R. Ahmed Heriot-Watt University United Kingdom An Analysis of Micro-Plasto-Hydrodynamic Lubrication Using a Strip Drawing Rig R. Ahmed Heriot-Watt University United Kingdom M. P. F. Sutcliffe Cambridge University United Kingdom Industrial Collaborator(s) Corus / Avesta Sheffield, UK

STRUCTURE of PRESENTATION Context of the Problem Experimental Analysis Mathematical Modelling Results Conclusions

CONTEXT OF THE PROBLEM - Lubrication Mechanisms Lubrication Regime dictates the tribology and hence the functional requirements such as surface gloss. Hydrodynamic oil entrainment at the inlet to the bite and expulsion of entrapped oil in isolated pits due to relative sliding (MPHL). Reduced rolling speeds and high scrap rate plague productivity.

SEM OBSERVATIONS (Shot blasted Surface) Lubricant Entrapment

SEM OBSERVATIONS (Micropits and grain Boundaries)

Schematic of inlet and MPHL Lubrication Mechanisms Strip Roll Oil drawn out of pit due to MPHL action Oil drawn at the inlet due to entrainment action Sliding of roll relative to strip

STRIP DRAWING RIG Indentation Ram Drawing Ram Shackle Die Specimen Strip Die Holder

Direction of sliding of workpiece MPHL Model p  Rigid tool Lubricant Pressure exerted by trapped lubricant Normal Load Direction of sliding of workpiece of workpiece Micro-plasto-hydrodynamic lubrication Flow of lubricant Schematic of micro-plasto-hydrodynamic lubrication. Sliding P*= Average pressure Oil AoLo Lo L  Tool

AFM PLOT (pit geometry) AFM measurement to reveal geometry of remnant pits (1 = 10o ; 2 = 20o ; 3 = 7o ; 4 = 17o ; 5 = 25o)

OPTICAL COMPARISON (Rolling and Strip Drawing) Cold Rolling

SCHEMATIC OF STRIP INDENTATIONS Vickers indentations Micro-Vickers indentations Knoop indentations Brinell indentations 25 mm 2 mm 45o

Pit Behaviour Through Bite During Strip Drawing

RESULTS (a)Sliding distance (cm) Area ratio and film thickness for pit angle of 35 degree, V-68 oil (Ao=0.5; Lo=300m; *=0.7; u=16 m/s; B=0.0219; C=1.99E-06 (b)Sliding distance (cm)

CONCLUSIONS Hydrostatic pressure build-up in the entrapped oil can significantly reduce sheet conformance. A transition from hydrostatic to hydrodynamic conditions caused by sliding in the bite can assist elimination of individual pits. This may cause problems in sheet conformance in an area around the pits due to oil extrusion. Pit angle, spacing and depth can have a significant effect on the MPHL and consequently on the evolution of surface.