Influence of Gating System Design (Filling Speed and Feeding Capacity) on Shrinkage Cavities and Porosity

If the filling speed of the gating system is too fast (> 1.5 m/s), it is prone to cause splashing and gas entrainment of molten iron, forming oxidative slag inclusions; if too slow (< 0.5 m/s), it may lead to cold shuts and incomplete filling. Additionally, insufficient riser size (height < 2 times the wall thickness of the casting) or improper positioning can result in inadequate feeding of thick sections, forming shrinkage cavities (diameter > 5 mm) or shrinkage porosity (aggregation of micro-voids). Typical Defects:Shrinkage cavities mostly occur at the hot spots where the casting solidifies last (such as the root of flanges or junctions of rib plates), presenting as irregular holes with rough inner walls; shrinkage porosity appears as cloudy low-density areas under X-ray inspection, reducing the casting’s airtightness and fatigue strength. 

Control Points:Adopt an "open gating system" (total area of inner runners > 1.5 times that of the sprue) to match the filling speed with the casting structure: 1.0–1.2 m/s for thin-walled parts and 0.8–1.0 m/s for thick-walled parts. For riser design, follow the "feeding distance" principle: the diameter of cylindrical risers should be ≥ 1.5 times the diameter of the hot spot circle, with a height 1.2–1.5 times the diameter. Meanwhile, set up 0.5 mm deep feeding channels below the risers to enhance feeding efficiency by 40%, reducing the shrinkage cavity defect rate from 8% to below 1%.