Although the manufacturing process of various enamel products is similar, the enamel of water heater inner tank has many specialties compared with ordinary enamelware, especially the manufacturing process, material requirements and equipment for manufacturing water heater inner enamel, etc.

1. Surface treatment

There are two commonly used surface treatment methods for water heater enamel inner tanks:

The first is surface chemical cleaning and degreasing and sulfuric acid derusting and surface roughening. The traditional immersion type has very low cleaning efficiency on the inner surface. An ultrasonic generator can be installed in the washing tank to improve the cleaning efficiency. Operators on site should do some protection for their ears.

2. Enamel coating

The commonly used coating methods for water heater inner tanks are as follows:

① Dry powder electrostatic spraying. The inner tank of the water heater is hung on the conveyor chain hanger and transported to the spray gun in a rhythmic manner. The spray gun rises vertically into the inner cavity, and the up and down movement is controlled by PLC. Product rotation. After spraying, the spray gun is withdrawn, and the inner tank is pushed into the conveyor line of the firing furnace by the accumulation chain.

②Wet vertical hanging spray method. The inner tank of the water heater is hung on the conveyor chain, which is similar to the production process of dry powder electrostatic spraying. After spraying, the enamel product enters the drying room to dry, and then enters the furnace for firing.

③Wet horizontal spraying method. The inner tank of the water heater is placed horizontally on the conveyor. The conveyor runs in a rhythm, the spray gun enters and exits the inner cavity of the water heater, and the trajectory and the amount of enamel spray are controlled by PLC. The inner tank rotates on the conveyor. The finished sprayed products must be ferryed to the kiln conveyor chain for drying and firing by manual or mechanical hands.

④ Wet single-head or multi-head roll coating method. Two sets of self-rotating shafts are installed on a frame that can swing vertically and horizontally. Each shaft is equipped with two supporting wheels. The inner tank of the water heater is placed on the supporting wheels and can be rotated. The speed can be adjusted steplessly. The enamel slurry is injected into the inner tank of the water heater through a pump, and the inner tank embryo body rolls so that the enamel slurry is coated on the inner wall. The excess enamel slurry flows into the recovery tank through the lower opening when the swing frame gradually becomes vertical. The swing times and swing speed of the swing frame can be controlled and adjusted by PLC to ensure that the thickness of the ceramic layer in the inner cavity meets the requirements. By placing multiple rotating shafts on the swing frame, multiple water heater inner tanks can be rolled at the same time.

3. Drying and firing

① Dry. Water heater inner tank wet coating is to apply enamel slurry on the inner wall of the tank, the water is not easy to evaporate, if it is dried at a higher temperature, it will cause bubbles or the surface of the porcelain enamel layer is rough. Generally, hot air is blown into the inner tank for drying. Lower drying temperature is good for the smooth and clean porcelain enamel surface, but the drying time should be appropriately extended to ensure that the enamel layer is fully dried. The speed of dry hot air is generally above 5m/s. It is better to send hot air into the bladder continuously.

② Firing. The inner wall of the water heater has a thick steel plate, and the inner wall of the enamel layer is dark. The heat conductivity of the steel plate is good, and the temperature uniformity of the whole wall is better. The firing temperature of the inner tank depends on the type of porcelain enamel used, and the firing time requires that after reaching the best firing temperature, the constant temperature time should be determined according to the size of the product and the type of enamel.