Machines. Technologies. Materials. Vol. 16 (2022), Issue 1

MACHINES
- Exergy analysis of a complex four-cylinder steam turbine
  pg(s) 3-7
  This paper presents an exergy analysis of a complex four-cylinder steam turbine, which operate in a coal-fired power plant. Analyzed steam turbine consists of high pressure single flow cylinder (HPC), intermediate pressure dual flow cylinder (IPC) and two low pressure dual flow cylinders (LPC1 and LPC2). The highest part of cumulative mechanical power (787.87 MW) is developed in IPC (389.85 MW) and HPC (254.67 MW), while both low pressure cylinders develop a small part of cumulative mechanical power (70.29 MW in LPC1 and 73.06 MW in LPC2). Cylinder exergy destruction (cylinder exergy power loss) continuously increases as the steam expands through the turbine. The lowest exergy destruction has HPC (13.07 MW), followed by the IPC (20.95 MW), while the highest exergy destructions are noted in low pressure cylinders (24.37 MW in LPC1 and 27.17 MW in LPC2). Cylinder exergy efficiency continuously decreases as the steam expands through the turbine. The highest exergy efficiency has HPC (95.12%), followed by the IPC (94.90%) and LPC1 (74.25%), while the lowest exergy efficiency of all cylinders is obtained in LPC2 (72.89%). Exergy efficiencies of LPC1 and LPC2 are much lower in comparison to other low pressure dual flow cylinders from comparable steam power plants. The whole observed steam turbine has exergy
  efficiency equal to 90.20%.
- On the study of some characteristics ensuring loading capacity of rack drives
  - Emilia Abadjieva
  pg(s) 8-12
  This research deals with the study of some kinematic characteristics, which can be used to ensure the loading capacity of the rack drives, including its hydrodynamic component. A brief analysis of the spatial rack drives in terms of their load capacity is realized. When mutually enveloping tooth surfaces are synthesized, it is possible to appear singular contact points appear on the active tooth surfaces. Two kinds of singular points exist, depending on the normal vector to the meshed tooth surfaces in their common points: singular points of firstorder (called ordinary nodes), and singular points of second-order. Singular points of first order should be registered and eliminated from the mesh region since increased specific friction, worsen lubrication, and heat transfer are present, which result in a decreased loading
  capacity of the gear set A special accent is placed on the registration and elimination of singular points on the tooth surfaces of the synthesized rack drives. Analytical expressions are written defining total transference velocity and its normal component to an instantaneous contact line at an arbitrary contact point.
TECHNOLOGIES
- The technology of obtaining copper-ferrochrome composite material
  - Lyudmila Ryabicheva
  - Alеksandr Dyadichev
  pg(s) 13-14
  The research of the technology of obtaining new copper-ferrochrome composite material has been done. The results of its structure and properties analysis are presented. The material structure consists of the copper base, non-dissolved coarse inclusions of ferrochrome, diffused zones, forming around these inclusions and phases, having formed in the place of completely dissolved inclusions of ferrochrome fine particles. The material has good mechanical properties and a high wear resistance due to the formed solid solutions of the carbides in the copper.
- Study of the microstructure evolution during forging in a new design strikers implementing alternating deformation by finite element method
  pg(s) 15-18
  The study of the microstructure evolution during forging in a new design strikers implementing alternating deformation based on computer modeling by the finite element method was carried out. The influence of the flat face inclination angle was studied, for which models with an inclination angle of 0, 15, 30 and 45 degrees were studied. It was established that the most optimal option is the use of strikers with an angle of 30°. On this strikers configuration the influence of the workpiece heating temperatures and the punch movement speeds was studied. The analysis of these technological parameters on the microstructure evolution showed that both parameters affect the structure grinding intensity, while the influence of the heating temperature is more significant.
- Analysis of specific absorption rate of electromagnetic field, generated by smartphone
  - Magdalena Garvanova
  pg(s) 19-22
  This article analysеs the Specific Absorption Rate (SAR) and outlines the thermal effect in depth of the human head. SAR is the most important dosimetric value when the human body is irradiated with signals in the radio frequency range. For this purpose, a computer model is created using COMSOL Multiphysics software, taking into account the specific characteristics of the human head and the parameters of a working smartphone. This model is suitable for studying the effects of radio waves on humans
- Electricity generation from PV plants up to 2MWp in Albania. Case study: Tërbuf-Divjaka Municipality
  pg(s) 23-28
  Albania has a significant potential of Renewable Energy Sources (RES) and therefore represents a promising energy source for Albania. The use of PV for electricity generation supports the long-term objective of the country’s energy policies set out in the national energy strategy 2018-2030, including support for the development of economic sectors, increasing security of energy supply and environmental protection. The use of Renewable Energy Sources (RES) will help reduce dependence on energy imports and increase the security of energy supply, with quality and without interruption. The possible benefits generated by the PV system implementation for the selected region should be highlighted, as well as the effects of the most sensitive parameters. The solar potential in Tërbuf-Divjakë showed that PV can be the best solution to provide electricity installed on saline non-agricultural lands near the Adriatic coast.
MATERIALS
- Microstructure and hardness of Cu-Al-Ni-Fe alloy after precipitation hardening
  pg(s) 29-32
  Nickel aluminum bronze with the composition CuAl9Ni3Fe3 was investigated in this paper. After casting, the alloy was annealed at 900 °C followed by quenching. Thermodynamic calculation of the existing phases was performed using the ThermoCalc software. Quenched NAB samples were further aged for 1 h at 300 °C, 350 °C, and 400 °C. During the experiment, the values of hardness and microhardness were examined using standardized Vickers measurement methods. Microstructural analysis was performed using scanning electron microscopy equipped with an energy-dispersive spectrometer. During the precipitation hardening, β’ martensite eutectoidly decomposed into α and κ phases causing an increase in mechanical properties.
- Caprolactam distillation: implementation engineering solutions for rotary thin film evaporator
  pg(s) 33-37
  The paper proposes a reconstruction of the distillation of caprolactam for more complete removal of water from the finished product, removing the droplet phase during the process in thin-film evaporators, will improve the final product performance by eliminating the inappropriate indicators alkali content and the optical density of the final product and to ensure its stable high quality. The relevance of the work presented directions for improving the process of production of caprolactam – raw ingredient for the preparation of polymeric materials used in various sectors of the economy. Describes the causes affecting the quality characteristics of the finished products produced from caprolactam. the implementation the liquid distributor and the centrifugal separator would reduce 5 – 6 times droplet entrainment to ensure complete removal of moisture from the final product, will reduce the alkali content in the final product, reduce the rate of optical density and thus bring trademark caprolactam by indicators «alkalinity» and «optical density» to the level of the highest quality product.
- Influence of heat treatment on metallographic and mechanical properties of ductile iron
  pg(s) 38-40
  Due to the mechanical properties (toughness, elongation, tensile strength) that characterize ductile iron, its application in foundry technology is becoming more pronounced every day. The chemical composition and heat treatment of ductile iron have a great influence on the required mechanical properties. Given the operating conditions, the main purpose of heat treatment of ductile iron is to change the desired mechanical properties. Since the specific mechanical properties of ductile iron are generally related to the regularity of the mined graphite nodules, the main objective in production is to produce ductile iron with the highest possible percentage of ductility. In the experimental part of the paper, microstructure and hardness tests were carried out on specimens of ductile iron NL 400 and NL 700 before and after heat treatment by soft annealing (ferritization) and improvement. It was found that the type and corresponding parameters of heat treatment significantly affect the microstructure and the achieved hardness values of the ductile iron test specimens.
- Structural researching of the inner, primary supporting layer from ductile cast iron with a bimetalic roller shell with high-crome material used as an external (working) layer, during a centrifugal casting method of production with a vertical axis.
  - Petar Ivanov
  pg(s) 41-43
  The processes accompanying the formation of the so called carrier (inner) layer, which is formed in the production of bimetallic castings by the method of centrifugal casting are analyzed. Attention is paid to the structural changes caused by the diffusion processes occurring during the casting and crystallization process. Modification with a spheroidizing modifier with a Cr content in the melt above 0.6% was successfully carried out.

International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Machines. Technologies. Materials.
Vol. 16 (2022), Issue 1

Table of Contents

MACHINES

Exergy analysis of a complex four-cylinder steam turbine

On the study of some characteristics ensuring loading capacity of rack drives

TECHNOLOGIES

The technology of obtaining copper-ferrochrome composite material

Study of the microstructure evolution during forging in a new design strikers implementing alternating deformation by finite element method

Analysis of specific absorption rate of electromagnetic field, generated by smartphone

Electricity generation from PV plants up to 2MWp in Albania. Case study: Tërbuf-Divjaka Municipality

MATERIALS

Microstructure and hardness of Cu-Al-Ni-Fe alloy after precipitation hardening

Caprolactam distillation: implementation engineering solutions for rotary thin film evaporator

Influence of heat treatment on metallographic and mechanical properties of ductile iron

Structural researching of the inner, primary supporting layer from ductile cast iron with a bimetalic roller shell with high-crome material used as an external (working) layer, during a centrifugal casting method of production with a vertical axis.