Michel Vermeulen

Assessment of steel surface roughness and waviness in relation with paint appearance

Abstract Paint appearance is an important factor in the overall product quality of steel sheet, especially in the automotive industry. The present paper deals with the functional behaviour of the surface texture according to paint appearance. The main results on the improvement of paint appearance of outer car body panels, obtained with coated and uncoated cold rolled steel, textured with EBT-rolls, is reviewed. There are different methods to relate steel sheet surface texture to the appearance after painting. From the literature it is found that waviness has a detrimental effect on the surface appearance after painting. Different roughness and waviness parameters are compared in order to find a good relation with paint appearance. The following surface texture parameters are evaluated in this study: roughness parameters Ra, peak count Pc, waviness parameters Wca and amplitude between 0.5 – 5mm (Fourier analysis) and envelope parameters motif W and Ra-macro, measured with a spherical stylus of radius 1.5mm. Classical parameters such as Ra and Pc are only able to evaluate paint appearance for one single texturing process, and within very limited range. The ability to predict paint appearance by Ra-macro and Wca also seems to be limited, because of their dependency on the roll texturing technique. Based on extensive testing, it is suggested that Fourier analysis might be the best approach to predict the appearance after painting, and this independently of the texturing process. The results clearly show the improved appearance of Sibetex textured sheets compared to conventional textured sheets. This is due to the fact that, with Sibetex sheet, a reduction in waviness can be achieved.

Micro-hydrodynamic effects in EBT textured steel sheet

Abstract The paper describes the tribological behaviour in the steel sheet and die contact occurring in deep drawing applications. In more detail, sheet surfaces produced by the EBT (Electron Beam Textured) process have been investigated, both theoretical and experimental. By a stepwise theoretical analysis, it is demonstrated that a substantial part of the load supported by sheet surface can be generated by micro-hydrodynamic effects on the curved hills of the sheet surface. Thereto, an original concept of dominant summits has been introduced in order to distinguish from the classical definition of a roughness “peak”. It is shown that the latter fails in explaining the experimental behaviour, both in friction and in galling. The new approach clearly demonstrates its potential for a better modelling of the tribo-behaviour.

Wear research on large-scale test specimen☆

Abstract Wear tests were performed on a large-scale test specimen, used in bearing applications with diameters up to 1 m, such as shipbuilding, off shore applications, barrage installations etc. Special designs of bearing liner, or lubrication groove patterns are impossible to scale down in classical small test specimen wear apparatus. Composite materials filled with fibres become anisotropic when using a small test specimen. Two examples of test series clearly illustrate the use and applications of a large test rig, built for loads up to 6500 kN. In one test program, the behaviour of a bronze-Inconel combination has been investigated under different conditions: dry running, grease lubrication in an ambient environment and grease lubrication in seawater. Initiated firstly by accident, the lubrication cut-off behaviour has been further investigated in detail. A comparison with small scale tests revealed that seawater had a different influence. In a second test programme, glass fibre thermoplastic discs, reinforced with a steel core, were tested running against chromium-plated steel. Wear rate was strongly influenced by contact pressure. Some remarkable temperature cycles could be observed.

3D-characterisation of EBT-steel sheet surfaces

Abstract The paper describes some results of the analysis of Electron Beam Textured (EBT) steel sheet structures by means of the parameter set, proposed by the BCR-working group. Special attention is given to the correlation between the parameters and the functional behaviour. The frictional behaviour is compared with respect to the galling tendency, as it occurs in deep drawing applications. Some aspects related to painting are discussed as well. It is found that some of the proposed parameters are closely related to functional behaviour, but others will need further refinement. For the EBT-deterministic patterns presently used in steel sheet production, it is possible to characterise them fully by three parameters for the mill rolls and by four parameters for the steel sheet produced by these rolls.

SCOUT - Surface Characterization Open-Source Universal Toolbox

Surface topography plays a significant role in functional performance situations like friction, lubrication and wear. A European Community funded research programme on areal characterization of steel sheet has recently assisted research in this area. This article is dedicated to the software that supported most of the programme. Born as a rudimentary collection of procedures, it grew steadily to become an integrated package, later equipped with a graphical interface and circulated to the research community employing the Open-Source philosophy.

Application of statistical filtering technique to single and double electron beam textured surfaces

Abstract The texturing of steel surfaces is well known to affect their functional performance. Different processes (e.g. forming, painting) are affected by different wavelengths of surface structures which, in order to study the phenomena, are usually separated through filtering processes. New texturing processes call for new filtering techniques, and amongst the latest ones, the Gram-Schmidt (GS) decomposition technique proved to be suitable for deterministic patterns such as Electron-Beam Textured (EBT) surfaces. Optimisation lead to new textures, with more dense patterns, so extending the GS methodology seemed natural and meaningful. This paper describes how the technique was algorithmically adapted and how it will benefit process control.