Satish Kumar Ajmani

Single strand continuous caster tundish furniture comparison for optimal performance

Abstract Analysis of a single strand 36 t thin slab caster tundish has been conducted with different sets of furniture using a three-dimensional computation fluid dynamics model taking heat losses into account. Five distinct and optimised cases and a base case were used for simulation. The cases were built considering tundish furniture that is readily and economically available and provides ease of maintenance, thus targeting an optimal set of furniture. The performance of different sets of furniture was assessed based on residence time parameters like plug volume fraction, mixed volume fraction, dead volume fraction, etc. Other performance indicators used in the analysis were temperature distribution, observing cold spot, surface velocity and nature of flow in the tundish. Insight from the base case reveals the desired flow characteristics that help to achieve the target performance. Inferred results suggested the use of a turbulence inhibitor in combination with a dam as the optimal set of furniture. Use of a non-isothermal model is important, as it was found that even a small change in temperature (2·3°C) plays a vital role in the fluid flow inside the tundish.

Mathematical simulation of surface wave created in a mold due to submerged entry nozzle

Two‐dimensional numerical simulations have been performed using a finite volume method that employs unstructured grids with cell‐wise local refinement and an interface‐capturing scheme to predict the shape of the free surface, thus simulating the surface wave that is created in a mold due to the flow from the submerged entry nozzle (SEN). Simulation has been done for 1:6.25 aspect ratio of the mold having a height of 2 m with parallel rectangular ports as well as 15° upward and downward ports. It has been found that for low inlet velocity of the SEN (<1 m/s) the maximum wave amplitude of the surface remains below 12 mm and no outside air is entrapped by the wave to form a bubble. However, for high inlet velocity (2 m/s or more) there is considerable fluctuations on the free surface and the maximum wave amplitude shoot up beyond 70 mm at the start up and slowly falls to about 30 mm entrapping air bubbles from the surroundings. The movement of the air bubble within the mold and its rise to the free surface ...

Optimisation of dual purging location for better mixing in ladle: a water model study

Abstract Mixing time studies were performed on a one-fifth scale aqueous model of a single tapered ladle with different bottom purging locations. Two porous plugs were used simultaneously to purge compressed air as an analogue to argon and this was referred as dual purging. KCl solution (1 N) was used as the tracer for measuring mixing time. The scaled down gas flowrate varied from 10 to 80 L m–1. Around 400 experiments were done including all possible dual purging locations and the location which gives least mixing time was identified. The results were compared with corresponding single purging experiments and it was found that dual purging can reduce mixing time to a great extent even in the lower flowrate range and a location better than ±R/2 has been suggested. Effect of differential flow on mixing time has also been reported.

Optimum taphole length and flow induced stresses

Abstract The flow induced shear stress on the wall of a blast furnace hearth has been computed by solving the Navier–Stokes and Darcy flow equations in the hearth numerically. The Navier–Stokes equations were used to compute the flow field in the coke free zone, while the Darcy flow equation was used for the flow of liquid metal in the coke packed porous zone (known as the deadman). The computed velocity field was utilised to determine the shear stresses on the side wall of the hearth for various lengths of taphole and different types of deadman when the hearth is filled with liquid metal. It was found that the peak stress on the wall of the blast furnace reduces significantly as the length of the taphole increases. However, the peak stress again increases above a certain length of taphole, for a floating deadman, indicating an optimum taphole length to be used to minimise the fluid induced shear stress. For the case of a sitting deadman the increase of peak stress with taphole length, above the optimum length, is marginal, but it was possible to determine a clearly defined optimum taphole length. For the case of no deadman the peak stress was found to decrease continuously with increase in taphole length; hence, an optimum taphole length could not be determined. It was also found that the location of the maximum equivalent shear stress shifts in the increasing direction of θ almost linearly with an increase in taphole length.

Numerical analysis of unsteady hydrodynamics and thermal transport in five-strand asymmetric tundish

Abstract In this work, a numerical study was carried out to characterise the hydrodynamics and heat transport in a five-strand asymmetric billet caster tundish. Employing a three-dimensional computational fluid dynamics model, several numerical experimentations were carried out to capture the exact physics of complex fluid flow and thermal transport in the tundish. Plant practices were simulated by considering seven distinct cases and analysed in detail. Tundish filling operation was tried out with volume of fluid methodology. The effects of thermal buoyancy, its effect on thermofluidic heat transfer and the abrupt change in thermal gradients at different zones in the tundish flow domain were explained after detailed analysis. Refractory heating simulations were performed, and results were analysed in detail. This is the first time that such an exhaustive numerical study on an asymmetric tundish has been reported.

Physical modelling investigation of influence of strand blockage on RTD characteristics in a multistrand tundish

Abstract In the continuous casting process, the tundish acts as a continuous molten steel distribution vessel. The importance of the tundish during the molten steel delivery becomes more significant when it supplies liquid steel to more than one mould. In the present work, a water model of a six strand billet caster tundish has been used to study the effect of strand blockage on the residence time distribution (RTD) characteristics at the strands. All the experiments were performed under steady state conditions. Potassium chloride was used as a tracer for the study. The effects of blockage on the strand dissimilarity among the open strands were also studied. Both single and dual strand blockage experiments were performed. Blockage of strands deteriorated the RTD characteristics at the open strands. The results reveal the most preferred options for strand blockage when the plant operation needs to do so.

An Approach to Heat Transfer Analysis of Wire Loops Over the Stelmor Conveyor to Predict the Microstructural and Mechanical Attributes of Steel Rods

To understand and predict the microstructure evolution in various grades of steel, a heat transfer coupled with phase transformation model has been formulated with an enhanced stelmor cooling module. This module is capable of handling both blower assisted high cooling and retarded cooling using hoods. The stelmor module incorporates the change in ring spacing of the wire loops on the stelmor due to a change in mill speed and conveyor speed of the wire rod mill. A geometrical approach to convective and radiative losses taking into account the void fraction and shape factor of wire loop is reported. This makes the model robust by strengthening the heat transfer formulation. This paper deals with the correlation of wire rod mill process parameters on the cooling curve of wire rods. The cooling of wire rods is dependent on the stelmor operating parameters. Commercial high carbon grades require high capacity blowers for efficient cooling to refine the pearlite microstructure and impart greater strength. Welding grade wire rods (low carbon grades) on the other hand require retarded cooling to increase the ferrite grain size and decrease the ultimate tensile strength.

Resolving operational issues encountered during continuous casting of micro-alloyed Al killed steel

Nozzle clogging of low carbon micro-alloyed Al killed steel is a crucial castability problem at steelmaking shop. The nozzle clogging index (NCI) was earlier developed by R&D and implemented in the control room of the caster. This parameter gives the clogging status of submerged entry nozzle. In the present work, the root cause for higher NCI was identified by developing a correlation with the upstream parameters. A correction parameter was applied to avoid some misleading NCI values (encountered during the process). Primarily wide variations in bath killing practices by Al bar addition and higher lime addition at TAP were found to have significant impact on NCI during casting. Subsequently, higher Al wire injection at on line purging station and relatively lower lime addition at ladle furnace were also found to have higher NCI. Based on the statistical analysis, the optimum ranges of the upstream parameters were suggested to conduct a plant trial for getting lower NCI. Overall the NCI was reduced from an average value of 0.66 (bad heats) to 0.26 (good heats) for a complete trial casting sequence.