Inclusion Removal Research Articles

Removal of Inclusions from Aluminum Through Filtration

Filtration experiments were carried out using both an AlF3 slurry-coated and an uncoated Al2O3 ceramic foam filter to study the removal of nonmetallic inclusions and impurity elements. The results showed that the 30-ppi ceramic foam filter removed up to 85 pct inclusions from aluminum. Several pictures of two- and three-dimensional morphologies of both nonmetallic and intermetallics inclusions also have been presented. The following contributing mechanisms for the removal of nonmetallic inclusions in the deep-bed filtration mode are proposed: (1) collision with walls and interception effect and (2) the formation of both intermetallic and nonmetallic inclusion bridges during filtration. Fluid dynamics modeling of inclusion attachment to the filter walls showed that most inclusions, especially those with larger sizes, are entrapped at the upper part of the filter, whereas smaller inclusions are dispersed well throughout the filter. The calculated inclusions removal fractions for the 30-ppi filter showed that almost all inclusions >125 μm are removed, and inclusions ~5 μm in size are removed up to 85 pct. The interfacial energy between two collided same-size inclusions was calculated, indicating that a strong clustering of inclusions may result within the filter window. Magnesium impurities were removed up to 86 pct by the AlF3 slurry-coated filter. The filter acted in active filtration mode in addition to the contribution of the air oxidation of dissolved [Mg], which was calculated to be 13 pct. The total mass transfer coefficient of dissolved [Mg] to the reaction interface was calculated to be 1.15 × 10−6 m/s.

Microstructural Aspects of the Degradation Behavior of SnO2-Based Anodes for Aluminum Electrolysis

The performance of ceramic anodes doped with copper and antimony oxides was examined in cryolite alumina melts under anodic polarization at different cryolite ratios, temperatures, times, and current densities. The corroded part consists of a narrow strong corrosion zone at the anode surface with damage of the intergrain contacts and a large increase in porosity, a wider moderate corrosion zone with a smaller porosity increase, and a Cu depletion zone, where the ceramic retains its initial microstructure and a slight porosity increase occurs due to the removal of the Cu-rich inclusions. Mechanical destruction of the anode was never observed in the 10–100 h tests. A microstructural model of the ceramic was suggested, consisting of grains with an Sb-doped grain core surrounded by an to 500 nm grain shell where was simultaneously doped with Sb and . The grains were separated by a few nanometers thick Cu-enriched grain boundaries. Different secondary charge carrier (holes) concentrations and electric conductivities in the grain core and grain shell result in a higher current density at the intergrain regions that leads to their profound degradation, especially in the low temperature acidic melt.

Improving the reliability of welded joints in bulk-quenched electrosteel rail

Metallurgical methods of improving the reliability of the weld seam in bulk-quenched electrosteel rail are considered: optimization of the chemical composition in terms of the basic elements and total impurity content; improvement in plastic properties of the rail by reducing the hardness; and removal of nonmetallic inclusions from the steel. Instability is seen in the weldability of the rails and also in the composition, with the same set of mechanical properties. The need for improvement in welding technology is shown; without the elimination of existing problems, the weldability of electrosteel rail cannot be guaranteed.

Numerical Simulation for Collision and Growth of Inclusions in Ladles Stirred with Different Porous Plug Configurations

A mathematical model has been developed to predict the collision and aggregation among inclusions in the ladle with different porous plug configurations. The numerical results showed that the porous plug configuration has a profound effect on the inclusion removal process in ladle. The eccentric bottom blowing is better than the central bottom blowing. The terminal inclusion removal efficiency decreases with the increasing porous plugs. The inclusions captured by the top slag accounts for the majority of the removed inclusions, inclusion adhesion to the sidle wall is the minor manner, and inclusions adhered to the ladle bottom wall can be negligible. In order to avoid newly generated large inclusions to be remained in the liquid steel after about 16 min of treatment, it is necessary to prolong the treating time on the condition of one porous plug configuration.

Evaluation of filtration efficiency for single layer and double layers alumina filter using aqueous suspension

The quality of molten aluminum is dependent on the methods used for its treatment to remove impurities. Of these, rigid media tube filter (RMF) has been the most reliable. RMF bound coarse grain of alumina by 9Al2O3·2B2O3 has been used widely all over the world. The purpose of this study was to examine the filtration efficiency of RMF using an aqueous suspension of ceramic powder instead of molten aluminum. During actual operation, inclusions accumulate on the surface of RMF to form a cake layer. But the cake formation was not expected in aqueous suspension, since its filtration efficiency showed initial operational conditions, i.e. surface and internal filtration. The results of our experiment clearly showed that filtration efficiency of RMF depended upon pore size and the operation condition. Namely, the filtration efficiency of small pore RMF allowed as high as possible removal of fine inclusions. It was confirmed that maximum inclusion size that could possible be filtered, was approximately 10% of maximum RMF pore size. Also, the operation conditions for higher filtration efficiency, was a slower flow rate and an aqueous suspension of low inclusion concentration. The filtration performance for double layers RMF was influenced by a smaller pore size and the filtration resistance reduced as compared to single layer. As the result of aqueous suspension was similar to that of TiB2 added molten aluminum, it was assumed that the aqueous suspension examination method was reliable.

Transient Fluid Flow Phenomena during Continuous Casting: Part II—Cast Speed Change, Temperature Fluctuation, and Steel Grade Mixing

Many complicated phenomena are associated with transient stages during the continuous casting process, especially inside the casting mold cavity. A deep understanding of the phenomena and optimized control over the process ensure the high quality product and low costs. This work presents a three-dimensional numerical simulation of transient fluid flow phenomena during steel continuous casting. In the Part II, the process of casting speed change (increase or decrease), temperature fluctuation, and steel grade mixing in a slab mold were investigated. The phenomena, such as flow pattern, inclusion removal fraction, temperature variation, top surface profile, and steel transportation, were addressed to evaluate the process and enhance product quality.

Growth of Small Alumina Clusters during Ladle Deoxidation

The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions.Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles.In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow.The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.

Modeling of electromagnetic separation of inclusions from molten metals

The presence of inclusions greatly influences the mechanical and the corrosion resistance of metallic alloys. These influential effects become more crucial when using metallic scrap, due to the high levels of inclusions and other contaminants such as non-metallic and oxides particles. Metal cleanliness requirements are becoming more striking, enforcing higher demands on the efficiency and flexibility of refining methods. Recently electromagnetic separation technique has been considered as a new method for the production of metals free from inclusions. In this study, a mathematical model has been developed to simulate the flow of molten metal through a channel in the presence of electromagnetic force field generated by interaction between a stationary electromagnetic field and DC current passing through the melt. A generalized model based on Newton's second law of motion was developed for the motion of inclusions in the melt flowing through the channel of separator by considering different forces acting on particle including electromagnetic force. A physical model was designed and constructed to visualize the inclusion separation phenomena and to verify the mathematical model. The predicted particle trajectories and separation in the physical model were compared with those obtained from experiments which showed reasonably good agreement. Parametric studies were performed using the mathematical model to evaluate the effects of various parameters, such as electromagnetic force strength, particle size and melt inlet velocity on the inclusion removal efficiency.

Removal of inclusions from silicon

The removal of inclusions from molten silicon is necessary to satisfy the purity requirements for solar grade silicon. This paper summarizes two methods that are investigated: (i) settling of the inclusions followed by subsequent directional solidification and (infiltration by ceramic foam filters. Settling of inclusions followed by directional solidification is of industrial importance for production of low-cost solar grade silicon. Filtration is reported as the most efficient method for removal of inclusions from the top-cut silicon scrap.

Effects of flux containing YCl 3 on the yttrium loss, mechanical and corrosion properties of Mg–10Gd–3Y–0.5Zr alloy

New fluxes containing YCl 3 were developed to refine Mg–10Gd–3Y–0.5Zr (GW103K) alloy, with the aim to suppress the loss of expensive heavy rare earth element Y, but also to improve the removal of nonmetallic inclusions. The Y loss, microstructure, mechanical and corrosion properties were investigated. It was found that the loss of Y in the alloy decreased with the increasing of YCl 3 in the flux. Thermodynamic calculation indicated that the main reason could be attribute to the decline of the Gibbs free energy, which slows down the reaction rate between MgCl 2 and Y. The study demonstrated that the fluxes containing 5 wt.% YCl 3 additions also exhibited excellent capability of removing nonmetallic inclusions. This greatly improved the mechanical and corrosion properties of GW103K alloy.

Magnetohydrodynamics applied to materials processing

Abstract In the processing of liquid materials various operations are performed, e. g., alloying, homogenisation of the composition, refining or inclusion removal. As was realised early on by Charles Crussard, electromagnetic effects can be used to process electrically conducting materials without any contact. When alternating magnetic fields are used, the material is directly heated and melted thanks to the induced electric currents. The induced electromagnetic forces are capable of shaping the free surface, levitating a liquid blob and stirring the liquid bulk or its surface. The latter principle may be applied to electrically conducting liquids such as metallic alloys, but also to poorly conducting materials such as oxides, glasses or plasmas. Those effects are used in many processes such as induction furnaces for liquid metals or glasses, refining ladles, electromagnetic levitation, continuous casting of aluminium or steel. In this paper, typical effects based on the use of electromagnetic systems are reviewed, as well as the corresponding applications.

Numerical Simulation of the Multiphase Flow in the Rheinsahl–Heraeus (RH) System

Knowledge of gas–liquid multiphase flow behavior in the Rheinsahl–Heraeus (RH) system is of great significance to clarify the circulation flow rate, decarburization, and inclusion removal with a reliable description. Thus, based on the separate model of injecting gas behavior, a novel mathematical model of multiphase flow has been developed to give the distribution of gas holdup in the RH system. The numerical results show that the predicted circulation flow rates, the predicted flow velocities, and the predicted mixing times agree with the measured results in a water model and that the predicted tracer concentration curve agrees with the results obtained in an actual RH system. With a lower lifting gas flow rate, the rising gas bubbles are concentrated near the wall; with a higher lifting gas flow rate, gas bubbles can reach the center of the up-snorkel. A critical lifting gas flow rate is used to obtain the maximum circulation flow rate.

Forced flotation of inclusions in tundish

With increased usage of steel for critical applications, the demand for cleaner steel has increased. Existing technologies have been improved and new technologies are being introduced all along the process route to minimise the size and quantity of inclusions. In continuous casting, the function of tundish has changed from its early role as a liquid steel buffer to a multifunctional vessel, dominating quality adjustments, specifically inclusion flotation. To meet stringent cleanliness requirements, a methodology of forced flotation of inclusions by controlled bubbling of inert gas in tundish was developed and investigated. Location of the bubbling arrangement was optimised using the flow profile generated by water modelling experiments. Optimum gas flowrates were calculated mathematically and further adjusted with a series of experiments. Extensive plant scale trials were used to optimise the process parameters and bring the technology to practice. There was a 33–70% reduction in inclusions of size greater than 50 μm and a 13–36% reduction in inclusions 25–50 μm. Inclusion removal reduced at higher casting speeds. Under steady state conditions, efficiency of inclusion flotation was found to be a function of casting speed. Additionally, a significant reduction in oxide build-up and nozzle clogging was observed thus lengthening refractory life.

Water Modeling of Swirling Flow Tundish for Steel Continuous Casting

A conventional turbulence inhibitor is compared with a swirling chamber from the points of view of fluid flow and removal rate of inclusion in the tundish. Comparing the RTD curves, inclusion removals, and the streamlines in water model experiments, it can be found that the tundish equipped with a swirling chamber has a great effect on improving the flow field, and the floatation rate of inclusion is higher than the tundish with a turbulence inhibitor. Because of the introduction of the swirling chamber, the flow field and inclusion removal in a two-strand swirling flow tundish are asymmetrical. Rotating the inlet direction of swirling chamber 60 degree is a good strategy to improve the asymmetrical flow field.

Mathematical Modeling and Computer Simulation of Molten Aluminum Purification by Flotation in Stirred Reactor

The removal of inclusions by flotation in mechanically agitated vessels is widely used in liquid aluminum treatments. Originating from different sources (oxide skins, refractory, or recycling wastes), inclusions may have disastrous repercussions such as deterioration of the physical properties of the cast products or difficulties during forging processes. With the aim of both a better understanding of the physical processes acting during flotation and the optimization of the refining process, a mathematical modeling of the behavior of the population of inclusions has been set up. Transport phenomena, agglomeration of inclusions, and flotation are considered here. The model combines population balance with convective transport of the inclusions, in order to calculate the time evolution of the inclusion size distribution. An operator-splitting technique is employed to solve the coupled population balance equation (PBE) and the transport equation. The transport equation is solved using a finite volume technique associated with a total variation diminishing scheme, whereas the PBE resolution relies on the fixed pivot technique developed by Kumar and Ramkrishna. A laboratory-scale flotation vessel is modeled and the results of a two-dimensional (2-D) simulation are presented.

Influence of flux containing YCl 3 additions on purifying effectiveness and properties of Mg–10Gd–3Y–0.5Zr alloy

In order to improve the purifying efficiency of RJ6 flux, 5 wt.% YCl 3 additions were introduced into the flux to refine Mg–10Gd–3Y–0.5Zr (GW103K) alloy. The results show that the RJ6 flux containing 5 wt.% YCl 3 additions exhibits excellent adsorption ability to nonmetallic inclusions. Thermodynamic analysis indicates that the main reason could be attributed to the decrease of the surface tension of the flux. Moreover, the mechanical, corrosion and fluidity properties of the alloy were investigated. It was found that these properties were improved to a certain degree due to the removal of nonmetallic inclusions in the alloy.

Modeling Study of Turbulent Flow Effect on Inclusion Removal in a Tundish with Swirling Ladle Shroud

AbstractThe present study is focused on the assessment of a new concept of ladle shroud capable to control the turbulence promoted by the steel entry jet in a continuous casting tundish; the new proposal is a Swirling Ladle Shroud (SLS). It presumed that the SLS decreases the impact velocities in the tundish bottom close to 1/3 of that provided by a conventional shroud. In this mathematical study an analysis of turbulence control and particle removal is made by comparing the SLS with two different conventional tundish arrangements. Particle sizes included 1, 5, 20, 40, 60, 80, 100, 120, 140 and 160 microns. Simulations also included the effects of the mass flow rate on the removal efficiency of non‐metallic inclusions, considering 3.8 and 7.6 ton/min mass flow rates. It was found that the SLS is capable to handle different mass flow rates, opposite to the conventional arrangements where at any increase of mass flow rate, these devices become inefficient to control turbulence, reducing considerably the inclusion removal efficiency. These results illustrate that using a SLS, the turbulent flow control and the particle removal may be better with this new proposal.

Model Experiment on Inclusion Removal by Bubble Flotation Accompanied by Particle Coagulation in Turbulent Flow

Inclusion behavior like nucleation, diffusional growth, coagulation and removal in steel refining are complicated process, whereas mathematical simulation makes it possible to describe each behavior in detail. Many works have been performed in respect of the individual mechanism of inclusion behavior. However, the whole behavior is not clearly understood yet, and especially, an experimental evaluation of combined phenomena has not been carried out sufficiently until now. In this study, a cold model experiment of bubble flotation accompanied by coagulation of polystyrene particle in an electrolyte solution has been conducted in an agitated vessel under turbulent flow condition. In addition, an empirical equation of bubble flotation in a turbulent flow has been proposed from observed results of the water model experiment. This empirical equation has been combined with the population balance equation on particle coagulation, and removal rates have been predicted. Furthermore, a correction has been adopted in the population balance equation proposed by Nakaoka et al. Resultantly, a linear coupling model with bubble flotation and coagulation has been verified its applicability to a prediction of time dependence of particle number density and size distributions under various conditions.

Structure Optimization of Horizontal Continuous Casting Tundishes Using Mathematical Modeling and Water Modeling

The configuration of a tundish for a two-strand horizontal continuous caster was designed and optimized using water modeling, mathematical modeling and industrial trials. Five designs were studied: the original tundish without flow control devices, the tundish with a turbulence inhibitor at the bottom, the tundish with a deep inlet launder and a tilted dam at the end of the inlet launder, the tundish with two dams with holes, and the tundish with a shallow inlet launder and a high dam in the main chamber. Water modeling was used to measure residence time and investigate dead zone fractions and fluid flow patterns. In the mathematical modeling, fluid flow, heat transfer and inclusion motion and removal were calculated. In industrial trials, the total oxygen, nitrogen pick-up, and inclusions in steel samples taken from the tundish and the billets were analyzed. The results indicated that the tundish with an inlet launder and a dam either at the end of the chamber or in the main chamber was the best design.

Ti surface alloying of an AISI 316L stainless steel by low energy high current pulsed electron beam treatment

Ti has been added into the surface layer of an AISI 316L stainless steel—by means of rapid surface alloying of Ti powder—using the low energy, high current pulsed electron beam (LEHCPEB) technique with the aim of enhancing its corrosion resistance. The alloyed layer contained a mixture of the α and γ phases and its depth increased with the number of pulses. Compared to the samples treated under the conventional LEHCPEB treatment (i.e., without surface alloying), Ti addition improved further the corrosion resistance. This can be attributed to the addition of Ti into the surface layer together with the removal of MnS inclusions. However, the homogeneity of the Ti distribution decreased when the number of pulses increased. Therefore, contrary to the conventional LEHCPEB treatment, as a result of this decreased homogeneity, the corrosion resistance decreased when the number of LEHCPEB was too high. Therefore, a good control of the processing parameters is required to take the full advantage of the surface Ti addition by LEHCPEB.