Antioch Process:

This was primarily developed to overcome the restriction of the conventional plaster moulds. If undried moulds are dehydrated partially and then permitted to hydrate without being disturbed, gypsum crystals gradually recrystallise into granules around the size of the sand grains and the mould attains a porous structure of relatively high permeability. Recrystallisation does not take at the surface of the mould, since no water is exists and therefore the surface is smooth.

These moulds also have a superior heat capacity since they are composed of closely 50% sand. Unlike conventional plaster moulds the Antioch moulds do not reduced. Actually they expand throughout processing. Due to their porous nature the moulds contains low dry strength. This promotes untimely collapse of cores as the casting cools and minimizes warm tears in the castings. For big castings it is taken care of using the internal reinforcement. Antioch procedure is well suited to the processes along angular blade as nozzles and sections-rotor. For dehydration the molds are placed in appropriate racks in a standard autoclave. The autoclave is steam and sealed admitted. The autoclave is operated along a steam pressure of 105 kPa. The dehydration is followed through hydration at room temperature up to 14 hours. Drying follows this, along the temperature ranging from 175 to 230° C and drying time is 1 to 70 hours. Most copper based alloys are cast using this procedure. Commonly Yellow brass is cast using the Antioch procedure. Metals that have melting temperatures above 1040°C may not be cast using this procedure.