SURFACE-TREATMENT OF STEEL FOR STRUCTURAL ADHESIVE BONDING

Methods of surface preparation of steel for adhesive bonding are reviewed. With advanced adhesives joints of unprepared oily steel can prove very strong, but for durability in adverse environments one must remove all contamination and provide a new, chemically active surface of high surface energy. Degreasing, organic or inorganic, can improve the characteristics of the bond, but even better results can be achieved by mechanical removal of the outer, inactive contaminated layer. Specially formulated chemical etching (with a nitric-phosphoric acid solution) can produce a receptive and active substrate surface for the adhesive that results in both high initial strength and good durability. On the basis of the available information, mechanisms of bond formation and deterioration in humid atmospheres are clarified and suggestions for the improvement of durability are discussed.