Role of Nickel Dip in Enameling of Sheet Steel

Abstract

An investigation was made of the effects of (a) the firing time and (b) the weight of nickel deposited from the nickel‐dip solution on the adherence developed by a cobalt‐free and a cobalt‐bearing ground‐coat enamel on both enameling iron and a titanium‐bearing low‐carbon steel. At 1550°F. the nickel improved the measured adherence index the most during the 2‐minute firing. The effect of the nickel, however, decreased markedly with longer firing times. There was an optimum nickel deposit for maximum adherence, an optimum that varied from 50 to about 120 mg. per sq. ft., depending on the type of cleaning used and on the type of enamel applied. The nickel dip reduced the tendency to fish‐scale. Furthermore, there was an apparent relation between fish‐scaling resistance and good adherence; no specimen with an adherence index of 70 or above showed fish‐scaling tendencies. Metallographic studies of the interface of coated specimens showed that nickel dipping of the steel before enameling brought about a surface roughening during the firing operation. A relationship was noted between the degree of roughening and the measured adherence index. The roughening of the steel surface was ascribed to galvanic corrosion.