Mold Powder Research Articles

Development of the Mathematical Model for Ingot Quality Forecasting with Consideration of Thermal and Physical Characteristics of Mould Powder

This paper presents the results of physical modelling of the mould powder skull in the gap between an ingot and the mould. Based on the results obtained from this and previous works, the mathematical model of mould powder behaviour in the gap and its influence on formation of surface defects was developed. The results of modelling satisfactorily conform to the industrial data on ingot surface defects.

PCAS공정에 의한 고융점 소결체 열전달 해석 및 특성분석

In this study, the effects of internal heat treatment associated sintering temperatures were simulated by the Finite Element Method (FEM). The sintering mechanism of pulsed current activated sintering process (PCAS) is still unclear because of some unexplainable heat transfer phenomena in coupled multi-physical fields, as well as the difficulty in measuring the interior temperatures of metal powder. We have carried out simulation study to find out thermal distributions between graphite mold and Ruthenium powder prior to PCAS process. For PCAS process, heating rate was maintained at <TEX>$100^{\circ}C/min$</TEX> the simulation indicates that the sintering temperature range was between <TEX>$1000^{\circ}C$</TEX> to <TEX>$1300^{\circ}C$</TEX> under 60 MPa. The heat transfer inside the Ruthenium sintered-body sample was modelled through the whole process in order to predict the minimum interior temperature. Thermal simulation shows that the interior temperature gradient decreased by graphite punch length and calculation results well agreed with the PCAS field test results.

Investigation of the current state of isostatic graphite production technology

The study of isostatic graphite production process and its development trends in the world market was conducted. It was established that the isostatic graphite production is a complex and multistage process that requires careful preparation of raw materials, the usage of powerful specialized pressing equipment, the use of elaborate heat treatment modes etc. As a result, it creates a high final price comparing to other brands of graphite materials. Methods of synthesis, analysis and systematization of available information regarding the isostatic graphite production were used for the study. The peculiarities of foreign isostatic graphite production technology were determined, which allows to set directions of improvement by Ukrainian producers, namely: - choice of components and their composition for coke and pitch mixture; - adding special modifiers; - optimization of particle size distribution of the filler; - setting the pressure for pressing moulding powder; - choice of modes of blanks thermal processing etc. The level of future growth in global demand is determined for isostatic graphite materials and products based on it, which is more than 5 % of the annual global volume of production. The results enable further research in order to develop equipment and rational modes of grinding, mixing and pressing coke-pitch compositions using available Ukrainian brand coke and pitch. Furthermore, it will allow in the future to conduct a study of pressed billets heat treatment to reduce the unit cost of electricity and improve the process of isostatic graphite material manufacturing.

A short history of mould powders

The success of the continuous casting process owes much to the performance of the mould powder. Mould powders have been used for more than 50 years and our knowledge of how they work and perform has increased steadily over this time. The performance of the mould powder should always be judged by how it affects the steel shell. Since this is frequently due to the nature of the slag film formed between the shell and the mould, the performance of the mould powder can also be judged by the nature of the slag film formed. However, other factors (such as the depth of the molten pool) must also be taken into account since they affect the formation of defects. Our current state of knowledge on how mould powders work is summarised.

Optimization of Chemical Composition of the Mould Powder for Casting Ø 170 mm Billets from C45 Steel

Abstract Physico-chemical properties of mould powders and assumed casting parameters for the particular steel grade influence the way of lubricating the surface of the skin of concast billets formed in the mould, as well as heat transfer along its circumference. The paper presents research which main aim was to improve the surface quality of continuous casting round billets (Ø 170 mm) cast from C45 steel. Improvement of the surface quality can be obtained by designing the chemical composition of mould powder for local casting conditions and the technical and technological parameters of CC equipment. Based on the experimental casting from C45 medium carbon steel it was found that there are relationships between the physicochemical properties of mould powder and intensity of skin lubrication and heat transmission to the mould wall.

Understanding mould powders for high-speed casting

The development and application of mould powder for high-speed continuous casting of steel is described. For thin slab casting, the main requirements are proper powder melting, undisturbed slag infiltration, adequate strand lubrication and the control of mould heat transfer. For increased casting speeds i.e. up to 8 m/min, slag infiltration and in particular the control of mould heat transfer via crystallisation of the slag film becomes even more important. It was found that a low powder consumption and hence a thin slag film is no restriction for an undisturbed thin slab casting process. Given a stable casting process and machine condition, the mould powder properties are not as critical as widely assumed.

F-free mould powders for low carbon steel slab casting – technological parameters and industrial trials

The choice of the mould powder for slab casting is a difficult task because mould powders have many important functions during the continuous casting of steel. CaF2 is a key ingredient in conventional mould slags since it reduces the viscosity, the liquidus temperature and the break temperature. Fluorine in mould powders is undesirable from the environmental and health points of view due to the following reasons: (i) evolves easily from slags, producing health-injurious gaseous substances, such as hydrofluoric acid; (ii) creates problems for storage and utilisation of solid waste and (iii) causes machinery corrosion. Aim of the present work is to describe the development of a new F-free mould powder for low carbon steel slab casting replacing CaF2 with B2O3. Laboratory tests and industrial trials were performed considering the technological parameters viscosity, break temperature and crystallisation tendency. From laboratory tests it was concluded that important technological parameters are similar when comparing the F-bearing mould powder (reference) and the new F-free B-bearing mould powder for low carbon steel slab casting: viscosity at 1300°C, break temperature, and crystallisation tendency. It was observed during industrial trials that a significant decrease of the submerged entry nozzle erosion was observed. The results were similar when comparing the F-bearing and the F-free performance: slag pool thickness measurements, melting behaviour, Al2O3 absorption, mould powder consumption and slabs superficial quality.

Investigation of the mold powder film structure and its influence on the developed surface in continuous casting

In the continuous casting of steel, samples of the of the mold flux films are taken from the mold. The mineralogical composition of the crystalline, intercrystalline, and amorphous phases is determined. The influence of the morphology of the cuspidine crystals on the surface macrogeometry of the film is established. The frictional coefficient between a copper counterbody and the mold flux film surface is determined. The wear of the counterbody is greater on interaction with the crystalline surface.

Processing, Microstructure, and Oxidation Behavior of Iron Foams

With its historically long popularity in major structural applications, the use of iron (Fe) has also recently begun to be explored as an advanced functional material. For this purpose, it is more advantageous to use Fe as a porous structure, simply because it can provide a greater surface area and a higher reaction rate. This study uses a freeze-casting method, which consists of simple and low-cost processing steps, to produce Fe foam with a mean pore size of 10 μm. We examine the influences of various parameters (i.e., mold bottom temperature, powder content, and sintering time) on the processing of Fe foam, along with its oxidation kinetics at 823 K (550 °C) with various heat-treatment times. We confirm that Fe2O3 and Fe3O4 oxide layers are successfully formed on the surface of Fe foam. With the Fe oxide layers as an active anode material, the Fe foam can potentially be used as a three-dimensional anode current collector for an advanced lithium-ion battery.

Characterization of diatomite from Sig region (West Algeria) for industrial application

Purpose – Diatomite also known Kieselguhr, is a non-metallic mineral composed of the skeletal remains of microscopic single-celled aquatic algae called diatoms. The purpose of this paper is to test and to evaluate the diatomite of Sig region (West Algeria) to substitute the main mould powder used in continuous casting of steel for thermal insulation and lubrication. Design/methodology/approach – To assess the behavior of diatomite at different temperatures, a combination of simultaneous scanning calorimetric and thermogravimetric testing was used and to evaluate the structure of diatomite, the scanning microscopy method was applied. Findings – The results showed different endothermic and exothermic peaks, mainly at 84.7°C and 783.5°C for endothermic peaks and 894.9°C for exothermic peak. The scanning microscopy method was used and a large porosity was observed. The trial industrial in continuous casting of steel showed a weak loss temperature of steel. Originality/value – This product may be used for thermal insulation in continuous casting of steel. Also the characterization showed the hot behavior of this product with the various transformations and could give the possibility to other use.

Optimization of the EMS process parameters in compocasting of high-wear-resistant Al-nano-TiC composites

Understanding of the electromagnetic stirrer (EMS) process parameters–wear relation in nanocomposite is required for further creation of tailored modifications of process in accordance with the demands for various applications. This study depicts the performance of hybrid algorithm for optimization of the parameters in EMS compocasting of nano-TiC-reinforced Al–Si alloys. Adaptive neuro-fuzzy inference system (ANFIS) coupled with particle swarm optimization (PSO) was applied to find the optimum combination of the inputs including mold temperature, mix time, impeller speed, powder temperature, cast temperature and average particle size. The optimized condition was obtained in minimization of objective function. The objective function is calculated by ANFIS and then minimized by PSO. The optimized parameters were used to produce semisolid cast aluminum matrix composites reinforced with nano-TiC particles. The optimized nanocomposites were then studied for their tribological properties.

Attachment of Alumina on the Wall of Submerged Entry Nozzle During Continuous Casting of Al-Killed Steel

The mechanisms of the formation of different attachments on the walls of submerged entry nozzle (SEN) were studied for the processes of Al-killed steel (Ca-treated, HSLA) and ultra-low carbon Al-killed steel (ULC). To understand the mechanism, the types of inclusions in the steel taken in tundish and in bloom (or slab) were identified. In the case of ULC, the reoxidation product, micro-alumina particles were found to be the source of attachment on the inner wall of the SEN. To avoid reoxidation of the steel by the top slag, removal of the slag could be considered in order to improve the situation. No attached layer was found on the outer surface of the SEN after casting of the ULC steel. In the case of HSLA steel, an attached layer composed of plate-like alumina crystals was found in some trials. The entrainment of oxygen through the mold powder due to improper operation would be the reason for the formation of this type of attachment. The formation of the plate-like crystals was discussed with the help of CFD calculation.

Calculation of Physical Properties for Use in Models of Continuous Casting Process-Part 1: Mould Slags

Physical properties of both steels and mould slags are needed as input data for the mathematical modelling of the continuous casting process. Routines for calculating the properties of mould slags and for estimating steel properties have been developed and are described in Parts 1 and 2, respectively. Many mould powders, with differing compositions, are used in casting practice and their properties vary significantly. Reliable models have been developed to calculate these property values as a function of temperature from their chemical composition since this is available on a routine basis. Models have been developed to calculate the following properties: heat capacities, enthalpies, thermal expansion coefficient, density, viscosity, thermal conductivity and surface tension. Solid mould slags can exist as glassy or crystalline phases or as mixtures of the two (i.e. slag films) and the properties for the various phases can vary considerably; methods have been developed to calculate property values for these various states. The software used to calculate the properties is available via the link (i) http://www.mxif.manchester.ac.uk/resources/software (ii) https://sites.google.com/site/shyamkaragadde/software/thermophysical-properties.

Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 1 Conventional Mould Powders

Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 1 Conventional Mould Powders

Velocity Monitoring of Molten Steel in a Continuous Casting Mold Using Three Submerged Entry Nozzle Designs

The horizontal and vertical velocity components of molten steel in a slab continuous casting mold produced by three different two-port Submerged Entry Nozzle (SEN) designs are monitored and compared using Computational Fluid Dynamics (CFD) simulations. These two ports designs correspond to a conventional cylindrical SEN, a plate SEN and an anchor-shaped SEN. Four monitoring points at the molten steel in the centered vertical plane were selected to track the horizontal and the vertical component of the velocity vector. Two of them are located near the free surface and the remaining two are located in the vicinity of the SEN discharge nozzles. Some statistical values of the time series of above the velocity components are analyzed and correlated with the Kelvin-Helmholtz instability and the Karman vortex streets, which cause mold powder entrapment in the molten steel.

Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 2 Specialist Mould Powders

Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 2 Specialist Mould Powders

Failure analysis of bullnose refractory in reheating furnace of Hot Strip Mill

This paper presents the failure analysis of aluminosilicate based castable used in the bullnose structure of the recuperative type reheating furnace of Hot Strip Mill, where there is a greater wear with respect to the other areas in the furnace. The wear of the refractory was envisaged after a major shutdown that took place at Hot Strip Mill of Tata Steel. The various characterisation tests yielded that there is a reaction between alumina and alkali oxide (sodium oxide) from the mould powder in the presence of silica forming sodian anorthite which undergoes volume expansion and thus generates stresses in the pre-assembled bullnose blocks. These developed stresses were leading to the problem of sagging of the refractory in the reheating furnace. The source of alkali was identified as mould powder along with mill scale getting deposited on the refractory through hot air acting as a carrier and causing reaction. As it was considered as the major problem in the reheating furnace, an elaborate work was done on providing a viable solution which entails study of effect of addition of silicon carbide in alumina based refractory mix.

Continuous Casting of High-Al Steel in Shougang Jingtang Steel Works

Reaction between mold flux and liquid high aluminum steel is considerably strong. It changes the physical property of the mold powder greatly and leads to a larger fluctuation of heat flux in the mold. Transverse depression and longitudinal cracks were often found on the slab surface. Three casting trials were carried out to investigate the effects of mold powder and slab width on castability and surface quality of high aluminum steels. The result shows that the SiO2 content of liquid mold powder decreases while Al2O3 content increases during the casting process. It was found that the degree of slag-metal reaction, addition and consumption of mold powder determined the final equilibrium content of SiO2 and Al2O3. Under the same process condition, it takes more time for the mold powder content to reach equilibrium when casting wide slabs than narrow ones. Considering the sticking and slab surface quality, mold powder A with high melting point and high viscosity is suitable for casting 1 200 mm-width slab and mold powder B with low melting point and low viscosity is suitable for casting 1 900 mm-width one.

Characteristics and Evolution of Inclusion Induced Surface Defects of Cold Rolled IF Sheet

Cold rolled IF sheet has a high requirement for surface quality. Nowadays, more than half of surface defects in cold rolled sheet are caused by non-metallic inclusions generated in steelmaking and casting process. Three types of surface defects as sliver, peeling and hole were found in industrial samples. To investigate the evolution process of inclusion induced surface defects, hot rolling and cold rolling of industrial slab samples were carried out in pilot mill, then surface defects after cold rolling were analyzed with scanning electron microscope equipped with energy dispersive spectrometer (SEM-EDS). The results show that, the inclusions which create surface defects are mainly from deoxidation products and entrapped mold powder. Surface defects like pockmark, peeling, dent and scratch in cold rolled IF sheet are determined by position, size and property of the inclusions. Subcutaneous big size inclusions can lead to peeling and dent, while surface inclusion particles would lead to pockmark and scratch or sliver. To improve surface quality of cold rolled sheet, some measures should be adopted to further decrease and remove macro inclusions, and avoid hard inclusions to be bare to the slab surface.

Design of mould fluxes for continuous casting of special steels

The melting behaviour of mould powder during continuous casting is an important consideration with respect to caster performance, production rate and steel quality. Two important factors, powder composition and carbon addition, are critical to control the properties and melting behaviour of the mould flux. In this study, the effect of different carbonaceous materials on the melting characteristics of mould powders was evaluated. Correlations were established between the structural factors and chemical reactivity of carbon and melting behaviour of mould flux. In addition, two examples are given of the effect of flux composition on casting performance for specific steels. A flux with reasonable basicity and additives was designed for the casting of heat-resistant steel (Incoloy 800) to reduce surface cracks. Another flux was designed for the casting of non-magnetic steel containing high aluminium by partially replacing SiO2 with Al2O3 to limit aluminium oxidation by SiO2.