Machines. Technologies. Materials.
Vol. 19 (2025), Issue 5

Table of Contents

  • MACHINES

    • Thermodynamic evaluation of a 250 MW three-cylinder steam turbine from CCPP

      pg(s) 163-166

      In this paper are presented isentropic analysis results of a steam turbine, their cylinders and cylinder parts which nominal power is equal to 250 MW. The analyzed steam turbine is a complex three-cylinder turbine which operates in a CCPP (Combined Cycle Power Plant). Considering all cylinders, the dominant mechanical power producer in the observed turbine is LPC (Low Pressure Cylinder) which produces 111.80 MW of mechanical power in real (polytropic) steam expansion process (almost half of the real mechanical power produced in the whole turbine). Developed mechanical power in turbine cylinders and isentropic losses are directly proportional – higher produced mechanical power will result in higher isentropic losses and vice versa. Whole analyzed steam turbine, their cylinders and cylinder parts show very good isentropic performance and high isentropic efficiencies of around 90%. The isentropic performance of the whole analyzed steam turbine, their cylinders and cylinder parts is in the range of the steam turbines (and their cylinders) from supercritical and ultrasupercritical power plants which are proven to be the best steam turbines from isentropic point of view.

  • TECHNOLOGIES

    • Тhе new features in magmasoft for optimization and improvement the casting technologies

      pg(s) 167-171

      In this issue the main new opportunities in MAGMASOFT® 6.1 /last version of software package MAGMASOFT/ are presented and illustrated. The presentation will introduce you in all general innovations as general innovations in geometry perspective, new options for heat treatment of castings, new possibilities in continuous casting and a new innovation – MAGMA ECONOMICS. With the last option you can now also keep an eye on costs and emissions. With MAGMA ECONOMICS you can add a decision criterion to your decision base. Calculate the costs or look at the carbon footprint and make more informed decisions.

    • A method for correcting the systematic error of thermocouple readings

      pg(s) 175-178

      A mathematical approach is presented for estimation of inertia of thermocouples in unsteady heat transfer processes. The approach allows to estimate the systematic error in measured data and to make a first-order correction, bringing the measurement data significantly closer to the real ones. The efficiency of the method is illustrated by computer simulation of two examples from foundry practice. The symmetry of heat transfer processes is used to identify an important and determining parameter of the inertia of the thermocouple.

    • A mathematical model of the movement of a gas bubble in a viscous liquid

      pg(s) 179-183

      A mathematical model is proposed, describing the movement of a gas bubble in a viscous liquid medium under the action of the Archimedean force. In addition to Archimedean forces and fluid viscosity it takes into account the influence of temperature and pressure of the fluid and of the gas in the bubble. Solutions have been obtained for the movements of a gas bubble in the conditions of a solidifying casting, considering the influence of the bubble size, the pressure in the liquid and the viscosity of the medium on the speed of movement. Software based on the FORTRAN language has been created, which implements the solutions of the model for specific values of the input parameters. The capabilities of the model are illustrated by numerical experiments under different conditions.

  • MATERIALS

    • Effect of laser machining on the change of the microstructure of the surface layer of AlSi11 alloy castings

      pg(s) 184-187

      Laser processing is often used in many technological processes for welding, cutting, marking, etc. However, it has been gaining popularity for several years as a surface modification process, including cleaning, polishing, surfacing, and hardening. These methods are used to modify the physicochemical properties to enhance hardness, wear resistance, corrosion resistance, and the propagation of microcracks on the metal surface. It has been found that the effectiveness of laser radiation (short pulses of laser light) depends on the thermal properties of the alloy being treated and the process parameters. Also significant is optical absorption, which determines the coupling of laser radiation energy to the workpiece during the melting of its surface. The study, considered preliminary, was conducted on flat sparrows of AlSi11 alloy under argon shielding. It was possible to fragment the microstructure components of the studied alloy at depths of several micrometers, depending on the laser power density, spot size, and travel speed. The fragmented α(Al) dendrites in the melted laser zone are oriented toward the temperature gradient. At the very surface, they gradually lose their secondary arms, assuming the morphology of compact cells. This method can harden large or local areas that are inaccessible to other surface treatment methods, such as piston ring gaps in internal combustion engines, specifically the part of the piston shell that operates under extreme thermo-mechanical and tribological stresses.

    • Investigation of the thermal properties of X155CrVMo12-1 steel after quenching and tempering

      pg(s) 188-190

      This paper investigates the effects of oil quenching and tempering at various temperatures on the mechanical and thermal properties of X155CrVMo12-1 tool steel. The steel specimens were austenitized at 1030 °C for half an hour, followed by quenching in oil and tempering at temperatures ranging from 50 °C to 700 °C. Mechanical properties were assessed by measuring the microhardness of the samples after each heat treatment. Thermal properties were investigated using the Xenon flash method (DXF analysis) to measure thermal diffusivity, thermal conductivity, and specific heat. The results show that the highest microhardness values were achieved after quenching,
      while the lowest values were observed for thermal diffusivity and thermal conductivity. Following quenching, the microhardness values gradually decreased with an increase in tempering temperature, whereas the values of thermal diffusivity and thermal conductivity increased. Even after tempering at 500 °C, the microhardness values remained quite high, with only a 23.41% decrease from the quenched state. Furthermore, there was a significant improvement in thermal properties, with thermal diffusivity increasing by 38.34% and thermal conductivity improving by 23.99%.

    • Influence of iron and manganese on the microstructure and mechanical properties of AlSi9Cu3(Fe) alloy castings

      pg(s) 191-194

      The study concerns cooling curves of AlSi9Cu3(Fe) alloy, into which iron (in the form of Al-Fe master alloy – as a substitute for scrap) was introduced with a content of 0.5 to 1.5wt.%. Crystallization analysis by ATD and microstructure studies of Al-Si-Mg(Fe) alloys revealed that up to approximately 0.4wt.% Fe, the formation of iron phases does not significantly affect the microstructure. They are part of multicomponent eutectics such as α(Al)+(Al2Cu,Fe)+β(Si) or α(Al)+(AlXFe;CuYSiZ)+β(Si), which crystallize after the formation of the α(Al)+β(Si) eutectic. In the range of about 0.5wt.%Fe to 0.9wt.%Fe, there is a pre-eutectic crystallization of iron phases, mainly the lamellar-neutectic phase β-Al5FeSi. At more than 1.0wt.%Fe, the morphology of this phase becomes even more unfavorable (due to primary crystallization) and is accompanied by numerous clusters of shrinkage porosity. Such a microstructure has an adverse effect on mechanical properties, primarily affecting plastic properties (yield strength and elongation). To prevent this, the positive impact of manganese additive (in the form of AlMn20 master alloy) was found to transform the morphologically unfavorable β-Al5FeSi phase into α-Al15(Fe,Mn)3Si2 phase with dendritic structure.

    • Mechanoactivated silicatecontaining modifiers for thermoplastic polymers

      pg(s) 195-200

      Compositions of mechanoactivated silicatecontaining particles used as modifiers of polymer matrices have been developed. The morphology, particle sizes of the modifier, the nature of their distribution in the polymer matrix, as well as the topography of the friction surface of samples from modified polymers were studied using scanning electron and optical microscopy. Introduction of mechanically activated particles in concentrations from 0.01 to 2 wt. % into the polymer matrix of a reactoplastic polymer based on epoxy resin leads to multilevel modification, expressed in a change in the morphology of the test sample at the supramolecular, intermolecular and molecular levels. The effect of additives of nanophase modifiers on the wear rate of the developed nanocomposite materials is investigated. The introduction of composite mechanically activated nanodispersed particles into a reactive polymer based on epoxy resin leads to a decrease in the coefficient of friction in the studied range of modifier concentrations, loads and test speeds. Studies of the morphology of the surface of the analyzed samples have shown the presence of a separation layer on the surface of rubbing bodies, contributing to a significant decrease in the coefficient of friction. In the structure of this coating, the presence of nanophases is observed, which have a positive effect on the wear resistance of the developed composite material.