1. Brushing and swabbing
2. Dip coating
3. Spraying
(1) The pressure of compressed air system is usually 500-600kpa.
(2) The droplet velocity carried by the air flow is very high, and there are many rebound after impact on the surface, which affects the surface quality of the coating.
(3) Most of the casting coatings are hard abrasives. The spray gun used for spraying can not bear its friction effect, and the nozzle is easy to wear.
(4) The deep cavity of the mold is easy to produce pressure, which leads to shielding effect and difficult spraying.
3.1 high pressure air spraying method
There are two types of commonly used spray guns: suction type and pressure type.
3.2 low pressure hot air spraying
A large amount of low-pressure air (pressure 0.035-0.07mpa), which is produced by portable turbine, is heated up to 20 ℃ higher than room temperature by friction. It is suitable for zircon powder coating with high density because of its large diameter.
3.3 low pressure spraying
The agitator is driven by a pneumatic motor and is used for spraying at a short distance (300-380mm) and a large flow rate.
3.4 high pressure airless spraying
This process uses liquid pressure to spray paint. The coating is stored in a high-pressure vessel and dispersed into small drops through a special nozzle on the spray gun. Because there is no reaction, it is suitable for deep cavity spraying and quick drying coating. .
The diameter of the nozzle is generally less than 1mm, and the flow rate is up to 4kg / min. The main flow and auxiliary flow are drawn from the paint in the container by the pump through the pipette.
4. Flow coating method
Flow coating (flooding) is a kind of low pressure casting coating method.
The advantages of flow coating are as follows: (1) fast coating, saving the working time of sand mold (core) coating compared with brush coating and spray coating. (2) The thickness of coating is uniform, and the coating quality will not be affected obviously due to the change of operators; (3) coating saving, cleaning and less environmental pollution.
5. Applicability of various coating methods
The correct application method depends on the shape, size, batch size of sand (core) and whether it is core or mold.