Machines. Technologies. Materials.
Vol. 19 (2025), Issue 10

Table of Contents

  • MACHINES

    • Green waste composter with energy cogeneration – energy storage and utilization

      pg(s) 362-365

      Microbial fuel cells (MFCs) have significant potential for sustainable energy production and waste management, but despite this, they are still not widely commercialized due to several main reasons, such as relatively low power generation, technical challenges, scalability, and others. In the present study, we tested the possibilities for storage and utilization of energy from our developed green waste composter with cogeneration of energy. The composter consists of 24 stacked solid phase microbial fuel cells. The generated energy was increased through a voltage boost converter and used for charging batteries, power banks, and low-energy consumption devices. The composter demonstrated stable operation, and the obtained results regarding the storage and utilization of the energy generated by it are promising for its commercialization.

    • Simulation of roll leveler housing in heavy plate leveling

      pg(s) 366-368

      Roll leveling is a technological process of metal forming, used to minimize the flatness of sheet plates and reduce the level of residual stresses. The report presents the design of a 13-roll leveler for straightening sheet plates of complex configuration. The straightening precision is directly affected by the stiffness of the leveler housing. To determine the characteristics and patterns of deformation, the equivalent finite element model of the leveler housing are established and then the features of stress and strain about the leveler housing are studied.

    • Evaluation of waste heat recovery system design in a commercial cooking oven prototype

      pg(s) 369-372

      In line with the Paris Climate Agreement, the European Union’s Green Deal targets achieving net-zero greenhouse gas emissions by 2050. Accordingly, research and development efforts to minimize the carbon footprint of industrial production processes and products have gained increasing importance, particularly in light of border carbon adjustment mechanisms and compliance requirements. Therefore, reducing the environmental impact of products already in use through innovative design and development is a critical priority. This study addresses these challenges by proposing a novel waste heat recovery (WHR) system integrated into a gas-fired (natural gas and LPG) commercial cooking oven prototype. The main objective is to enhance energy efficiency and reduce emissions by reusing exhaust gases (CO, CO₂ , etc.) generated during cooking. The recovered waste heat is used to preheat the air–fuel mixture, lowering fuel consumption and contributing to energy optimization and environmental sustainability. Inspired by the Exhaust Gas Recirculation (EGR) concept used in automotive applications, the proposed system was adapted for commercial cooking appliances. Simulation studies guided the design process, enabling the development of an original WHR system through university–industry collaboration. The findings highlight the potential of waste heat recovery in commercial cooking ovens to reduce carbon emissions, improve fuel efficiency, and support the transition towards sustainable industrial practices.

  • TECHNOLOGIES

    • REPowerEU and the Hydrogen Gamble: Ambitions, Challenges, and the Road Ahead

      pg(s) 373-376

      The European Union’s REPowerEU strategy places green hydrogen at the center of its plan to eliminate fossil fuels and accelerate the green transition. The strategy targets 20 million tonnes (MTPA) of green hydrogen per year by 2030: 10 MTPA to be produced domestically and 10 MTPA imported. Achieving this requires scaling electrolysis capacity from the current 0.3 GW to 120 GW, a remarkably ambitious, if not unrealistic, target. Current green hydrogen production costs range from 100 to 200 €/MWh, several times higher than natural gas prices, which fluctuate between 20 and 40 €/MWh. In contrast, blue hydrogen, which is produced through natural gas reforming combined with carbon capture and storage (CCS), generally costs between 50 and 100 €/MWh. To bridge the cost gap between hydrogen and fossil fuels, the EU established the Hydrogen Bank with €3 billion to kick-start the market through competitive funding mechanisms. The REPowerEU hydrogen targets have drawn criticism due to limited availability of renewable electricity, underdeveloped infrastructure, and the slow pace of electrolysis deployment. Concerns also focus on the inefficiency of hydrogen use in sectors such as passenger transport, short sea shipping, residential and commercial heating, where direct electrification is significantly more effective. Nonetheless, the EU is advancing regulatory frameworks, developing over 40 Hydrogen Valley Projects, and establishing international import corridors to support market growth. This paper examines REPowerEU’s hydrogen ambitions, balancing its potential as a key decarbonization tool against economic, technical, and logistical challenges that may hinder its realization.

    • Analysis of the correspondence of the obtained involving surfaces of gears designed with CAD systems with the real surfaces

      pg(s) 377-378

      The paper addresses the problem of designing 3D models of gears, how well the resulting involute profile corresponds to the real one. Very often are used 3d models of gears to produce various gears through 3d prototyping. Some of the most used CAD systems (Solid Works, Solid Edge or Autodesk Inventor) are used to design the 3D models. The comparative analysis made shows the accuracy of modelling the involute profile of the 3D models from different CAD systems compared to the real profile, what are the deviations and how suitable it is to use them for 3D prototyping of gears. Solutions are presented to obtain realistic gear tooth profiles.

    • Parameters optimization for manual laser welding of thin metal sheets

      pg(s) 379-383

      Laser welding has become a highly effective technique for joining of metal sheets, offering precision and minimal thermal distortion. The quality of the welds, however, is significantly influenced by the proper selection and control of process parameters. This study focuses on the optimization of key parameters like laser power, welding speed, wire feed rate, and beam oscillation through experimental welding trials.
      The practical part of the research involved welding thin sheets with LW-2000W device at various parameter settings, followed by visual inspection and metallographic analysis of the final welds. The findings provide insights into how parameter optimization can enhance consistency and overall process reliability, offering valuable guidelines for industrial applications where high precision is required.

    • Comparative analysis of conventional and innovative 3D manufacturing of products

      pg(s) 384-387

      With the development of the world, innovative technologies are increasingly used for the purpose of faster, higher quality and cheaper production of machine parts and household materials. Advantages and disadvantages of conventional and innovative production of metal and polymer products are presented, as well as the possibility of replacing metal parts with plastic ones. The mechanical parameters of different types of materials produced through traditional and innovative production are compared. The comparative analysis shows that both conventional and modern 3D manufacturing have their place in modern industry, taking into account all factors and applications.

    • Research into the benefits of composite bricks and brick blocks in building structures

      pg(s) 388-391

      A study was conducted after the production and installation of building composite bricks and brick blocks in a real environment. The studied bricks are products made of a composite material consisting of clay mass from a respective deposit, spherical foam glass granules of various sizes, manufactured using a specially developed technology and straw fibers or plant grain husks, which bricks and brick elements are being pressed and only dried without being fired. These bricks have a standard shape and dimensions and certain physical and mechanical properties, heat, sound insulation and fire protection properties. The purpose of the study is to install them in a construction site – mainly single-family houses and to determine the efficiency and effectiveness of the process of installing the innovative building bricks in a real building structure.

    • Optimizing latent thermal energy storage geometry for storage capacity maximization

      pg(s) 392-395

      In the paper, geometry parameters of a longitudinally-finned vertical shell-and-tube latent thermal energy storage (LTES), which uses paraffin as the phase change material (PCM) and water as the heat transfer fluid (HTF) have been optimized with the objective of maximizing its storage capacity, i.e. the amount of stored and released thermal energy. Three objectives were set: maximization of stored thermal energy in 8 h, maximization of released thermal energy in 12 h and a combination of the two, in which each objective was given equal significance. There geometry parameters were optimized; fin number, fin width and tube diameter. Optimization has been performed using response surface methodology and Box-Behnken approach. Responses have been obtained numerically, through an experimentally validated modeling procedure and solver scheme. The responses for each objective were fitted with a regression polynomial function and the fitness quality was evaluated through a coefficient R2. Optimization procedure offers different optimum values of analyzed parameters for each objective and provides guidance for choosing the favorable values of LTES geometry parameters in order to enhance LTES thermal performance.

    • Laser-induced plasma (LIP) based on high-resolution spectroscopic analysis

      pg(s) 396-399

      This study focuses on Laser-Induced Plasma (LIP) diagnostics based on high-resolution spectroscopic analysis to improve the reliability of Laser-Induced Breakdown Spectroscopy (LIBS) for elemental characterization. The inherently non-uniform and temporally unstable nature of laser-induced plasmas remains one of the major challenges affecting the accuracy of quantitative LIBS results. In this work, we combined deterministic and stochastic modeling approaches to describe plasma evolution, with a particular emphasis on ionization–recombination dynamics. Plasma parameters such as electron temperature (Tₑ) and electron density (nₑ) were derived using Stark broadening and Boltzmann plot methods, while the effects of temporal fluctuations were evaluated using stochastic differential equations (SDE) solved by the Euler–Maruyama algorithm. Experimental validation was performed with StellarNet Nd:YAG-based LIBS systems on a variety of metallic samples. The results demonstrate that incorporating stochastic fluctuations into traditional deterministic models significantly improves plasma parameter estimation. This integrated methodology strengthens the diagnostic capability of LIBS, reduces uncertainty in quantitative analysis, and provides a robust framework for applying high-resolution spectroscopic techniques to the study of complex materials.

    • Research method for assessing the presence of internal-crystallization admixtures in hardened concrete structures

      pg(s) 400-403

      The use of internal-crystallization chemical admixtures of different types is increasingly practiced as an essential part of new innovative waterproofing systems for buildings and facilities, capable of successfully replacing many conventional waterproofing systems – plaster coatings, sprayed, rolled, membranes, etc. The principle is known of action of different types of internal crystallization additives in the composition of the concrete, as a result of which an additional increase in the impermeability of the concrete section is sought, resp. with a contribution to the general waterproofing of buildings and facilities. In such a connection, especially in the presence of established defects, a case for arbitral assessment of the adequate presence (or not) of such admixtures reasonably arises, provided that they have been previously agreed upon between the parties in the investment process. The report discusses a proposed innovative research method for qualitatively and quantitatively assessment to establish the presence of a crystallization admixture in the composition of hardened concrete used for the construction of the defective building structure with impaired waterproofing ability.
      Standard test methods are able to determine basic physical and mechanical characteristics of both types of concrete – without and with additives. The specialized structural methods (low-temperature gas adsorption BET-method, differential-thermal analysis and scanning electron microscopy) in turn have a high information capability regarding the features of the formed internal structure of the two types of concrete in question. On the basis of the obtained integral results, an objective conclusion can be formed as to whether or not such a chemical admixture has been added to the project concretes.

    • Computational Fluid Dynamics (CFD) Optimization of a Fire Monitor for Enhanced Flow Performance

      pg(s) 404-406

      This study investigates the application of Computational Fluid Dynamics (CFD) to optimize the flow performance of a fire monitor. Geometric modifications were implemented and analyzed using CFD simulations, comparing the original design with a modified version. The results demonstrate that the optimized design achieved a notable increase in outlet velocity (0.76 m/s) and a significant reduction in internal pressure (13,328 Pa). These findings highlight the potential for design simplification to improve operational efficiency and reduce costs.

  • MATERIALS

    • Effect of titanium addition on the microstructure of precipitation-hardened martensitic stainless steel

      pg(s) 407-410

      The work aimed to evaluate the effect of microalloying titanium in proportions of 1 to 5 wt.% on the microstructure and microhardness of a precipitation-hardenable martensitic stainless steel. The standard chemical composition of martensitic steel 17-4PH was used, to which 1; 2; 3; 4 and 5 wt.% Ti was added, respectively. Microstructural analyses revealed changes in the crystal grains and precipitation effects from the solid solution of the alloy. Microhardness measurements were also performed, which demonstrated that withincreasing Ti content in the alloy the metallic matrix becomes harder. The study confirms that microalloying with Ti is beneficial for the development of martensitic stainless steels to increase mechanical properties, even without the application of subsequent heat treatments.
      The results obtained in this work represent a starting point for the development of new customized alloy recipes, adapted to specific applications, where a high value of hardness, as well as microstructural stability or wear resistance are required.

    • The Convergence of Artificial Intelligence and Machine Learning in Advanced Laser Processing

      pg(s) 411-412

      The application of laser technology across manufacturing, from automotive to aerospace, has been a key driver of modern industrial efficiency. However, traditional laser processes often rely on static parameters and manual oversight, which can lead to inconsistencies and defects. The recent integration of artificial intelligence (AI) and machine learning (ML) is fundamentally transforming this landscape, moving laser processing from a static, pre-programmed task to a dynamic, self-optimizing system.

    • Effect of Combined Heat and Mechanical Processing on the Hardness and Wear Resistance of X160CrMoV12 Tool Steel

      pg(s) 413-416

      This study investigated the effect of cold plastic deformation at Bridgman anvil chamber temperature on the hardness and wear resistance of X160CrMoV12 steel using hardness testing, X-ray diffraction (XRD), abrasive grinding wear (AEMW) testing, optical examination, and scanning electron microscopy (SEM). Three batches of samples were prepared for the experiment: I – hardened, II – hardened and then tempered at 600°C for 1.5 hours, III – hardened and then plastically deformed. The samples were hardened at three temperatures: 1100, 1150, and 1200 °C. The highest amount of retained austenite, reaching 69.02%, was observed when hardening at 1200°C, while at lower temperatures, 17.36% and 38.14% were formed, respectively. After hardening (batch II), the amount of retained austenite decreased proportionally by approximately 7 times for each hardening temperature. The effect of plastic deformation (batch III) is observed by analysing the hardness of samples from the surface to the depth, reaching an average hardening depth of 0.08 mm. To check how well it holds up to wear, the surfaces of three test batches were tested using an abrasive grinding test with a load of 5N. Hardened and plastically deformed specimens showed greater resistance to abrasion than hardened and tempered specimens. The results confirmed that the optimal hardening temperature for achieving maximum wear resistance of this steel is 1100°C.

    • Anatase or Rutile TiO2 Nanolayer Formation on Ti Substrates by Laser Radiation: Mechanical and Photocatalytic Properties

      pg(s) 417-420

      A laser-induced oxidation method for the formation of a TiO2 layer on a Ti substrate was used. The TiO2 phase can be controlled by an Nd:YAG laser with fundamental frequency at an intensity I = 52.8 MW/cm2 and three different doses. Dose D1 = 3.1×1020 phot/cm2 forms a TiO2 layer in the anatase phase, which possesses the highest photocatalytic, antibacterial and adhesion properties. As the laser dose increases, the TiO2 layer thickness increases from 40 nm to 100 nm, but the photocatalytic decomposition reaction constant decreases. The observed super-linear increase of the TiO2 layer thickness with the laser dose is explained by the presence of positive feedback during the irradiation process. The temperature rises with increasing of the thickness due to the interference-caused decrease of the reflection coefficient. As the thickness increases, TiO2 on Ti structure adhesion decreases from 800 mN to 400 mN due to the formation of a layer with a mixture of phases.

    • Extraction of Antimony as a Critical Element from Secondary Waste Sources

      pg(s) 421-423

      Recovering antimony from secondary sources is increasingly important to ensure a sustainable and secure supply of this critical metal. Industrial residues, waste materials, and by-products offer opportunities for recycling and reprocessing, reducing economic dependence on primary ores. This paper reviews potential waste streams and processing methods for achieving high-yield antimony recovery.