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

Summary

The 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.

Additional information

Notes on contributors

M.O.W. Richardson

Dr M. O. W. Richardson is currently a lecturer in the Department of Materials Engineering and Design, Loughborough University. He is active in lecturing, research and consultancy areas associated with composite materials, paint films corrosion and insulated building structures. He has published over 60 papers and patents, and is the author of the book Polymer Engineering Composites.

D. B. Freeman

Brian Freeman was educated at Willesden County Grammar School and London University. After National Service he joined Pyrene as a chemist in 1952. Now Technical Director he is author of many technical articles and patents in the field of chemical surface treatment and will shortly publish a book on the subject. He is currently Chairman of the BSI Technical Committee in Conversion Coatings.