量子ドットを活用した冷間圧延時のロールバイト油膜厚さ分布の測定

During the cold rolling of flat steel products, lubrication is critical to achieve stable rolling. However, the oil film thickness distribution in the roll bite and its effect on friction between the work roll and strip have not been clarified thus far. This study aimed to elucidate the relationship between the oil film thickness distribution and friction by focusing on the rolling oil viscosity and steel grades, because they significantly affect the friction between the work roll and strip. Rolling oil was prepared with quantum dots as the fluorescent additive and used in rolling experiments to identify its distribution. Furthermore, cold rolling experiments were conducted using two types of oil with different viscosities and three different steel grades, namely low-carbon steel (LCS), high-strength steel (HSS), and advanced high-strength steel (AHSS) with tensile strengths of 270, 590, and 1180 MPa. Subsequently, the oil film thickness distribution on the steel strip surface was visualized using quantum dots by fluorescence microscopy. It was demonstrated that the higher the tensile strength of the steel or the higher the oil viscosity, the wider the rolling oil distribution on the strip surface. Numerical analyses revealed that the rolling oil distribution on the steel sheet surface was more widespread for AHSS and HSS than for LCS. The high surface pressure between the roll and steel plate may have increased the oil leaching area by increasing the oil viscosity. These findings demonstrate that rolling oil permeation from the oil-pits reduces the friction between the work rolls and strip.