Shell Molding Croning Process

As a final example of modeling thermoset processing, the process called the shell molding or Croning process will be analyzed. This is just one of many processes found in a variety of industries (automobile, electronics, sports goods, furniture, etc.) that involve the cure of thermosetting polymers. The selected example is a typical process used in foundries. 

Among the foundry processes, the shell molding or Croning process has evolved into an accepted production method using both shell molds and shell cores. Invented in Germany in 1943 by J. Croning, this process has been industrially adapted because it offers high production rates. A scheme of the process is described in Fig. 9.16. Its principles are as follows  

A set of metal pattern plates is heated to 200°C-280°C and coated with a silicone release agent. 

Dry sand, precoated with a phenolic novolac-hexamethylenete-tramine (hexa) formulation, is dropped upon the pattern. After about 15 s-30 s, the mold is turned over (180°C), leaving a shell of several millimeters of sand adhered to the metal pattern. The rest of the sand that falls upon mold inversion is supplemented with fresh coated sand and used in the following cycle. 

The cured shell is ejected from the mold and postcured for several minutes in a continuous oven, at temperatures close to 300°C. 

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