The coated sand casting

The coated sand casting process is a commonly used method in metal casting. It involves covering the surface of the mold with a layer of special coating material to improve the surface quality of the castings and enhance production efficiency. This article introduces the basic principles, advantages and disadvantages of the coated sand casting process, as well as a detailed explanation of its process.

1. Basic principles of coated sand casting:
   The basic principle of the coated sand casting process is to cover the traditional sand mold with a layer of coating material, which can be a special thermoplastic or thermosetting material. This coating forms a protective layer during the casting process, preventing direct contact between the metal liquid and the mold material, and protecting the sand core material from being eroded by the metal liquid, thereby improving the surface quality of the castings.
2. Advantages and disadvantages of coated sand casting:

Advantages:

Improved surface quality: Coated sand casting reduces defects such as pores and shrinkage, improving the surface quality and accuracy of the castings, and reducing the need for subsequent machining processes.

Enhanced mechanical properties: The coating layer prevents the reaction between the metal liquid and the mold material, reducing the generation of impurities and gases, thus improving the mechanical properties of the castings.

Increased production efficiency: Compared to traditional sand casting processes, coated sand casting requires no drying or other pre-treatment processes, saving time and cost and enhancing production efficiency.

Disadvantages:

Higher cost: The use of special coating materials increases the cost of coated sand casting compared to traditional sand casting.

More complex process: Coated sand casting requires the preparation and coating of the coating layer on top of traditional casting processes, requiring operators to have certain professional knowledge and skills.

III. Process of coated sand casting:
The process of coated sand casting mainly includes the following steps:

Preparation of cores: Prepare the required cores according to product requirements.

Preparation of molds: Mix the coated sand with a binder to prepare the mold used for casting. The coated sand is uniformly applied to the mold surface.

Coating treatment: After applying the coating to the mold, use a dedicated coating machine or other methods to process the mold to form a uniform and strong coating layer.

Pouring of metal liquid: After the coating layer is dried, pour the metal liquid into the mold to fill the entire cavity.

Cooling and solidification: After the metal liquid cools down, the mold and cores gradually solidify, forming the overall structure of the castings.

Shakeout: After solidification is complete, shake and remove the mold, then remove the sand cores, resulting in the castings.

Post-processing: Inspect the castings for dimensions, surface quality, etc., and then perform necessary post-processing such as deburring and trimming.

Coated sand casting has various derived variants and improvements in practical applications. These variant processes can be selected based on different requirements and material characteristics. Two common variants are:

Cold-box coated sand casting: In this process, the coating material is directly sprayed onto the surface of the cold, hard mold without the traditional hot mold pre-treatment. This process is suitable for materials with poor heat dissipation or special casting requirements. It significantly reduces the process temperature, improves production efficiency, and saves energy.

Continuous coated sand casting: This process combines continuous sand belts with coating equipment to achieve continuous production. The sand is continuously coated with the coating material as it moves along the conveyor belt, forming a continuous sand mold. The advantage of this process is high production efficiency, making it suitable for large-scale and continuous production requirements.

In summary, the coated sand casting process provides an effective way to improve the quality of castings and enhance production efficiency. Despite its higher cost and certain process complexity, its advantages are still highly valuable in many casting applications. With continuous advancements and innovations in science and technology, we can expect further breakthroughs and improvements in the development and application of coated sand casting in the future.