Experimental and numerical study of O/W emulsion lubricated strip rolling in mixed film regime

An experimental and numerical study of cold rolling lubricated by O/W emulsion has been carried out. The strip rolling experiment was carried out on a Hille experimental rolling mill with a view to study the performance of emulsion lubrication in terms of practical rolling parameters. Accordingly, rolling parameters such as rolling force and torque were measured. The experimental measurements compare favourably with the computed results from a numerical scheme developed by the authors. The scheme, based on a two-phase lubricant model, is capable of calculating the oil concentration at any point within the inlet zone and work zone, rolling pressure, film thickness, and fractional contact area ratio associated with strip rolling under mixed film lubrication at different rolling speeds. Using this scheme, the intertwined effects of an emulsion’s parameters such as: oil concentration, mean oil droplet size, and rolling speed on strip rolling were investigated. The numerical study encompassed the mixed film regime for speed, S ranges from 10⁻⁴ to 10⁻², supply oil concentration level λ_ds from 1 to 10%, and oil droplet size D _S from 5 to 10. Experimentally, the differences between water, oil and emulsion-lubricated rolling are not discernible except for film thickness. At a low speed of 10 RPM, force and torque of water-lubricated rolling are marginally higher than oil- or emulsion-lubricated ones. However, the difference between emulsion and neat oil is not apparent. The numerical results show the occurrence of a moderate oil concentration increase in the inlet zone followed by a sharp one at the beginning of the work zone. The effect of the concentration process is predominantly seen in the film thickness and the lubricant pressure whilst its effect on the total pressure is less pronounced. The analysis of the results suggests that it is possible to lower the emulsion oil concentration without any adverse effect on the rolling process. This principle can be used to control the outlet lubricant film thickness and hence the surface quality of the rolled strip.