In order to improve the quality of castings, refractory coatings are often used in the production process, but if used improperly, it will cause defects in the casting products. The use of refractory coatings on sand types and cores can effectively improve surface finish, control the heat transfer characteristics of castings and microstructure of castings, improve core exhaust, and prevent some defects in castings.
As with other processes, how to properly use coatings is critical in order to achieve the desired results and avoid new quality problems.
Foundry can use four methods in sand type, sand core using paint, each of the four methods have advantages and disadvantages. Brush coating: Brush the paint on the sand type can provide a good, controllable coverage. This method can be easily applied to multilayer coatings, as well as to a variety of types of coatings. This method can be well coated on the surface of the sand type sand core, for the angle or façade of the spraying has a certain help.
However, brush coating operations are labor-intensive and slow, with the result that the operator varies. Spraying: This method is faster than brushing, can easily cover large areas, and will not leave brush marks. However, as with brush coating, the spraying effect may vary from operator. Operators may ignore areas or be difficult to properly apply to deeper recesses, or they may experience excessive spraying.
Spraying solvent-based coatings can also result in emissions that are not easily collected.
Flow coating: Fast flow coating speed, less labor intensity than brush coating or spraying, easy to automate, is the best choice for large sand core and sand type, but the flow coating system needs regular maintenance. Immersion coating: Some foundries choose to immerse their sand core or sand type in the coating. This process provides good coating coverage and can be mechanized. Automatic dipping effect is uniform, consistent, very suitable for mass production.
And the artificial immersion labor intensity is large, and the speed is slow. Because the volume of water and solvents in the heating will be significantly inflated, so regardless of which method described above, it is necessary to apply refractory paint after a period of drying, the specific drying method depends on whether the coating is water-based or solvent-based.
Some solvent-based coatings can use fire to ignite combustible components in the coating to dry the coating. There are a variety of optional refractory coatings on the market, the chemical composition and formulation design of these coatings are different, the need to correctly apply according to specific process parameters in order to achieve good results, including the best coating thickness, drying time, viscosity and the dispersion of refractory particles in the solution.