Abstract:

Since the surfaces of painted steel sheet materials reveal the final quality of the product in sectors such as automotive, white goods, etc., it is one of the important factors that the consumer takes into account. Steel sheet materials used in these sectors are generally produced as rough in the last step of the cold rolling manufacturing process in terms of dyeability and shaping. The roughness profile on the surface affects the paintability of sheet materials. At the same time, since sheet materials can be supplied in different roughnesses, it is obvious that their adhesion strength and paintability are different. In addition, rolling parameters and surface roughness parameters affect the adhesion strength and paintability of paints and coatings to the material surface. In this study, the effect of reduction ratio of skin-pass rolling on the paintability of HC420LA sheet materials was investigated. Firstly, the sheet material samples were subjected to skin-pass rolling process with different crushing amounts. The roughness parameters of the surfaces of the skin-pass rolled HC420LA sheet material samples were determined. Steel sheet materials rolled with different crushing amounts and having different roughness are coated with polyurethane acrylic based paint. Finally, the adhesion strength of the painted surfaces, thus their ability to be painted, were obtained from the cross-cut test. As the reduction ratio of skin-pass rolling increased, changes occurred in the roughness profile of the surface. It was determined that the adhesion strength of the paint decreased as the reduction ratio of skin-pass rolling increased (in the range of 0-1%) and the adhesion strength of the paint increased with an increase above 1% reduction ratio. It was concluded that the peaks heights (Rpk) and valleys depths (Rvk) were highly effective on the adhesion strength of the paint.

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