Jian Zhong Xu

Formation and control of strip scale pores in hot rolling

Abstract In order to solve the problem of strip surface pores generated by the combination of the tertiary scale on strip surface with black oxide layers produced on the roll surface, the mechanism of strip scale pores formation was analyzed using several instruments such as the SEM, the AHM-2-HL optical microscope and the Oxford ISIS EDAX energy spectrometer. A method of control is advanced to reduce strip scale pores, which is effective and clearly beneficial for enhancing the strip surface quality in practice.

FEM Analysis of Stress on Roll Surface Black Oxide Layers Exfoliation in Hot Strip Rolling

To understand the mechanism of formation and exfoliation, black oxide layers were investigated, and the effects of stress on the exfoliation were analyzed by finite element method (FEM). The roll surface on which black oxide layers form is composed mainly of Fe3O4, which is caused by the oxidation of the roll material itself. Cracks form and are easily propagated along M3C- and M7C3-type carbides, which leads to further cracking along M3C and M7C3 carbides as a result of contact stress fatigue produced by cyclic mechanical stresses that normally occur during the rolling process. Thermal fatigue of the roll surface is produced by the thermal cycles created alternately by contact with the hot strip and the cooling water on the roll. The generation and propagation of cracks in the black oxide layers during rolling is promoted by circumference compressive stress at roll surface. Under this stress, the exfoliation of the black oxide layers happens on the roll surface.

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.

Study on Predictive Model of Plate Camber

The plate camber is one of the thorny problems in the plate rolling process. The characteristic variables of plate camber at the delivery and at the entry sides of the mill were illustrated based on the primary concepts of camber. The relationship between the plate characteristic variable and velocity distribution in the deformation area of the plate was also determined. This paper focuses on the features of asymmetry in the transverse direction during rolling, an elastic deformation mathematical model of four-high mill has been developed to optimize the predictive model of plate camber, which ensures the theory of influence factors of plate camber to be applied in plate rolling.

Study on Diagnostic Strategy for Plate Camber

During the past two decades, progress has been achieved for the plate production in various areas, from the level of equipment to the processing techniques, and from the product size to the quality of the products as well. However, plate camber which may affect the stability of rolling has been one of those thorny problems due to the complexity and variation of plate camber. Analysis of the factors which may lead to plate camber, including slab wedge, temperature uniformity across the plate width, side-guide alignment, stiffness difference at two sides of the mill and the inclination of the roll gap, the features of the plate camber have been studied. Using measurement and quantitative analysis of plate camber, process data analysis of the plate, equipment monitoring and operation adjustment, a systematical diagnostic strategy of plate camber has been carried out. It has shown that the developed diagnostic strategy is satisfactory in one domestic Plate Mill.

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.

Model Building of Finishing Temperature Control for Accelerative Hot Strip Rolling

In order to build finishing temperature control model for accelerative hot strip rolling, the method to index acceleration rate of steel and the relation between acceleration rate and steel temperature is denoted, according to the character of heat transfer in different positions of finishing temperature control area, the heat transfer process is elaborated, the cooling calculation unit and the sample tracking method are discussed, when the steel is on different position of the rolling line, the average temperature and the steel surface temperature are used respectively to stand for the calculation temperature of steel. The finishing temperature control model is build based on the theory model of heat transfer and the calculation result meet the measured data gathered in certain strip mill well. Introduction With the increase of the product precision of the hot rolling strip and of the service performance due to the consumer, the finishing temperature control becomes an important theme. The precision of finishing temperature effects not only directly the setting of draught pressure, shape of strip, load distribution and the strip thickness precision at finishing rolling exit but also structure properties of hot rolling and products[1-4]. Accelerative rolling developed companied with the development of TMCP (Thermo-Mechanical Control Process)[5-8] made the control of finishing temperature complex and hard. At present, for the finishing temperature control, the feed-forward control is the main mode and the set model is the key. Model setup model includes the rolling speed setup, strip elements describe, inter-stand heat transfer calculation and steel element tracking strategy. The structure and precision of the setting model are important for finishing temperature control. 1 Finishing Temperature Control and the Facilities Water cooling is a economic method for steel TMCP, steel finishing temperature control and coiling temperature control are important to product mechanical properties[ ,1 ] as shown in Fig. 1. When steel is rolling in finishing mill, the process is complex, the steel temperature change is nonlinear to the rolling speed, so it’s hard to control by level 1(automation control system ) using feedback control. Finishing temperature is one of the key parameter and it’s very important to steel’s run out table cooling because finishing temperature is the start temperature of laminar cooling and direct quenching. Precise and stable finishing temperature may enhance the control precise of rolled cooling process. In the days of steel constant speed rolling, the finishing setup function(FSU) made a setup of strip temperature during rolling, the temperature control task was carried out by feedback control system based on the finishing mill exit temperature measured by pyrometer through tuning inter-stand spray status. Acceleration rate became a method to amendment finishing temperature since accelerative Key Engineering Materials Online: 2007-06-15 ISSN: 1662-9795, Vols. 340-341, pp 633-638 doi:10.4028/www.scientific.net/KEM.340-341.633

A Method to Analyse of Roll Bending Force Effect Rate in 4-High Hot Strip Mill

A method to analyse the crown effect rate of hot strip was developed successfully by using influence coefficient method. The effect of the roll bending force effect rate in hot strip rolling was investigated in details. Results show that the roll bending force effect rate decreases significantly with the increase of strip width, the difference between the roll bending force effect rate and its base value increases with the reduction, unit width rolling load and work roll diameter. For the strip width 1.85 m, when reduction of 10 mm, unit width rolling load of 15 kN/mm and work roll diameter of 760 mm, the errors to calculate the strip crown base on a base value of the roll bending force effect rate reach 4.6 μm, 6.6 μm and 19.275 μm respectively. However, based on the developed roll bending force effect rate model and the determined relevant coefficients of a six power polynomial expression, the difference between the results obtained from the developed model and the theoretical calculation is 2.5 μm when strip width is 1.85 m, so the calculation accuracy for strip crown can be improved significantly. Introduction Recently, some new technologies such as schedule free rolling [1-6] and strip profile controlling [7], were applied in the field of hot strip steel rolling production. With the further improvement and widely application of Automation Gauge Control [8], the strip gauge control has reached a high level. As a result, the problem of strip shape becomes more and more important. In order to meet the demand of strip crown and profile control, it is important to generate a general analytical tool for calculating the model parameters of strip shape control. Previous research shows that many strip shape theory and engineering problems are analysed with effect function method [9]. However, the application is limited in the certain conductions and the model accuracy is not high enough to produce a high precision production in practice. In this paper, the authors developed a general simulation method to calculate the strip crown effect rate by using the influence coefficient method. Strip Crown Calculation Theory Base Strip Crown and Derivative Strip Crown. To analyse strip crown, calculations are first made for so-called base case in which roll diameter, unit width rolling load, roll bending force, roll crown, strip initial crown and load distribution etc. are equal to base values. The strip crown obtained under these conditions is identified as base crown. In order to determine the effect of one given parameter such as the initial crown, rolling load on strip crown, the values of all remaining parameters related to the base case are set constants. A change of the selected parameter will produce a new value of the strip crown, which is called derivation strip center crown [10]. Strip Crown Effect Rate. Strip crown effect rate i K , as shown in Eq. (1), is a ratio of the Key Engineering Materials Online: 2004-10-15 ISSN: 1662-9795, Vols. 274-276, pp 517-522 doi:10.4028/www.scientific.net/KEM.274-276.517