The paper investigates the mathematical modeling of anaerobic fermentation for the utilization of animal wastes. It analyzes various approaches to the mathematical modeling of anaerobic digestion processes. However, most of the models previously proposed do not take into account a number of key parameters such as the levels of micro and macronutrientls (such as K, Na, Ca, Mg, Mo, etc.), values of volatile fatty acids, C/N ratio, pH levels, extent of grinding, moisture, and others. This paper proposes a new mathematical model of anaerobic fermentation under industrial scale conditions. The model was developed on the basis of regression analysis and correlation. It found empirical relationships between biogas yield and 26 different parameters. These parameters are measured by appropriate biosensors in industrial production. Some of them have more significant influence on the fermentation process than others. Overall, the developed mathematical model has the potential to provide useful insights into biogas production and can be used to optimize anaerobic fermentation processes.

This study investigates the thermal response and surface modification of low-carbon manganese-alloyed 20GL steel during electrolytic plasma hardening. The objective was to evaluate the feasibility of surface hardening 20GL steel—traditionally considered difficult to quench—by combining high-rate surface heating with rapid cooling in an electrolyte medium. To achieve this, a transient two-dimensional heat conduction model was developed to simulate temperature evolution in the steel sample under three voltage regimes. The model accounted for dynamic thermal properties and non-linear boundary conditions, focusing on temperature gradients across the thickness. Experimental temperature measurements were obtained using a K-type thermocouple embedded at a depth of 2 mm, with corrections for sensor inertia based on exponential response behavior. A comparison between simulation and experiment was conducted, focusing on peak temperatures, heating and cooling rates, and the effective thermal penetration depth. Microhardness profiling and metallographic examination confirmed surface strengthening and structural refinement, which intensified with increasing voltage. Importantly, the study identified a critical cooling rate threshold of approximately 50 °C/s required to initiate martensitic transformation in 20GL steel. These findings provide a foundation for future optimization of quenching strategies for low-carbon steels by offering insight into the interplay between thermal fluxes, surface kinetics, and process parameters.

This study investigated the electrolytic-plasma hardening (EPH) of cast 20GL steel, used for railway spring beams. The main objective was to analyze the spectral characteristics of the cathodic discharge and establish correlations between the plasma parameters, processing regimes, and resulting surface properties. Optical emission spectroscopy revealed that the plasma at 260 V exhibited a high-energy state with an electron density of ~5.3 × 10¹⁶ cm⁻³ and an electron temperature of 10,031 K. Using these parameters, the heat flux from the plasma to the steel surface was estimated at ~1.5 × 10⁷ W/m², confirming that the discharge provides sufficient energy for surface austenitization. Microstructural analysis demonstrated that the electrolyte flow rate, which determines the cooling rate, is the key parameter controlling phase transformations. At low flow rates, ferrite–pearlite and bainitic structures formed, while a fully martensitic structure and maximum hardness (1046 HV) were achieved at 10 L/min. Tribological tests confirmed the superior wear resistance of the martensitic layers, showing a friction coefficient of 0.454 and a wear volume 3.4 times lower than in the as-cast state. These findings verify that EPH offers an energy-efficient, low-cost method for improving the surface performance and service life of 20GL steel components in heavy-duty railway applications.

The study is devoted to the preparation of the AlMgSi1 (6082) aluminum alloy for the study of its mechanical and physico-chemical properties under rolling conditions. The purpose of the work is to develop a methodology for preparing an alloy that provides reproducible analysis of its properties. The main directions include the study of rheological and plastic properties of the material, as well as thermal effects during deformation. The scientific significance of the work lies in the analysis of the effect of heat treatment and deformation parameters on the plastic fluidity and corrosion resistance of the alloy. The practical significance lies in improving the quality of materials for various industrial applications. The methodology included experiments with heat treatment and rolling, analysis of the microstructure and mechanical properties of the alloy. The tests were carried out on samples at different temperatures and strain rates using the STD 812 torsion plastomer. The results showed that the plasticizing stress of the alloy increases with deformation at low temperatures and decreases at high temperatures. The conclusions confirm the significant influence of temperature and strain rate on the properties of the alloy.

The article deals with the influence of lubricating and cooling technological medium and cutting temperature regime on the efficiency of the cutting process. The article presents the results of experimental studies, which showed that the use of optimal lubricant and cutting temperature control allows to increase the efficiency of the cutting process in the following directions:– Increase of tool durability. The application of coolant allows to reduce the temperature in the cutting zone, which leads to a decrease in tool wear.– Reduction of roughness of the machined surface. The use of coolants allows to reduce the temperature in the cutting zone, which leads to a decrease in the deformation of the machined material and, as a consequence, to an improvement in the quality of the machined surface.– Reduction of cutting forces. The application of coolants allows to reduce the temperature in the cutting zone, which leads to a decrease in friction between the tool and the processed material and, as a consequence, to a decrease in cutting forces.The obtained results indicate that the use of optimal coolant and cutting temperature control are effective ways to improve the efficiency of the cutting process.Recommendations on the use of coolants (lubricating and cooling liquids) and types of coolants to improve the accuracy of the surface layer of machine parts; Recommendations on the creation of new types of environmentally friendly coolants are given.A multifaceted method of selecting new compositions of coolants is proposed. The method is based on the fact that the chemical composition of the part and tool material, machining methods, cutting modes, requirements to accuracy and quality of the surface layer of the part are taken into account when selecting coolants.

This study investigates the effect of plasma spraying energy input on the microstructure and properties of APS-sprayed ZrO2-Y2 O3 (YSZ) coatings deposited on 12Cr18Ni10Ti stainless steel substrates. The coatings were produced under different spraying conditions by varying arc current, arc voltage, plasma gas flow, powder feed rate, and stand-off distance. A specific energy input to powder was used as a comparative parameter to characterize the thermal loading of particles during spraying. The microstructure of the coatings was examined by scanning electron microscopy, and porosity was evaluated from cross-sectional images using image analysis. Microhardness was measured under HV0.1 and HV0.3 loads, surface roughness was assessed using the Ra, Rz, and Rt parameters, and corrosion behavior was studied by potentiodynamic polarization in a 3.5 wt.% NaCl solution. The results show that spraying conditions significantly affect coating density, porosity, microhardness, roughness, and electrochemical response. The lowest porosity was obtained for the coating produced under intermediate spraying conditions and amounted to 3.2 ± 0.5 %, while coatings formed under lower and higher energy input exhibited porosity values of 4.5 ± 0.3 % and 6.7 ± 1.6 %, respectively. A decrease in microhardness with increasing porosity was observed, particularly at the HV0.3 load, due to the influence of interlamellar defects on the effective load-bearing area. The corrosion behavior of the coatings was found to depend not only on total porosity but also on defect morphology and pore connectivity. Overall, the results confirm that plasma spraying energy input strongly influences the structure and performance of APS-sprayed YSZ coatings and can be used to optimize spraying conditions. Keywords: atmospheric plasma spraying, YSZ coatings, energy input, microstructure, porosity, microhardness, roughness, corrosion behavior.