X.H. Liu

Numerical modelling of the thermal deformation of CVC roll in hot strip rolling

Abstract An accurate prediction for the thermal crown of the continuously variable crown (CVC) work roll is a key to improve the accuracy of the computer on-line control model. In this paper, the authors have developed a finite difference model to simulate the thermal deformation of the CVC work rolls in hot strip rolling. The effects of the heat generation produced by the strip deformation and friction, heat conduction and convection on the thermal crown are introduced in the simulation. A comparison of the calculating roll temperature and measured values shows that they are in good agreement. Result shows that a model of calculating the thermal crown of the CVC rolls can be obtained based on the finite difference method. The modelling of the thermal crown of CVC rolls in hot strip rolling can improve the accuracy of on-line control model.

Simulation on temperature field of 50CrV4 automobile gear bar steel in continuous rolling by FEM

Abstract The temperature field of 50CrV4 automobile gear bar steel in continuous rolling is simulated by FEM. The temperature variations of the bar during continuous rolling are obtained. The cross-sectional temperature field for some passes has been solved simultaneously. It is clear that the surface temperature of a bar calculated by FEM accords well with the temperature found in practice. The simulated results in this paper describe the temperature pattern of rolling in great detail. Especially, this paper offers reference data for the TMCP treatment of bar steel.

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.

Discrete-Time Optimal Control of Photovoltaic Grid-Connected Inverter Based on Particle Swarm Optimization

This paper is concerned with the problem of optimal control of photovoltaic grid-connected inverter. Firstly, the discrete-time nonlinear mathematical model of single-phase photovoltaic grid-connected inverter in the rotating coordinate system is constructed by the Delta operator, which simplifies the control process and facilitates direct digital realization. Then, a novel optimal control method which is significant to achieve trajectory tracking for photovoltaic grid-connected inverter is developed by constructing a control Lyapunov functional against the difficulty of solving HJB (Hamilton-Jacobi-Bellman) partial differential equations. More importantly, the performance matrix of the controller which is very meaningful to many performance indicators of the system is also optimized via the particle swarm optimization. Finally, two numerical examples are provided to illustrate the effectiveness of the proposed method.

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.