What is a mould?
A mould is a hollowed-out block that is filled with a liquid
like plastic, glass, metal, or ceramic raw materials .The
liquid hardens or sets inside the mold, adopting its shape. A
mold is the counterpart to a cast.
Classification of moulding sands
According to their use in the foundry, moulding sands are
classified into following categories:
1. Green sand:
The term "green sand" is known principally because of the
moisture content within the sand. The sand undergoes a
"mulling" process in which various clay and chemical
additives that act as binders are blended with the sand,
which results in a compound which is suitable for the sand
It is sand used in the wet condition for making the mould. It is
mixture of silica sand with 15-25 per cent clay and 6-8 per cent
Green sand moulds are not dried and metal is poured in them in
the wet condition.
Being damp the sand can be easily worked with hand to give it
any desired shape.
This sand is used for producing small to medium sized moulds
which are not very complex.
2. Dry sand:
Dry sand is the green sand that has been dried or baked after
preparing the mould.
Drying sand gives strength to the mould so that it can be used
for larger castings.
3. Loam sand:
Loam sand is sand containing up to 50 % clay which
has been worked to the consistency of builder mortar.
This sand is used for loam sand moulds for making
very heavy castings usually with the help of sweeps
and skeleton patterns.
4. Parting sand:
This sand is used during making of the mould to ensure
that green sand does not stick to the pattern and the cope
and drag parts can be easily separated for removing the
pattern without causing any damage to the mould.
5. Facing sand:
Facing sand is the sand which covers the pattern all
around it. The remaining box is filled with ordinary floor
Facing sand forms the face of the mould and comes in
direct contact with the molten metal when it is poured.
6. Backing sand:
Backing sand is the bulk of the sand used to back up
the facing sand and to fill up the volume of the flask.
The main purpose for the use of backing sand is to
reduce the cost of moulding.
7. System sand:
This is the sand used in mechanized foundries for
filling the entire flask.
Sand, cleaned and reactivated by the addition of water and
binders is used to fill the flask. Because of the absence of any
fresh sand, system sand must have more strength,
permeability and refractoriness compared to backing sand.
8. Core sand:
Core sand is the sand used for making cores. This is silica
sand mixed with core oil. That is why it is also called oil
Green sand Moulding
Green sand molding is more wide develop than any
Green sand molding is replacing many of the more
expensive moulding methods as sand control is being
Why we use Green sand Molding
-High productivity (Economical).
-Easily adaptable to manual , semi-auto and automatic
1 Green sand for moulding must fulfill and pack
tightly round the pattern under pressure. It must
2 Green sand for moulding should be able of
being deformed slightly without cracking, so that
the pattern can be withdrawn. In other words, it
must exhibit “Plastic” behaviour.
3 Green sand must have sufficient strength to
strip from the patterns and support its own
weight without deforming, and withstand the
pressure of molten metal when the mould is cast.
It must therefore get “Green Strength”.
4 Green sand should be “Permeable” , so gases
and steam can escape from the mould at the
beginning of pouring to avoid any kind of defects.
5 Green sand must get “Dry Strength” to prevent
erosion by liquid metal during pouring as the
mould surface dries out.
6 Green sand must guarantee a good
“Refractoriness” to withstand the high
temperature involved without melting or fusing
with the metal.
Green sand components
Bentonite is one of the most important
component of green sand.
RULE OF BENTONITE = THE SAND
These molds are relatively inexpensive to
produce , since material is readily available.
Complex patterns can be accommodated in the
mold design, at affordable costs.
Easily adapts to automated production