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Title

WORK ROLL ROUGHNESS TOPOGRAPHY AND STRIP CLEANLINESS DURING COLD ROLLING AUTOMOTIVE SHEET.

Authorship

Gaspard, Claude; Cavalier, Daniel; Wahlund, Stefan

Gaspard, Claude

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Cavalier, Daniel

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Wahlund, Stefan

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DOI

10.5151/9785-9785-32212

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Abstract

A point of great importance of the cold rolling process for automotive sheet is the cleanliness of the STRIP. This is particularly critical when batch annealing with poor efficient cleaning lines. in these specific cases, pollution of the strip surface could be prohibitive when rolling in the early stands of tandem mill with conventional forged rolls as ground: the strip cleanliness strongly deteriorates during rolling mainly with high roughness rolls and iron fines coming from the strip surface are progressively sticking on the sheet. it is well known that chrome plating the conventional forged rolls in the early stands delays the onset of strip cleanliness degradation during rolling. this paper summarizes the results of 3d surface roughness topography study on forged work rolls with and without chrome plating combined with sheet cleanliness measurement during rolling. it shows that a well determined topography has to be obtained on the work rolls used in early stands in order to roll in the mixed lubrication regime minimizing the friction coefficient and therefore optimizing the cleanliness of the rolled sheet. the main roughness parameters to take into account for that purpose are the roughness level SA and even more the kurtosis parameters Sk, SPK, SVK, SSK and SKU. THE IDEAL SURFACE MORPHOLOGY PROMOTES DEEP VALLEYS TO THE DETRIMENT OF PEAKS, LEADING TO A ROLL SURFACE CAPABLE TO RETAIN / TRAP Oil in the valleys while peaks are minimize reducing the abrasive effect in the roll bite and consecutively the amount of iron fines produced. To achieve such objective, new grinding wheel technologies are currently developed in partnership with wheel manufacturers to create such ideal morphology of roughness well adapted to forged HSS ROLLS.

Keywords

Surface Roughness - Sheet cleanliness - forged hss rolls