The Properties of Steel Enamel Ground Coat

Enamel ground coat is divided into single frit ground coat and mixed ground coat. According to the classification of use, it is also divided into cast iron enamel ground coat and steel enamel ground coat. The ground coat of steel enamel is usually enamel fired on the steel at 820~870℃. If the temperature is too high, the steel will be deformed and the oxidation will increase, making it difficult to control the quality of the enamel product.

The ground coat of steel enamel must have the following properties:

1. Fully adhere to the surface of the steel.

2. Good fluidity at the firing temperature.

3. Wide firing temperature range.

4. The thermal expansion is appropriate, and it is not easy to produce cracking or large deformation after firing.

In order to strengthen the adhesion between the ground coat and the steel, a blue ground coat containing 0.3~0.6% cobalt oxide is usually used, and 1.5% manganese oxide and 0.4% nickel oxide are added to increase the adhesion. However, when all the oxides replace the cobalt oxide, the binding force is reduced.

There are many reasons why a small amount of cobalt oxide promotes the adhesion of the ground coat and the steel. 1. The enamel frit added with cobalt oxide can corrode the iron surface and cause the surface to be uneven and rough, thus strengthening the adhesion between the enamel and the steel. 2. During firing, a small amount of iron oxide dissolves into the ground coat. If the ground coat contains cobalt oxide, the dissolved concentration can be controlled to produce the best conditions for the ground coat to be closely attached to the steel.

The ground coat of steel enamel softens and flows at the firing temperature of 820~870℃, and infiltrates the surface of the steel. In order to prevent large distortion in the ground coat layer when cooling after firing, the expansion coefficient of the ground coat of steel enamel should be higher than that of the steel. Slightly smaller, because when the temperature is above 400℃, the expansion coefficient of the steel enamel ground coat is large, and the low temperature expansion coefficient is averaged, and the two are about the same.