Adhesion of enamels

Adhesion of Enamel to Steel. Cobalt compounds are used both to color and to enhance adhesion of enamels to steel (55). Cobalt oxide is often incorporated into the ground frit at rates of 0.5—0.6 wt %, although levels from 0.2 to 3 wt % have been used. The frit is fired for ten minutes at 850°C to give a blue enamel that is later coated with a white cover coat. 

No special strict requirements are put forward with respect to cast iron composition because in this case adhesion of enamel is of a mechanical nature. The carbon content is usually 3.4 —3.7%, of which 2.5 —3.0% is in graphite form. The base material should be mostly pearlitic, since free cementite in the form of larger crystals is responsible for bubble formation by oxidation. The quality of enamels is adversely affected by sulphur. 

Adhesion of enamel coatings. The dried coaling is porous so that it is permeable... 

---