A study of lubrication mechanism of oil-in-water (O/W) emulsions in steel cold rolling

Purpose - Oil-in-water (O/W) emulsion has been used in industrial rolling mills for many decades, but its lubrication mechanism is still not adequately understood. There is a need to understand the role of chemical ingredients and emulsifier in lubrication and tribological characteristics of rolling oil. With this purpose, the authors selected three commercially available OM emulsions of different generations and of known industrial performance. The aim is to understand the lubrication mechanism of these rolling oils and to correlate the laboratory findings with that of industrial rolling mills. Design/methodology/approach - The lubrication mechanism has been studied with the help of an ultra thin film interferometry EHD test rig, an advanced experimental rolling mill and a Coulter LS 230 instrument. Film thickness, rolling parameters and droplet size were measured. The coefficient of friction was computed with the help of the measured values of rolling parameters. Emulsion stability and saponification value (SAP) of the selected emulsions were also determined. The results of film thickness, rolling parameters and droplet size have been presented. The lubrication mechanism of the emulsions has been explained on the basis of film thickness, droplet size, emulsion stability, SAP value and coefficient of friction. Findings - Results of the present study reveal that chemistry of OM emulsions plays an important role in their film forming and tribological behavior. Rolling emulsions of relatively low stability, higher droplet size and high SAP value are found to provide better lubrication and lower coefficient of friction. The results of the present study correlate well with the actual industrial experience except those obtained on EHD test rig. Research limitations/implications - Coulter LS 230 instrument was available with M/s LUBRIZOL CORP., USA. Only limited study on droplet size was carried. Although the study carried out has given good information but it would have been more practical if the emulsion samples taken from the experimental mill stand would have been studied for droplet size. Practical implications - From understanding point of view of lubrication mechanism of O/W emulsion, it will be useful for oil technologists, tribologists and rolling mill users. Originality/value - The study is original in nature and gives information on lubrication mechanism of O/W emulsions in steel cold rolling of steel strips.