Jagged crack line through the casting
Indicates that the metal filled the mold, but cracked at solidification (the metal shrinks as it solidifies and tears apart due to restriction)
Note: some metals are more prone to hot tearing than others
Causes of this defect are evident in the shell, metal and other portions of the process; to cure, R&R recommends taking the following actions:
Shell is too strong.
Reduce shell strength, number of coats.
Shell is too hot.
Reduce shell temperature.
Poor crushability of ceramic mold (high post fired strength).
Reduce post fired strength.
Metal is too hot.
Reduce/control metal temperature.
Modify to reduce cooling stress/shrinkage.
Movement of shell before metal solidifies.
Allow time for metal to solidify before movement.