热轧工作辊热磨削辊型的数值模拟与实验研究

热轧工作辊下机后冷却不充分即进行磨削,存在的残余热变形使得上机辊型,很难达到工艺设定值。针对轧辊下机后得不到均匀冷却辊型及准确热凸度的特点,以下机时测量的热辊型与其它时刻测量的热辊型的差值作为热变形实测依据与仿真对比。采用有限差分法对工作辊下机后的温度场和热变形变化过程进行仿真,其仿真值和实测值吻合较好。进而应用该模型对工作辊热磨削辊型进行研究,为轧辊热磨削辊型的设定提供了理论依据。     

面向辊形磨削的热带钢连轧机工作辊热变形研究

热带钢连轧机工作辊下机后尚未完全冷却即进行磨削,残存的不均匀热变形导致磨削的工作辊辊形在空冷一段时间上机时很难达到工艺设定值.针对热辊形不易测量的特点,制定合理的物理测量方式,准确地测量了工作辊下机后的温度分布和热辊形.考虑复杂的工作辊换热边界条件,采用有限差分法对工作辊空冷时的温度场和热变形进行了数值模拟,计算结果与测试结果吻合良好.对工作辊下机后不同时刻的热变形进行仿真,通过将目标上机辊形和磨削时热辊形叠加来设定磨削辊形,为实现合理的辊形磨削提供了依据和计算方法.     

热连轧轧辊瞬态温度场研究

考虑水冷、空冷、轧辊与轧件接触热传导等动边界条件，采用有限差分法，建立了热连轧轧辊瞬态温度场变步长分析计算模型。该模型能实现轧辊温度场的动态分析和精确计算，预测轧制时以及终轧后空冷的轧辊瞬态温度场。试验和仿真结果表明，所建立的分析计算模型考虑因素全面、合理，计算精度较高，计算值与实测值吻合良好，真实地反映了轧辊的温度变化情况。     

基于多目标遗传算法的工作辊温度场计算与分析

等效换热系数是热连轧机工作辊温度场仿真模型的核心输入参数,多采用遗传算法优化得到,某1800 mm 热连轧机存在品种、规格交替轧制,等效换热系数的准确计算比较困难.选取多组典型工艺条件下的工作辊下机后表面温度作为优化目标,采用多目标遗传算法进行优化,并通过改变遗传算子有效避免了算法早熟及局部收敛等问题,获取了具有较强适应性的等效换热系数.仿真和实测数据的对比结果证明了优化模型的可靠性.利用仿真模型分析了主要工艺参数对工作辊热凸度的影响,并提出同宽交替时,工作辊热凸度随轧制进程呈指数变化,而在品种、规格交替编排轧制工艺下相邻带钢轧制时工作辊热凸度存在6-21.8μm 的波动,且随轧制进程趋于稳定.      

基于遗传算法的工作辊温度场参数优化模型

针对热连轧机工作辊热辊形计算中温度场模型的热交换等参数难以确定的问题 ,建立了基于遗传算法的参数优化模型 ,可以解决复杂条件下的热参数的求解问题。利用优化参数计算的轧辊温度场与实际测量结果一致。     

Analysis of Strip Temperature in Hot Rolling Process by Finite Element Method

 The program was developed by finite element method to calculate the temperature distribution in hot strip rolling. The heat transfer coefficient of air cooling, water cooling and thermal resistance between work roll and strip were analyzed. A new heat generate rate model was proposed according to the influence of source current density, work frequency, air gap and distance to edge on induction heating by finite element method (FEM). The heat generate rate was considered into the thermal analysis to predict the temperature distribution in the induction heating. The influence of induction heating on the strip temperature was investigated with different strip thicknesses. The temperature difference became more and more obvious with the increase of thickness. The strip could be heated quickly by the induction heating both in surface and center because of the thermal conductivity and skin effect. The heat loss of radiation has important influence on the surface temperature. The surface temperature could be heated quickly with high frequency when the strip is thicker.     

某热轧1580生产线工作辊热凸度分析研究

热轧精轧机换辊、轧制中断、轧制节奏明显变化等工艺条件下,容易出现较大偏差,导致轧制不稳定、板形有质量缺陷等问题。对首钢某热轧1580生产线工作辊冷却方式进行改造,由辊身均匀冷却方式改为中段集中冷却方式,以便降低工作辊中部温度、减小中部与端部的温差,从而获得较好的工作辊热凸度轮廓曲线,轧制出板形和表面质量良好的带钢产品。     

热轧带钢传热模拟及变形区换热系数的确定

采用数值模拟方法研究了带钢热轧区轧件传热和温度场分布规律.结合现场生产中测温数据,建立了轧制变形区内轧件与轧辊接触传热界面换热系数(HTC)统计模型.分析了辊缝变形区中轧件断面上温度演变和分布特点.研究结果表明,热轧带钢热轧区传热数值模拟计算结果与实际吻合良好;变形区内轧件与轧辊接触传热界面换热系数不仅与平均单位压力相关,而且与轧制速度相关;轧件在轧制变形区存在很大的温度梯度.     

宽带钢工作辊轧制中凸度的研究与控制

工作辊热凸度与轧制时间、轧制速度、轧制节奏、轧辊冷却水等有着密切的关系,充分了解轧辊热凸度在轧制过程中的变化,不仅可以提高宽带钢热连轧机组热辊形的模型控制及预报精度,而且可以通过及时调整轧制节奏和轧辊冷却水系统的工作情况来调整轧辊热凸度,对于板形控制具有重要意义。     

Temperature and thermal stresses in work rolls during the hot rolling of strip

In this paper the solution of the unsteady, three-dimensional heat transfer in work rolls was derived by using Bessel functions and the δ-function and expressed by an infinite series. In this manner other problems of heat transfer in solid cylinders and hollow cylinders can also be calculated. The temperature profile of the work roll due to the distribution of the temperature in the axial direction can cause unregular pressure distribution between work roll and backup roll and can influence the quality of strip. Therefore, the thermal crowns must be considered at various moments during rolling. The thermal crown can be determined by using the FE-Method or others. The reason for the fire-cracking in the roll surface can be determined as the thermal shock load in the contact zone, in which the sharp compressive stresses lead to local plastic deformation. The local plastic deformations are followed by residual deformations. Therefore, residual tensile stresses occur in the cooling zone. On each revolution, the surface undergoes plastic strain in compression and in tension. The result is thermal fatigue. The fine network of cracks in the roll surface can result in a sharp stress concentration which is dangerous for the rolls loaded with a bending moment. The maximum tensile stresses due to the temperature distribution occur in the roll core, which usually do not lead to damages of the rolls.     

Two-Dimensional Transient Temperature Field of Finish Rolling Section in Hot Tandem Rolling

Comprehensively considering the factors such as descaling cooling, air cooling, watercooling, frictional heat and deformation heat in gap of every stand, heat conduction betweenwork roll and strip etc, a model of two-dimensional transient temperature field of finish rollingsection in hot tandem rolling was built with finite difference method to calculate the temperaturefields of strip and work roll. So two-dimensional accurate analysis and calculation of strip tem-perature were realized, and the theoretical basis for predicting and controlling strip temperaturewas provided. The simulated results show that the model is practical and reliable.     

Numerical Simulation of Temperature Field and Thermal Stress Field of Work Roll During Hot Strip Rolling

  Based on the thermal conduction equations, the three dimensional (3D) temperature field of a work roll was investigated using finite element method (FEM). The variations in the surface temperature of the work roll during hot strip rolling were described, and the thermal stress field of the work roll was also analyzed. The results showed that the highest roll surface temperature is 593 ℃, and the difference between the minimum and maximum values of thermal stress of the work roll surface is 1457 MPa. Furthermore, the results of this analysis indicate that temperature and thermal stress are useful parameters for the investigation of roll thermal fatigue and also for improving the quality of strip during rolling.     

Modelling recalescence after stock reduction during hot strip rolling

Abstract

The relationships between stock recalescence time/distance and process variables, such as exit thickness, reduction, rolling speed, work roll diameter and slab–roll heat transfer coefficient during hot strip rolling, have been established. The behaviour of the temperature gradient was analysed and used to estimate the slab and transfer bar mean temperatures from measured surface temperature in three hot strip mills located in northeast México. It was found that the recalescence critical variables, in order of importance in minimising temperature measurement variation, are slab–roll heat transfer coefficient, reduction, exit thickness and roll speed.     

Roll cooling and its relationship to roll life

Combined experimental and numerical research has been conducted to investigate the roll cooling system used in steel rolling mills and its relationship to roll life. Roll cooling has been identified as a critical factor in the problems of excessive roll wear or spalling, which cause shortened roll life. A special laboratory apparatus resembling the cooling systems used in the steel mills has been developed to evaluate the corresponding heat transfer coefficients. These coefficients have then been utilized for numerical simulation of the rolling processes. In simulation, the thermal behavior of both the roll and the strip have been considered with emphasis on roll temperature and the induced cyclic thermal stresses. An understanding of the cyclic stress can be utilized to evaluate roll wear, and leads to reduction of the roll spalling, or to extension of the roll life by minimizing the cyclic stress or the resultant fatigue stress. As indicated by the present study, in order to minimize the cyclic or fatigue stresses, the roll should be subjected to uniform cooling, as the sharper the heat transfer coefficient distribution, the higher the thermal stress induced.     

Evaluation of deterioration mechanisms and roll life of different roll materials

Evaluation of wear loss of rolls in operation is very difficult since the rolling conditions are hard to keep under control. To solve this problem a high temperature test rig was designed. A conventional roll material was compared to a hot work tool steel. The main wear mechanisms were different. The conventional roll grade was mainly subjected to thermal fatigue as could be expected. The hot work tool steel was mainly subjected to abrasive wear, and no evidence of thermal fatigue was found. The rate of material loss was 6 times higher in the hot work tool steel, but when the deterioration caused by thermal fatigue of the cast iron is taken into consideration, the deterioration rate was of the same order in both materials. The friction between the hot steel and the roll materials were of the same order. The frictional value should be a measure of the wear rate. Since the wear mechanisms are not equal, the coefficient of friction found in the test rig is only qualitatively related to roll wear.     

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。     

热轧酸洗钢表面麻坑缺陷控制研究

为提高热轧酸洗钢的表面质量,控制下游厂商反映的表面麻坑缺陷,结合现场生产跟踪及缺陷样品的微观形貌分析,得出带钢酸洗后的表面麻坑缺陷是热轧时三次氧化铁皮压入基体导致的。对于厚度偏薄宽度偏宽的极限规格而言,热轧过程中存在轧制温度过高、轧制计划编排不合理以及轧辊表面氧化膜剥落等问题。因此,本文根据轧制规格设计了轧制温度的目标值及控制范围,编排了极限规格在每个轧制单位的位置以及集中轧制的最多块数,提出了通过限制轧辊使用次数、优化冷却水和轧制油的使用、合理分配轧制负荷来保护轧辊氧化膜的措施,为满足下游厂商的需求及酸洗钢市场拓展创造了有利条件。     

Analysis of the change of roll thermal crown in 1750 mm hot strip mill

Studied the distributing of roll temperature and the change rule of thermal crown in 1 750 hot strip mill,the result of the test showed that the change of roll thermal crown was affected by the condition of roll cooling and equipmentthe roll thermal crown was obviously improved after altering the pipe and water nib of cooling equipment.From the rule of roll thermal crown changing with the number of strip rolling know that the thermal crown of work roll of Standi is the largest,and Stand 6 is the smallest...     

热连轧机轧辊热辊型及冷却制度研究

针对热带钢连轧机由于带钢规格变化(主要指窄料和宽料)导致轧辊热辊型的大幅度波动,对轧辊温度场、热凸度和冷却效应进行了分析。采用有限差分法对轧辊温度场和热凸度进行了数值模拟,计算值和实测值吻合较好。进而应用该模型根据来料规格、压下规程等因素来确定工作辊冷却水轴向分布,为热带钢连轧机工作辊冷却系统的改造提供了可靠依据。     

Development of Fine‐Grained High‐Carbon Steel in High Reduction Low Temperature Rolling

After blanking and bending to form parts with the desired shape, high‐carbon steels are quenched and tempered to produce various machine parts. Thus, the spheroidization, formability and hardenability are very important properties for high‐carbon steels. Thermo‐Mechanical control Process of rolling has been widely used in the steel industry. However, it is difficult to apply this process to high‐carbon steels because of the heavy rolling load. Thus, fine‐grained high‐carbon hot strips were developed through high‐reduction and low‐temperature rolling by using single roll rolling mills with different diameters and laminar flow cooling devices in the finishing train, the grain size of these steels was about 3 microns. Also developed annealed strips with fine homogeneously dispersed spheroidal cementite had many excellent characteristics. For example, burring formability investigated by the hole‐expanding and surface hardness evaluated by laser hardening of the developed high‐carbon annealed steels, were excellent.