A kinematic analytical approach to predict roll force,rolling torque and forward slip in thin hot strip continuous rolling

Abstract

A kinematic analytical approach has been developed to predict the roll force, rolling torque and forward slip in thin hot strip continuous rolling under various rolling conditions. The approach is based on formulating a velocity field in the roll bite zone that expresses the effect of interfacial friction on the distribution of axial velocity and longitudinal stresses across the strip thickness. The results obtained from the proposed approach are in fair agreement with finite element simulation results, whereas available analytical methods, which are usually valid for billets and thick plates, have given considerable error in the results. The proposed approach is applied to study the effect of thickness reduction ratio, coefficient of friction, work roll diameter and front and back tensions on the roll force, rolling torque and forward slip in thin hot strip rolling. The main merit of the proposed analytical approach, as compared to finite element simulation, lies in the drastic reduction in the computational time required in finite element simulation, which favours its use in online control of rolling thin strips.     

板材轧制头部翘曲的非线性有限元研究

根据宝山钢铁集团公司2050 板材热轧生产工艺,采用弹塑性有限元法建立了热力耦合非对称轧制仿真模型.利用该模型分析了非对称轧制过程的非对称机理,研究了不同轧制工艺下的辊速比、上下表面温差对板材头部翘曲的影响规律,同时实现了通过调整辊速比控制厚向非对称温度分布造成的板材头部翘曲.根据不同工艺参数下控制部翘曲的计算结果,利用Matlab程序回归建立了控制上下表面温差引起板材头部翘曲的辊速比设定数学模型.     

带材异步冷轧时大变形弹塑性有限元模拟和实验

采用纠正的拉格朗日列式和基于弹塑性乘法分解的超弹性－塑性本构关系建立了大变形弹塑性有限元程序，并对铝带在不同条件下的异步冷轧过程进行数值模拟，同时对计算结果进行实验验证。结果表明，在异步轧制时，轧制压力对工作辊辊径的变化表现出非敏感性，而且变形区内静水压力绝对值比同步轧制时要小得多。     

六辊轧机非对称板形调控特性研究

针对冷轧板带产品的非对称板形缺陷问题,建立六辊轧机辊系-带钢耦合有限元模型。分别针对压下倾斜、非对称中间辊弯辊和非对称工作辊弯辊三种手段对板带轧机非对称板形调控特性进行了分析。结果表明,压下倾斜对1次板形效果较显著,非对称工作辊弯辊对3次板形效果较显著,而非对称中间辊弯辊的调控效果较小。各手段相互配合可控制不同的板形模式,为冷轧板形控制策略提供理论依据。     

Development and application of roll contour configuration in temper rolling mill for hot rolled thin gauge steel strip

Abstract

In order to improve the flatness of hot rolled thin gauge steel strip, a new type of roll contour configuration was developed for a four-high temper rolling mill based on the finite element method analysis. The roll contour configuration consists of a variable contact back-up roll contour and a positive crown work roll contour. Both can be described as sixth order polynomial functions. The variable contact back-up roll not only reduces the roll stack deflection and contact stress concentration between work and back-up rolls, but also increases the control capability of the bending force of the work roll. Positive crown work roll contour is utilised to compensate roll wear and in turn the length of temper rolling schedule can be prolonged. After this roll contour configuration was applied on the temper rolling mill of Qiangang Company of Shougang Group, the flatness of hot rolled thin gauge strip was improved by 10% and the working efficiency was also increased as the length of temper rolling schedule was increased.     

Stress levels for elastic buckling of rolled strip and plate

Abstract

Elastic buckling of a thin plate is considered in the context of flat rolling of metal plate and strip. The residual stress in the plate some distance away from the roll gap can have regions of high compression and tension whose average value is quite moderate. These are induced by mismatches between the inlet strip profile and the outlet profile defined by the roll gap. In this paper the stress levels at which elastic buckling will occur are predicted together with the form of the buckling. A fast solution technique is described in which the actual stress is replaced by piecewise constant stresses within elements across the strip. Exact solutions for the deflection due to constant stresses are employed, along with the continuity conditions at the element junctions. Various known buckling solutions are reproduced to validate the technique. Stress distributions typical of those expected to occur in flat rolling are considered and both edge and centre buckling solutions are presented.     

THE COMPACTION OF METAL POWDERS BY ROLLING. I.—THE PROPERTIES OF STRIP ROLLED FROM COPPER POWDERS

Abstract

The investigation described is an extension of earlier work (“Symposium on Powder Metallurgy 1954”, p. 131. 1956: London (Iron and Steel Institute), and Sheet Metal Ind., 1955, 32, 589) which described the effect of rolling pressure and sintering conditions on the mechanical properties of strip rolled from copper powders. The directional variation of U.T.S. and of elongation of sintered strip are shown to be the same as those of solid copper with a similar microstructure, at least for material with up to 16% porosity. The shape of powder particles and the particle-size distribution have a marked effect on the strength of sintered strip by virtue of their effect on the shape and size of the pores in the sintered material. Measurements of electrical resistance reveal a linear relationship between conductivity and porosity over wide ranges of porosity in both “green” and sintered strip. The conductivity increases rapidly during the first few minutes of sintering at 1000° C. Measurements of the resistance in the rolling direction and in the transverse direction, which are independent of local variations in density, have been made on green sheet; the resistance in the rolling direction is the higher. A correlation between this result and the mode of particle deformation is proposed, and is elaborated in Part II of this paper.     

Analysis of rolling load generated by pair crossed rolling mill

Abstract

Although a pair crossed rolling mill has a very high control capability of strip crown, a frictional force always occurs in the strip width direction between the strip and the work rolls. An analysis of rolling load was carried out, considering the shear deformation of strip cross-section caused by the frictional force. From the examination of the calculated results for a large-scale mill for production, the following conclusions were obtained: (a) the cross angle hardly influences the rolling force and torque, (b) the thrust force on the roll induced by the frictional force decreases as a result of shear deformation, (c) the thrust factor, i.e. the thrust force divided by the rolling force, is little influenced by the strip deformation resistance and the friction coefficient between the work rolls and the strip during hot rolling, (d) the thrust force applied to the rolls during hot rolling is 3–6% of the rolling force for the cross angle of 1° and this is not an obstacle related to the design of rolling mills.     

Analysis of Sheet Curvature in Asymmetrical Cold Rolling

 In asymmetric cold rolling, the workpiece is often bent downwards or upwards. A two-dimensional explicit dynamic finite element model with Arbitrary Lagrangian Eulerian (ALE) adaptive meshing technique has been employed to simulate asymmetrical sheet rolling, in which asymmetrical conditions are here due to different roll radii. To validate the simulation, the results of simulation and experiment are compared. Effects of asymmetry due to roll radii mismatch on the normal and shear distributions and on sheet curvature variations are discussed. An optimum roll radii ratio could be found to produce flat sheet. Trials were conducted to investigate the effectiveness of roll radii mismatch as an approach of sheet curvature control.     

Applicability of the laws of elasticity for the determination of the elastic-region length in the deformation zone during cold rolling

The errors of calculating the energy-force parameters of cold rolling are analyzed. They appear because of the assumption of the classic rolling theory about the applicability of the Hertz formula, which is known in the theory of elasticity, to the calculation of the elastic-region length in the deformation zone. The Hertz formula, which is used to calculate the half-width of the contact area between a fixed cylinder and a plane that bounds an elastic half-space, is shown not to take into account the following factors that are characteristic and important for the roll-strip contact: the cold working of the strip, the strip thickness, the rotation of rolls accompanied by sliding friction, and the wear that decreases the initial roll roughness (i.e., changes in the friction coefficient). A method is proposed for taking into account these factors in the calculation of the energy-force parameters of cold rolling; it is based on the statistical processing of the parameters that are measured in operating mills and are present in the databases of their process control systems. The application of this method decreases the errors of calculating the rolling forces by 35–40% and refines some laws of the state of stress in a rolled strip.     

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.     

异径轧制低碳钢的力学性能参数与粗糙度实验研究

通过一系列薄带异步轧制的实验，给出了压下率、轧制速度、轧件宽度及润滑条件等参数对轧制力和轧制力矩的影响．轧制力和轧制力矩随着轧件压下率、轧件宽度的增加而增加；轧制速度增加时，轧制力和轧制力矩降低；在轧件涂抹润滑剂的轧制条件下，轧制力和轧制力矩也降低．轧制完成后，薄带的表面粗糙度的值减少．同时也探讨了异径轧制过程中轧件表面的粗糙度的演变．     

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.     

镀锌板光整过程表面粗糙度控制技术

 热镀锌带钢是高端汽车板的主要原料，用户对其表面质量控制提出了较高要求。首钢某热镀整机组的镀锌带钢出现了上下表面粗糙度分布不均匀，表现为带钢下表面粗糙度值高于上表面。针对此问题进行了大量的现场试验和理论研究。分析认为，光整过程的非对称因素是造成镀锌带钢表面缺陷的主要原因。以非线性有限元软件ABAQUS为仿真平台，建立二维平整轧制有限元模型，通过非对称仿真计算验证了镀锌带钢表面缺陷的产生原因，并且提出了优化光整轧制力 张力配比、辅助辊调整的改进措施，从而圆满地解决了镀锌带钢的表面质量问题，研究结果对生产实践具有借鉴意义。     

PRODUCTION OF PURE NICKEL STRIP BY THE DIRECT-ROLLING PROCESS

Abstract

Results are presented of an investigation into the production of pure nickel strip, 6 in. wide × 0·030 in. thick, from carbonyl-nickel powder, using compacting rolls 7 ? in. in dia., arranged in a horizontal plane. Special reference is made to the factors affecting the quality and output of green strip: roll-gap dimensions, the head of powder above the roll gap, rolling speed, and raw-material properties. It is shown that for a given compacting mill, the thickness of green strip that can be produced is strictly limited and that it becomes progressively more difficult to achieve the limiting thickness with increase in rolling speed. A method of reducing the detrimental effect of high rolling speeds is described.

The continuous sintering and subsequent processing of directly rolled strip, using conventional cold-rolling and annealing plant, are then considered, and the properties of fully processed material are compared with those of strip produced from melted and cast carbonyl-nickel pellet. It is concluded that the direct-rolling process is capable of producing on a commercial basis nickel strip having properties which compare favourably with those of conventionally produced material.     

Defect prediction in hot strip rolling

Abstract

In steel manufacturing, enormous amounts of data are gathered from many kinds of processes and it is difficult to distinguish useful knowledge from the resulting extensive databases. The recorded databases in the rolling process contain hundreds of features, and new methods are needed to reveal the novel and useful information. In the present study, the data from a hot strip rolling process were analysed in order to identify the rolling conditions in which some common defects, such as too thin or too narrow strip, do and do not occur. At the beginning, the dataset was reduced from its original size of over 200 features to 17% by using basic statistical analysis and linear correlation. After this, self-organising maps, parallel coordinates display, and k means clustering were used to find out the conditional probabilities of the common defect types. As a result, the method presented here revealed the rolling conditions for the four common defect types, i.e. coiling temperature close to the limits, too thin strip, too narrow strip, and torn tail end. Most important, the knowledge gained can be used to reduce the number of these defects.     

Solid reaction between Al and B4C

Abstract

In the present work, solid reaction products formed by a mixture of aluminium and boron carbide (B₄C) powder heat treated under low pressure were studied. No significant reaction between B₄C and Al could be detected for reaction temperatures of 600°C or less. However, at 640°C, and over a short treatment time (1 h), a solid reaction took place between boron carbide and aluminium with the formation of A1₃BC and AlB₂. Meanwhile, over a longer treatment time (36 h), the detectable product phase between boron carbide and aluminium was AlB₁₂.     

CSP连轧过程温度和轧制力的有限元分析

借助Marc商用软件,采用弹塑性大变形热力耦合有限元法,对0.19%～0.20%C钢68 mm薄板坯CSP 6道次连轧过程的温度以及轧制力进行模拟,分析了轧制过程中各道次轧件温度和轧制力的分布与变化规律。结果表明,在轧件变形过程中,接触热传导和变形热是影响温度变化的主要因素,二者的综合作用决定了轧件的温度变化规律;轧制结束后,轧件从表面向内在一定厚度范围内出现明显的温度梯度,超过该临界厚度值,轧件温度基本保持不变。在轧制稳定阶段,轧制力在微小范围内波动。     

Three-Dimensional Model for Strip Hot Rolling

Steel stripis widely usedin many fields such asautomobile ,building,transportation and householdappliance ,etc·. Withthei mprovement in productiv-ity and automation of strip processing,the require-ments for crown and flatness of strip have been in-creasingly severe ,and“crown free”steel strips arerequired for some special applications such as for au-tomobile parts andtinplate cans .In order toi mprovethe strip quality , an effective three-di mensionalmodel is needful to further study on the…     

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.