INVESTIGATION OF TRIBOLOGICAL BEHAVIOUR OF PA12 SLIDING BEARINGS PRODUCED BY SELECTIVE LASER SINTERING

This research examines dry sliding of journal bearings made of Polyamide 12 (PA12) using additive technologies, addressing the gap in knowledge related to tribological behaviour in real conditions. In contrast to traditional tribological tests on flat surfaces, in this paper, full-scale journal bearings are tested under radial load. Three different pressure-velocity (PV) regimes were used to determine their effect on the coefficient of friction (COF), contact temperature, and surface morphology change. The results show that after a period of running-in, all tested samples reached a steady state with friction coefficients around 0.1 with insignificant oscillations, which indicates a stable and repeatable friction behaviour. Contact temperatures vary with operating conditions, where they reach their maximum at the most loaded regime, around 90 degrees, but it is still below the PA12 Vicat softening temperature (175°C), which indicates thermal stability. Scanning electron microscopy (SEM) analysis of the surface before and after testing confirms microstructural changes at the contact zone, showing a transition from a particulate to a smoother structure. The intermediate mode used in the test shows an optimal balance between frictional performance and thermal stability. The obtained results demonstrate that SLS-printed PA12 bearings can be applied in conditions without external lubrication, thereby enabling maintenance-free systems with operational parameters suitable for use. This work provides significant insight into industrial applicability and provides a basis for future tests that will deal with long-term tests and comparative evaluation with bearings produced via other additive manufacturing techniques

Electrocoagulation as a new and advanced technology for future challenges in the steel industry's water treatment plants

Water is a basic necessity of life, and it may seem inconceivable to imagine living without it. The environmental impact, together with social and the economic impact of past and traditional water treatments in the steel industry plants and inevitable fact of water scarcity are leading and driving a shift to a new paradigm in water treatments. Nowadays, many communities and countries are approaching the limits of their available water supplies and because of that, many steel industry plants are facing a big problem with water availability. Although water reclamation and reuse is practiced in many countries around the world, current levels of reuse constitute a small fraction of the total volume of industrial effluent generated. In addition, to meet their growing water supply needs, communities are considering other non-traditional sources of water which could lead to water saving. Water reclamation and its reuse have become an attractive option for conserving and extending available water supply by potentially applying different solution based on biological, chemical and mechanical improved solutions. Since these trends are emerging developments in the field of water reclamation and reuse, there are a number of research needs associated with these topics. Here proposed research is needed to better understand the issues present in traditional water treatment plants in steel industry plants, to propose and explain innovative technologies, which are improving traditional solutions of the water treatment plants, and to develop tools and other assistance for the steel industry plants to implement successful water reclamation and reuse projects

APPLICATION OF SEM ANALYSIS IN THE EVALUATION OF SURFACE CHARACTERISTICS OF CONTEMPORARY PROSTHETIC MATERIALS AFTER PROFESSIONAL HYGIENE PROCEDURES

Scanning electron microscopy (SEM) offers a high-resolution method for detecting microstructural surface changes in dental materials caused by routine professional hygiene procedures. This in vitro study utilized SEM to investigate the effects of ultrasonic scaling and professional brushing on the surface microtopography of zirconia restorations, fabricated by CAD/CAM milling or veneered with ceramic. Specimens (n = 36; 4 × 4 × 2 mm) were obtained from 3Y-TZP-LA zirconia blocks and divided into four groups based on surface finish (polished or glazed) and fabrication method. Each subgroup was subjected to either ultrasonic scaling or brushing with an abrasive polishing paste for 1 minute, repeated in 10 cycles to simulate the effects of five years of clinical maintenance SEM imaging at 150×magnification (Model JSM-6390, JEOL, Japan) was performed before and after treatment to evaluate micromorphological changes. SEM allowed precise identification of surface defects, including microcracks, abrasive wear and glaze degradation. The most significant changes were observed in glazed samples exposed to ultrasonic scaling, with surface alterations measured at 88.31 μm for veneered zirconia and 45.38 μm for CAD/CAM-milled zirconia.The results demonstrate that standard professional hygiene procedures can significantly affect the surface integrity of glazed zirconia restorations. SEM analysis proved to be an essential diagnostic tool for early detection of clinically relevant surface damage, offering insights into material behavior and supporting the development of tailored maintenance protocols

Unsteady Fluid-Structure Interaction Characteristics of a Reversible Mixed-Flow Pump in Micro-Pumped Hydro Storage

The reversible mixed-flow pump (RMFP) is widely employed in micro-pumped hydro storage to efficiently meet the energy storage and generation demands of microgrids. However, frequent switching between operational conditions intensifies the fluid–structure interaction effects in RMFP, leading to operational instability and blade fatigue damage. In this paper, the unsteady flow and dynamic characteristics of RMFP in pump and turbine modes are systematically investigated through numerical simulation and experimental verification. Comprehensive comparative analysis was conducted on the pressure distribution, radial force, as well as the deformation and stress distribution at different locations of the impeller blades under various operational conditions in both pump and turbine modes. The results show that: In pump mode, the pressure distribution on the blade’s pressure side is uniform, while in turbine mode, a localized high-pressure region forms at the inlet under high head condition (9 m). Significant fluctuations in radial force are observed under low flow rate pump condition (0.8Qd). The maximum deformation of the impeller is 0.1236mm in pump mode under low flow rate condition (0.8Qd) and 0.184mm in turbine mode under high head condition (9 m). Equivalent stress concentrations predominantly are observed at the blade inlet in turbine mode and the blade outlet in pump mode, with significant stress accumulation at the hub-bearing connection. These findings provide valuable insights for the operational stability of the RMFP rotor system and offer guidance for the structural optimization of impeller blades

Drying Kinetics and Stability of Fatty Acids in Grape Pomace Seeds Under Mild Thermal Conditions

Grape pomace, a significant by-product of the wine industry, is rich in health-promoting compounds, including polyunsaturated fatty acids, dietary fiber, and polyphenols, and holds strong potential for use in functional foods and nutraceuticals. This study investigates the effects of low-temperature convective drying at 40°C on the drying behavior and fatty acid composition of grape seeds from ten Vitis vinifera L. cultivars. To model the drying process, six thin-layer drying models were applied. Among them, the Logarithmic model provided the best fit for most cultivars, showing excellent agreement between predicted and experimental drying curves. Effective moisture diffusivity values varied considerably among cultivars, reflecting differences in pomace structure and seed composition. Fatty acid analysis via gas chromatography revealed that polyunsaturated fatty acids—particularly linoleic acid—were the predominant lipid class in fresh grape seeds. After drying, a moderate reduction in polyunsaturated fatty acids was observed, accompanied by a corresponding increase in saturated fatty acids. Despite these changes, certain cultivars, such as Prokupac and Merlot, retained favorable nutritional profiles. The results support the application of mild drying protocols to preserve the functional quality of grape seeds while improving energy efficiency. This research contributes to the sustainable valorization of grape pomace and highlights its potential applications, such as functional oil ingredients, antioxidants in skincare, and encapsulated nutraceutical formulations.Contract No. 451-03-137/2025- 03/200116 and Contract No. 451-03-137/2025-03/ 20010

VAT PHOTOPOLYMERIZATION RISK ASSESSMENT USING THE KINNEY METHOD

Additive manufacturing technologies are becoming increasingly prevalent across industries, educational institutions, and even households. Their primary application lies in the production of prototypes and components with intricate geometries. However, despite their widespread adoption, the potential risks these technologies pose to occupational safety and human health remain insufficiently explored. This paper presents a risk assessment of one of the most widely used additive manufacturing processes—Vat Photopolymerization. The evaluation was conducted using the Kinney risk assessment method to identify potential hazards associated with the technology. Based on the findings, appropriate safety measures were proposed to mitigate risks and enhance workplace safety

EVALUATION OF SPECIMEN GEOMETRY FOR RELIABLE MECHANICAL TESTING OF THERMOPLASTIC ALIGNER MATERIALS

A thorough understanding of the variuos mechanical properties of thermoplastic materials is crucial for effective aligner treatment. The appropriate testing parameters and specimen shape for mechanical testing of aligners must be determined in order to obtain reliable results and accurate testing conditions. The aim of this study was to evaluate whether the rectangular shaped specimens, as proposed in previous studies, are suitable for Digital Image Correlation (DIC) testing. In this experimental study, a single type of material was used: Leone aligner PET-G sheet. Material was used in its original, uniformed, and flat form without thermoforming process prior to testing. Rectangular specimens of 1 mm thickness were laser cut to 20x5 mm. A total of five specimens were tested. Each specimen was spray painted with white and black acrylic paint to generate high contrast spots. All specimens were tested individually after fixing them manually in the universal testing machine. The tensile test was performed at speed of 1 mm/min. The specimens’ behaviour under load was evaluated using DIC method. The results showed that rectangular specimens did not consistently fracture in the central region where the stress was expected to be the highest. Instead, fractures occurred in the clamping areas, indicating that the stress concentrations were introduced by the fixation, rather than the material itself. Based on these results, rectangular specimens are not recommended for mechanical testing of aligner materials, as they showed inconsistent fracture locations and non-uniform strain distribution

Using CFD as a Replacement for Expensive Experiments in Education

In this paper, the authors analyzed the use of computational fluid dynamics (CFD) in education. The teaching of fluid mechanics today is mostly based on the theoretical approach. Although, throughout history, it has been shown that the earliest knowledge of fluid mechanics was gained through practical experience and experiments. Apart from this advantage, laboratory exercises and experiments also have numerous disadvantages. Experiments require significant financial resources, equipment and device maintenance. Many complex and specific experiments are not easy to perform in laboratory conditions. This leads to repeating the same experiments over generations. Student safety is also an important factor. During certain experiments, an increase in pressure or temperature may occur, leading to the risk of explosion or fire. Here we consider the possibility of replacing laboratory exercises by using CFD software. Computational fluid dynamics is gaining more and more importance as an alternative to classical laboratory exercises. This technology enables reliable virtual simulation of various fluid phenomena. The application of CFD in education would allow students to experiment with different parameters and scenarios without exposure to hazards, with more accurate and deeper data analysis. The paper also compares CFD software. Software is generally classified into two groups: open source and commercial software. Two open source software are presented in detail: OpenFOAM and SimFlow. On the example of airfoil NACA 0012, in both software, the simulation results were analyzed

Structural response of Autoclave due to vibrations and optimisation of its supports by spring elements

This paper will present a novel approach to supporting a piece of process equipment subjected to long-term exploitation conditions, with the main goal of improving its reliability and safety. Optimising the supports of the process equipment (in this particular case, 16 autoclaves used for coal drying) began by measuring the load at the support points. It was followed by an analysis based on good engineering practice to develop a new technical solution. The old support solution represented a rigid connection between the autoclave envelope and the supporting structure. Meanwhile, the new approach introduced spring supports, thus providing flexible connections between the Autoclave and the structure. This flexibility ensures that the load on the vessel's shell is reduced significantly and that stress distribution at the support points is uniform. Simultaneously, the load distribution in the structure's support zone is significantly more favourable. The economic benefit of such an approach and a reflection on sustainability are also discussed