VARNISH DELAMINATION IN TINPLATE CUTTING AND DRAWING OPERATIONS: MINIMIZATION THROUGH APPLICATION OF FRACTIONATED EXPERIMENT DESIGN

Abstract

The aim of this work is to avoid varnish delamination during cutting and drawing operations, which are carried out in the manufacturing process of tinplate lids for cans intended for food storage. Delamination, which occurs in the periphery of tin discs during the cutting operation, generates a varnish “thread” that can be thicker than 200 ?m and may adhere to the cutting tool, compromising product quality and productivity. As a consequence, lengthy production downtimes for tool cleaning operations are required. By means of optical or electronical microscopy it is possible to determine the amount of varnish adhered to the tool, as it is directly related to the depth of the delamination layer. The experimental methodology followed a fractioned Design of Experiments with 8 factors, 2 levels and resolution IV. The research was carried out in an industrial scale and studied parameters were those inherent to the manufacturing process. It is concluded that the depth of the delamination layer is uneven and manifests two different behaviours depending on the direction: one in the direction of the fabrication line and other in the opposite direction. The factor with greater influence over the depth of the delamination layer is the stamping pressure. If the stamping pressure decreases, the thickness of the detached varnish thread also decreases. Tin plate thickness resulted to be another important process variable, being smaller thicknesses beneficial. A thicker varnish layer (amount of varnish applied) and a specific curing treatment are possible solutions to counter the deleterious effects of high stamping pressure and thicker tinplates respectively. Keywords: Varnish Delamination, Tinplate, Cutting, Drawing, Design of Experiments