Modernization of the Equipment of the Continuous Strip Caster of a Hot-Rolling Mill

To reduce metal consumption and improve the quality of the finished rolled product, ISPAT-Karmet has begun to modernize the equipment of its 1700 hot-strip mill. The modernization will include the following: automation of control of the thermal and temperature regimes for heating slabs in the continuous furnaces used with the mill; installation of newly designed manifolds in the hydraulic scale-removal system, with Lechler nozzles, to increase pressure in the hydraulic system from 120 to 160 atm; installation of heat-absorbing shields, designed by the Novokramatorsk Machine Plant (NKMZ), on the intermediate roller table between the roughing and finishing trains of the mill; use of rolls made of high-chromium cast iron in the finishing stands; modernization of the automatic process control system, with replacement of the existing equipment by Siemens programmable controllers and the installation of new Klek width gages after the final finishing stand; installation of a new NKMZ-made combination system for laminar cooling of the strip on the runout table of the mill; installation of a closed hydraulic system to control the configuration of the strip (the system was designed by the company Mess) on finishing stands 6–12; installation of a system to automatically regulate the speed regime during coiling. The results obtained from the initial modernization of the equipment on the 1700 hot-strip mill have already eliminated rolled-in scale on the strip surface, reduced metal consumption by 8.7 kg/ton through a reduction in the width tolerance for the strip, increased the service life of the work rolls in the finishing stands from 175,000 to 350,000 tons, expanded the product mix, reduced electric power consumption by 7.0 kWh, and reduced the consumption of comparison fuel by 0.8 kg/ton.     

Optimisation of work roll shifting and bending to roll thinner gauge HR coils using genetic algorithm

Abstract

Rolling of thin gauge hot rolled (HR) coils demands stringent flatness tolerance. Thin HR coils (≤3 mm) are rolled towards the end of any rolling campaign. The profile and flatness of the strip depend on the profile of the loaded roll gap in the mill stands. There are five key factors that influence the loaded roll gap: initial roll surface profile, roll thermal expansion, wear of roll, deflection of roll stack and shifting of work rolls. This paper deals with all these factors individually for the formulation of an objective function in order to minimise the flatness error. The shifting and bending of rolls are the controllable parameters that require optimising. This has been accomplished using a genetic algorithm (GA) optimisation technique.     

New parameters for the description of hot rolled strip transverse temperature distribution: preliminary applications

Abstract

Nowadays, it is possible to find experimental data about the longitudinal temperature distribution for a hot rolling strip production. However, it is much more difficult to obtain experimental results on the transverse temperature distribution on the strip surface. After a systematic analysis of the methods and results in the literature, the experimental data collected using a specific experimental apparatus to measure the transverse strip temperature distribution out of the last finishing stand of a 1800 mm wide thin hot strip rolling mill are presented. In order to logically classify all the results by identifying the main factors that influence the strip temperature profile, it is proposed to describe more clearly four new parameters of the strip thermal profiles which would allow the investigation of the reason for uneven transverse temperature distributions. The relationship between strip temperature distribution, strip geometry and temperature itself is also studied to provide a basis to build a mathematical model for the current problem.     

冷轧钢卷凸包缺陷治理

 针对冷轧带钢卷取过程中出现的凸包缺陷造成产品降级甚至报废问题,在开展重卷试验及断面形状实测基础上,分析了形成冷轧钢卷凸包缺陷的原因。通过合理编排轧制计划、控制精轧机组工作辊热凸度、优化精轧机组工作辊辊型曲线以及解决工作辊轧制润滑和冷却不均等技术措施,有效解决了热轧带钢边部增厚带来的冷轧钢卷凸包缺陷问题,凸包缺陷发生率从6.65％降低到0.33％,取得了显著效果。     

Roll Wear Evaluation of HSS,HiCr and IC Work Rolls in Hot Strip Mill

While it is acknowledged that roll wear is one of the most challenges to hot strip mills (HSM), very few studies which detail an exact prediction model have been published. The aim of this work is to evaluate and compare two prediction models with measured roll wear. The first prediction model, model 1, developed for a plate mill, was modified to use in strip rolling process. The second prediction model, model 2, is a simplified on‐line model. Data of two hot strip mills were used to investigate the influence of different rolling schedules. The rolls and strip properties were described and the rolling conditions were detailed. The influence of hot rolling factors, such as strip strength, roll grades, rolling temperature, rolling force, reduction and contact length, were also studied. When rolling with different work roll materials and strip grades, the modified prediction model has better prediction accuracy than the simplified model. The accuracy of both models becomes better at higher roll wear > 150 μm. HSS work rolls were confirmed to exhibit improvement of roll wear in comparison with HiCr rolls, the wear resistance was 3 to 4 times better. The influence of strip grade on roll wear was shown to be significant, with higher accuracy of the regression statistics for rolling with similar strip grades and lower regressed accuracy for rolling with mixed strip grades. The roll wear was evaluated at the centre of the barrel.     

Modeling the Thermal Regime of a Cold-Rolling Mill with Allowance for Differences in the Cooling Conditions for the Top and Bottom Rolls

A mathematical model is constructed to describe the thermal regime in cold rolling. The model links the perturbing and control variables together in a single algorithm based on a system of heat-balance equations solved in sucesssion for all of the stands of a continuous mill. Design parameters of the mill, parameters of the rolling regime, and thermophysical constants are used as the initial data. Heat-transfer coefficients that characterize conductive and convective heat exchange during the rolling operation are among those constants. Some numerical values for these quantities are given in the article, while other values are refined for each specific mill as part of the model's adaptation to the given situation. The reliability of the model was checked on a five-stand 1700 mill by measuring the temperature of strip at the inlet of the first stand and the outlet of the fifth and final stand. The temperatures of the work rolls in all of the stands were also measured immediately after roll changes. Testing of the proposed model showed that it can be used to improve the thermal regime and cooling systems of continuous cold-rolling mills. __________ Translated from Metallurg, No. 6, pp. 66–69, June, 2005.     

热轧带钢轧机精轧辊型设计及应用

叙述了某热轧带钢生产中，在遵循板凸度一定的条件下所进行的轧辊辊型设计，通过对精轧工作辊配置辊型来改善带钢板形，从而提高产品实物质量。     

VCR back-up roll and negative work roll contour design for solving roll spalling and transfer bar profile problems in hot strip mill

Abstract

During the first year of production in the 2250 mm hot strip mill of Qian'an Iron and Steel Company of Shougang Steel Corporation, roll spalling and broken rolls were frequent occurrences, especially on the second stand of roughing mill (R2), and resulted in enormous economic losses. In addition, improvements to strip shape were required. One of the factors resulting in strip shape defects after finish rolling is that the transfer bar usually had an unsound profile such as a large wedge, camber or negative crown after roughing rolling. To solve these problems, a variable contact back-up roll contour curve with six order of polynomials and negative crown contour was designed and applied to the back-up roll and work roll of roughing mill stands R1 and R2 instead of a conventional flat roll contour. After the application, roll spalling, crown and wedge quality of the transfer bar and strip quality all improved.     

Finishing mill thread speed set-up and control by interval type 1 non-singleton type 2 fuzzy logic systems

Abstract

The set-up of the finishing mill (FM) thread speed to achieve the desired strip temperature as measured by the finish mill delivery temperature sensor is made by an intelligent controller based on interval type 2 fuzzy logic system. The controller calculates the FM thread speed required to achieve the strip FM exit target temperature, and the interstand strip surface temperature profiles. The interval type 2 fuzzy set-up controller uses as inputs the predicted transfer bar FM entry temperature, the transfer bar thickness, the target strip FM exit temperature, the target strip FM exit gauge, last stand draft reduction, last stand work roll diameter, last stand rolling force, %C of strip, and target width. Taking into account that the measurements are modelled as type 1 non-singleton fuzzy numbers, the authors present the so called interval type 1 non-singleton type 2 fuzzy logic system controllers. As reported in the literature, interval type 2 fuzzy logic systems have greater approximation capacity than that of its type 1 counterpart and it has the advantage to develop more robust and reliable solutions than the latter. The experiments of these applications were carried out for three different types of coils, from a real hot strip mill. The results proved the feasibility of the developed system for FM thread speed set-up and control, and for interstand strip temperature profile prediction. Comparisons with the online mathematical based models show that the proposed interval type 2 fuzzy logic system equalises the performance in FM strip thread speed, and temperature set-up and control under the tested conditions characterised by high uncertainty levels.     

Simulation of the thermal conditions of rolls in a wide-strip hot-rolling mill to determine their effective cooling conditions

An advanced procedure is developed for the thermal calculation of the rolls in a wide-strip hot-rolling mill (WSHRM). It combines the following two adaptive models: the thermal balance in the active surface layer in a roll per revolution and the thermal balance in the main zones of work and backup rolls with axisymmetric temperature fields with allowance for the heat exchange between a strip, rolls, the coolant, and the environment. In contrast to the well-known models, this advanced procedure calculates the bulk mean temperature and the thermal profile in a roll more accurately, since the temperature drop across the surface layer in this procedure is calculated allowing for the intensities of the contact and convective heat exchange between rolls. Data on the coefficient of heat transfer from rolls to the coolant supplied at an excess pressure of 1.0–1.5 MPa are presented for the first time. This procedure is used in a 2000 WSHRM and improves the transverse profile of hot-rolled strips due to a stabilized thermal profile in rolls.     

宽带钢热连轧机选型配置与板形控制

通过测试并分析机组上游与下游机架对控制性能的不同要求、服役周期内工作辊和支持辊辊形变化及其对板形控制性能的影响,结合1700mm热连轧机进行的现场试验及工程应用实践,提出热轧上游机架应采用凸度控制能力较强的轧机机型,下游机架宜采用长行程窜辊型轧机机型,全机组均可采用强力弯辊和变接触轧制技术提高机组板形控制能力。     

宝钢150t超高功率直流电弧炉用耐火材料

介绍、讨论了宝钢１５０ｔ超高功率直流电弧炉耐火材料的设计特点,以及投产一年多来的使用情况,并根据操作经验认为：（１）造成泡沫渣埋弧操作非常关键;（２）镁铝尖不石底电极套筒砖性能优越;（３）冷态下底电极套砖接长修补是可行的;（４）采用高钙、低硅,适量的铁的烧结镁砂制成的炕底捣打料性能良好;（５）采用热态修补出钢口技术能大大延长出钢口砖寿命;（６）小炉顶的材质建议采用镁碳砖环状砌筑。     

热连轧工作辊热平衡的优化研究与应用

轧辊热膨胀对承载辊缝形状和带钢板形具有显著的影响,而准确预报轧制过程中轧辊热膨胀是板形控制中的难点之一。针对某热连轧生产线单辊期内热膨胀量与轧辊温度不收敛的问题,利用自主开发的与产线生产完全一致的板形模型分析测试系统对热凸度二级模型进行了仿真分析与研究,提出了一种有效提高工作辊热平衡收敛性的优化方法,并进行了生产应用。该优化方法的应用解决了该热轧产线单辊期内热平衡不收敛的问题,消除了轧辊温度计算值和实测值之间的偏差,不仅提高了模型的预报精度,也大幅提高了该产线轧制带钢的凸度控制精度。     

Application of the theory of rolling to rolling in the case of mill vibrations

Knowledge of the reactions of the roll gap according to variable gap geometry, especially of the roll force as a function of vertical displacement of the work rolls, is required to calculate the oscillatory behaviour of the roll stand. The basic equations describing the pressure distribution in the roll gap with variable geometry are formulated using the methods of continuum mechanics. The flattening of the work rolls is taken into account by using Hitchcock's formula. Exemplary calculations show that during vibration the tension between the stands can vanish or the neutral point can surpass the roll gap exit. Both effects may result in tearing the strip at the entry of the affected mill stand.     

高速钢轧辊在马钢CSP前机架应用研究

本文针对马钢CSP轧机的工作辊不均匀磨损严重影响出口板形质量的问题,对CSP轧机F3~F4不均匀磨损严重进行了分析,指出了使用高速钢轧辊的必要性。对高速钢轧辊的使用情况进行了大量的试验研究,并通过现场实际数据分析了高速钢轧辊情况下轧制力、轧辊温度、氧化膜情况,在大量现场试验的基础上制定了马钢CSP高速钢轧辊的使用工艺,并实现了工艺条件的长期稳定使用,通过现场实绩表明,使用高速港轧辊大大改善了机组的不均匀磨损,提高了机组的板形质量。     

热带钢连轧机工作辊冷却水优化设计

 轧辊热凸度是影响热带钢连轧机负载辊缝的重要因素,高效率的工作辊冷却水系统是生产高质量热轧板带的重要保证。为了设计工作辊的冷却水量及分布,建立了工作辊横断面温度场计算模型、轴对称平面温度场计算模型和热凸度计算模型。在此基础上,采用优化设计方法对1450热带钢连轧机工作辊冷却水量及其沿轧辊周向和轴向的分布进行优化设计。     

马钢CSP热轧PFC板形模型的分析与应用

利用有限元分析软件ANSYS对轧机承载辊缝变形的仿真,分析轧机轧制力、弯辊力及工作辊窜辊对承载辊缝的凸度影响程度,结合现场机架间带钢的浪形,优化二级板形模型设定参数,实现轧机稳定轧制。实践证明,人工修正轧机负荷分配以及CVC轧辊位置,可更好地控制前机架比例凸度,满足后机架间平直度目标的要求,从而提高板凸度的命中率及轧机轧制的稳定性。     

热带钢连轧机精轧机组板凸度仿真与实验研究

根据热带钢连轧机的特点,将以变分法为基础的金属模型和用分段离散法建立的辊系弹性模型进行迭代求解,最终求出各道次轧件出口厚度横向分布。在攀钢１４５０ｍｍ六机架热带钢连轧机现场轧制过程中突然抬辊,获得含有完整的六个道次变形区的阶梯板,其实测数据与计算值吻合很好。     

Thermomechanical Behavior of Work Rolls During Warm Strip Rolling

A mathematical model was developed to assess thermomechanical behavior of work rolls during warm rolling processes. A combined finite element analysis-slab method was first developed to determine thermal and mechanical responses of the strip being rolled under steady-state conditions, and then, the calculated roll pressure and temperature field were utilized as the governing boundary conditions for the thermomechanical problem of the work roll. Finally, the thermomechanical stresses within the work rolls were predicted by a thermoelastic finite element approach. The results of the model indicate that, in warm strip rolling, thermal and mechanical stresses developed in the work rolls are comparable, and thus, both thermal and mechanical aspects of the problem should be considered in such a problem. Besides, the model was shown to be capable of determining the effects of various rolling parameters on the thermomechanical behavior of the work rolls during warm rolling process.