Development of One-side Galvanizing Process Using Stop-off Coating Method in Continuous Inline-anneal Type Hot Dip Galvanizing Line

Abstract

A new method of one-side galvanizing using a suitable stop-off coating in continuous inline type hot dip galvanizing line (CGL) has been developed. The stop-off coating is a water slurry comprising of water glass, alkali, H₃BO₃ and MgO or Mg(OH)₂. The process is a continuous stepwise treatment system of cleaning-coating of the slurry-firing (combined with anneal)-galvanizing-removing of stop-off coating film.
One-side galvanized steel manufactured by this process offers a good corrosion resistant material for automobile body. Galvanized side of the product has good corrosion resistance and strong sacrificial corrosion protectability as a conventional galvanized steel sheet. These properties are effective in controlling aggressive local corrosion such as 'perforation' at the inside surface of auto body. The bare steel surface on the reverse side has good appearance similar to the conventional cold rolled steel sheet and better rust resistance, phosphatability and higher resistance against under-film corrosion. This superior corrosion resistance of the bare side of the one-side product originates in its exceptionally pure surface layer which is caused by cleaning action of the stop-off coating during annealing in CGL.