One layer of refractory coating hung on the outer surface of the foam plastic model is one of the three key technological factors in the lost foam casting process. External coating is the key factor to reduce casting surface defects and prevent other defects.
The foam plastic model is buried in the sand box. Although the material in the sand box has been wrapped around the foam model, the shape of the material is almost spherical. In fact, the contact between the materials is also a point contact rather than a surface contact, which results in many small gaps between the materials. In addition to the effect of vacuum pumping, the liquid metal is very easy to enter the mold gap, resulting in product fleshy phenomenon and casting failure. Therefore, usually before the expendable pattern is cast, a refractory coating is coated on the exterior surface of the foam mold. The purpose of this is:
① At room temperature, the strength and stiffness of the plastic model can be effectively improved, which can prevent the model from deformation or damage by dry sand in the process of transportation between processes and sand filling vibration, so as to ensure the stability of the cavity.
② During liquid metal pouring, the fire-resistant coating of lost foam casting can effectively separate the liquid metal from the molding sand, so as to effectively prevent the liquid metal from penetrating into the molding sand and causing unnecessary chemical reaction with it, so as to effectively prevent the defects such as sand sticking and sand holes of product castings, and greatly reduce the occurrence of mold collapse.
One layer of refractory coating hung on the outer surface of the foam plastic model is one of the three key technological factors in the lost foam casting process. External coating is the key factor to reduce casting surface defects and prevent other defects.
The foam plastic model is buried in the sand box. Although the material in the sand box has been wrapped around the foam model, the shape of the material is almost spherical. In fact, the contact between the materials is also a point contact rather than a surface contact, which results in many small gaps between the materials. In addition to the effect of vacuum pumping, the liquid metal is very easy to enter the mold gap, resulting in product fleshy phenomenon and casting failure. Therefore, usually before the expendable pattern is cast, a refractory coating is coated on the exterior surface of the foam mold. The purpose of this is:
① At room temperature, the strength and stiffness of the plastic model can be effectively improved, which can prevent the model from deformation or damage by dry sand in the process of transportation between processes and sand filling vibration, so as to ensure the stability of the cavity.
② During liquid metal pouring, the fire-resistant coating of lost foam casting can effectively separate the liquid metal from the molding sand, so as to effectively prevent the liquid metal from penetrating into the molding sand and causing unnecessary chemical reaction with it, so as to effectively prevent the defects such as sand sticking and sand holes of product castings, and greatly reduce the occurrence of mold collapse.
③ Lost foam casting external coating can adsorb or permeate the decomposition residue of foam plastic mold, so that the decomposition products and residues of foam plastics can be effectively discharged during the casting process, so as to prevent casting defects such as carbon defects and blowholes.