Analysis of Surface Defect Generation Behavior of Wire Rolling Defects: Establishment of the analysis technique to determine the occurrence of surface defects

Abstract

If surface defects on hot rolled wire rod subsequently remained, it might become the starting point of cracks in the forging process. Therefore, the surface quality for hot rolled wire rod is strongly required. In order to avoid surface defects, it is important to establish methods for predicting the positions and the criteria of the defects as a function of rolling conditions.
In this paper, we assume that the defect is a kind of plastic instability on the surface. We analyze the criteria of the defects by using a geometrical velocity field. By using FEM, we calculate the velocity vector and the geometry of the surface during rolling. The angle between the normal vector and the velocity vector on the surface is constantly changing during rolling. In order to analyze the phenomena, we introduce the new parameters η = v→·n→ and ψ = dη/dθ.
Comparing with the experimental results of the position of defects, the velocity gradient (ψ) is a good index for prediction of the defect position. In that case, ψ is locally changing near the inlet on the roll bite. A plastic instability might occur on the surface, as a result of this condition.