Water-cooled Mold Research Articles

Conjugate gradient method with regularization in estimating mold surface heat flux during continuous casting

The reconstruction of the boundary heat flux between solidifying steel and water-cooled mold wall using measured temperature data is recognized as an inverse heat conduction problem (IHCP). A Tikhonov spatial regularization approach to enhance the smoothness of the Conjugate Gradient Method (CGMr) was proposed which incorporates three different orders of spatial regularization: zeroth, first, and second order. The optimal regularization parameter was selected using a modified L-curve method. The accuracy of the CGMr is investigated with Case 1: a triangular time-spatial variation heat flux, and Case 2: a step change in the form of rectangular variation heat flux. The effects of measurement noise, grid points and time-step size are investigated. The results show that the minimum relative error (eRMS) of the predicted Case 1 heat flux is 1.98%, 7.64%, and 8.02% for zeroth-, first-, and second-order spatial regularization, respectively. The corresponding values for the predicted Case 2 heat flux are 3.82%, 13.42%, and 14.91%. Subsequently, CGMr algorithm is applied to calculate the heat flux in a mold simulator experiment. By comparing the relationship between heat fluxes reconstructed by CGMr after different iteration numbers, it is observed that the recovered heat flux of 2.14 MW/m2 with zeroth regularization remains highly stable.

The Start-Up Phase of Aluminum Billet Production Using Direct Chill Casting

Direct chill (DC) casting has been considered as one of the promising casting methods that can be used to produce aluminum alloys billet. The process is conducted by pouring aluminum metal into a water-cooled mold. The billet shell begins to form when molten aluminum contact directly with the mold (this is also known as primary cooling). Afterward, the starting block is pulled downwards at a specified casting speed to achieve desired aluminum billet. The start-up phase during the DC casting process is considered a crucial step since it may determine the formation of defects in the casting products. This research aims to investigate the casting defects on the aluminum alloy that were formed during the start-up process of DC casting. The results show that the billet failed to form following the downward movement of starting block. Meanwhile, the billet tended to stick to the mold wall due to several factors, such as too low a pouring temperature, a less-round mold shape, the poor quality of the hot top and graphite ring, and the water that entered the mold during the casting process. It also noted several markers of the casting defects that occurred during the DC casting process such as liquation or bleeding, cold folding, billet stuck in the mold, butt structure, and rough billet surface.

Fabrication and thermo-mechanical properties of Ag9In4 intermetallic compound

To ensure optimal working conditions for the next-generation power modules, a comprehensive understanding of the thermo-mechanical properties of the joint layer between the chip and substrate is essential. The Ag9In4 intermetallic compound is a promising candidate for the joint layer; however, related material data are not available. This study proposes a straightforward method to fabricate densified and pure Ag9In4 bulk samples. Bulk Ag9In4 with less than 0.1% porosity was fabricated by pouring molten alloy into the water-cooled mold, followed by a two-step heat treatment at 520 °C and 250 °C for 40 h each. Properties, including Young's modulus, hardness, creep behavior, and coefficient of thermal expansion, were measured from 30 °C to 250 °C. As the temperature increased, the Young's modulus of Ag9In4 decreased linearly from approximately 117.9 GPa–95.9 GPa. Correspondingly, the coefficient of thermal expansion increased linearly from 19.2 μm/m/°C to 22.69 μm/m/°C, with an average value of 20.58 μm/m/°C. Moreover, the hardness decreased from 4.1 GPa to 1.7 GPa following an exponential relationship with temperature. At 250 °C, a significant creep phenomenon was detected in Ag9In4. The creep mechanism changed from dislocation climb to dislocation diffusion, with creep stress exponents of 33.1 and 10.6 at 30 °C and 250 °C, respectively.

Electroslag Hollow Ingots for Nuclear and Petrochemical Pressure Vessels and Pipes

The paper presents ground reasoning and results of experiments and modeling of heavy hollow ingot manufacturing using advanced electroslag technology. The requirements for ingots for huge diameter reactor pressure vessels include high density, homogeneity, and minimal segregation, which are very difficult to achieve by traditional casting. In the electroslag remelting process (ESR), hollow ingots form in between two copper water-cooled molds under effective heat removal. This improves the solidification pattern due to the shortening of a solidifying volume thickness more than twice compared with a solid ingot of the same diameter. The shallow liquid metal pool and narrow mushy zone at the ESR hollow ingot solidification assure their high metallurgical quality. Due to the dense and low segregation structure, ESR hollow ingots proved to be used for as-cast pipes and heavy wall billets for further forging. The results of a mathematical simulation within the range of simulated dimensions (the outer diameter up to 2900 mm, wall thickness up to 750 mm) also predict the favorable solidification pattern for thick-wall hollow ingots of big diameters. The analysis made and the modeling results provide a framework for scaling up the sizes of hollow ingots produced by ESR and widening their application for manufacturing heavy wall large diameter shells for nuclear and petrochemical industries. The higher reachable productivity of hollow ingot formation and lower capacity of power supply source than that for solid ingots of the same diameter and weight are also preconditions of their energy saving and cost-effective manufacturing.

Production, Mechanical and Functional Properties of Long-Length TiNiHf Rods with High-Temperature Shape Memory Effect.

In the present work, the possibility of manufacturing long-length TiNiHf rods with a lowered Hf content and a high-temperature shape memory effect in the range of 120-160 °C was studied. Initial ingots with 1.5, 3.0 and 5.0 at.% Hf were obtained by electron beam melting in a copper water-cooled stream-type mold. The obtained ingots were rotary forged at the temperature of 950 °C, with the relative strain from 5 to 10% per one pass. The obtained results revealed that the ingots with 3.0 and 5.0 at.% Hf demonstrated insufficient technological plasticity, presumably because of the excess precipitation of (Ti,Hf)2Ni-type particles. The premature destruction of ingots during the deformation process does not allow obtaining high-quality long-length rods. A long-length rod with a diameter of 3.5 mm and a length of 870 mm was produced by rotary forging from the ingot with 1.5 at.% Hf. The obtained TiNiHf rod had relatively high values of mechanical properties (a dislocation yield stress σy of 800 MPa, ultimate tensile strength σB of 1000 MPa, and elongation to fracture δ of 24%), functional properties (a completely recoverable strain of 5%), and a required finishing temperature of shape recovery of 125 °C in the as-forged state and of 155 °C after post-deformation annealing at 550 °C for 2 h.

On online texture quality control and management of continuous processes for the production of non-ferrous sheets

The results of the studies of the connection of texture parameters and the quality characteristics of commercial batches of the finally rolled or finally annealed tape made of fcc- materials, which differ in the value of stacking fault energy, phase composition and processing technology are considered. Strips of brass L68 and L63 containing ~62.5 and ~64% of copper and aluminum alloy AMg2 were hot rolled from ingots that were cast in water-cooled and electromagnetic casting mould respectively. Cold rolling was carried out with intermediate annealing to the state of complete recrystallization in the resistance heating furnace (AMg2) or in the induction annealing line (brass) to the finite thickness: ~0.3 mm (AMg2) and 0.6–1.0 mm (brass), varying the degree of the finite plastic deformation. During the final annealing of the brass strip in the line of induction annealing and etching, the speed was varied. The tape was tested for breaking, Vickers hardness number, cutting-out and draw-forming of “glasses” in the combination die. In particular, we controlled the characteristics of the anisotropy of plastic properties, the magnitude of the relative earing and intensity 200 and 220 lines of the texture on the general purpose diffractometers in Fe Karadiation by the Schulz reflection method. The texture parameters T and Т, expressing the ratio of the components of the recrystallization texture and the rolling texture of fcc-materials, were determined. It was found that the accuracy of texture control during annealing of brass L63 rolled products using the same texture parameters is reduced in comparison with materials with high stacking fault energy due to the small fraction of {100} <hkl> recrystallization texture component and the dependence of the structure and phase ratio on small, 1.5% for copper, fluctuations in the chemical composition. At the same time, it remains high enough to control the process of organizing feedback when managing the process online. That is, texture control can be extended to annealing materials with very low stacking fault energy, which contain the second phase. At the same time, there are serious restrictions on the degree of deformation during rolling and on the annealing regimes, in which it is reasonable to use the texture control, as well as the absolute need to determine regression dependences of the properties on the texture when changing the technological processing scheme. In each individual case, the necessary condition for organizing the texture control is the presence of the “close” correlation between the texture parameter and the controlled characteristic. The proposed structural scheme of the texture control during rolling is discussed.The authors gratefully acknowledge S. G. Khayutin, Doctor of Technical Sciences, a founder of a texture control research area in Russia, globally pione ering in texture control of mechanical properties, taking part in acquiring some experimental data used in the research paper, and giving important recommendations at the initial stage of preparing the presented paper.

Investigation on machinability in turning of as-cast and T6 heat-treated Al-(3, 7, 12%)Si-0.6%Mg alloys

The machinability in turning of Al-Si-Mg alloys under as-cast and heat-treated conditions has been investigated. Three alloys with 3%, 7% and 12%Si and 0.6%Mg contents (wt%) were prepared. Unsteady solidified ingots were obtained in a vertical upward directional solidification apparatus using an instrumented cylindrical water-cooled mold. Samples extracted from the ingots were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) examinations and by Brinell hardness tests, before and after T6 heat treatments (540 °C solutioning temperature for 10 h, water quenching at 25 °C and artificial aging at 155 °C for 5 h). Specimens in both the as-cast and heat-treated conditions were subjected to machinability tests as a function of cutting force in face turning operation using a CNC lathe machine, fixing parameters as cutting depth, feed rate, cutting speed, and cutting tool. The as-cast microstructure consists of a dendritic α-Al rich phase and an interdendritic eutectic microconstituent (α-Al + Si particles). As the alloy Si content increased, the solidification cooling rate increased, the amount and size of α-Al dendrites decreased while the amount of eutectic mixture increased. After heat treatment, Si particles were found to be more rounded and an increase in fraction of Mg2Si was observed. The hardness profile declines along the length of the as-cast ingots, however the values improved with both alloy Si content and heat treatment. The as-cast alloys showed maximum cutting force at the beginning of the process, decreasing during machining progress, whereas in the heat-treated condition the cutting forces showed values almost constant. The results suggest a more stable machinability behavior during turning of the heat-treated alloys as a consequence of a more homogenous microstructure and hardness.

The Casting Rate Impact on the Microstructure in Al–Mg–Si Alloy with Silicon Excess and Small Zr, Sc Additives

The study investigates the effect of casting speed on the solidification microstructure of the aluminum alloy Al0.3Mg1Si with and without the additions of zirconium and scandium. Casting was carried out in steel, copper, and water-cooled chill molds with a crystallization rate of 20 °C/s, 10 °C/s, and 30 °C/s, respectively. For each casting mode, the grain structure was investigated by optical microscopy and the intermetallic particles were investigated by scanning and transmission microscopy; in addition, measurements of the microhardness and the electrical conductivity were carried out. An increase in the solidification rate promotes grain refinement in both alloys. At the same time, the ingot cooling rate differently affects the number of intermetallic particles. In an alloy without scandium–zirconium additives, an increase in the ingot cooling rate leads to a decrease in the number of dispersoids due to an increase in the solubility of the alloying elements in a supersaturated solid solution. With the addition of scandium and zirconium, the amount of dispersoids increases slightly. This is because increasing the solubility of the alloying elements in a supersaturated solid solution is leveled by a growth of the number of grain boundaries, promoting the formation of particles of the (AlSi)3ScZr type, including those of the L12 type. In addition, the increase in the crystallization rate increases the number of primary nonequilibrium intermetallic particles which have a eutectic nature.

Improved hole wall roughness and corrosion resistance of U-shaped hole prepared by casting

The corrosion resistance of the cooling channel in the water-cooled mold has an important impact on the application of the mold. In this paper, the influence of experimental temperature on roughness and corrosion resistance of U-shaped cooling channels prepared by casting is analyzed in detail. The results show that the experimental temperature increased from 998 to 1048K; the hole wall roughness of the U-shaped hole decreased from 83.264 to 76.287. However, the hole wall roughness increased with a further increase in temperature. Because the low experimental temperature will promote the formation of micro bulges and river ripples on the hole wall. However, with the temperature gradually increased, it will promote the aluminum matrix to react with the carbon fiber, which will increase the roughness. The corrosion performance analysis results show that a reasonable experimental temperature is beneficial to reduce the roughness of the hole wall and improve the corrosion resistance of the cooling channel. When the roughness is large, the ravines on the rough surface are easy to be the starting point of corrosion. At the same time, it is easy to cause the aggregation of Si elements to the hole wall at high experimental temperature, which will also cause corrosion. As a result, reasonable experimental temperature plays an important role in improving the corrosion resistance of the U-shaped cooling channel.

Виготовлення електрошлаковим наплавленням ударної частини молотків механізму струшування електрофільтрів

The expediency and relevance of the development of technological solutions that make it possible to increase the efficiency of electric precipitation filters, which are the main gas cleaning equipment at thermal power plants, metallurgical and cement industries, have been considered. It is recommended to improve the operation of the shake mechanism of the electrical precipitator by forming the impact part of the hammer with a material resistant to plastic deformation under impact loads and provides a minimum and constant area of impact contact of the hammer with the shaking anvil beam throughout the life cycle. Review and analysis of publications in the field of surfacing revealed the lack of data on the properties of the proposed material deposited by electroslag method, as well as its use in the impact mechanisms of electrical precipitators. The impact part of the hammer was made of the proposed material by electroslag surfacing in a special detachable copper water-cooled mold with a powder electrode. The structure and properties of the metal of the hardened part of the hammer have been studied. As a result, it has been found that the chemical composition of the metal of the deposited impact part of the hammer is close to the composition of the metal deposited with the OZN-300M electrodes with a low content of sulfur and phosphorus; this being due to the effect of refining in electroslag remelting. The surfacing process provides the formation of a tight monolithic, homogeneous dispersed and defect-free structure characteristic of cast electroslag metal. In the cast metal, the presence of non-metallic inclusions of predominantly globular shape with a characteristic average size of 2.5-4.5 μm in the form of oxides and sulfides with a volume percentage (0.60-0.70)×10-2 and (0.51-0.60)×10-2, respectively has been revealed

ЗАСТОСУВАННЯ ЕЛЕКТРОШЛАКОВОГО НАПЛАВЛЕННЯ ДЛЯ ВИГОТОВЛЕННЯ МОЛОТКІВ УДАРНОГО МЕХАНІЗМУ СТРУШУВАННЯ ОСАДЖУВАЛЬНИХ ЕЛЕКТРОДІВ ЕЛЕКТРОФІЛЬТРІВ

У статті представлено основні дані про технологічні можливості виготовлення деталей для ударного механізму струшування осаджувальних електродів електрофільтрів. Запропоновано й аналітично обґрунтовано перспективність зміни технологічного процесу виготовлення молотка ударного механізму з метою максимального збільшення коефіцієнта корисної дії електрофільтру при одночасному збільшенні експлуатаційної надійності молотків і зниженні вартості їх виробництва. Встановлено, що процес виготовлення молотка практично можна звести до однієї операції – електрошлакового наплавлення. Водночас для вихідних заготовок (хвостовик і витратний електрод) застосовуються стандартні стали стандартного сортаменту. В результаті дослідження якості металу наплавленої ударної частини молотка встановлено, що процес електрошлакового наплавлення забезпечує формування монолітної і бездефектної структури; мікроструктура наплавленого металу – ферито-перлітна, досить однорідна і дисперсна, що характерно для литого металу в водоохолоджуваному кристалізаторі. Ударнівипробування молотків, отриманих з використанням електрошлакового наплавлення, проводили на спеціальному ударному стенді, який забезпечує енерго-кінематичні параметри удару молотка по балці струшування, аналогічні промисловому електрофільтру. Випробування показали їх високу надійність (руйнувань не було) і тим самим підтвердили можливість їх промислового застосування. Розрахований очікуваний економічний ефект від застосування технології електрошлакового наплавлення при виготовленні молотків ударного механізму струшування стосовно розробленої конструкції молотка становив близько 350–400 грн за штуку. Отриманів роботі результати можуть бути використані на виробництві, при проектуванні технологічних процесів виготовлення деталей, що мають складний технологічний процес виготовлення.

Flow-solidification interaction: A numerical study on solidification of NH4Cl – 70 wt.%H2O solution in a water-cooled mould with a large sample thickness

This study focuses on the flow-solidification interaction during the solidification of NH4Cl – 70.43 wt.%H2O solution in a water-cooled mould with a large sample thickness (100 × 80 × 10 mm3). First part of the paper is to use a volume-average-based dendritic solidification model to reproduce an experiment in which transient flow is monitored in-situ using particle image velocimetry, and the solidification sequence is recorded with a light camera. The striking features of the solidification experiment are that the crystal morphology is dominant in a columnar structure, and four typical flow regimes appear in the bulk solution during cooling/solidification, namely pure thermal convection, unstable turbulent flow caused by double diffusive convection, turbulent-stratified flow, and meandering flow. The results show that there is quantitative agreement between the simulation and experiment results. The focus of this paper (second part) is to study the flow-solidification interaction by correlating the above flow regimes with the solidification quantities in the mushy zone. Owing to the enhanced mass (solute) and energy transport by advection, flow suppresses the growth of the mushy zone, while speeding up the solidification inside the mushy zone, leading to the formation of dense mush and massive columnar dendrite trunks. The crystalline morphology of NH4Cl, as presented by a dendritic envelope and described by morphological parameters, is an important factor that influences the flow; as a feedback, the flow further influences the solidification inside the mushy zone. The numerical model also provides valuable information about the formation of freckle trails.

Development of gas mixture composition for the improvement of nickel-based cathodes for the ionic-plasma coating

Modern power plants and aero-engines work at enhanceable temperatures that may reach over 1 700 °С. Heat-resistant coatings on the basis of nickel are applied to provide the work at high temperatures. The service life of shoulder-blades, first of all, depends on the quality factors of the coatings (evenness, absence of pores, inclusions, chemical homogeneity). Quality of coating is determined by the application process and quality of cathode. As a rule, cathodes are alloys that are spread with the special geometry. There are a few technologies of making cathodes, with their advantages and defects. One of the methods is ingot melting layer by layer to produce cathodes in copper water-cooled mold with the use of unfluxible electrode. Purpose of research. To enhance the quality of nickel-based cathodes (Ni − Cr − Al − Y) by the improvement of technological modes of ingot melting. The tasks are set to reduce defects such as pores, to increase homogenity of structure and chemical composition. Methodology. The equipment, namely vacuum arc unit, was improved with helium cylinder. Test samples in a way of "pucks" (127 mm in diameter and 40-mm thick) were obtained to study the microstructure and chemical composition. The modes of remelting are worked through. Research of chemical composition was conducted with the use of SEM of РЕМ 106І equipped with microanalysis system. Scientific novelty. Optimal correlation of protective gases on ingot quality factors for further cathode production was identified. At gas correlation of 70/30 % high quality ingots were obtained. Conclusions. Based on the results of research on the effect of the concentration of gas mixture on the structure and composition of cathodes, technological melting conditions were established, which made it possible to improve the quality indicators and economic indicators of the studied cathodes. This will positively affect the number of cathode defects, serviceability of parts that contain coatings and the service life of aircraft engines in general.

The structure of AlFe5 master alloys produced from recyclable scrap steel and its effect on the properties of aluminium alloys

Due to growing production of aluminium alloys and development of resourcesaving production, great amounts of waste products are widely used in the production process. Use of recyclable iron-containing waste in cast and wrought aluminium alloy production diverts the common traditional understanding that iron can affect the cast structure. At the same time, for the low diffusion capacity of iron in aluminium, it would be interesting to consider Al – Fe alloys. This paper describes the results of a study that examined how the structure of AlFe5 master alloys influence the structure and properties of Al – Si – Cu (AK12M2) and Al – Cu – Mg (AK4) alloys. The test AlFe5 master alloys were prepared by chopping waste steel wire into 1 and 3 mm pieces. The alloy melts solidified in a crucible and a water-cooled roller mould. Before pouring, some of the alloy melts were exposed to electromagnetic acoustic fields for additional conditioning. The authors looked at how the size of the steel pieces and the way they were obtained changed the structure of the test master alloys. A relationship was established between the size of the material and the dimensions and quantity of FeAl3 intermetallics. In all experiments, the bigger FeAl3 intermetallics were found in alloys produced with 3 mm steel pieces. Exposure to electromagnetic acoustic fields would result in 3–5 times smaller FeAl3 intermetallics while their quantity would increase by 4–10 times. The chemical compositions of alloys obtained from fine-crystalline master alloys proved to be in compliance with applicable regulations. The principal phases in the resultant alloys had a fine-dispersed structure. The eutectic silicon in the АК12М2 alloy became 1.4 times smaller, while the dendritic aluminium in the АК4 alloy structure became 1.65 times smaller. The optimized structure led to improved physical and mechanical properties of as-cast alloys. Thus, their ultimate strength increased by 10–13%, while their specific elongation almost doubled. The results of the study indicate that recyclable scrap steel wire can be effectively used in the production of aluminium alloys.This research study was funded by the Ministry of Education and Science of Russia as part of a governmental assignment; Project ID: 0718-2020-0030.

The influence of heat treatment on the structural phase state and durometric properties of small-sized castings from a copper alloy Cu-Cr-Al

The effect of heat treatment on the structural-phase state and hardness of small-sized castings made from the Cu-Cr-Al copper alloy obtained by casting in a water-cooled metal mold is studied. Using X-ray diffraction analysis, it was found that the castings consist of a matrix solid solution based on copper. The increased value of the crystal lattice parameter of the copper phase is associated with aluminum atoms dissolved in it. After a low-temperature (450 °C) tempering for 10 hours, the crystal lattice parameter of the matrix solid solution decreases, which is associated with the formation of the Al8Cr5 intermetallic compound on the surface of the casting.It is established that after heat treatment (hardening and tempering), the hardness of castings from the Cu-Cr-Al alloy increases by 1.5 times.

Effects of Transition Metal Oxides ZrO2, Y2O3, and Sc2O3 on Radiative Heat Transfer of Low-Reactive CaO-Al2O3-Based Mold Slag

To control heat transfer between the solidifying shell and the water-cooled mold during continuous casting, the transition metal oxides, ZrO2, Y2O3, and Sc2O3, were separately added into the developed low-reactive CaO-Al2O3-based mold slags to investigate the effect on radiation heat transfer. Two kinds of master mold slags were taken into account, one included 18 pct Al2O3 and 18 pct SiO2, and the other one included 28 pct Al2O3 and 8 pct SiO2. The slag viscosity and melting temperature were measured with rotating cylinder viscometer and hemisphere-point method, respectively. The optical parameters of the slag films having different contents of transition metal oxides were measured by Fourier transform infrared spectrometer, and an optical-process model was constructed to consider the radiation from the shell surface and hot and cold sides of the solid films to the mold plate. When ZrO2, Y2O3, and Sc2O3 contents up to 4 pct, the viscosity at 1573 K fluctuated in the range of 0.05 Pa s, the melting temperature varied within a range of 15 K, except for the case of 2 pct Sc2O3, for which the melting temperature was 27 K lower than that of the master mold slag with 8 pct SiO2 and 28 pct Al2O3. The incorporation of the three transition metal oxides up to 4 pct did not have a notable effect on the viscosity or melting temperature. The addition of ZrO2 and Y2O3 effectively decreased the radiation, whereas Sc2O3 had no direct relationship with radiation. When the ZrO2 (Y2O3) concentration was increased from 0 to 4 pct, the reduction rate of radiation transfer was 26.6 pct (13.3 pct) for the mold slag containing 18 pct Al2O3 and 18 pct SiO2. The current study provides a new direction for developing low-reactive mold slag and reducing heat transfer during continuous casting.

Structure, Core Losses, Curie Temperature, Defects in the Structure of the Bulk Amorphous Alloy Fe55Co15W2Y8B20

This paper presents studies relating to the structure and soft magnetic properties of the bulk amorphous alloys Fe55Co15W2Y8B20. Samples were made using the method of injecting a liquid alloy into a copper water-cooled mold in the form of plates. The structure and microstructure were examined using X-ray diffractometry. Magnetic properties were investigated from static and dynamic measurements. For the samples, the core losses were measured. The influence of structure defects on the magnetization process in strong magnetic fields was also investigated. For this purpose, the theory developed by H. Kronm�ller was used. It was shown that the magnetization process in strong magnetic fields is associated with two-dimensional defects, so-called pseudo-location dipoles.

Influence of the Pressure of Open-Close Water-Cooled Moulds on Casting/Mould Interface Heat Transfer and Casting Solidification Process

In this paper, the experimental model for a self-designed open-close water-cooled mould was utilized to measure the temperature curves of various points inside the casting and mould under different mould pressure. The Interface heat transfer coefficient(IHTC) of the casting/water-cooled mould interface was calculated by using the Beck nonlinear estimation back-calculation method, and on this basis, the rule of how pressure affects heat transfer coefficient was obtained. Then the coefficient can be defined as the boundary condition(BC) to simulate the solidification process of the experimental casting. The results showed that the simulation outcome considering the influence of pressure was completely different from those of general water-cooled moulds, which can be proved by the about 35% solidification time decrease, visibly reduced shrinkage porosity area in the casting and more accurate simulation results. The anatomical results of the experimental casting also confirmed this.

NUMERICAL SIMULATION OF TEMPERATURE DISTRIBUTION ON METAL CASTING IN VERTICAL SOLIDIFICATION

The metals and alloys solidification can be defined as a transient heat transfer process. A liquid/solid transformation is followed by thermal energy liberation, with a movable boundary separating two phases with different thermophysical properties. The solidification is of great interest to mechanical and chemical engineers. It is a non-linear transient phenomenon, where heat transfer between the casting and the mold plays a important role. This paper aims to propose a study of heat flow from the casting to the mold using a numerical technique to compute the temperature history of all points inside the casting. The cooling process consists of water-cooled mold with heat being extracted only from the bottom, resulting in unidirectional vertical solidification. The ANSYS software was used to obtain the temperature distribution in the casting. Good agreement was obtained when the simulation results were compared with the experimental data.

Use of Directional Solidification for Improving Tubular Workpiece Quality of Different Cast Irons

A new efficient method of casting tubular billets by directional solidification without the use of a core is proposed making it possible to obtain a fine-grained dense structure of cast iron due to intensive onesided heat removal and excess supply to the solidification front of superheated liquid phase during the entire billet formation time in a metal water-cooled mold (crystallizer). It is shown that the method makes it possible to obtain a prescribed final cast iron structure by creating a certain cooling regime for castings outside the mold. In the positive effect of directional solidification of the melt inherited by iron a decisive role is played by the formation of a dense structure and a more dispersed carbide eutectic with a favorable carbide morphology, which determines the good cast iron wear resistance. The results of studies confirm that the new casting method provides production of workpieces with a prescribed phase composition and improved physical, mechanical, and operating properties. The effect is considered of various factors of the formation of workpieces from different types of cast iron: gray alloyed with lamellar graphite, high-strength and high-chromium, and also Niresist cast iron, on the structure, properties and service life of components for critical purposes of general, mining and oil refining engineering.