The process of coated sand involves mechanically blending powdered thermosetting phenolic resin with sand and then curing it through heating. Subsequently, coated sand is produced by using thermoplastic phenolic resin, latent curing agents, and lubricants through the coating process. When coated sand is heated, the resin on the sand particles melts, and under the effect of the methylene released by the curing agent, the molten resin transforms from a linear structure to an immobile, solid structure, thereby solidifying and shaping the coated sand. Next, I will introduce the relationship between the casting mold of coated sand and temperature.

Film-coated sand is produced through either cold or hot methods. Due to the simpler process of hot film-coated sand manufacturing, it offers superior surface quality, clean sand mold contours, and good strength and fluidity. Consequently, the hot film-coating process is predominantly chosen for its production.

The thermal process involves initially heating the raw sand to a specific temperature, followed by mixing it separately with resin, uric acid solution, and calcium stearate, and then cooling, crushing, and sieving the mixture. The processing steps of the thermal process demonstrate the importance of temperature control for the raw sand.

The film-coated sand heating temperature ranges from 200-300°C, with a curing time of 30-150 seconds and an injection pressure of 0.15-0.60 MPa. Therefore, during the processing process, it is necessary to control the strength of the film-coated sand to reduce the gas generation and improve its dispersibility.

However, for the simplified shape cores and the good fluidity coated sand, a lower sand injection pressure can be chosen. For thin cores, a lower heating temperature is preferred. When the heating temperature is low, the curing time can be appropriately extended.

The molding temperature of coated sand is one of the main factors affecting shell thickness and strength, typically controlled around 220-260°C, providing the necessary heat for the resin softening and curing on the coated sand; ensuring the shell thickness meets requirements without carbonization on the shell surface; and attempting to shorten the shell formation and hardening time to enhance productivity.