Separation Of Non-metallic Inclusions Research Articles

Directional separation of nonmetallic inclusions from copper melt reinforced by supergravity

An emerging method of supergravity fields was introduced to separate nonmetallic inclusions from liquid copper. The copper melt containing oxide inclusions was treated via solidification at a certain cooling rate under different gravity fields, and the separation effect and moving behavior of inclusion particles were investigated systematically. The results show that the occurrence of oxide inclusions floating toward the top of the sample rapidly was intensified by the supergravity field, and some oxide inclusions can be absorbed in the covering slag. The oxygen content in the melt is significantly reduced after treatment with supergravity, and the separation effect can be greatly improved by increasing the gravity coefficient G. The separation efficiency of inclusions is only 38.43% under a normal gravity field (G = 1), whereas the separation efficiency can reach 90.11% after treatment in a supergravity field of G = 308. Moreover, the separating velocity of particles obtained by theoretical calculations increases greatly with an increasing gravity coefficient. The particle moving velocity in the direction of supergravity agrees well with Stokes velocity calculated via Stokes’ law.

Separation of non-metallic inclusions from high strength low alloy steel by electromagnetic stirring

Non-metallic inclusions are the impurities that solidified during steel continuous casting. The compositions, sizes and shapes of inclusions significantly affect the steels’ mechanical properties such as ductility, formability and toughness. This paper mainly focuses on the observation and characterization of non-metallic inclusions in high strength low alloy steels, and especially is devoted to the homogenization of molten steel within the copper mold of continuous casters, as the primary purpose of this project is to discover the optimum operation parameters for electro-magnetic stirrers surrounding the copper mold. In this paper, non-metallic inclusions in high strength low alloy steel were observed and characterized, and separation of non-metallic inclusions from high strength low alloy steel by electromagnetic stirring was specifically studied. The nonmetallic inclusions in the billet can be greatly reduced when the electromagnetic stirring parameters of the mold are 300 A current and 3 Hz EMS frequency.

Novel concept of fine inclusion removal using carbonate powder injection through the ladle shroud

ABSTRACTTundish is the last refractory vessel in the steelmaking process. The fluid phenomena in tundish have a strong effect on the separation of non-metallic inclusions. In this paper, a new inclusion removal approach using powder injection through the shroud has been proposed and the devices have been set up. The plant trials have been carried out and the ruling factors have been analysed. The results indicate that this novel technique is beneficial to separate the small non-metallic inclusion removal from the molten steel. Compared with conventional inclusion removal technology, the number of the oxide inclusions can be decreased to a lower level and the inclusion becomes finer.

Separation of Non-metallic Inclusions from a Fe-Al-O Melt Using a Super-Gravity Field

An innovative method for separating non-metallic inclusions from a high temperature melt using super gravity was systematically investigated. To explore the separation behavior of inclusion particles with densities less than that of metal liquid under a super-gravity field, a Fe-Al-O melt containing Al2O3 particles was treated with different gravity coefficients. Al2O3 particles migrated rapidly towards the reverse direction of the super gravity and gathered in the upper region of the sample. It was hard to find any inclusion particles with sizes greater than 2 μm in the middle and bottom areas. Additionally, the oxygen content in the middle region of the sample could be reduced to 0.0022 mass pct and the maximum removal rate of the oxygen content reached 61.4 pct. The convection in the melt along the direction of the super gravity was not generated by the super-gravity field, and the fluid velocity in the molten melt consisted only of the rotating tangential velocity. Moreover, the motion behavior of the Al2O3 particles was approximatively determined by Stokes’ law along the direction of super gravity.

Separation of Non-metallic Inclusions from Molten Steel Using High Frequency Electromagnetic Fields

The current work is to investigate the removal of non-metallic inclusions from molten steel using electromagnetic separation under high frequency magnetic fields. A certain amount of aluminum nuggets were added to the molten steel to generate alumina inclusions in the current experiments. A layer of alumina clusters close to the wall of the crucible was observed. Models for the entrapment of inclusions by EM fields were developed, indicating that over 91 pct inclusions were captured within the skin depth (2.31 mm from the wall) and the calculation agreed well with the experimental observation. The fluid flow, solidification of the steel and the motion and entrapment of inclusions were studied by three-dimensional mathematical modeling. The separation mechanism of inclusions from molten steel by EM fields was discussed. Both the experiments and the simulation show that EM separation is a feasible and high-efficient method to remove inclusions from the molten steel.

Ways of improving steel quality in the tundish

The role of the tundish in the continuous casting process has evolved from that of a buffer between the ladle and mold to being a grade separator, an inclusion removal device and a metallurgical reactor. For both grade separation and inclusion removal, the flow patterns inside the tundish play an important role. The separation of non-metallic inclusions at the interface between the steel and the slag in the tundish is to a great extent controlled by interfacial phenomena in the steel-slag-inclusion system. One constant in the world of high-purity, low-residual and clean steels is the continual drive to reduce and control the frequency of the inclusions. For example, there are high-purity, low-residual clean steels such as IF- steel sheets for automobiles which require the absence of oxide inclusions with diameters larger than 100 micrometers. Great efforts have been made to optimize the flow and turbulence in the tundish through weirs, dams or other systems. Furthermore, a new system, the porous annular well block for injecting argon, has been developed to optimize the bubble size and distribution and hence to achieve a high efficiency in trapping inclusions and in decreasing the hydrogen content in steel. Consequently, the steel quality is further improved in the tundish. Tested with success in a seamless steel shop, the new system gives results in agreement with the water models.

NUMERICAL CALCULATIONS ON INCLUSION REMOVAL FROM LIQUID METALS UNDER STRONG MAGNETIC FIELDS

A numerical method is developed to calculate/simulate the separation of non-metallic inclusions from an aluminum melt by using a strong magnetic fleld (e.g., 10 Tesla) with high gradient generated via a superconducting magnet. The cases with and without imposed DC current on liquid aluminum in a cylindrical channel are discussed and compared. The migrating velocities of the non-metallic inclusions in an aluminum melt are calculated through force analysis and Navier- Stokes equations. In addition, the trajectories and removal e-ciencies of the inclusions are evaluated. It is found that particle trajectories are in∞uenced by the imposed ∞ow rate and inclusion particle size. In addition, the removal e-ciency is improved signiflcantly, especially for small inclusions, e.g., < 10m, by an imposed DC current on liquid aluminum in the high gradient area of a magnetic fleld.

Application of Complete Gurson Model for Prediction of Ductile Fracture in Welded Steel Joints

Ductile fracture process includes three stages: void nucleation, their growth and coalescence. The voids nucleate due to the fracture or separation of non-metallic inclusions and secondary-phase particles from the material matrix. Micromechanical models based on the Gurson plastic flow criterion are often used for analysis of ductile fracture. They consider the material as a porous medium in which the effect of voids on the stress-strain state and plastic flow cannot be neglected. Another important property of the Gurson criterion is that the hydrostatic stress component influences the plastic flow of the material.

Effect of Dam Design on the Fluid Flow in T-Shaped Continuous Casting Tundish

In the continuity casting technology of steel-manufacturing process, the tundish has two important functions: the preservation and distribution of molten metal and the reaction container able to perform float-out separation of nonmetallic inclusions. The residence time affects the effective removal of the nonmetallic inclusions. In this study, a T-shaped tundish with a submerged entry nozzle (SEN) and three strands was investigated for its ability to extend the residence time. Analysis conditions were the shape of the dam which was transformed to three cases. Fluid flow and non-metallic inclusion movement were also analyzed. The movement and removal of nonmetallic inclusions was determined by residence time distribution (RTD) analysis. As a result, the number of float-out, non-metallic inclusions was increased when the deviation of mean residence time was reduced.

A Mathematical Model to Study Liquid Inclusion Behavior at the Steel-Slag Interface

The separation of non-metallic inclusions at the interface between the steel and the slag in the ladle, tundish and mold is an essential part of the production of clean steel. It is therefore, of great importance to have a deep understanding of the phenomena controlling the transfer of inclusions from the steel to the slag layer. In this work a mathematical model, derived from the equation of particle motion, have been used to study the transfer of liquid inclusions to slags. The effects of the drag, added mass, buoyancy and rebound force on the inclusion transfer are considered. The model relies, to a great extent, on the availability of accurate information of the magnitude of a number of physical properties of the involved phases. Among those properties, the interfacial tension between the phases and the slag viscosity were found to be the most critical. Due to the fact that the availability of experimentally obtained high-temperature physical property data, relevant to the industrial conditions, is scarce in the literature several different model descriptions have been used in this work to estimate these properties. The mathematical model has been used to investigate the separation of liquid non-metallic inclusions, of different size and composition, to a number of different industrial ladle slag compositions.

Solid Inclusion Transfer at a Steel-Slag Interface with Focus on Tundish Conditions

The separation of non-metallic inclusions from the steel to the slag phase in the ladle during secondary steel making operations and in the tundish and mold during casting is very crucial to the pr ...

Magnetohydrodynamic study of electromagnetic separation of nonmetallic inclusions from aluminum melt

Magnetohydrodynamic flow around the nonmetallic inclusions in aluminum melt and the force exerted on the inclusions were explored by dimensional analysis and numerical calculations. Dimensional analysis shows that the invariant \(A = {{JB\rho _f d_p^3 } \over {\mu _f^2 }}\) characterizes the force exerted on the inclusions and the flow intensity of the melt. The physical significance of A is represented as a modified particle Reynolds number that reflects the effects of electromagnetic force. The fluid flow around the particle becomes unstable when A>2×103. It is shown that the neglect of the inertial terms has little effect on the force exerted on the inclusions in the range of A≤1×106. However, the analytical solution of the maximum velocity inside the melt does not apply due to the appearance of turbulent flow in the case of A>2×103.

Study of electromagnetic separation of nometallic inclusions from aluminum melt

Several methods using the concept of electromagnetic separation of nonmetallic inclusions from an aluminum melt were analytically studied and compared in this article. The migration rate of inclusion particles for each method by exerting different types of electromagnetic field, viz. DC electric field with steady magnetic field, AC magnetic field, and AC electric field, was calculated and compared with the gravity settling velocity. Effects of various operating parameters, such as the imposing time of electromagnetic field, the radius of circular pipe, and the magnitude of electromagnetic force, on inclusion removal efficiency were analyzed and illustrated for each case. It was found that the removal efficiency increases with the increase of imposing time and decreases dramatically with the increase of pipe radius, especially for the AC electric field method. As far as the removal of small inclusions is concerned, the AC magnetic field method is the most favorable one because it has the least dependence of removal efficiency upon the particle size. However, high frequency is needed in order to get the optimum results, and the best values of a/δ are in the range of 2 to 3.