Enameling of Inner Tank of Enamel Water Heater

Generally speaking, there are two methods for coating the inner tank of enamel water heater: wet method and dry method.


The wet process mainly includes spraying, dipping and rolling enamelling. By rotating the inner tank of the water heater in a three-dimensional space, all the internal surfaces are coated with enamel slurry. Excess residue and liquid must be removed to ensure that the steel surface is covered with only a thin, uniform and continuous enamel slurry. There are many factors that affect the quality of enamel, such as the viscosity of the enamel slurry, the pretreatment of steel, the adhesion of the metal surface, the quality of welding, and the structure of the inner tank.


The dry method is mainly electrostatic spraying. Compared with wet system, electrostatic spraying has many advantages. It reduces costs, saves energy, and the material utilization rate can reach 97%. In addition, it also reduces environmental pollution. At present, some large-scale water heater manufacturers basically all adopt electrostatic spraying dry method.


Most water heater manufacturers only spray a layer of enamel. Only for some applications with harsher temperature and pressure conditions, such as water tanks, two-layer spraying is used. Some use a special pre-coating to cover the enamel frit.


When the inner pot of the enamel water heater is at 700°C, it begins to melt and form a porcelain layer. The firing temperature is generally maintained at 830~860, and the time varies from 7 to 15 minutes. The red-hot inner pot was taken out of the furnace and gradually cooled to room temperature. Usually the firing process is continuous and can be repeated once more to form a second layer of enamel. It is even repeated many times to obtain the multi-layer enamel required under harsh application conditions.