The large difference between shell mold and normal sand mold is that in the former process phenol resin has been used as the binder of mold sand, but on the contrary in the latter clay or bentonite has been used as the binder. Phenol resin decomposes easily at high temperature.
  The author has investigated the properties of shell mold at high temperature to make distinct the cause and counter-measure of defects of shell mold castings.