In the industry, the enamel without ground coat(one time enamelling) is called the direct-on enamel process. The direct-on enamel is directly applied to the steel without additional enamel ground coat, which can save raw materials and shorten the process of applying the enamel layer. The direct-on enamel method is especially suitable for parts with a simple structure, which are not subject to high mechanical force and high heat during use. The most suitable steel for enamelling is zero-carbon steel with a small amount of titanium. The carbon content is 0.0001~0.0003%, and it has undergone special heat treatment, which prevents bubbles, burnout and other defects in the one-step enamelling process.

Titanium steel is too expensive for mass production. Although zero-carbon steel is a little more expensive than standard steel, it reduces the amount of enamel frit and the simplification of the enameling process. The cost is also very cost-effective.

The technical attention of the primary enamel method is to be careful when equipping the metal surface, because when the conventional enamel ground coat contains cobalt, the enamel reacts with the metal surface to produce bonding force. If one-time enamelling process is used, it will give the metal surface a certain degree of brittleness, and coat a layer of metallic nickel on the steel plate to prevent excessive oxidation and improve the bonding force. At the same time, the firing temperature should be increased by 20~40℃ during one-time sintering.