Defect characteristics and detection methods

Dark gray clusters or single distribution on the upper horizontal surface of the casting, or at the inlet of the pouring gap, or at the junction of the two casting walls, or the blind end and the inside of the casting. Found after X-ray, sandblasting or machining.

Causes of formation

1. Slag inclusion in raw materials and remelting materials
2. Slag and other non-metallic oxides in alloy liquid are not removed
3. The design of pouring system is unreasonable, and scum is drawn into the mold cavity during pouring
4. The speed of alloy liquid entering the cavity is too high, and oxide film or slag is drawn into the cavity
5. Incomplete cleaning of slags after refining, insufficient standing time or too much stirring of alloy liquid under high temperature, resulting in reoxidation
6. Cut off during pouring

Prevention methods and remedial measures

1. Use qualified raw materials and remelting used materials
2. Strictly abide by the alloy smelting process to ensure that pure alloy liquid is obtained
3. Adopt bottom pouring or gap open pouring system, set skimming, slag collecting structure, install filter screen, and strengthen slag retaining function of pouring system
4. Pour slowly, steadily and continuously to ensure the qualified alloy liquid does not break, and never pour large capacity mold (piece) in small capacity ladle
5. Fully refine the alloy liquid, and be sure to stand for 3-5min before pouring, and properly reduce the pouring temperature of the alloy liquid
6. The slag blocking ladle with partition shall be used for pouring, and the oxide skin and slag on the surface of alloy liquid shall be removed before pouring