A Combined Experimental and Modelling Approach to the Characterisation of the Fluid Film in Dynamic Shape Roll Pads

In steel rolling, the flatness of the finished product is important in terms of the quality of the product and in extreme cases can be responsible for more serious defects. A number of flatness control systems are in common use such as the Continuously Variable Crown system which incorporates the use of axially shifted rolls with a complex (coke bottle shaped) profile. Dynamic Shape Rolling (DSR) is a new technology which promises improved shape control and reduced costs over current systems. It is in current use in lower load applications, such as aluminium rolling, but thus far when used in higher load applications, such as steel rolling, it has suffered from a single catastrophic failure mode. This has been attributed to the breakdown of the oil film within the thrust type pads which control the system. The aim of this work is to develop an experimental and modelling approach to further understand and characterise the fluid film in the interface between the pad and sleeve within a steel rolling mill stand with DSR-type flatness control. An existing test rig, which was supplied by Siemens / Primetals, was developed to incorporate ultrasonic transducers which were directed at the oil film. The signals collected from these transducers were then interpreted to deduce fluid film thicknesses at discrete points on the pad surface which enable the characterisation of the oil film in situ for a range of operating conditions. Fluid film profiles were then used to validate a bespoke model which was developed to characterise the oil film. This model is a novel approach which incorporates finite element analysis and a unique method of oil film pressure profile calculation which iterates until a map of the fluid film can be produced. The output of the model matches that of the recorded measurements to within 14% of the measured load conditions. The work presented here offers the first insight into the true nature of the oil film in the DSR pad-sleeve contact and improves upon the modelling technique employed to predict the said film