Dianyao Gong

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. Key words: asymmetrical rolling; finite element method; radii ratio; sheet curvature

Effect of initial crown on shape of hot rolled strip

Based on the influence coefficient method, the effect of entry strip crown on the shape of hot rolled strip was analyzed using the software of roll elastic deformation simulation. According to the practical condition of a domestic hot rolled strip plant, the unit strip crown change from the first stand to the last stand was calculated when the entry crown of hot strip varies. The calculated result shows that the entry strip crown does not significantly affect the target strip crown at the exit of the last finishing stand in respect to a fixed strip shape control reference (such as bending force). The calculation was analyzed, and the research is helpful in modeling strip shape setup and shape control.

EFFECT OF ASYMMETRICAL STAND STIFFNESS ON HOT ROLLED STRIP SHAPE

The difference of elastic springs between the operating side (OS) and driving side (DS) of rolling mill has a significant influence on the strip shape not just the strip thickness. Based on the slit beam and roll deformation theories, the roll force distribution was analysed considering the asymmetric stiffness of the OS and DS of rolling mill, and the work roll and backup roll deformation equations were deduced respectively, and the thickness distribution in lateral direction of the hot rolled strip at exit was discussed. Using the roll elastic deformation analysis software which was developed previously based on the influence coefficient method, the roll flattening distribution, roll pressure distribution and the rolling force distribution caused by the asymmetric stand stiffness were calculated and analysed, and the exit strip profile of the rolling mill was also presented. The relationship between the mill stiffness difference and the strip wedge shape or single wave was obtained. Effect of the upstream asymmetric mill on strip crown and flatness of the downstream stands was discussed.

Study on Model of Thermal Crown of Single-Stand Irreversible Foil Mill

Based on the principles of heat transfer, finite difference method was adopted to develop program of calculating thermal crown of single-stand irreversible foil mill. The temperature distribution and thermal crown of roll were calculated for one rolling schedule. The temperature of each layer calculated was analyzed. The computed and measured surface temperature was compared, which shows good consistence with each other. The law of thermal crown changes with time conformed to practical account.

Setup Models of Finishing Temperature and Rolling Speed for Hot Strip Mill

Various analytical rules of mixture are commonly used to take into account heterogeneous features of a material and to derive global properties. But, with such models, one may not be able to fulfil the requirements for separating appropriately the different lengthscales. This might be the case for some issues such as strain localisation, surface effect, or topological distributions. At an intermediate lengthscale, which we refer to as the mesoscopic scale, one can still apply continuum mechanics. So why not perform calculations using the finite element method on volumes of material to obtain the response of Representative Elementary Volumes (R.E.V.). The construction of digital microstructures for such calculations is performed in two steps. First, a series of R.E.V.s with statistics of features of real materials should be defined. Then, finite element meshes should be produced for these R.E.V.s and updated when calculations involve large strains. Powerful automatic three-dimensional mesh generators and remeshing techniques prove necessary for this latter task. This strategy is applied to create digital R.E.V.s which match statistical features of forgings. Measurements provide micromechanical parameters of each subvolume. As an example of calculations, numerical simulations provide the anisotropic fatigue properties of forgings.

Analysis of ZDDP Films on Sticking Defects by FEM during Hot Rolling of Ferritic Stainless Steel Strips

The aim of this study is to understand the effect of zinc dialkyl dithio phosphate (ZDDP) films on sticking defects during the hot rolling of ferritic stainless steel strips. The surface characterisation and crack propagation are very important for the sticking defects of ferritic stainless steel strip. A finite element method (FEM) model is constructed with different crack size ratios, in which the profile of the strip roughness and ZDDP films are taken into consideration. Simulation results show that the widths of cracks tend to be reduced with the introduction of ZDDP films, improving the sticking defects, which is confirmed by the hot rolling trials.

RE-Boronizing below Beta Transus Temperature on TC4 Titanium Alloy Surface

Ti6Al4V (TC4) slices were boronized with rare earth oxide (RE) addition in the agent at 950°C (below β phase transus of TC4). The morphology, phases, properties and structures of TC4 matrix and boride layers were studied. The results show that the boride layer on the surface of TC4 consists of TiB2 and TiB dual compounds. The boride layer is compact, uniform and less porous compared with that obtained at 1050°C (above β phase transus of TC4), and the hardness profile and brittleness of the layers are improved to a certain extent. Lower temperature boronizing can effectively prevent the growth of coarse β phase grains. Duplex microstructure is obtained in TC4 matrix, and the work piece distortion is reduced.

Development of HOFC Work Roll Curve for Strip Rolling Mill

The HOFC (High Order Flatness Control) work roll curve was designed using Matlab. It has great flatness control ability, for the roll diameter in the position of the 1/4 roll length can be altered with the changing of angle and index parameters. Combined with the data from a hot strip factory, the elastic deformation of the HOFC work roll was analyzed following the influence coefficient method. The distribution curves of the exit thickness, roll force, work roll bending, pressure between rolls, roll flatting, and roll gap geometry were given under the conditions of different roll parameters. Results show that the HOFC work roll curve can eliminate the high flatness defects, reduce the edge drop, improve the lateral thickness uniformity, and maximize the available cross section of the strip effectively.

Advanced Flatness Control Strategies for Multivariable Optimisation Flatness Control System of Foil Rolling Mill

In cold strip or foil rolling, flatness control is an integral part of modern mill. This paper introduces two typical flatness control systems, pattern recognisation flatness control system and multivariable flatness control. It is found that the latter is effective and has wider application fields. The FEM models of its core parameters, flatness actuator efficiency, are constructed. Influencing factors, such as the rolling force, bending force as well as the tilting force are discussed. Control strategies are proposed for foil rolling. The results demonstrate that the control strategies can reduce flatness error and improve flatness quality.

Mechanics of design and model development of CVC-plus roll curve

The mathematic model of CVC-Plus work roll curve is built. The ratio of the initial shifting value to the target crown is determined, and the mathematical model considering the relationship between the coefficients A2, A3, A4, A5 and is established. According to the theoretical analysis, the distance between the maximum or minimum point of the high order equivalent crown for work roll with CVC-plus roll curve and the rolling central point is the times of the roll barrel length. In general, the initial shifting value of the CVC-plus roll curve is not equal to the initial shifting value of the 3-order CVC roll curve . The coefficient A1 can also be obtained by optimizing the target function with minimizing the axial force.