The gating system is the channel in a sand mold that guides molten metal into the mold cavity. The success of the casting process depends on the properties of the metal, the characteristics of the mold, and the structure of the gating system. A well-designed gating system should be based on the structural characteristics of the casting, technical requirements, and type of alloy. The design includes selecting the type of gating system, determining the entry point, and calculating the cross-sectional dimensions.
Principles of Gating System Design
1. Guide the molten metal to fill the mold smoothly and continuously, avoiding excessive turbulence that may cause air entrapment, metal oxide inclusions, and erosion of the cores.
2. Control the flow direction and velocity during the mold filling process to ensure clear and complete casting contours.
3. Ensure that the mold cavity is filled within an appropriate time frame to prevent defects such as sand inclusions, cold shuts, or surface wrinkles.
4. Regulate the temperature distribution within the mold, facilitating solidification shrinkage, reducing casting stresses, and preventing defects like deformation and cracks.
5. Provide slag-trapping and overflow capabilities to purify the molten metal.
6. Keep the gating system structure simple and reliable, minimize metal loss, and facilitate post-casting cleaning.
The gating system of a typical casting consists of four main parts: the pouring basin, sprue, runner, and ingate.
Types of Gating Systems
There are two common methods of classifying gating systems:
1. Based on the cross-sectional proportions of the gating system components, the types include: Closed gating system, Semi-closed gating system, Open gating system, Closed-open gating system
2. Based on the relative position of the ingates on the casting (entry position), the types include: Top gating system, Middle gating system, Bottom gating system, Step gating system
In investment casting, closed gating systems and bottom gating systems are the most commonly used.
Principles for Selecting the Molten Metal Entry Point
1. Facilitate solidification and shrinkage compensation of the casting.
2. Improve the as-cast microstructure of the casting.
3. Enhance the surface quality of the casting.
4. Ensure the molten metal fills the mold cavity smoothly.
5. Minimize shrinkage stress and prevent cracks in the casting.
6. Simplify post-casting cleaning.
In gray iron sand casting, the design of the molten metal entry position should prioritize facilitating the solidification and shrinkage compensation of the casting to ensure its integrity and quality.
Post time: Jan-17-2025