Effects of ferrous powders on tribological performances of emulsion for cold rolling strips

An attempt was undertaken to obtain a better understanding of the effects of ferrous powders (FPs) on tribological performances of oil-in-water (O/W) emulsion for cold rolling strips. The particle size distribution of FPs in the working emulsions, which were collected from the industrial field of 1550 rolling unit, was analyzed by Malvern MS2000 laser diffraction particle size analyzer. Emulsion samples containing FPs with different particle sizes were prepared to simulate the condition of working emulsions containing FPs, and the particle sizes of FPs added in the emulsion samples were decided according to the analysis result of the particle size distribution of FPs in working emulsions. Tribological tests were further explored to evaluate load carrying properties, anti-wear and friction-reducing performances of the emulsion samples. In subsequent rolling tests, strips were also lubricated by the emulsion samples and morphologies of rolled surfaces were studied in more detail in order to obtain the mechanisms of FPs acting during rolling process. Results show that the tribological performances of emulsions are benefited from FPs with sizes smaller than or equal to 3.0 μm because of their micro-scrolling effect between rolls and strips, as well as supporting the oil film of emulsions, but FPs with sizes bigger than 3.0 μm performs as abrasive particles and aggravates abrasion, which may also leads to instability of lubricating performance of emulsions and deteriorate the quality of rolled surfaces. Benefiting from the polishing and grinding effects of FPs with sizes smaller than or equal to 3.0 μm on asperities, roughness of strip surfaces is decreased and the smoothness of surface morphology is improved.