Abstract
In this paper, the fundamental experiments on the castability of molten iron and on the mechanical properties and microstructures of the castings are included, when gray iron was cast into natural sand moulds which varied in the moisture content from 0 to 17%. The results were as follows :
(1) Castability
i) The fluidity of the molten iron is extremely high when the metal was cast into dry sand moulds, and is slightly lower than before when the metal was cast into moulds with moisture content from 4 to 8%.
ii) The surface of the casting is at its most beautiful stage when the moisture content in the moulds is from 8 to 9%.
iii) The shrinkage cavities grow in number with the increasing of the moisture content. The total shrinkage also becomes larger with the increasing of the moisture content up to 8.5%, but over that it does not develop any more.
iv) When cores, with moisture content of less than 8.5%, are used, the blow scarcely occured in the casting with the dimensions by which we carried out the experiment.
(2) Mechanical properties
In general, the mould with a moisture content from 2 to 4% yields a casting that has good mechanical properties.
(3) Chill test
The depth of clear chill varies slightly with the moisture content in mould, while the total chill does not.
(4) Microscopic test
There are little differences in graphite structure between the inner and outer surfaces of the casting, and the chilling effect is very little.
Summarily, the castability of the molten iron is found to be good when the metal is poured into the mould with a moisture content of 4%. However, the surface of the casting is not so good at that time. The mechanical properties are also good when the moulds have moisture content from 2 to 4%, when natural sand is used for the mould, the moisture content in the mould must be increased to the greatest extent, unless there are difficulties in making moulds. Even in this case, it should not go beyond 9%.
