Physical modelling of fluid flow in electric arc furnace caused by impinging gas jets

Abstract

The interaction of liquid steel and an inclined impinging oxygen jet in an electric arc furnace (EAF) is of interest both commercially and scientifically. The bath activity in the EAF may vary from a surface splash ejected to high elevation to intense subsurface mixing. The system is appropriately modelled using water and nitrogen with scaled flowrates. In previous work, the gas/liquid contact was investigated by use of a geometrically similar 1/3rd scale three-dimensional water model. The cavity formed by the jet contacting the liquid surface was characterised by four modal regimes. These regimes were seen to depend on the lance angle, the height of the lance and the jet flowrate. To investigate the evolutionary mechanisms of the cavity regimes, a two-dimensional water model study was undertaken. The two-dimensional water model was a rectangular viewing tank with an inner movable glass wall that allowed a very thin slice of the system to be obtained. The shape of the cavity formed on the water surface was seen clearly along with the expected cavity oscillations. High speed video footage of the two-dimensional system allowed the cavity oscillation to be directly observed. The gas-liquid interaction produced a wave that travelled along the surface of the cavity until it reached the cavity crest where it was torn from the liquid surface and dispersed in a splash. It is the regular progression of the wave's nodes and antinodes along the cavity surface that makes the cavity appear to oscillate. When the wave reaches the crest of the cavity, it will either fall back into the path of the gas jet or be projected as a splash depending on the verticality of the cavity surface. The two-dimensional work, along with the initial three-dimensional investigation, has shown that the troublesome splash in the EAF is caused by how the lance is positioned directionally or azimuthally. By changing the lance angle or height the deleterious splashing of molten metal may be prevented, ameliorated or controlled. The frequency of the wave production was determined from the high speed video footage. The cavity oscillation was found to be a function of the size of the cavity, the inclined height of the lance and the modal regime being produced. Alterations to the flow through the lance had only a moderate effect on the frequency of oscillation indicating that velocity was not the major influential factor.     

Design of steels for high speed machining

Abstract

Historical analysis of metal cutting shows that metal removal rates have been increasing in the course of the century, predicated by the advancement in tool materials but the steel design has lagged behind. This paper examines the mechanisms of chip formation and tool wear as a function of cutting speed in metal cutting. Chemical wear is identified as the dominant mechanism of tool wear at high cutting speeds caused by temperature rise due to shear localisation in the primary and secondary shear zones of chip. Shear localisation in the primary shear zone is shown to be influenced by both microstructural parameters, i.e. matrix hardening and second phase particles, and metal cutting variables, i.e. cutting speed (strain rate) and feed (pressure). Shear localisation in the secondary shear zone is caused by the tribological conditions of seizure at the tool/chip interface. Chemical crater wear is caused by the dissolution of tool into the workpiece (chip) by diffusion mechanism and can be prevented by suppressing the tribological condition of seizure. The design of steel for high speed machining is based on engineering glassy oxide inclusions in steel, which are designed to form a viscous layer in situ at the tool/chip interface at high cutting speeds. The viscous layer lubricates the tool/chip interface and prevents the occurrence of seizure, thereby suppressing chemical crater wear. In comparison with the large volume fraction of inclusions required for promoting ductile fracture at low cutting speeds, the amount of inclusions required for lubricating the tool/chip interface is very small and is in the range that is typical of clean steel. Thermodynamic modelling is shown to be a powerful tool to engineer glassy oxide inclusions in steel     

Effect of casting parameters on permeability in lower part of blast furnace

Abstract

Maintenance of adequate permeability in the lower zone of a blast furnace is crucial for stable and efficient furnace operation. Permeability in the lower zone is influenced by the changing levels of hot metal and slag in addition to other operational factors. Thus, accumulation of liquids in the hearth and inadequate drainage will lead to deterioration in permeability, thereby limiting wind acceptance and furnace productivity. Therefore, the knowledge of the liquid level in the hearth and factors influencing drainage would be helpful for ensuring high permeability. Effort has been made in the present study to analyse the effect on liquid level of casting parameters such as casting rate (CR), production rate, gun up to knock out time (GKT), slag delay, cast duration (CD) and number of casts (NC). The relationships between casting parameters, liquid level and permeability resistance in the lower zone have been derived mathematically based on material balance. From known casting parameters, the liquid levels have been estimated. The prediction of liquid levels by the model was in good agreement with the furnace data on permeability resistance. In order to maintain high permeability in the lower zone, the optimum values of GKT, NC and CR for different production rates have been suggested to the plant.     

Permeability of potlining refractories at high temperatures

Abstract

The degradation of refractory barrier bricks used in the cathode of aluminium electrolysis cells is mainly caused by the chemical attack of fluoride melts and sodium vapour. As the bricks react with the corrosive agents they experience a number of physical and chemical transformations, ultimately impairing the efficiency of the cell operation and even shortening its life.

Recent studies on the characterisation of aluminosilicate refractories showed a reasonable correlation between the materials’ permeability and their resistance to a chemical attack. Nevertheless, in all reported cases this property was measured at room temperature, which does not reproduce the real situation. With the aid of newly developed equipment, various experiments were carried out in the present work to investigate how the permeability varied from room temperature up to 700°C, attempting to find a better representation of the actual conditions to which the barrier bricks are subjected. The room and high temperature results were compared and an analysis was presented in order to suggest the best approach for the selection of aluminium cells refractory lining.     

Effects of the lamination temperature on the properties of poly(ethylene terephthalate-co-isophthalate) in polyester-laminated tin-free steel can — I. Characterization of poly(ethylene terephthalate-co-isophthalate)

The effects of lamination temperature on the properties of poly(ethylene terephthalate-coisophthalate) (co-PET), such as thermal, mechanical, and barrier properties, have been investigated in co-PET laminated steel. The variation of the degree of crystallinity and the orientation of the co-PET film during the lamination process was examined using DSC, X-ray diffraction, and birefringence, and water vapor permeability was also measured with varying lamination temperature. Both the degree of crystallinity and the orientation of the co-PET film decreased and water vapor permeability increased with increasing lamination temperature. The stress-strain curves of the co-PET films were different, depending on the lamination temperature. The stress in the co-PET film laminated at higher temperature was lower at a given strain, due to the increase of the amorphous region. The effects of annealing temperature and the extent of drawing on the residual stress in co-PET/tin-free steel (TFS) joints were investigated by examining the stress relaxation behavior of co-PET. It was necessary to heat co-PET/TFS joints at more than 150°C in order to eliminate the residual stress.     

39—THE FLOW OF LIQUID FROM A JET THROUGH A COMPRESSIBLE POROUS LAYER. PART III: THE CHARACTERISTICS OF LIQUID FLOW THROUGH A COMPRESSIBLE LAYER OF LOOSE WOOL

The effects on the conditions of flow of the surface and configurational properties of the fibres in a compressible porous layer are discussed. The characteristics of a layer of wool are evaluated, and its compressibility is determined. It is shown that, when a liquid of initial uniform pressure flows through a compressible porous medium, the pressure gradient within the medium increases with the distance of flow. The resulting pressure drop is found to depend on a function of the ratio of the downstream to the upstream porosity of the compressible medium. Experimental results are reported for permeable flow through various layers of loose wool; these indicate that, when the flow is disturbed turbulent, the pressure drop through the layers is proportional to the square of the filter velocity. This result is not readily apparent from the graphs of pressure drop against filter velocity because of the compressibility of the fibres.     

Determination of rapid heating cycles for binder removal from open pore green ceramic components

Abstract

Rapid heating cycles have been determined for the thermal removal of binder from open pore green ceramic components. The samples are multilayer green bodies with barium titanate as the dielectric, and the binder consists of poly(vinyl butyral) and dioctyl phthalate. The kinetics of binder decomposition, the gas permeability of the green body and the conditions at failure of the green body were determined from a combination of experiments and modelling. These results were then used with an algorithm based on variational calculus to develop successful rapid heating cycles without causing failure of the component.     

Effect of phenol formaldehyde resin on the adhesion properties of butyl rubber–polyester proofed fabric

Phenol formaldehyde resin was used as an adhesion promoter additive to two bonding system: resorcinol and m-phenylenediamine. These two systems were used to produce butyl rubber–polyester proofed fabric. The addition of resin led to better adhesion properties. The coated fabrics were exposed to heat aging and ionizing radiation. The permeability, dielectric properties, and the electrical resistivity of the coated fabrics were examined.     

Numerical modelling of permeability variation with composition in aluminium alloy systems and its relationship to hot tearing susceptibility

Abstract

A numerical micromodel has been developed to simulate the evolution of equiaxed primary phase grains during the solidification of alloys in the systems Al–Cu, Al–Si, Al–Mg, and Al–Zn. The microstructures generated have then been used to model liquid permeability as a function of composition for each system, for a given solid fraction and cooling rate. In all systems a marked minimum occurred in the permeability curve at a value < ～1 wt-% solute. The composition corresponding to the minimum permeability tended to increase with increasing equilibrium partition coefficient. It is argued, for each system, that the composition displaying minimum permeability would correspond to that composition exhibiting maximum susceptibility to hot tearing. Comparison of the permeability data with experimental hot tear test data for the same systems reveals the limitations of most hot tear tests.     

Temperature Dependence of Permeability of Co66Fe4Mo2Si16B12 Alloy

At different annealing temperatures, the saturation magnetostrictions and the correlation between the permeability μi and the temperature T (μi-T curves) of the Co66Fe4Mo2Si16B12 alloy were investigated using a small-angle magnetization tester and core tester. The experimental results showed that the μi-T curves had different shapes at different ranges of annealing temperature;the permeability μi of the alloy improved with the increase of the annealing temperatures below 460℃; when the alloy was annealed above 480℃, the poor magnetic properties were considered to be caused by larger saturation magnetostriction.