Influence of process variables on development of camber during hot rolling of strip steel

Abstract

Experimental design techniques have been used to study the effects of variations in horizontal scale breaker process parameters in relation to camber generation during the early reduction stages in a hot strip mill. A fractional factorial experiment was designed and performed to identify which process variables are most influential to camber generation. The parameters which emerge from this analysis as being significant are: slab wedge, temperature differentials across the strip width, the deviation of the slab from the mill centreline, and mill tilt. A full factorial experiment was then designed and performed to further investigate these significant process parameters to determine where to set influential and controllable variables so that camber is minimised. The results show that none of the process parameters is significant to camber generation when acting alone; however, they are all significant when combined with one or two other process parameters. This study has enabled a predictive equation to be developed which is able to predict camber to within ±4 mm. This equation may be used in conjunction with mill tilting strategies to reduce camber in the early reduction stages of a hot strip mill.     

THEORIES OF HOT PRESSING

Abstract

A survey has been carried out of the literature on hot-pressing theories and models. Theories as to the mechanism governing the process may be divided into two principal groups:

(1) Mathematical representation of densification. Equations have been derived for mechanisms controlled by plastic or viscous flow. Also equations of a purely empirical nature have been advanced. In this group there is a trend towards a hyperbolic hot-pressing equation, which, according to tests, is valid for metals and metallic compounds over wide temperature ranges.

(2) Theories asserting that the densification process is controlled by various processes, e.g. particle gliding, fragmentation, plastic flow, and volume diffusion. No complete mathematical formula has been proposed on this basis to describe the entire hot-pressing process.     

Estimation of liquidus temperatures for steels using thermodynamic approach

Abstract

Alternative schemes for the prediction of liquidus temperatures have been tested against a large compilation of experimental measurements for steels ranging from low carbon to stainless steels. The best agreement overall was obtained with thermodynamic solutions using the IDS (model of interdendritic solidification) database, although certain empirical equations from the literature were adequate for low alloyed steels. Version L of the commercial ThermoCalc thermodynamics package was outperformed for some steel types by the empirical equations, prompting a reassessment of the Fe–Cr–Ni, Fe–Cr–Si, and Fe–Ni–Si systems used in the IDS database. Additionally, regression equations were determined from several thousand predictions computed by the IDS thermodynamic approach, and these performed almost as well as the proper thermodynamic approach at a fraction of the central processing unit time, also outperforming the earlier approaches.     

Predictability of Charpy impact toughness in thermomechanically control rolled (TMCR) microalloyed steels

Abstract

A number of empirical equations, based primarily on average metallographic grain size and carbide thickness, exist to predict the Charpy impact transition temperature in steels. Some of these commonly used equations, successful for normalised steels, have been shown in this paper to be inadequate for predicting the transition temperature for thermomechanically control rolled (TMCR) microalloyed steels. Thermomechanical control rolling can produce clusters of small grains with low angle grain boundaries, i.e., the steel shows mesotexture. The cleavage facet size in TMCR steels has been found to be significantly larger than the optical grain size and it was also observed that individual cleavage facets can be comprised of multiple grains. In contrast, it was observed for a heat treated steel that the facet size matches the optical grain size and that individual facets consist of single grains. It is concluded that in TMCR steels, the average microstructural unit experienced by the crack front is larger than the optical grain size because mesotexture causes groups of closely orientated grains to be treated as single 'effective' grains. This paper shows that the 50% and 27 J impact transition temperatures can be predicted for TMCR steels using the existing equations if mesotexture and grain boundary carbide size are taken into account.     

Sustainability–steel and the environment

Abstract

A two-dimensional heat and fluid flow model was used to simulate the plasma arc furnace, where the flow is governed by the steady state incompressible Navier–Stokes equations. The flow has been taken as turbulent and the standard k-epsilon model was used to simulate the turbulence in the flow. The coupled non-linear differential equations were solved with suitable boundary conditions and temperature dependent plasma properties at atmospheric pressure by employing an efficient finite volume method. The calculations and heat transfer to various parts of the furnace were calculated for argon, nitrogen and hydrogen plasmas. The voltage–current characteristic for the different types of plasma and the effect of other process parameters on heat transfer are discussed.     

Fast model of thermal camber evolution in metal rolling for online use

Abstract

Mill engineers aiming to improve the geometry of rolled strip require knowledge of the temperature distribution in the roll. Theoretical evidence shows that the core temperature evolves more slowly than surface temperatures and governs the thermal expansion of the work roll. For practical purposes then, a model that predicts core temperature will allow online prediction and tracking of roll cambers. The present paper builds on previous work in developing rapid models of roll core temperature. A previous model derived using Laplace transforms is improved using a matrix formulation and conversion from an explicit to an implicit time discretisation. The implicit solution is more stable and allows for larger time steps than the explicit formulation or iterative methods used previously. The model has been tested and found to make good qualitative predictions but to underestimate the camber in comparison with actual plant data and a two-dimensional finite difference model.     

轧辊交叉对中间坯镰刀弯生成过程的影响

粗轧过程中出现的轧辊两侧轴承间隙差异较大的情况,会造成轧辊交叉,导致板带两侧轧制力失衡,进而引起或加剧中间坯的镰刀弯缺陷,影响最终产品质量精度和后续精轧的轧制稳定性.为研究轧辊交叉对中间坯镰刀弯生成过程的影响,建立了轧辊交叉、偏移的轧件-辊系耦合动态有限元模型,利用模型分析了不同工况条件下,轧辊交叉位置、交叉角度对中间坯楔形、弯曲量及两侧轧制力差的影响,进而总结了由轴承间隙引起的轧辊非对称交叉对中间坯镰刀弯弯曲量的影响规律.结果表明:镰刀弯弯曲量与交叉角、交叉位置比分别呈线性关系,与辊系间隙比呈二次曲线关系.      

CMPO-TRUEX Process and its Application in the Separation of Actinides from High-Level Liquid Wastes

Abstract

Basic studies have been carried out on the high active PUREX raffinate to determine the distribution characteristics of actinides in different extraction systems. The data have been utilised in conducting a series of counter-current extraction experiments, which have led to the establishment of a viable flow-sheet based on a unique PNC salt-free process, that has great potential in minimizing secondary radioactive waste generation. The process was successfully applied to the present purex system, and a decontamination factor DFαof > 10³ has been achieved resulting in the formation of a much less toxic HLLW.

NMR studies carried out on the Ln Complex extracts have yielded valuable data on their thernio chemical and activation parameters. Consideration on the mechanism of degradation/regeneration/decomposition of TRUEX Solvents are also included.     

Mathematical Model of the Blast Furnace

Abstract

During recent years there have been important developments in blast furnace knowledge which enable us to give a simple scheme of the process and thus derive a mathematical model of the blast furnace. The model developed here consists mainly of two simultaneous equations to which it is nece s sary to add a third one giving some limitation from the thermal standpoint.

Such a model may be used for a number of calculations, particularly to predict performances resulting from improvements in blast furnace practice as injections.

Applying this model to the permanent state of the process, it is possible to derive another that gives a dynamic picture of the blast furnace, which is necessary from the point of view of automation.     

Coal pyrolysis and kinetic model for non-recovery coke ovens

Abstract

In heat recovery non-recovery coke ovens, the volatile gases generated are burnt, and the heat generated is used for cokemaking. The extra heat, along with the flue gases, is utilised in boilers for power generation. JSW Steel has 1·2 Mtpa non-recovery coke ovens to meet the coke requirement of blast furnaces. Until now, very limited work has been carried out on heat distribution in non-recovery coke ovens. In this work, the heat distribution in non-recovery coke ovens is studied to determine the variables influencing the flue gas temperature and thereby power generation. A mathematical model has been developed to predict the power generation using functional group, depolymerisation, vaporisation and cross-linking for non-recovery coke ovens at JSW Steel. Gas generation, heat generation, power generation and total heat distribution are calculated using the model. The present paper details the study on heat distribution, thereby various factors affecting the power generation, and also quantifies the effect of coal quality in particular volatile matter on gas generation, flue gas temperature and power generation.     

Mathematical modelling of electroslag remelting P91 hollow ingots process with multi-electrodes

Abstract

Electroslag remelting (ESR) hollow ingot process with T-shape current supplying mould is a new metallurgical technology. A mathematical model was developed to describe the interaction of multiple physical fields of this process for studying the process technology. Maxwell, Navier-Stokes and heat transfer equations have been adopted in the model to analyse the electromagnetic field, magnetic driven fluid flow, buoyancy driven flow and heat transfer using finite element software ANSYS. Moreover, the model has been verified through the metal pool depth measurements, which were obtained during remelting of 10 electrodes into Φ900/500 mm hollow ingots of P91 steel, with a slag composition of 50–60 wt-% CaF₂, 10–20 wt-% CaO, 20–30 wt-% Al₂O₃, ≤8 wt-% SiO₂. There was a good agreement between the calculated results and the measured results. The calculated results show that the distribution of current density, magnetic induction intensity, electromagnetic force, Joule heating, fluid flow and temperature are symmetric but not uniform due to the multi-electrode arrangement in two symmetric groups. Simulation of the ESR hollow ingot process will help to understand the new technology process and optimise operating parameters.     

A simulation study of reduction kinetics for sponge iron production in a rotary hearth furnace

ABSTRACT

A mathematical model has been developed by coupling genetic algorithm (GA) with heat and material balance equations to estimate rate parameters and solid-phase evolution related to the reduction of iron ore-coal composite pellets in a multi-layer bed Rotary hearth Furnace (RHF). The present process involves treating iron ore-coal composite pellets in a crucible over the hearth in RHF. The various solid phases evolved at the end of the process are estimated experimentally, and are used in conjunction with the model to estimate rate parameters. The predicted apparent activation energy for the wustite reduction step is found to be lower than those of the reduction of higher oxides. The thermal efficiency is found to decrease significantly with an increase in the carbon content of the pellet. Thermal efficiency was also found to increase mildly up to three layers. Multilayer bed remains as a potential design parameter to increase thermal efficiency.     

粗轧板坯镰刀弯控制模型的研究与应用

针对经常困扰热轧生产的粗轧板坯镰刀弯缺陷,本文结合弹跳方程和解析法,分析了引起板坯镰刀弯的主要因素——轧机两侧纵向刚度偏差、来料楔形及轧件运行走偏,分别计算了其对应的调整量,建立了基于轧机两侧轧制力差的镰刀弯调平控制模型.该模型可反映轧机两侧纵向刚度差、来料楔形及轧件运行走偏等主要因素与镰刀弯的定量关系,进而计算出控制镰刀弯的粗轧机各道次辊缝倾斜调整值.与现场实测值进行离线验证对比,实测值与计算值比值平均为0.977,结果表明镰刀弯调平模型能够预估板坯各道次辊缝倾斜调整值.将模型投入2250 mm热轧机组使用后,板坯镰刀弯弯曲量未达标率从24.88%下降到6.62%,提高了镰刀弯控制效果,使粗轧板坯镰刀弯问题得到了很大缓解.      

Development of novel RH degassing process with powder injection through snorkel nozzles

Abstract

A novel decarburisation process in an RH (Ruhstahl hausen Process) degasser (RH aside spray technique) has been proposed, plant trials have been carried out and the ruling factors have been analysed. The results indicate that the decarburisation process is accelerated, which results in a shorter treatment time of at least 3 min. Enlargement of the interfacial reaction area is considered to be the main decarburisation mechanism. Further study is recommended.     

Model based optimisation of continuous annealing operation for bundle of packed rods

Abstract

A typical industrial thermal processing operation has multifold complexity, with varying charge dimensions, multiple grades and inconsistent loading patterns as well as the absence of in situ sensors. These operational characteristics and restrictions invariably lead to empirical design for the temperature time cycles, which often results in suboptimal operation in terms of higher energy consumption, inconsistent quality and lower productivity. In the present work, a process model is proposed for designing the heating cycles for bundles of packed rods with different rod diameters, bundle diameters and packing fractions in a continuous annealing furnace. The process model has the capability of predicting spatial and temporal evolution of temperature and hardness in the bundle as it traverses through the furnace. Interestingly, the model based process cycles are found to be counterintuitive as compared with the empirically designed cycles normally employed in the plant. It is shown that instead of designing the process cycles on the basis of rod diameters, which is the general practice in the plant, it should be based on bundle characteristics, such as bundle diameter and packing fraction. These concepts have been implemented in an industrial operation resulting in around 20% energy reduction and 15% productivity enhancement.     

A simplified model of heat generation during the uniaxial tensile test

The temperature rise in a sheet tensile specimen has been calculated by the finite difference method for a plain-carbon steel at various strain rates and in several environments. Prior to necking, a uniform heat generation function is used with the governing flow equation while during the post-uniform strain, an empirical heat generation function is used. The empirical function is based on a strain distribution equation generated by curve fitting of experimental data. The effect of heat transfer conditions on the temperature increase has been discussed. The maximum temperature rise in air may reach 42 K at the center of an I.F. steel specimen at a strain rate of 10^-2/s. The instability strain during tensile testing has been predicted by taking into account strain hardening, strain-rate hardening, and deformationinduced heating. The results show that significant deformation heating can occur during tensile testing in air at “normal” strain rates near 10^-2/s, and that the uniform elongation can be affected markedly. Predictions for other alloys based on tabulated data are also presented.     

Review of mathematical models of fluid flow,heat transfer,and mass transfer in electroslag remelting process

Abstract

The electroslag remelting (ESR) process has been used effectively to produce large ingots of high quality based on the controlled solidification and chemical refining that can be achieved. Despite the widespread application of industrial facilities, there are still issues that prevent an effective control of the process. This is particularly critical considering the large ingots produced industrially which makes the traditional trial and error approach prohibitively expensive. Thus, mathematical models of the process are a good alternative as a process control tool. To predict the relationship between operating parameters such as power input and type, fill ratio, depth of electrode immersion, and slag chemistry and the casting rate, microstructural features, and ingot chemical composition, it is then necessary to develop mathematical models based on differential equations describing the fluid flow, heat transfer, and mass transfer phenomena that take place during the process. In the present paper, mathematical models of the transport phenomena occurring during ESR are reviewed. Although the models have evolved to a point where several features of the process can be predicted and the dominant transport mechanisms have been elucidated, more effort is required before the models can be applied to define actual operating conditions.     

A simplified model of heat generation during the uniaxial tensile test

The temperature rise in a sheet tensile specimen has been calculated by the finite difference method for a plain-carbon steel at various strain rates and in several environments. Prior to necking, a uniform heat generation function is used with the governing flow equation while during the post-uniform strain, an empirical heat generation function is used. The empirical function is based on a strain distribution equation generated by curve fitting of experimental data. The effect of heat transfer conditions on the temperature increase has been discussed. The maximum temperature rise in air may reach 42 K at the center of an I.F. steel specimen at a strain rate of 10^-2/s. The instability strain during tensile testing has been predicted by taking into account strain hardening, strain-rate hardening, and deformationinduced heating. The results show that significant deformation heating can occur during tensile testing in air at “normal” strain rates near 10^-2/s, and that the uniform elongation can be affected markedly. Predictions for other alloys based on tabulated data are also presented.     

Carbothermic Reduction of Alumina: A Thermodynamic Analysis

Abstract

using new thermodynamic data for Al₄C₃, stability relationships in the Al-C-O system have been determined. A Pourbaix-Ellingham diagram has been constructed and is used to evaluate the equilibrium carbothermic-reduction process. The analysis indicates that liquid Al can never be obtained below 2100° K and that appreciable amounts of Al₂O(g) are present in the vapor. Analysis is also made of an alternate reduction path which Al vapour is produced by decomposition Al carbide. The Al₄O₄ and Al₂OC oxycarbide phases are considered to be metastable, but their possible influence on the equilibrium reduction process is briefly discussed.     

CHEMISTRY AND OPTIMAL CONDITIONS FOR COPPER MINERALS FLOTATION: THEORY AND PRACTICE

Reliable information on the surface state of sulphide copper minerals and regularities of sulphidization and flotation of oxidized copper minerals, the composition of sorption layer on the mineral surface forming during its interaction with xanthate or dixanthogen, and the influence of collector forms sorption on the copper minerals floatability and on the optimal conditions for these minerals flotation and depression has been obtained at present. The determined physicochemical models in the form of quantitative equations have been derived for the optimal conditions of flotation and depression of copper minerals under changing pH value and of sodium sulphide, lime, cyanide, zinc–cyanide complexes additions. The equations derived were proven in the laboratory and industrial scale and can be used both in automatic control systems at plants and for improvement of technological processes of selective flotation of copper containing ores.