Technical properties of the various moulding types

2 Moulding with clay-bonded sand (green sand moulding) 

1 Preparation of clay-bonded sand by vacuum mixing and cooling 

The use of steam in the absence of air leads to a quick activation of the bentonite, resulting in a very quick attainment of the optimal compressive strength for the bonded sand. 

The disadvantage of the system is the operation and management of the vacuum system. The process also affects the sand technical properties (e.g. compressive and tensile strength, permeability), which diminish after 72h ( the 72h effect )- This can be prevented by re-mixing for about 90s. 

Reduction of the total airflow results in a reduced off-gas volume and amount of dust for disposal, as well as a reduced consumption of binder as compared to conventional cooling and mixing plants (although this also depends on the efficiency of the regeneration plant). Additionally, the system uses less energy. 

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Table 4.20 Technical properties of the various moulding types [42, US EPA, 1998]...

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