Porcelain enamel chipping of enamel products means that the porcelain layer is peeled off from the product in pieces, and some of the ground coat is exposed after the peeling off, and some of the metal surface of the green body is exposed. Large pieces of the porcelain layer falling off the base metal is called "peeling porcelain"; after firing and cooling, the small pieces on the surface of the porcelain layer bursting off are called "scale explosion" or "fish scale explosion".

1. Peeling porcelain

The reasons for peeling porcelain are as follows: ①The expansion coefficient of enamel frit is inappropriate, which causes large internal stress. ② If the radius of curvature is too small, excessive internal stress is likely to occur there. ③The immersion time of the iron billet is too long, and a large amount of hydrogen is produced. ④The pretreatment is not in place, the ground coat is not well infiltrated, and the adhesion is poor. ⑤The quality of the adhesive is poor or the dosage is insufficient. ⑥The enamel slurry has too much soluble salt, the enamel slurry is ground too finely, and the storage time is too long. ⑦The fuel combustion exhaust gas rushes into the burning zone and interferes with the formation of the adhesion layer. ⑧ Underburning (low furnace temperature or short time) adhesion formation is insufficient. ⑨Porcelain layer is too thick, repeated firing, and accelerated cooling. ⑩ The surface of the ground coat layer is contaminated, which makes the ground coat and cover coat poorly bonded. ⑪The semi-finished product is impacted, and the porcelain layer has cracks.

2. Scale burst

The scales are in the shape of a half moon to remove the porcelain. The width of the porcelain removal is less than 1mm, and the metal surface is not exposed, and the large ones can reach more than 10mm and expose the metal surface. Acute fish scale occurs when drying, called "process scale explosion", most of the fish scale can be seen within 3 days after firing, and some are stored for 10 days or even months before being detected.

Reasons for fish scale: The recognized cause of fish scale is hydrogen evolution from the blank metal. Hydrogen accumulates in a large amount between the iron billet and the porcelain layer or in the porcelain layer, generating high pressure and breaking the porcelain layer. The source of hydrogen: during the process of steel smelting and rolling Dissolved hydrogen, hydrogen absorbed by the steel plate during pickling, and hydrogen displaced from water during firing are dissolved in the steel plate. Other reasons for scale explosion: scorched and burnt ground coat, high ambient water vapor concentration, excessive high temperature viscosity of the ground coat, and poor clay quality.

The prevention of fish scale mainly includes the following measures: ① Selection of steel plate: first choice of special steel for enamel, second choice of non-continuous casting cold-rolled plate, hot-rolled plate is more likely to produce scale and explosion. ②Surface treatment should not be pickled, less pickled, fast pickled, and corrosion inhibitor should be added during pickling. ③Choose a ground coat combination with moderate high temperature viscosity. ④ Add quartz, carbonate, potassium chlorate, and high-quality clay appropriately. ⑤ Reasonable firing, do not burn or burn the ground coat. ⑥ Use appropriate anti fish scale agent, but the amount should be controlled, otherwise the porcelain surface will be boiled, there will be many pinholes, and the enamel coating performance of the enamel slurry will deteriorate.