Rat Tailing or Oxidation Crazing
River-like depressions, mostly linear grooves, in the casting
Indicates that the primary coats cracked slightly, giving access to oxygen
The reaction between oxygen and the metal follows a crack in the shell
Causes of this defect are evident in the shell and other portions of the process; to cure, R&R recommends taking the following actions:
See shell causes for finning.
See shell cures for finning.
Use a high quality primary binder.
Low quality primary binder or poor slurry control.
Avoid very low refractory loadings and control the slurry.
Oxygen reaction with metal.
Eliminate/reduce oxygen presence after pouring.
Chromium (Cr) oxides form when oxygen is present during solidification.
Avoid contact with oxygen during solidification. Implement canning practice once shells are poured.
CO gas forms through reaction between C in steel with the refractories of the mold.
Use carbon stucco, put molds in sand and use alternative refractories.