Hot Bulging or Creep

Hot bulging or creep present as a thickening, oversized or inflated casting. This defect could be similar to buckling, but typically without the sharp peak. This defect indicates that there was hot deformation of the ceramic mold under pressure of metal, forcing the shell to move or creep at a given temperature and pressure.

The causes of this defect are evident in the shell and metal portions of the process. To cure these causes, R&R recommends taking the following actions.








  1. Weak hot strength of shell.
  2. Hot deformation due to shell materials and presence of alkali materials.
  3. Shell firing temperature is too high/hot.
  4. Shell is too thin.
  5. Low backup refractory loading, low silica solids in backup binder, inadequate refractory choice or part geometry (large, flat surfaces).
  1. Increase SiO2 level, burnout time or temperature. Use a stronger shell system.
  2. Use a more refractory material in backup slurry or as stucco.
  3. Reduce/control shell temperature.
  4. Add more coats.
  5. Stiffen surfaces or check backup slurry and refractory.


  1. Metal is too hot.
  1. Reduce/control metal temperature.




Return to Defect Analysis