Slag Formation Research Articles

A Study on Spatter Tracking Algorithm for a Vertical GMA Welding Process

GMA (Gas Metal Arc) welding has the advantage of no slag formation and is becoming the most suitable technology for automated welding. Recently, robot welding and machine welding have been replaced by GMA welding. However, welding spatter has always been a problem with GMA welding, especially GMA welding using CO2 gas as a shielding gas. Therefore, it is necessary to minimize the occurrence of spatter. In this paper, the spatter generation process was analyzed and the amount of generated spatters was minimized by controlling the unstable waveform of the current. In addition, we developed a spatter tracking algorithm to confirm the effect of spatter reduction. Key words: Gas metal arc, Spatter, Spatter tracking algorithm, Welding automation

Effect of H2 addition on process of primary slag formation in cohesive zone

Based on the technology of gas-injection blast furnace (BF), the characteristics of primary slag formation with H2 addition were researched. The results indicate that, compared with traditional BF, the primary melt is formed at a lower temperature, which promotes the deformation of the solid burden particles. With the increase in temperature and H2 content, the quantity of formed melt containing FeO decreases sharply, corresponding to the crystallization of solid 2CaO·SiO2 during reduction. A wider softening range and narrower melting zone could be found in the gas-injection BF with a higher reduction potential. The permeability of burden layer is ameliorated as a result of decreased melt quantity. The influence of H2 on the high-temperature properties of burden is not so conspicuous when the H2 addition is from 10 to 15 vol.% against 5 to 10 vol.%. What is more, the slag shows a better liquidity with the decrease in basicity, owing to the transformation of melt composition from a primary phase field with high melting point to that with low melting point. The process of slag forming in gas-injection BF is characterized by earlier melt formation, less primary slag, higher melting temperature, better permeability and better liquidity, and the phase compositions of primary slag are close to those of final slag.

Effect of direct charging of hot recycled slag on hot metal pretreatment dephosphorization in a dephosphorization furnace

Industrial experiments were carried out to investigate the effect of the direct charging of hot recycled slag (DCHRS) on hot metal pretreatment dephosphorization in a dephosphorization furnace. The bulk compositions of semi-steel and slag show that a better dephosphorization effect could be achieved by applying the DCHRS process in the dephosphorization furnace. Compared with the bulk compositions in normal heats, the mean contents of phosphorus in the semi-steel and total Fe in the final slag were decreased by 0.006 and 1.93 wt.%, respectively, with an increase of approximately 6 °C in the semi-steel temperature. According to mineralogical observations, the dephosphorization slags in normal heats and test heats were similar in petrographic constituents, but the metal loss was markedly decreased in the DCHRS process. Thermodynamic calculations show that even though the dephosphorization slag in the DCHRS process had the same dephosphorization capacity as that in the normal refining process, the phosphorus distribution between slag and hot metal in the new process was slightly higher and closer to the reaction equilibrium. Meanwhile, proper operating conditions, including slag basicity, total Fe content in the final slag, bath temperature, slag formation and slag volume, were optimized to improve the dephosphorization efficiency under the condition of the DCHRS process. The consumption of lime, light-burnt dolomite and oxygen during blowing was significantly decreased by the DCHRS process.

Análisis de las propiedades del sistema CaO – FeO – SiO2 para su aplicación en escorias

The study of ternary phases systems in pyrometallurgy is used for the adequate formation of slags, because they are an important foundation in establishing the conditions of operation in the separation of undesired elements. In this area, the CaO - FeO - SiO2 system is generally used for the determination of liquidus temperature and other properties mainly in the metallurgy of Pb and Fe. In this article we review the main properties of this system, such as density, surface tension and electrical conductivity. In addition, a compilation is carried out on the values obtained from the viscosity made by different authors at different compositions and temperatures, in order to verify the interaction that each component delivers to the equilibrium of the system. Through this research, the aim is to obtain the knowledge to predict the behavior of the slag that leads to making the decisions that improves the processes and this is only through reliable and consistent information.

Influence of Na2CO3 and CaCO3 additions on the aluminate slag formation during a single-stage reducing roasting of red mud

Influence of Na2CO3 and CaCO3 additions on the aluminate slag formation during a single-stage reducing roasting of red mud

Mathematic simulation of atomic structure of multicomponent oxide-fluoride melt for continuous casting machines

Determination of relation between oxides melts properties, based on silicates and calcium alum-silicates and magnesium and their chemical composition and structure is an important condition to provide a rational slag mode in a continuous casting machines mold. A mathematical simulation of slag melts and casting powders accomplished. The oxide-fluoride system was chosen for the simulation, for which the structure after solidification was determined by experiment. Results of molecular-dynamic simulation of CaO–SiO2–Al2O3–MgO–Na2O–K2O–CaF2–FeO system, correspondent to industrial casting powders composition, used during steel casting for slag formation in a CCM mold (35.35 % SiO2; 30.79 % CaO; 8.58 % Al2O3; 1.26 % MgO; 13.73 % CaF2; 7.57 % Na2O; 0.88 % K2O; 1.82 % FeO). Taking into account the concentration, a re-calculation was accomplished to mole shares and correspondent number of ions in the model for each component calculated. Simulation of the 8-component oxide-fluoride melt with 2003 ions size in the main cube (a side length of 31.01 Å) was accomplished at the experimentally determined temperature of solidification onset (1257 K) under periodic boundary conditions and fixed volume. The Coulomb interaction was taken into account by the Ewald–Hansen method. The time step was 0.05t0, where t0 = 7,608×10–14 sec is the internal unit of time. The melt density was taken as 3.04 g/cm3 based on the experimental data. The inter-particle interaction potentials were chosen in the Born–Mayer form. According to the simulation results, the structure of sub-crystalline groups of atoms present in the melt at the temperature of the onset of solidification was determined. A discussion of the simulation results and their comparison with the literature data presented.

Technology of Melting an Invar in an Induction Furnace

A process of melting a 32NKD superinvar alloy from industrial wastes in a 1100-kg FS (core-free) induction furnace is developed. The preparation of a charge, namely, fraction composition, oxidation, the content of harmful impurities, and a method of charging, is considered in detail to ensure the maximum resistance of a crucible and to optimize melting. The methods of decreasing the height of the meniscus that forms on the melt surface because of the specific features of induction heating and the related features of slag formation are analyzed.

Improved prediction of critical-viscosity temperature by fusion behavior of coal ash

Coal ash slag viscosity is critical for slag tapping in entrained-flow coal gasifiers, so the accurate prediction of slag viscosity and the critical temperature of viscosity (Tcv) will help the coal selection, flux addition and gasifier operation. Many empirical correlation models based on ash fusion temperature have been proposed to calculate Tcv. In order to correlate the viscosity with the fusion behavior and then improve the prediction of Tcv, we measured the viscosity of several synthetic coal ash slags with a high-temperature rotary viscometer and studied their ash fusion behavior through thermomechanical analysis. X-ray diffraction was used to compare the mineral transformation before and after Tcv combined with the FactSage calculation. The viscosity measurement shows that the viscosity above Tcv of glassy slags is higher than that of the crystalline type. The mineral transformation from FactSage also demonstrates that the precipitation rate of solid phase is lower for glassy slags. The fusion behavior for the glassy and the crystalline slag is also distinctly different.The fusion range from deformation temperature (DT) to flow temperature (FT) of the ash for the glassy slag was larger than that of the crystalline one, and the shrinkage above FT in TMA trace slopes gently. The correlation between the fusion behavior and viscosity-temperature behavior for the glassy slag is reasonable, because the large temperature range from DT to FT and the low shrinking rate of the stage III indicate the high viscosity of the liquid phase formed and the slow melting of the remained solid phase respectively, which are also the correlative condition prefer for the formation of glass as mentioned above. For the crystalline slag, the small fusion range from DT to FT means the rapid melting of the solid phase and the high flowability of the liquid phase which are indicative for the rapid precipitation during cooling. The slow rate of the stage III indicates the slow melting of the remained solid which can be the crystal nucleus. When the viscosity of the liquid phase is low, it also benefit for the formation of crystalline slags. The characteristic in fusion behavior for different type of slag also suggested that the predicting Tcv by applying one method to all the crystalline slags and non-crystalline slags is not appropriate.

A Review of Steel Scrap Melting in Molten Iron‐Carbon Melts

In the current economic climate, the recycling of steel scrap is become one of the most interesting tasks for the optimization of integrated steel plants. Steelmaking aspects such as jet/bath interaction, slag formation or foaming, lime dissolution as well as slag/metal reactions have received more attention in recent years than the melting and dissolution phenomena of steel scrap in molten steel baths. Since the dynamic modeling of steelmaking processes ‐ especially the Linz Donawitz oxygen steelmaking process (LD) ‐ is becoming more important, interest in the melting and dissolution behaviour is increasing. Several researchers have investigated the complex transactions of coupled heat and mass transfer in the past. Small‐scale experiments are carried out under conditions where only mass transfer or heat transfer were considered. A few authors have reported on pilot‐scale investigations or commercial converters. The coupled heat and mass transfer has also been analyzed by several authors in mathematical models and numerical simulations. The present paper reviews the research on steel scrap melting and dissolution done in the last 50 years. A summary of all reported heat and mass transfer coefficients will be given and the differences between natural and forced convection will be explained. In addition, an overview of recently published numerical simulation describing the problem will give an outlook for future work.

Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization.

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative environmental impact and slag formation. The selected short rotation coppice (SRC) willow wood has a high ash content ( = 1.96%) and, therefore, a high content of emission and slag precursors. Therefore, the reduction of minerals from SRC willow wood by low temperature microwave assisted hydrothermal carbonization (MAHC) at 150 °C, 170 °C, and 185 °C is investigated. An advantage of MAHC over conventional reactors is an even temperature conductance in the reaction medium, as microwaves penetrate the whole reactor volume. This allows a better temperature control and a faster cooldown. Therefore, a succession of depolymerization, transformation and repolymerization reactions can be analyzed effectively. In this study, the analysis of the mass loss, ash content and composition, heating values and molar O/C and H/C ratios of the treated and untreated SCR willow wood showed that the mineral content of the MAHC coal was reduced and the heating value increased. The process water showed a decreasing pH and contained furfural and 5-methylfurfural. A process temperature of 170 °C showed the best combination of energy input and ash component reduction. The MAHC allows a better understanding of the hydrothermal carbonization process, while a large-scale industrial application is unlikely because of the high investment costs.

Development of Manufacturing Technology for High-Sulfur Steel with a High Aluminum Content in the Volga Pipe Plant Electric-Melting Workshop

Continuous casting of steel with a high sulfur content is difficult due to clogging of the submerged nozzle. Physicochemical calculations and studies of a submerged nozzle inner cavity showed that clogging occurs due to formation of calcium sulfide and a low slag assimilation capacity. With serial melting of steel there is entry of slag into the tundish. Development of a slag forming mixture with whose application in the steel-pouring ladle there is formation of slag of this composition, which enters the tundish without worsening slag assimilation properties. Use of this development makes it possible to reduce submerged nozzle clogging and recycling of melts considerably due to stopping casting.

Combustion behavior and slagging tendencies of kaolin additivated agricultural pellets and of wood-straw pellet blends in a small-scale boiler

The aim of this study was the modification of agricultural biofuels to allow for low emission combustion in domestic biomass boilers without slagging or other ash related problems. Four agricultural biomasses were additivated with kaolin. Fuel blends were produced from wheat straw and woody biomass. All fuels were combusted in a 30 kW biomass boiler while emissions and slag formation were measured. Due to additivation or fuel blending, total particle and CO emissions were reduced by 53–77% and 69–95%, respectively. At the same time, slag formation (determined as the mass of agglomerates > 3.15 mm) strongly declined. For fuels containing high amounts of sulphur or chlorine, kaolin additivation may lead to increased HCl and SOx emissions. Moreover, NOx-formation may be higher during combustion of additivated fuels (up to 21%). Overall, additivation with kaolin or blending of fuels might be an interesting option for the utilization of agricultural biomasses. The selection of the optimal upgrading method should consider the chemical and physical biomass properties and address the minimum amount of additive or blending ratio to achieve a sufficient reduction of emissions and slagging.

INFLUENCE OF B2O3 AND CaO–SiO2 –B2O3 –Al2O3 SLAG SYSTEM BASICITY ON CONCENTRATION OF MAGNESIUM OXIDE SATURATION

Study of the effect of boron oxide and basicity of CaO – SiO2–B2O3 – Al2O3slag system on MgO saturation concentration was carried out using the simplex lattice method of experimental design, which allows one to construct mathematical models describing dependence of studied property on composition as a continuous function. Synthetic slags, corresponding in composition to vertices of studied simplex, were smelted in graphite crucibles from previously calcined oxides of analytical grade. Slag compositions corresponding to the remaining points of local simplex plan were obtained by counterblending slags of simplex tops. Using experimental data, mathematical models adequately describing effect of slag composition on saturation concentration of MgO were constructed. Graphic image of mathematical modeling results is represented by the composition diagram – saturation concentration of MgO. Analysis of experimental data presented in diagram made it possible to obtain new information on the effect of boron oxide and basicity of CaO – SiO2 – B2O3slags system containing Al2O3on MgO saturation concentration. It was established that in slags formed in basicity range of 2 – 3 and B2O3content of 1 – 3 %, saturation concentration of MgO varies from 3 to 9 %. Increase in B2O3content in slag to 4 % leads to an increase in MgO saturation concentration in slag of 11 – 13 %. Displacement of slags to area of increased basicity up to 3 – 4 is characterized by a decrease in MgO saturation concentration to 2 – 5 %, with 1 – 3 % of В2О3content and an increase to 7 – 9 % at 3 – 4 % В2О3in slag. Formation of slags in basicity range of 4 – 5 and B2O3content of 1 – 3 % does not lead to a significant decrease in concentration of slag saturation with magnesium oxide. Saturation concentration of MgO in slag in this area of basicity varies from 2 to 4 % and practically does not reach 7 % with an increase in В2О3content to 4 %. At the same time, there is an increase in cost of steel due to an increase in consumption of lime and material containing boron oxide.

Steel Micro-alloying with Boron: A Perspective Direction to Reduce the Consumption of Manganese Ferroalloys

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Formation of solid residues in combustion of boron-containing solid propellants

Boron-containing solid propellants are promising propellants for ducted rockets. The experimental data show that combustion of boron-containing propellants is accompanied by an intense conglomeration of the boron particles near the burning surface. As a result, the boron particles conglomerates which are the branched coral structures composed of sintered boron particles are formed in combustion of boron-containing solid propellants. This results in decrease in combustion efficiency of ducted rockets. To calculate the ignition and combustion of a conglomerate in the secondary combustor of a ducted rocket, it is necessary to know the size, structure and shape of the boron particle conglomerates that can significantly affect these processes. In this paper, we consider a model and a method for calculating the boron particles conglomeration in combustion of the boron-containing solid propellants. The process of the boron particles conglomeration is considered as a result of competition between two main processes: the formation of adhesive bonds between the contacting boron particles and rupture of these bonds under the action of the aerodynamic detached force from the side the flow of gaseous combustion products of solid propellant. The criterion of formation of residues (slag) on the burning surface of boron-containing propellants is considered. It is shown that depending on the propellant burning rate law, two different types of propellants with different conglomeration behavior can exist. The results of calculations of the boron particles conglomeration which demonstrate the slag formation are shown.

Model Development for Refining Rates in Oxygen Steelmaking: Impact and Slag-Metal Bulk Zones

A new approach has been adopted to predict the contribution of the impact and slag-metal bulk zones to the refining rates of impurities in a top blown oxygen steelmaking process. The knowledge pertaining to the behavior of top-jets and bottom stirring plumes (water model and industrial studies) was adapted. For the impact zone, the surface renewal generated by the top jet as well as bottom stirring plumes is incorporated in the current model, whereas in the case of slag-metal bulk zones the surface renewal is caused solely by the bottom stirring plumes. This approach helped in achieving a more explicit use of process parameters in quantifying the slag formation. The results suggest a minor contribution of these two zones to the overall refining of impurities throughout the oxygen blow.

Cupola Furnace Slag: Its Origin, Properties and Utilization

A cupola furnace is the most frequently used furnace aggregate for cast iron production. A by-product of the production of cast iron in cupola furnaces is cupola slag. Its amount is 40–80 kg per 1 tonne of the produced cast iron, and that is one of the reasons why this material is not as favoured as, for example, the blast-furnace slag. The purpose of this article is to provide the basic information on the formation of slag in a cupola furnace, and its chemical composition, structure and current potential applications. The greatest potential for the use of cupola slag is in the building industry; therefore, a section of the present article deals with the property that plays an important role particularly with regard to the use of slags in the building industry, i.e. the slag hydraulicity. The achieved results indicate that the hydraulicity of the cupola slag is incomparable with the hydraulicity of the blast-furnace slag; this may be associated with the problems that arise when the slag of this type is used in the building industry. The authors used the air-cooled as well as granulated slags from cupola furnaces in the production of concrete that was made from the slags alone. While the air-cooled slag may be used as a partial replacement for the blast-furnace slag in concrete mixtures, the use of granulated slag from cupola furnaces as a replacement for granulated blast-furnace slag in cement-free concrete has not proven to perform well.

Time-Resolved Study of Silicate Slag Formation During Combustion of Wheat Straw Pellets

Ash formation during single-fuel pellet combustion of wheat straw at 700 and 1000 °C was studied throughout fuel conversion by quench cooling and analysis at different char conversion degrees. The combination of X-ray microtomography analysis and scanning electronic microscopy with energy-dispersive X-ray spectroscopy showed that ash accumulated in rigid net structures at 700 °C with streaks or small beads surrounding the char, and the pellet mostly maintained its size during the entire fuel conversion. At 1000 °C, the ash formed high-density melts that developed into bubbles on the surface. As the conversion proceeded, these bubbles grew in size and covered parts of the active char surface area, but without entirely blocking the gas transport. The successive char conversion dissolved increasing amounts of calcium in the potassium silicate melts, probably causing differences in the release of potassium to the gas phase. Similarities were found with slag from a combustion experiment in a domestic boiler, w...

Influence of B2O3 and Basicity of CaO–SiO2–B2O3–Al2O3 Slag on the Saturation Concentration of Magnesium Oxide

The influence of boron oxide B2O3 and the basicity of CaO–SiO2–B2O3–Al2O3 slag on the saturation concentration of magnesium oxide MgO is studied by means of simplex experiment-design lattices. That permits the formulation of mathematical models describing the dependence of the specific property on the composition in the form of a continuous function. Synthetic slags corresponding in composition to the vertices of the given simplex are produced in graphite crucibles from preroasted analytically pure oxides. The slag compositions corresponding to the other points of the local simplex design are obtained by cross-mixing of the slags at the vertices. The experimental data provide the basis for mathematical models describing the influence of the slag composition on the saturation concentration of magnesium oxide MgO. The results of mathematical modeling are presented as a graph of the slag composition against the saturation concentration of magnesium oxide MgO. By analysis of the results, new information is obtained regarding the influence of the boron oxide and the basicity of CaO–SiO2–B2O3–Al2O3 slag on the saturation concentration of magnesium oxide MgO. It is found that, for slags formed in regions of basicity 2—3 with 1–3% B2O3, the saturation concentration of magnesium oxide MgO varies from 3 to 9%. Increase in the B2O3 content to 4% increases the saturation concentration of magnesium oxide MgO to 11–13%. Switching to slags of basicity 3–4 lowers the saturation concentration of magnesium oxide MgO to 2–5% with 1–3% B2O3 and to 7–9% with 3–4% B2O3 in the slag. Slag formation in the region of basicity 4–5 with 1–3% B2O3 does not significantly decrease the saturation concentration of magnesium oxide in the slag. In this basicity range, the saturation concentration of magnesium oxide MgO in the slag varies from 2 to 4% and hardly reaches 7% with increase in B2O3 content to 4%. In that case, the cost of the steel rises, on account of the increase in the consumption of lime and the material containing B2O3.

Corrosion mechanisms of magnesia-chrome refractories in copper slag and concurrent formation of hexavalent chromium

Magnesia-chrome refractories have been essential materials for application as wear lining in copper production furnaces for many years. Formation of hexavalent chromium (Cr(VI)) has been a major concern despite its admirable corrosion resistance in copper slag. Magnesia-chrome refractory specimens (9, 12, 15 and 18 wt% Cr2O3) with addition of Al2O3 and TiO2 were fabricated and subsequent corrosion tests using copper slag was conducted in air. The corrosion mechanism between magnesia-chrome refractories fabricated and synthetic copper slag were investigated by means of X-ray diffraction (XRD) and scanning electron microscope (SEM), and concurrent formations of Cr(VI) were assessed effectively by leaching test. All the magnesia-chrome specimens prepared are composed of periclase and composite spinel Mg(Al,Cr,Ti)2O4 phases after firing at 1700 °C. Densification of the specimens decreases with the increase in Cr2O3 content due to the increased volume expansion, while TiO2 addition can improve their densification as mass transfer is enhanced during the sintering process. The corrosion resistance of the specimens decreases slightly with the Cr2O3 content due to the increased apparent porosity, which would result in penetration of more corrosive slag at the initial stage of the corrosion test while a newly formed (Mg,Cu)(Cr,Fe)2O4 spinel dense layer between the slag and penetration layer effectively hinders further penetration of slag and well protects the specimens. The Cr(VI) in the specimens prepared increases obviously with the Cr2O3 added content, while the TiO2 addition can suppress the formation of Cr(VI) effectively and the copper slag can cause the formed Cr(VI) to be reduced further during the corrosion process. For all the specimens, concentrations of Cr(VI) in the leachates is much lower than the US-EPA limit of 100 mg/kg but exceeds the European limit of 2 mg/kg after the corrosion test.