Sand Casting
Sand casting is the most economical casting process.
The main advantage is the low cost for the moulds: they are made of wood
or plastic and their costs is really lower than the one for die
castings. Moreover, such process enable to produce castings with
cavities and with complex internal structures, since any shapes, hole
and thickness (not less than 4mm), can be obtained directly from
castings, with the consequent cutting of times and costs of finishing
and machining
This type of process is mainly used in order to produce little and medium
series, or in order to produce prototype parts that then have to be mass produced with die casting system. For this casting process the
pattern is made in the shape of the desired part and usually is composed by two "half, called split patterns, and by core boxes,
were they are required on bases of the complexity of the desired casting.
Before using, the sand used for sand moulding has to be expertly mixed with
binder and inhibitors, that allow the sudden hardening of the sand,
and in the meantime it prevent from undesired metal reactions, when
the melted metal comes in contact with the sand.
The
sand hardens around the pattern, and once this last one has been
extracted from the sand, it remains the stamp of the shape of the
desired casting. Mow, the cores (themselves made of sand) can be
placed into the obtained stamp, in order to get the cavities of the
casting.
On the overturned drag (complete of cores), has to be placed also the other “half” called cope obtained through the same
process of pressed sand around the pattern.
After dosing of the two half, everything is ready for the casting. In special furnaces magnesium alloys ingots have been melted, and
casting consists of pouring the melted metal using special recipients called "ladle".
The poring temperature of the metal is really important because on its
bases good sliding is assured, and slow cooling is avoided, since it
would cause porosity and voids.
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