for the second and third samples 2000; for the first and second samples a 1 electrode system was used, for the third and fourth samples a 3-electrode system. The hardness of the samples was measured using the Vickers method. The first specimen, sintered with 1000 pulses and 1 electrode system, has the highest hardness of 456.84 HV10. This is related to the fact that this sample showed the best tribological properties: the lowest friction coefficient of 0.39 and the lowest wear rate of 6.4∙10-4 mm3/Nm. It was observed that the samples sintered with 1000 pulses had lower average coefficients of friction: the average coefficients of friction of the first and fourth samples are 0.39 and 0.48 respectively, while the second and third samples are 0.54 and 0.51 respectively. The friction and wear characteristics of the first specimen, which has the best tribological properties, were compared with those of a Ti-Al-V alloy widely used in aviation. The Ti-TiC sample showed a better friction coefficient and better wear characteristics.

    • Analysis of the materials and defects of Helical Submerged Arc Welding pipelines

      pg(s) 176-179

      The work is performed by analysing spiral welded joints Helical Submerged Arc Welding and their most common errors, which they occur during the submerged arc welding process and can be detected by non-destructive tests. Pipelines were made of structural alloy steel, hot-rolled. Welded defects were detected by X-ray method. A microstructural test was carried out to detect internal errors of the weld joint. Mechanical tests were used to determine the effect on change of properties. After detecting errors on the end X-ray, they were welds subsequently corrected. Destructive or non-destructive testing of gas pipeline welds has its justification, mainly for safety reason.

    • Protection of aluminum and aluminum alloys from corrosion

      pg(s) 180-182

      This paper examines corrosion protection techniques for aluminum alloys, focusing on traditional and innovative surface treatment methods. Aluminum alloys are applicable in many industries due to their advantages derived from the good combination of chemical, physical, and mechanical properties. However, they are susceptible to various forms of corrosion, which can critically compromise the structure of the component and lead to damage that does not ensure safe operation. Coatings are necessary for the durability and effective protection of aluminum and its alloys from corrosion, ensuring safe and long-term operation of components in aggressive environments.