There are two processes for enamelling of plate heat exchange elements: wet and dry, both of which are applied at one time.

Wet enamelling is divided into dip enamelling, flow enamelling and electrostatic spraying. Dipping enamel has manual dipping and mechanical dipping.

1. Pre-treatment: In addition to the conventional alkaline degreasing, ultrasonic degreasing has been widely used in the pre-treatment of heat exchange components. In order to increase the adhesion strength of the product, reduce the pinhole rate, and lower the firing temperature, the metal body of the heat exchange element can also be coated with nickel.

2. Preparation of enamel slurry: the enamel slurry used in wet enamelling is made by mixing 2~3 enamel frits with different melting values ​​and expansion coefficients.

Examples of grinding ratios such as dipping enamel slurry ratio: mixed frit 100%, clay 5.0~6.5%, bentonite 0.1~0.2%, boric acid 0.2~0.3%, calcined quartz 10~15%, sodium nitrite 0.1~0.2% , Water 50%; grinding fineness 100ml enamel slurry•180 mesh sieve residue 3~4g.

Electrostatic spraying enamel slurry ratio: mixed frit 100%, clay 5.0~6.5%, bentonite 0.3~0.4%, boric acid 0.2~0.3%, calcined quartz 10~15%, sodium nitrite 0.1~0.2%, water 50%; Grinding fineness of 100ml enamel slurry•180 mesh sieve residue 0.5~1.0g.

3. Enameling: During dipping, if the fluidity of the enamel slurry is too large, it will cause a large difference in the thickness of the porcelain powder layer at the upper and lower ends of the plate heat exchange element. The edge of the half is easy to burn. At this time, a small amount of 40% sodium aluminate solution can be added to adjust. If the fluidity of the enamel slurry is too small, it can be mixed with a fluid enamel slurry, or a small amount of sodium pyrophosphate, oxalic acid and other enamel slurry decoagulants can be added for adjustment.

Whether it is manual dipping or mechanical dipping, the wrapping rate of the porcelain layer on the edge will be lower. In order to make up for the insufficient edge wrapping rate, manual piping can be done after the product is dried.

The workpiece is grounded during wet electrostatic spraying, and the atomized enamel slurry is negatively charged in the 60~120kV electrostatic field and is adsorbed on the surface of the workpiece. The plate-type heat exchange element positioning plate will produce Faraday shielding during electrostatic spraying. When the electrostatic voltage is too high, it will easily cause the coating in the groove of the positioning plate to be too thin and fail to meet the quality requirements.

The enamel slurry used in wet electrostatic spraying will have a certain amount of moisture volatilized after atomization. If the moisture volatilizes too fast, it will cause the workpiece to be sprayed with a thick and uneven adsorption layer, resulting in defects such as bubbles and black spots on the porcelain layer. Therefore, the wet method Electrostatic spraying requires the relative humidity in the spray booth to be controlled at about 70%.