Proceedings of the Institution of Mechanical Engineers,Part J: Journal of Engineering Tribology

Good surface finish is an important requirement for many stainless steel products essentially in terms of brightness. This article deals with an original numerical approach proposed in order to better control workpiece roughness during cold rolling. As a first step, to supply the numerical model, the blasted strip rheology is identified using an inverse finite element methodology based on Vickers indentations. As a second step, a fluid-structure strong coupling model is proposed to determine the flattening of steel strip asperities during the first passes of a cold rolling sequence. Fluid flowrate between each valley is solved using local Reynolds' equations. The volume of the lubricant trapped and its pressure are updated on the cold rolling model. At the same time, asperities are deformed from the entry to the exit to reach their final shape. Roughness sensitivity to the industrial process parameters, to the rheological parameters, and to the lubricant rheology is discussed.

A cold-rolling model taking into account mixed lubrication regime has been developed and included into a simulation software named MetaLub. The main objective is to enhance the performances of rolling mills from a lubrication point of view. It means that lubricant rheology but also roll diameters and roughness, etc. can be optimized to improve stability and efficiency of the rolling tool.

The main features of MetaLub are briefly presented in this article. Then, two studies of the influence of rolling speed and negative forward slip are discussed. The obtained numerical results are presented and compared to some experimental data from literature and from ArcelorMittal facilities in order to validate the model and to show its capacity to understand and help to improve industrial rolling conditions.

Oil-in-water (O/W) emulsions are widely used for steel-rolling processes. An efficient lubrication is required to control the oil film deposition on the strip surface. This article deals with phase separation in lubrication film formation before roll bite (plate-out). A model has been developed to simulate the behaviour of an emulsion droplet that impacts onto a moving plate. The typical configuration of emulsion droplet impact is considered in a calculation which controls the initial formation of the film. To describe hydrodynamic phenomena, wetting and three-phase contact line models have been integrated in a Navier–Stokes-based computational fluid dynamic code. Both models have been validated against data from the literature. Numerical studies carried out with the model have highlighted the importance of the oil concentration in the droplet on the plate-out occurrence. A ballistic study has also been performed to evaluate the influence of the droplet velocity on the film formation.

Formulation of efficient lubrication procedures for multi-pass steel wire drawing is a problem of prime importance. One studies the performances of industrial soaps in stainless steel wire drawing by experiments. Before drawing, the wire is pickled and covered with salt. One measures the drawing force, die average temperature, and the total residual film surface weight and observes the drawn wire surface by scanning electron microscope. The influence of the drawing velocity u in the range 0.1–10 m/s, the nature of the stearate (Na, Ca) and the filler amount, the salt surface weight, the wire roughness and yield stress, and the die angle are studied. Results demonstrate that quasi-hydrodynamic lubrication is induced by a mixture of salt and soap; calcium stearate is well adapted to the lowest velocities, whereas sodium stearate has better performances at the highest velocities. Rheological origins of these differences are discussed.

Downscaling of metal-forming operations from macro- to microscale implies significant changes caused by size effects. Among these, the friction increases as reported by researchers using indirect test methods such as the ring-compression test and double-cup-extrusion test. In this study, a new test equipment is developed for studies of the size effect in metal-forming friction in the range from macro- to microscale. Investigations confirm a significant friction increase when downscaling. Visual inspection of the workpieces shows this to be explained by the amount of open and closed lubricant pockets.

Swerea MEFOS pilot mill has been used as a rolling lubricant development tool. The objectives were to improve the lubrication during rolling and thereby improve the operation of the rolling mills. This was done taking into account both the technological aspect, rolling mill output, and the ecological aspect, investigating ways to use rolling lubricants that are more ecologic sustainable, i.e. alternatives to oil-based lubricants as well as the recycling/recovering of oil-based lubricants. Oil-in-water emulsions and an aqueous solution, by the producer termed a conditional emulsion, were tested where the lubricant formulation was altered to optimize the performance for hot rolling of aluminium. Cold-rolling tests were also run on steel coils, where the presence of rust protective oil was studied as well as the influence of aged emulsion behaviour compared with fresh emulsion. Finally, Sapa developed a vacuum evaporator system for recovering oil from dumped emulsion generated during aluminium hot rolling, followed by separation, centrifugation, and flocculation. The cleaned concentrates were reconditioned for reuse. The recycled and recovered emulsion was tested and compared with the original fresh emulsion in Swerea MEFOS pilot mill with results as good as the fresh emulsion.

For various reasons, manufacturers of cold-forged steel parts are becoming increasingly interested in forming at elevated temperatures below 500 °C. The objective of this study, published by the Institute for Metal Forming Technology (IFU) of the University of Stuttgart, is to evaluate the capability of various phosphate coatings in combination with MoS₂ lubrication for extrusion processes of steel parts at elevated temperatures; it emphasizes the temperature range between 250 °C and 500 °C. Temperature resistance and the lubricating effect of the tested lubrication systems were examined using the double-cup-extrusion-test. Additionally, friction factors were calculated by comparing the test results with finite-element analysis.

For cold rolling systems, in particular for tandem mills that are the major form of the process, conventional lubrication processes appear to have reached their limits. This paper proposes a new advanced lubrication concept called flexible lubrication which adjusts the friction levels at the three process time scales: the rolling campaign, the local scale (coil to coil), and the transient stages within two coils. The proposed approach is expected to increase roll campaign length, energy saving, mill capacity, and flexibility of production programming while at the same time avoiding the detrimental effects created by uncontrolled friction variations such as sudden increases in rolling force and chattering. Showing the conventional lubrication limits through a deep production analysis, this paper is then concerned with the study of the flexible lubrication concept at the laboratory scale and finally, initial results obtained in the first industrial application of this procedure are also reported.

Strip cleanliness in the industrial cold rolling mill must be controlled by optimizing the roll, strip, lubricant and process parameters. Obtained experimental evidence in this work shows which of these parameters have a significant influence on strip cleanliness. The experiments were carried out on a plate-out tester and on cold rolling pilot mills. New findings were the influence of thickness reduction on strip cleanliness: a high reduction in the first stands of a tandem mill results in poor strip cleanliness, but in the latter stands a high reduction results in a better strip cleanliness than a low reduction. Furthermore the beneficial influence of a chrome coating on the work roll was shown to be related to the better adherence of oil to this type of work roll. This article provides a concise overview of the experimental results achieved and their interpretation.