Defect characteristics: the pores in the wall of three castings are generally round or oval, with smooth surface, generally shiny oxide scale, and sometimes oil yellow. The surface pores and bubbles can be found by sand blasting, and the internal pores and bubbles can be found by X-ray fluoroscopy or machining. The pores and bubbles are black on the X-ray film
Causes(aluminum casting)
1. The pouring alloy is unstable and gas is involved
2. Organic impurities (such as coal dust, grass root horse dung, etc.) are mixed in mold (core) sand
3. Poor ventilation of mold and sand core
4. There is shrinkage cavity on the surface of cold iron
5. Poor design of gating system
Prevention methods(aluminum casting)
1. Correctly master the pouring speed to avoid getting involved in gas.
2. Organic impurities shall not be mixed in the mold (core) sand to reduce the gas generation of molding materials
3. Improve the exhaust capacity of (core) sand
4. Correct selection and treatment of cold iron
5. Improve the design of gating system