The principle of this process consists in freezing the wet unbounded moulding aggregate, where frozen water takes the role of a binder. The sand with a relative humidity of 5 to 7% is used. The process has been utilized in the UK since 1975 as Eff-Set Process. The moulding process can be divided into two stages:
- The pattern is stripped from the mould before freezing;
- The mould containing the pattern is the subject to be frozen.
To freeze the mould after the pattern has been stripped, as in the Eff-set process, it must exhibit at least some sufficient green strength, and so a little clay content is added to the sand. Liquid nitrogen is used to freeze the mould or the core. There are a few modifications of the freezing process:
- Freezing in a cryogenic chamber, or in a continuous cooling tunnel;
- Blowing the freezing media throughout the mould, or core;
- Pouring over or dipping the mould/core into a cryogenic liquid;
- Heat removal from the wet sand by direct contact with the cooled pattern equipment;
- Shooting the moulding aggregate into the core or moulding box, just after it is rapidly mixed of two components:
a) wet sand at the ambient temperature and
b) deeply cooled sand.