Many enamel factories found focal points or pitting on the porcelain surface after firing the ground coat of the enamel products, which seriously affected the quality of the products. What should I do in this situation? Based on 26 years of experience in the enamel industry, Xiaonuo has classified and summarized several common enamel pitting defects and analyzed the causes and solutions. All colleagues are welcome to communicate and give advice.

The enamel pitting phenomenon can be divided into concave coke pitting, convex coke pitting and Yin pitting according to the performance of the porcelain surface.

Concave coke pits are concave coke pits on the porcelain surface of enamel products after the ground coat is fired, which is generally caused by low furnace temperature, thin enamel ground coat, and long firing time. Or the melting time of the ground coat is too old, the softening temperature of the ground coat is high, and the nature is relatively hard. In this case, it is best to improve the temperature by increasing the furnace temperature, adjusting the consistency of the enamel slurry, controlling the degree of melting of the ground coat, lowering the softening temperature of the ground coat, and adding an appropriate amount of alkaline water.

Convex coke pits are focal points or coke spots that appear on the porcelain surface of enamel products after the ground coat is fired. Generally, it is caused by the rough structure of the thin steel plate, the surface treatment of the iron billet, the small bulk density of the enamel ground coat, the high firing furnace temperature, the low softening temperature of the ground coat, and the soft performance. We need to clean the surface of the iron billet, increase the bulk density of the ground coat, and control the firing temperature to prevent burning. Adjust the composition of the ground coat and increase the softening temperature.

Concave pits are pits that are not burnt after the enamel ground coat is fired. It may be that the magnesium sulfate content is too high during pulp mixing, the drying temperature is too low, the time is slow, or the iron billet is not rinsed after pickling, leaving residual acid. At this time, it is necessary to control the amount of magnesium sulfate and add an appropriate amount of sodium nitrite aqueous solution. Increase the drying temperature, shorten the drying time, and rinse the iron billet clean.

When the focus of enamel products occurs, in addition to the pretreatment of iron billets, improper control of firing time and temperature, etc., it may be that the quality of the enamel ground coat does not meet the requirements. When enamel manufacturers buy enamel frits, they need to pay attention to whether the enamel ground coat has good adhesion, large firing range and high elasticity, especially whether it has a good porcelain surface after firing. Defects such as hemp bubbles, focal spots, and cold explosions.