Vitreous Enamel - Industrial Enamel Application

Industrial Enamel Application

On sheet steel, a ground coat layer is applied to create adhesion. The only surface preparation required for modern ground coats is degreasing of the steel with a mildly alkaline solution. White and colored second "cover" coats of enamel are applied over the fired ground coat. For electrostatic enamels, the colored enamel powder can be applied directly over a thin unfired ground coat "base coat" layer that is co-fired with the cover coat in a very efficient two-coat/one-fire process.

The frit in the ground coat contains smelted-in cobalt and/or nickel oxide as well as other transition metal oxides to catalyze the enamel-steel bonding reactions. During firing of the enamel at between 760 to 895 °C (1,400 to 1,643 °F), iron oxide scale first forms on the steel. The molten enamel dissolves the iron oxide and precipitates cobalt and nickel. The iron acts the anode in an electrogalvanic reaction in which the iron is again oxidized, dissolved by the glass, and oxidized again with the available cobalt and nickel limiting the reaction. Finally, the surface becomes roughened with the glass anchored into the holes.