Research On The Surface Wrinkle Defects In The Hot Bar Rolling Process

The bar steel takes an important role during the development of the steel industry. The surface wrinkle defects play a very important role in the hot bar rolling. It has been proven by the factory that it maintains to the last roll systems and will never disappear or even enlarge by steps. It has a strong impact on the surface quality of the products. Analysis of the process of the surface defects in the bar steel during hot rolling is very important. Decreasing the surface wrinkle defects to improve the quality has an important practical significance to the factory.Fist of all, the true stress-true strain relationship for the samples at different conditions was studied through hot compression on Gleeble—1500 thermal-mechanical simulator. The constitutive equation of hot deformation is determined according to the principle of least square. Then the friction factor of the samples at different temperature in hot rolling was measured through the maximum angle of bite.The hot rolling was simulated through Finite Element Method(FEM)in order to study the process of the folded defects on the surface and improve the surface quality of the product. The fist pass of rolling was primary object of this study, while the model was made by using FEM software DEFORM and rigid plastic FEM. The actual parameters were applied to the simulation model, such as the constitutive model,friction actor etc. the stress and strain, the value of the velocity of the metal are got by numerical value operation.We concluded through the comparison of the result of the experiment at the laboratory and the numerical simulation that the position of the folded defects located in the round corner of the billet. The data shows that the grads of metal flow speed on the round corner have a great change. It is the main cause of the folded defects on the surface of the product. In order to eliminate the defects we should enlarge the billet round radius.decrease the billet width or increase the width of the roll, and the temperature has a large effect on the defects.A good fit between simulation results using this model and experimental shows that the algorithm has a good reliability. Good performance and satisfactory results in factory were obtained by applying the measures.