Shrinkage porosity
(aluminum casting)
Defect characteristics: shrinkage porosity of aluminum castings generally occurs at the thick part of the root of the flying riser near the inner sprue, the thickness transition of the wall and the thin wall with large plane. When as cast, the fracture is gray, light yellow, gray white, light yellow or gray black after heat treatment. It is cloud like on the X-ray film, and serious filamentous shrinkage and looseness can be found by X-ray, fluorescence low magnification fracture and other inspection methods
Causes
(aluminum casting)
1. Poor feeding effect of riser
2. Too much gas content in charge
3. Overheating near the ingate
4. The sand mold has too much moisture and the sand core is not dried
5. Coarse alloy grain
6. The position of the casting in the mold is improper
7. The pouring temperature is too high and the pouring speed is too fast
Prevention methods
(aluminum casting)
1. Add molten metal from the riser to improve the riser design
2. The furnace charge shall be clean and free of corrosion
3. A riser shall be set at the shrinkage of the casting, and the cold iron shall be placed or used in combination with the riser
4. Control the moisture content of molding sand and dry the sand core
5. Take measures to refine the grain
6. Improve the position of the casting in the mold and reduce the pouring temperature and pouring speed
