Relationship between chatter marks and rolling force fluctuation for twenty-high roll mill

Chatter marks on the surface of a rolled steel strip may seriously affect the final product quality. It is still difficult to discover the generation mechanism of chatter marks and develop an effective method to identify chatter marks. In this paper a rolling force fluctuation model is proposed based on the variation of the rolling force between the forward and backward skid area. A dynamic model coupling vertical and horizontal vibrations is also established to analyze the vibration characteristics of a Sendzimir twenty-high cold roll mill based on the rolling force fluctuation model. Good agreement between the simulated results and the experimental results verifies the effectiveness of the established models. Furthermore, various rolling forces and rolling speeds are taken into consideration in analyzing the vibration characteristics. The proposed models provide clear theoretical support for better comprehension of the mechanism of chatter mark generation.     

Rolling strain effects on the interlaminar properties of roll bonded copper/aluminium metal laminates

Metal laminates of copper/aluminium were prepared by roll bonding at 430°C with various rolling strains. The effect of the rolling strain on the interface development and bond strength of the laminates was examined. It was found that as the rolling strain increased the bond strength of the laminates was generally enhanced in both as-rolled and sintered conditions. Critical post-rolling sintering conditions were found to exist for achieving optimum bond strengths of the laminates. It is evident that the development of optimum strength for the laminates is related to the formation of various intermetallic phases at the interface which is in turn determined by the diffusion activity of the metallic elements in the area. The greatest strength enhancement was generally observed to develop in the 60% rolled samples, suggesting that rolling strain of the roll bonding process may impose great influence on diffusion of the metallic elements. A higher copper content, without significant Kirkendall void formation, was found to build up in the interface area of the material, leading to development of strong interfacial phases. It is believed that a higher rolling strain of the roll bonding process has provided a greater area of physical contact between the bonded metals and imposed diffusion enhancement of the metallic elements across the interface.     

H型钢万能轧制宽展分析

借助有限元分析软件MSC．SuperForm2004对H型钢万能轧制进行了模拟，着重讨论了轧件的万能轧制不同阶段，宽展在孔型中的变化规律，由模拟结果可知万能孔型中轧件翼缘的端部，不接触轧辊；变形主要靠变形渗透，变形量很小；且变形渗透随道次的增加而明显。轧边机孔型中，翼缘的端部也基本不接触轧辊，只是在最后一两道次才对翼缘端部进行加工。合理制定万能压下规程对翼缘压下量的设定可以对翼缘端部的宽展进行有效的控制。     

A Polycrystal Model to Evaluate Mechanical Properties of Asymmetrically Rolled AL Sheets

The asymmetric rolling process (ASR) differs from conventional rolling (CR) through the use of different roll circumferential velocities. Using proper parameters, asymmetric rolling imposes intense shear deformations across the sheet thickness, leading not only to the occurrence of shear texture, but also to grain refinement [1]. Some shear texture components are known to improve plastic strain ratio values, and consequently formability. In Simões et al. [4], a AA1050-O sheet was asymmetrically rolled and annealed. Shear texture was obtained, as opposed to typical gamma-fiber texture obtained on sheets rolled through the conventional process. Shear tests were used to evaluate strength and formability. A polycrystal plasticity model, as formulated by Gambin [2] and implemented by Alves de Sousa [3], was employed to evaluate texture evolution and to give a sounding theoretical basis for the improved mechanical properties on sheets after the process. For FCC materials, this approach avoids the uniqueness issue related to the choice of the set of active slip systems by applying a regularized Schmid Law. Consequently, it generates yield surfaces with smooth corners where the normal vector is always uniquely defined. In the following sections, implementation guidelines are given. The accuracy of simulation results and the advantages of the asymmetric rolling process, when compared to conventional rolling, are the main topics of discussion.     

Optimization of rolling process parameters for wurtzite boron nitride powders

The paper presents some results of experimental investigations of the influence of geometrical and physical-mechanical parameters of the process of rolling wurtzite boron nitride powders on the formation of a powdered rolled material, its characteristics, and technological properties of the granules prepared from this material. The process variables have been optimized to produce granules of required density through multiple rolling in the initial state or with premoistening. It is demonstrated that high-density BN_w granules are most efficiently produced by means of a rolling mill with 100-mm-diameter rolls propped up, with a zero roll clearance and a linear roll rotational speed varying from 0.8 to 1.5 m/min.     

基于轧件水平振动的轧机辊系振动补偿模型

考虑轧件水平振动对轧制力和摩擦力动态特性的影响,建立了一种基于轧件水平振动的轧机辊系振动补偿模型。根据广义耗散的Lagrange原理,分别沿轧制方向和垂直轧制方向建立动力学平衡方程。以某厂四辊板带轧机为例,仿真分析轧件水平振动速度和轧机辊系垂直振动位移随轧辊转速的变化规律,测试了5组不同转速下的轧制力数据;对模型补偿前后轧制力理论值与测试数据误差进行了对比。研究结果表明:补偿后的模型轧制力理论值与实测数据之间的误差大大减小。     

Hot rolling behaviors of whisker reinforced aluminum composites

Aluminium matrix composites reinforced by silicon carbide and aluminium borate whiskers were hot rolled at 550°C, and the hot rolling behaviors of the composites were studied by scanning electronic microscope and X-ray diffraction (anti-pole figure). The results indicated that the whiskers in composite were reorientated, and some whiskers were broken during hot rolling process. The cracks in hot rolled composites may be related to the interface slide which is dependent on the interface strength of the composites. The tensile properties of hot rolled composites were also investigated.     

ARB (Accumulative Roll‐Bonding) and other new Techniques to Produce Bulk Ultrafine Grained Materials

Accumulative roll‐Bonding (ARB) is a severe plastic deformation (SPD) process invented by the authors in order to fabricate ultrafine grained metallic materials. ARB is the only SPD process applicable to continuous production of bulky materials. In the process, 50 % rolled material is cut into two, stacked to be the initial dimension and then rolled again. In order to obtain one‐body solid material, the rolling in ARB is not only a deformation process but also a bonding process (roll‐bonding). By repeating this procedure, SPD of bulky materials can be realized. In this review paper, various kinds of new SPD mechanical properties of the ARB processed materials are indicated.     

Microstructure and Eutectic Carbide Morphology of the High Speed Steel Strips Produced by Twin Roll Strip Casting Process

The M2 high-speed steel strip was produced by using the laboratory scale twin roll strip caster. The microstructure and eutectic carbide morphology of thus produced products were observed and analyzed, and the comparison of those with conventional products was carried out. The effects of the processing parameters such as the melting temperature, the pouring temperature, rolling speed and separating force on the microstructure and eutectic carbide morphology and their distribution were analyzed. The spheroidizing process of the strips in the annealing process was investigated. The relations between the growth and spheroidizing of the eutectic carbide and the annealing technology were obtained, and the mechanism of the twin roll strip casting process improving the eutectic carbide spheroidizing was discussed. The theoretical instruction for determining the subsequent treatment process was provided.     

Deformation of polyoxymethylene by rolling

The deformation due to rolling of polyoxymethylene (POM) was investigated by using wide and small angle X-ray techniques and electron microscopy. Tensile tests of rolled POM indicate that the yield stress increases along the roll direction. This is accompanied by a decrease in the yield stress perpendicular to the roll direction. Wide angle X-ray data from uniaxially rolled POM, obtained by means of pole figures, indicate that molecular chains tilt preferentially at approximately 30° to the roll direction at low rolling deformation, and align in the roll direction when the sample is rolled to its fullest extent. A lamellar tilt of of about 30° is also observed. Thus, the chains must tilt within the lamellae. When samples are fully rolled, small angle patterns indicate at least partial breakup of lamellae. Biaxial rolling produces no such breakup, but a uniform tilting of lamellae through the entire range of deformation.     

1220冷连轧机带钢表面振纹机理的研究

针对某1220冷轧机带钢表面振纹形成的原因进行了跟踪测试和深入研究。在对1220冷轧机振动测试的基础上,通过对机架动态特性分析及工作辊周期内各阶段振动信号的分析研究,发现在支撑辊使用中后期,轧机以600Hz左右的第7阶固有振动为主;在轧制速度为中高速稳定轧制阶段,工作辊对中间辊的相对运动形成工作辊表面振纹;该辊面振纹反作用于轧机,引起轧机强迫振动,进一步加速振纹的形成,轧机的振动为共振与强迫振动共存。在分析振纹产生机理的基础上,结合振纹间距与振源的关系,找到了引起1220轧机产生振纹的原因,提出了振纹抑制措施,并取得了很好的抑制效果。     

Phenomenological Anisotropic Study of Surface Finish in Pack Rolling

A phenomenological anisotropic model has been presented for the surface roughness modeling of pack rolling. The model is an assembly of grains in different orientations and sizes. The grain size is assumed to be in log-normal distribution. To model the macro anisotropic mechanical behavior of the grains induced by the slip deformation, the grains are assumed as isolated anisotropic units. The units have different mechanic behavior, and depend on the crystallographic orientations and the external loading as well as the interaction of the adjunctive grains. In the paper, the material properties of the grains are assumed as uniform distributions. The roughness of the contact surfaces depends on the distribution types and the scatters of the distributions. It is found that the initial roughness of the contact surfaces has a little influence on the surface roughness when the rolling deformation is large. The comparison between the phenomenological model and crystallographic model shows that the phenomenological model can also give out a reasonable result, while it only takes much less CPU time. The agreement between the single sheet model and the pack rolling model shows that in a certain degree the pack rolling model can be replaced by the single sheet model to decrease the CPU time.     

变厚度区薄板轧制的辊缝设定模型与试验

为实现高精度的变厚度轧制,需要对变厚度轧制的厚度控制模型进行研究.基于离散化的控制思想和轧制弹跳方程建立了一种TRB变厚度区轧制辊缝设定模型,用于单机架可逆式四辊冷轧机厚度控制系统.研究了辊缝变化的非线性规律,基于误差分析提出了确定离散区间的方法;给出了一种TRB辊缝控制系统结构以及空载辊缝闭环和负载辊缝闭环的控制方程,并在实验四辊轧机上进行了单厚度过渡区的TRB轧制.结果表明,采用离散化的辊缝设定方法可以实现TRB板的50 mm变厚度区,尺寸最大厚度偏差为0.08 mm,长度偏差<1 mm.     

Formation of textures and microstructures in asymmetrically cold rolled and subsequently annealed aluminum alloy 1100 sheets

The formation of textures and microstructures in asymmetrically cold rolled and subsequently annealed AA 1100 sheets was investigated. The asymmetrical rolling procedure in this experiment was performed in a rolling mill with different roll velocities (roll velocity ratio of 1.5/1.0). In order to enhance the shear deformation, asymmetrical rolling was performed by a large reduction per pass and without lubrication. Asymmetrical rolling led to the formation of strong shear textures. The evolution of asymmetrically cold rolled textures was analyzed by FEM simulations. After recrystallization annealing, pronounced {111}//ND orientations prevailed in all thickness layers. Intensified shear deformations by asymmetrical rolling also led to the formation of ultra-fine grains after recrystallization annealing.     

3D coupled thermo-mechanical FE analysis of roll size effects on the radial–axial ring rolling process

Radial–axial ring rolling is an advanced but complicated incremental metal forming technique with multi-factors coupling interactive effects. During the radial–axial ring rolling process, the deformation and thermal behaviors of the ring mainly occur in the roll passes which are constituted by rolls. So, the rolls sizes have enormous influence on the quality of the rolled ring as well as the stability of the process. In this paper, the ranges of rolls sizes and forming parameters are reasonably determined at first, then a 3D elastic–plastic and coupled thermo-mechanical FE model of radial–axial ring rolling is developed using the dynamic explicit code ABAQUS/Explicit, and its reliability is verified theoretically and experimentally. Based on the valid 3D FE model, the size effects of rolls on the radial–axial ring rolling process are investigated. The research results provide valuable guidelines for the design and optimization of the rolls sizes in the actual radial–axial ring rolling production.     

The structures of fully eutectic aluminium-silicon alloy castings

Strontium-modified aluminium alloys containing 14 to 15 wt% silicon were cast with fully eutectic structures by using heated moulds and high-purity materials. In alloys containing the additional elements magnesium, copper or nickel, a distinct eutectic colony structure was evident outlined by intermetallic compounds. At the edges of the castings the eutectic colony structures and the aluminium grains (revealed by anodizing) were of a similar scale. Further from the mould walls the eutectic colonies contained several aluminium grains. This is believed to result from the blocking of growth of the aluminium phase by the silicon phase.     

Comparison of texture evolution during cold rolling between direct chill and continuous cast aluminium alloy 5052

Abstract

Hot bands of direct chill cast (DC) and continuous cast (CC) aluminium alloy 5052 were cold rolled to different reductions after being annealed at 454 ° C for 4 h. The texture evolution during cold rolling was investigated for both DC and CC AA 5052 by determining the orientation distribution functions of the cold rolled specimens via X-ray diffraction. Texture evolution during cold rolling was predicted by empirical formulas of the variation of the texture components with true strain. The results show that the processing method (DC versus CC) has an effect on the texture of annealed hot bands and the texture evolution during subsequent cold rolling.     

Influence of aluminium on solidification structure and initial deformability of continuously cast C–Mn–Si–N steel

Abstract

The solidification structure and the initial deformability of continuously cast steel were investigated by assessment of cracks on billets and on rolled product. Some billets were rolled directly off the casting machine and some cooled to ambient temperature, then reheated to rolling temperature. On direct rolled steels, the number of defects increases with increasing aluminium content, while virtually no defects are found on steel rolled after reheating. By increasing the aluminium content, the solidification structure of steel is highly modified and a columnar structure obtained over the entire section of the billet. It was shown by chemical analysis and fracture examination that the increased hot shortness is not related to the effect of AIN. It is concluded that the hot shortness is related to the effect of aluminium on the solidification structure.

MST/761     

Enhanced strip-roll coupling concepts for the numerical simulation of flat hot rolling

In the present paper, an enhanced iterative algorithm for the effective numerical simulation of the contact between an elastic roll stack and an elasto-viscoplastic strip or plate in hot rolling is presented. The underlying physical process treated here is the forming of metal within a rolling stand, that is, between a lower and an upper roll set, each of which may consist of one or more rolls. The strip material is described elasto-viscoplastically, whereas the roll stack is deformed elastically. Due to the high nonlinearity of the whole problem, the coupling between roll stack and rolled material is performed iteratively. The contact stress distribution resulting from the strip model describing the material flow bounded by the work rolls serves as input for the determination of the deformed work roll surface, which can be performed very accurately and effectively by applying the analytical and numerical methods outlined in this study. The new deformed work roll contours represent the “flow channel” for the next calculation step of the strip model. The accurate coupling of the strip model with the routines for the elastic roll stack deflection is a precondition to get reliable results concerning profile transfer, incompatible strains, and residual stresses inside the strip, which allows the prediction of flatness defects, such as buckling.     

多通带滤波技术及冷轧钢板振纹监测

分析数字带通滤波器的特点，结合低通、带通滤波器的设计特点，构造一种多通带的数字滤波器。这种滤波器能快速有效的提取出多个频段信息，并且能柔性地选择频段的上下限和频段数。分析冷轧钢板振纹的基本特点，再根据冷轧钢板振纹的在线监测要求实时显示出多个频段信息的特点，就需要一种高效的多通带滤波技术。鉴于此特点，设计一款基于VB. Net平台的冷轧钢板振纹在线监测软件，将所关心的低、中、高频段显示出来便于观察。此系统已经在某钢厂的冷轧车间中得到应用，结果证明对多频段的信号提取是比较理想的。