Method of setting Nozzle intervals at the finishing scale breaker

The scale is removed from the strip by high pressure hydraulic descaling at the FSB(Finishing Scale Breaker). Recently, the spray height of nozzle has a trend to be shorter for the purpose of increasing the impact pressure by the high pressure water jet. Here, the nozzle intervals should be decided after considering the impact pressure and the temperature distribution on the strip. In other words, the minimum of impact pressure at the overlap of spray influences the surface grade of the strip due to scale and the overlap distance of the spray affects the temperature variation in the direction of the width of strip. In the present study, the impact pressure of the high pressure water jet is measured by the hydraulic descaling system and calculated with regard to the lead angle of 15° and the offset angle of 15°, and then the temperature distribution and the temperature variation are calculated at the overlap distances of 0 mm, 10 mm, 20 mm, and 30 mm, respectively. The method of setting nozzle intervals is shown by utilizing these results.     

Prediction of precipitation kinetics during homogenisation and microstructure evolution during and after hot rolling of AA5083

Because previous history of the material such as heat treatment influences the microstructure evolution during hot working, modelling of the microstructure evolution along the process chain is necessary in order to predict the resulting microstructure and hence the mechanical properties. The precipitation kinetics during homogenisation was investigated using the thermodynamic calculation software MatCalc. A physically based internal state variable model was implemented into the commercial Finite Element (FE) analysis package FORGE 2008 for hot rolling simulations of AA5083. The model allowed to predict both the stored deformation energies, i.e. dislocation density, the subgrain structure during hot rolling ,as well as the statically recrystallised volume fraction (SRX) after hot rolling. Two nucleation sites for recrystallised grains were considered to achieve a better understanding of recrystallisation kinetics.To validate the simulation results hot rolling experiments were performed by means of a laboratory mill. The grain structure evolution was analysed by the electron backscatter diffraction (EBSD). The thermo-physical data of the investigated aluminium alloy were determined experimentally.The study shows the applicability of the model to describe the microstructure evolution from casting to the hot rolled product.     

A thermal analysis of strip-rolling in mixed-film lubrication with O/W emulsions

Increase of both roll and strip surface temperatures can significantly affect a rolling process, roll conditions and strip mechanical properties. A comprehensive thermal analysis in cold rolling, especially in a mixed film regime, is needed to understand how thermal fields develop in roll and strip during rolling. It requires a simultaneous solution of the mixed film model for friction in the roll bite and the thermal model for roll and strip thermal fields. This paper presents a numerical procedure to analyse strip rolling process using lubrication with oil-in-water (O/W) emulsions. The thermal model includes the effect of heat generation due to the strip deformation and frictional shear stress at the asperity contacts. The numerical analysis employs a coupled thermal model and a mixed film lubrication model for calculating the friction and the asperity deformation in the bite. The thermal model considers the initial temperatures of the roll and strip, temperature rise due to the strip plastic deformation and friction. While the O/W mixed-film lubrication model takes into account the effect of surface roughness and oil concentration (%vol) of the emulsion. The thermal effect is analysed in terms of strip surface temperature and roll temperature, which are influenced by rolling parameters such as reduction, rolling speed, oil concentration in the emulsion. The results of the parametric study indicate that the effect of oil concentration on the thermal field is relatively small compared to that of reduction ratio and rolling speed. The reduction ratio increases the maximum interface temperature in the roll bite. In the mixed film regime, rolling speed also increases the maximum interface temperature and alters the temperature field of the strip. The numerical procedure was validated against known experimental data and can readily be extended to hot rolling or used to analyse roll strip temperature subjected to different cooling system.     

Numerical study of droplet dynamics impinging onto steel plate covered with scale layer

The steel hot rolling process is inseparably connected to an oxide layer called “scale” at high temperatures. Hydraulic descaling of rolled material is a part of all rolling trains. Surface quality after descaling is fundamental for the final surface quality of a rolled product. The process itself is not theoretically well described; various different approaches have been used to clarify the descaling problem. This paper describes the dynamics of high-speed impact between the compressible water droplet and the steel scale layer. The phenomenon is known as water hammer effect. The purpose of this study is to numerically verify the fact that impact stress can be a significant factor during the descaling process. Considering a high droplet impact speed (100–300 ms⁻¹), inferential extremely short time interval (0.1–5 μs) peaks in impact pressure reaching 300 MPa can be found. Droplet dynamics was simulated with the help of LS-Dyna solver, whereas the stress analysis was performed in ANSYS interface. The extreme pressure peaks of very short duration in an impact area are a new phenomenon in the descaling theory.     

关键结构参数对高压除鳞喷嘴性能影响的研究

高压除鳞喷嘴广泛地应用在热轧除鳞工艺中,喷嘴结构参数的变化会对射流性能产生影响。通过数值模拟和实验测试相结合,研究了锥孔深度变化对外部射流的影响。研究表明:锥孔深度增加,射流水喷射角增加、射流速度沿轴向方向衰减变慢,射流距离增加。在相同射流距离下,锥孔深度的增加可以使打击力的大小增大、有效的射流宽度增大。     

Investigation of closure of internal cracks during rolling by FE model considering crack surface roughness

Internal cracks often appear in cast slabs, and their evolution during hot deformation directly affects the product quality. In this paper, the authors investigate the closure behavior of internal cracks during plate rolling using a finite element (FE) model that takes into account the roughness of the crack surface. Influences of the roughness and reduction ratio on the closure of cracks are analyzed. The simulated results show that the models with consideration of the initial crack roughness can be used to investigate the formation of residual voids around the crack after rolling. The simulation results are validated by experimental observations. Finally, we propose an explanation of the crack closure mechanism during rolling.     

大棒材轧制过程温度场的数值模拟分析

应用有限差分法建立大棒材热轧过程的温度模型.对轧制、高压水除鳞和空冷等过程进行模拟计算,得到轧件头尾的表面与内部温度分布规律.用此程序模拟计算某钢厂大棒材生产过程中的温度场,其计算值与实测值吻合较好.在此基础上分析了大棒材热轧过程中温度的变化规律.     

热带钢连轧多场耦合演变过程有限元分析

根据物理冶金组织演变规律和经验公式，开发了金属热变形过程耦合组织演变的计算模块。结合某厂2050热带钢连轧工艺过程，利用非线性刚塑性有限元法，建立热连轧过程热、力、组织的多参量耦合仿真模型。运用该模型对2050现场实际轧制过程进行模拟计算，分析了轧制过程轧件变形场、温度场及显微组织的演变规律。模拟得到的轧制力能参数、温度、组织分布与实测数据基本一致。     

金属粉末激光烧结温度场的三维有限元模拟

综合考虑热传导、热辐射和热对流及变热物性参数,基于ANSYS平台建立了连续移动的三维瞬态金属粉末直接激光烧结温度场的有限元模型;利用APDL参数化设计语言实现热源移动,利用焓处理相变潜热的影响,对水雾化铁粉的烧结成型温度场进行了模拟,系统分析了激光熔池的加热和冷却规律及温度场随时间的变化规律。模拟结果表明:随着时间的增加,由于热积累效应使得激光熔池的温度越来越高;彗星状温度云图的最高温度并不在激光光斑中心而是稍微滞后;模拟结果显示烧结过程中将产生液相,这与先前的实验结果吻合较好。     

Analysis of the roll hunting force due to hardness in a hot rolling process

A hot rolling operation is performed to alter the thickness of a metal by passing the material through a pair of rollers, forming a gap that is somewhat narrower than the thickness of the material. Therefore, the quality of the product is a function of the pressure applied by the rollers. However, in this process, a roll hunting force occurs in which the rolling force is irregularly changed during the rotation of the rollers due to various complex mechanisms, which include roll surface hardness, difference in rotational speed between rolls, heat treatment conditions, and roll wear. In this study, roll wear tests were conducted to analyze the roll hunting force caused by variation in the hardness of the work roll. The friction coefficient of the work roll was then examined based on hardness. Then, a two-dimensional finite element model was constructed to investigate the roll hunting force as a function of the change in friction coefficient of the work roll. This finite element model was verified in relation to the theoretical rolling expression. Finite element model analysis was performed for three friction coefficients, and the effect of the roll hunting force was determined based on the reduction ratio and temperature. In addition, the wear depth of the work roll by the hardness was predicted. The influence of the abrasion of the work roll on the hunting force was analyzed.

     

热轧板带高压水除鳞效果的分析

通过对高压水除鳞效果的分析，提出了保证除鳞效果的基本条件、数学模型、影响因素，对高压水除鳞系统的设计、改进、现场维护使用具有一定的参考价值。     

Cooling of a heated surface with an impinging water spray

Several important parameters, such as liquid mass flux, droplet size distribution, droplet velocity, and heating target conditions (roughness and surface temperature) are involved in the industrial spray cooling heat transfer process. In this study, we investigated the effect of liquid mass flux, heating target roughness, and the droplet size on the droplet wall direct contact heat transfer in spray cooling phenomena. Three different conditions of surface roughness were investigated. The measurement of test surface temperature was performed using a non-intrusive method, i. e., using an infrared thermometer. The droplet size distribution of water spray was measured with Malvern 2600. The results indicated that the most influential parameters were the liquid mass flux and the surface roughness. The droplet size and the velocity played a less important role in the direct contact heat transfer because the interactions between droplets were very strong in a dense spray. The smooth surface showed the highest heat transfer among the surfaces tested. At high air pressure ([7] kPa), however, the degree of roughness did not affect much the heat transfer rate.     

液滴低温气体雾化射流冷却换热理论分析与实验研究

论述低温气体雾化射流冷却原理及特点,以池内膜态沸腾为基础,将喷雾颗粒的冲击作为一种扰动,建立雾滴射流进入切削区冷却高温壁面的模型,讨论雾滴冷却高温壁面的换热系数,着重探讨工艺参数水流密度对喷雾冷却换热系数的影响.进行了不同水剂量的低温气体雾化射流冷却钛合金高温壁面的瞬态实验,获得了钛合金试件表面温度分别为100℃、150℃、200℃和250℃时,低温气体雾化射流冷却达到最佳冷却效果时水剂量,分析了水剂量对冷却效果的理论依据,结果证实该模型对实际应用具有一定的指导作用.     

铝热精轧轧制区温度场三维有限元模拟

根据某铝热连轧厂生产线实际结构参数和工艺参数,应用弹塑性有限元法,考虑轧件金属塑性变形热、摩擦热、界面接触热导等对轧件和轧辊传热的影响,运用大型通用有限元分析软件MSC.Marc建立了铝热连轧精轧机组F2机架的热力耦合三维有限元仿真模型.通过分析轧件温度场的分布规律,为更好地控制轧件的温度分布、提高产品的质量提供依据.     

Modeling the airside dynamic behavior of a heat exchanger under frosting conditions

A general distributed model with a non-steady-state heat exchanger model coupled with a frost model was developed to study the dynamic behavior of an airside heat exchanger in an air-to-water heat pump heater/chiller unit. The effects of water vapor diffusion and uneven fin temperature distribution were considered. The model was found to agree well with reported experimental results. Compared with the routine model, the present model has higher precision of frost layer thickness especially on the fin surface. Results include the propagation of frost formation along the tube and its effect on the dynamic characteristics of refrigerant, air, and tube sides. According to the results, the temperature difference between air and tube surface temperature was proposed to be the main driving force of frosting. Tube surface temperature is the most important factor affecting frosting when there is little variation in air humidity. Frost at the fin base was found to be thicker than that at the fin tip due to the fact that the frost layer grows faster with lower tube surface temperature.     

高速钢热轧辊表面温度场的测定与应用

根据热轧生产过程中轧辊的实际边界条件,借助于有限元软件ANSYS建立了高速钢和高铬铸铁热轧辊温度场的数值计算模型,对其工作时的温度场进行了对比分析。结果表明:模型的计算结果与现场下机后辊面温度的实测数据比较吻合;在相同的轧制参数和冷却参数条件下,下机后高速钢轧辊表面温度高于高铬铸铁轧辊的;由于高速钢轧辊的导热率及摩擦因数较高铬铸铁的大,使其旋转一周后达到的最高温度较高铬铸铁轧辊的高65℃左右,达到582.5℃;结合现场的情况,优化了高速钢轧辊的冷却参数,可使其下机后的温度保持在65℃以下。     

薄带铸轧工艺参数的分析和动态模拟

在建立洁净器区薄带坯凝固传热数学模型的基础上，通过计算机分析并动态模拟了铸轧过程中几个重要的工艺参数之间的关系及相互影响，分别模拟和分析了实现稳定铸轧所需的工艺参数范围，包括铸轧速度、浇注温度、熔池深度、铸轧压力、铸轧辊温度、冷却水流量及冷却水温度等重要参数，从理论上解决了铸轧奥氏体不锈钢薄带坯表面质量的关键技术问题，该方法对实际生产具有极其重要的应用价值。     

Experimental study on nanofludic heat pipe hot chuck plate in semiconductor wafer baking process

The temperature uniformity on a heat pipe hot chuck (HPHC) during semiconductor wafer processing has been an important factor to critical dimension (300 mm) uniformity as the feature size of semiconductors decreases and productivity density increases due to the new process of nano size special manufacturing technology. To design the present heat pipe hot chuck system, which has enhanced temperature uniformity for the wafer process, the heat distribution of the system was analyzed experimentally with various working fluids such as water, TiO₂, ATO, ITO, Al₂O₃, and Ag-nanofluids and 8 cell structures. Unlike the conventional solid state chuck, the present heat pipe hot chuck system consists of a heat pipe containing specially charged working fluid. Various working fluids have been tested to find best temperature uniformity feature on the top surface of hot chuck. TiO₂-nanofluid was used and tested as the working fluid of the heat pipe hot chuck system in this paper. The temperature uniformity of upper surface was sustained in the range of ±1°C. A nano-porous layer was observed on the surface with the good result of surface temperature uniformity compared with distilled water.     

黄磷喷淋塔数值模拟研究

以计算流体力学(CFD)为基础,多相流理论为依据,在三维坐标系下采用κ-ε标准湍流模型、传热模型求解温度及速度流场,并采用Lagrange模型追踪粒子轨迹,对喷淋塔进行模拟研究。研究结果表明,不同液气比、液滴初始温度及直径对喷淋塔的换热效率、冷凝性能有较大的影响,气液换热效率随着液气比、液体初始温度的增加逐渐增大;而液滴初始直径对气液换热效率的影响较为复杂,模拟结果可为黄磷喷淋塔的性能优化和改造提供参考和借鉴。     

板带粗轧过程热、力、组织耦合三维有限元模拟

根据某厂2050热带钢粗轧机组轧制工艺，借助物理冶金组织演变模型，利用非线性有限元法开发了热连轧过程热、力、组织耦合三维刚塑性有限元模型。运用该模型对低碳钢SS400的现场实际轧制情况进行仿真计算，得到轧件三维变形场、温度场及显微组织的分布规律。模拟得到的轧制力能参数、粗轧出口温度与现场实测结果吻合很好。