Casting coating is a specialized coating applied to the surface of castings, used to improve the surface quality and smoothness of castings. It can fill the loose pores on the surface of castings, level the gaps between casting sand particles, and improve the flatness and smoothness of the casting surface. During the casting process, casting coatings can also play a role in isolation, reducing the adhesion between the casting surface and the mold material, and improving the smoothness and brightness of the casting surface. This article will provide a detailed introduction to how to use casting coatings to improve the surface quality and smoothness of castings.

Choosing the appropriate casting coating is the key to improving the surface quality and smoothness of castings. The main components of casting coatings include pigments, binders, functional fillers, and solvents. Pigments can fill the gaps between sand particles, fill the loose pores on the surface of castings, and improve the smoothness of the casting surface. Gellants can fully bond coatings with the surface of castings, forming a dense protective layer after casting. Functional fillers can improve the adhesion and filling performance of coatings, prevent coating loss and penetration into the interior of castings. Solvents are the key to adjusting the viscosity and dilution of coatings, making them easy to apply and dry.

Before using casting coatings, it is necessary to treat the surface of the castings to obtain better adhesion and smoothness. The surface of castings should be free of sand residue, oxide skin, and stains. Surface treatment can be carried out by sandblasting, shot blasting, or mechanical grinding. Secondly, it is necessary to pre coat the surface to improve the adhesion of the coating. Common pre coating methods include pickling, galvanizing, and spraying primer. Pickling can remove surface oxide scale and stains, galvanizing can form a layer of zinc on the surface of castings, improving the adhesion of coatings, and spraying primer can fill the gaps between casting sand particles, increasing the adhesion between coatings and the surface of castings.

The application method of coatings is also an important factor in improving the surface quality and smoothness of castings. Common coating methods include brush coating, spray coating, and spot coating. Brushing is a common and convenient coating method, which evenly applies paint to the surface of castings through a brush. The advantage of brush coating is that it is easy to operate and suitable for small castings and situations with a small amount of coating. Spraying is a fast coating method that evenly sprays paint onto the surface of castings through a spray gun. The advantages of spraying are a large coating coverage area, uniform coating thickness, and suitability for large castings and large-scale coating. Spot coating is a coating method that immerses castings into coatings, allowing the coatings to penetrate and adsorb evenly onto the surface of the castings. The advantage of stain coating is that the coating can fully penetrate into the interior of the casting, fill in loose pores, and improve the density and smoothness of the casting.

The ratio and control of coatings are also important factors in improving the surface quality and smoothness of castings during the coating process. The coating ratio should be selected according to the shape and size of the casting, to ensure that the coating can fully cover the entire surface of the casting. The control of coatings mainly includes the dilution, viscosity, and bonding time of coatings. The dilution and viscosity of coatings directly affect their coating performance. Excessive dilution and viscosity can cause coating loss and penetration into the interior of castings, while low dilution and viscosity can lead to uneven coating. The bonding time of coatings refers to the time it takes for the coating to form a protective layer after drying. A short bonding time can cause incomplete drying of the coating, while a long bonding time can lead to weak adhesion of the coating, affecting the quality and smoothness of the casting surface.

For the coated castings, post-treatment is also required to ensure the quality and smoothness of the casting surface. Post processing can include coating removal, grinding, and polishing. Coating removal mainly involves removing the oxide scale and stains on the surface of the coating, which can be carried out through methods such as mechanical removal, chemical removal, and sandblasting. Grinding can further improve the flatness and smoothness of the surface of castings, using sandpaper, grinding wheels, and grinding machines. Polishing is a coating treatment method that uses scraping, wiping, and polishing to make the surface of the casting mirror like, increasing the reflection and refraction of light, and improving the smoothness and brightness of the casting.

In summary, using casting coatings to improve the surface quality and smoothness of castings requires consideration and operation from multiple aspects such as coating selection, casting surface treatment, coating method selection, coating ratio and control, and post-treatment. Only by comprehensively considering these factors can the surface quality and smoothness of castings be improved to meet the needs of different engineering and applications.