A novel sensor for lubrication and contact measurement in metal rolling

Ultrasonic sensors have been installed within the upper roll of a steel strip cold rolling mill. Both longitudinal and shear polarised ultrasonic transduces were used. The sensors emit and receive ultrasonic pulses reflected from the roll strip upper and lower interfaces. By continuously recording the pulse reflection it was possible to determine in-situ the roll bite width for various rolling elongations; in this way widths of 8 to 13mm for elongations of 7 to 28% were measured. The roll-strip interface is in mixed regime lubrication consisting of both liquid and solid contact. Longitudinal ultrasound can be transmitted by both solid and liquid contact, whereas shear ultrasound can only be transmitted by asperity contact. A model of the two reflection mechanisms was used to extract the stiffness contribution from the liquid part alone and hence determine the oil film thickness. Whilst at present the method is approximate, and suffers from spatial resolution limitations, film thicknesses in the region 0.2 to 0.5 μm were recorded.