Pretreatment and cathodic electropaint performance-use of the “ ratio”

Abstract

SummaryThe use of the ratio in predicting the corrosion performance of phosphated steel when coated with cathodic electroprimer and paint is discussed. Attention is drawn to the problems associated with adequately defining the ‘ratio ‘, its calculation and its broader relevance. Other factors contributing to corrosion resistance are highlighted in terms of method of phosphate application, bath working temperature, bath chemistry and chromium after-rinsing, etc. and it is suggested that these parameters may mask the effects due to relative hopeite and phosphophyllite contents. Attention is drawn to the strict definition of ratio and the fact that high levels are not always associated with good protection from corrosion.