The casting molds of gravity casting are mainly divided into four types: wet mold, dry mold, surface dry mold, and self hardening mold. The selection of each casting mold needs to be determined based on factors such as the weight, structure, and quality requirements of gravity casting parts, production batch size, and workshop production conditions.
1,2,1-Wet type is preferred. Wet casting is the most widely used type of gravity casting mold. The basic characteristics of wet casting method are that sand molds do not require drying and there is no hardening process. Its main advantages are high production flexibility, high productivity, short production cycle, easy organization of flow production for gravity casting parts, easy implementation of mechanization and automation in the production process, and low material cost. However, due to its high moisture content and low strength, gravity castings are prone to defects such as sand scars, rat tails, sand sticking, porosity, sand holes, and sand expansion. They are mainly used for mechanized production of small and medium-sized gravity castings. Wet type should pay attention to the following situations when using:
When the casting has a large horizontal wall during pouring, using wet molds can easily cause sand inclusion defects, and other sand molds should be considered.
When the gravity casting is too high and the static pressure of the metal exceeds the compressive strength of the wet mold, dry sand mold or self hardening sand mold should be considered.
When placing a large amount of cold iron inside the mold, wet molds should be avoided. Due to the rusting or cooling of the cold iron, water droplets may condense and cause porosity defects after pouring. If it is necessary to use cold iron, it should be preheated in advance and poured into the mold in a timely manner after being placed in the mold.
Gravity cast parts that require a long molding process or a long waiting time for pouring should not be wet molded, as placing the wet mold for too long will air dry, reduce surface strength, and are prone to sand flushing defects.
1.2.2-The characteristics of dry casting are high strength, good fire resistance and breathability, easy to ensure casting quality, but long production cycle and high cost. Dry casting is generally suitable for single piece or small batch production of gravity casting parts, as well as large, heavy, complex shape, and high technical requirements of gravity casting parts.
1.2.3-Surface dry molding is a casting process where only the surface layer is dried and poured after the sand mold is made. It overcomes some of the drawbacks of dry casting, maintains some of the advantages of dry casting, reduces costs, and improves productivity. It is commonly used in the production of large and medium-sized gravity castings.
1.2.4-Self hardening mold is a casting mold that hardens by the chemical reaction of the molding material itself after the sand mold is made, and generally does not require baking or low-temperature baking. Its advantages are high strength and high accuracy. In recent years, the application of hard gravity castings in production has become increasingly widespread.
