No abstract

Purpose The last stage of the cold rolling process is skin-pass rolling and one of its most significant goals is to obtain appropriate topography on the surface of the sheet steel used extensively such as in automotive industry. The purpose of this paper is to investigate the effect of thickness change and various reduction ratios on roughness transfer of DC04 grade sheet material. Design/methodology/approach DC04 grade sheet materials with different reduction ratios and several thicknesses were subjected to skin-pass rolling process in the rolling equipment with a two-high roll. Some roughness parameters were determined as a result of roughness measurements from the surfaces of roughened sheet materials. Findings While the roughness transfer is higher in 1-mm thick material in reduction ratios up to 430 micrometers; in reduction ratios above 430 micrometers, it is higher for 1.5-mm thick materials. As the reduction ratio increases in DC04 grade sheet materials, the homogeneity of the roughness distribution in 1-mm thickness sheet material deteriorates, while the roughness distribution in 1.5-mm thickness sheet material is more homogeneous. Originality/value This paper demonstrates how material thickness and reduction ratio affect the roughness transfer in skin-pass rolling. The results obtained can be used by optimizing in manufacturing processes.

This study investigated the surface roughness characteristics of rolls textured using the Shot-Blast Texturing and Electro-Discharge Texturing methods. The rolling tests were carried out in an actual cold rolling mill tandem line, and the surface roughness transferred from the roughened rolls to the material with these two methods was examined. The study measured and compared the surface roughness of roughened rolls and the materials rolled by them. The study observed that the transfer ratio of electro-discharge texturing rolls was higher, but the transfer ratio of SBT rolls increased towards the end of the rolling campaign. The study also examined the extent to which the surface roughness of the rolls changed after rolling. Therefore, the level of reduction and how much was preserved were determined by comparing the surface roughness of the rolls before and after the rolling campaign. Shot-blast texturing rolls were found to have lost 53% of their roughness while electrodischarge texturing rolls lost only 33%.

When producing cold-rolled steel sheets, the penultimate annealing process is followed by a final skin-pass rolling (or temper rolling) whose purpose is to eliminate any discontinuous yielding which creates stretcher-strain markings when the steel sheets are formed. To find out the critical reduction ratio eliminating the discontinuous yield phenomenon, the samples were annealed at 820°C for 3 min and then subjected to the temper rolling at various thickness reductions at room temperature. Results showed that the discontinuous yield phenomenon could not be eliminated in the case of a thickness reduction less than 0.5%, that a certain reduction ratio should be exceeded to eliminate the discontinuous yielding, and that the aging time varied depending on the reduction ratio. In addition, while the low-carbon steels did not undergo strain aging in three months with a 1% thickness reduction, they underwent strain aging in at least four months with higher thickness reductions.