Missing areas (a mix of round, irregular or angular shaped craters or cavities) of metal in the casting or black, crusty particles sitting on the metal surface
Indicates a presence of liquid and solid slag inclusions; which are being carried into the shell by the metal
Causes of this defect are evident in the metal and other portions of the process; to cure, R&R recommends taking the following actions:
Use a filter to remove slag from metal during pouring.
Poor deoxidation and/or poor deslagging practice.
When molten metal is exposed to air, it begins to oxidize, forming slag.
Determine proper temperature and control. Cast at lowest possible temperature.
Poor condition of refractory liners in ladles and furnaces (moisture).
Check on firing of new refractory linings.
Contamination from casting ladle or turbulent casting.
Inspect ladles and avoid turbulence.
Poor deslagging practice.
Use proper deslagging practices.