What is Moulding Sand?
Moulding Sand (or foundry sand) is a type of sand which can hold its shape and it tends to pack very well when it is moistened and compressed.
In the metal casting process, Moulding sand is used for preparing the mould cavity in which the molten metal is poured.
In most of the casting operations, the silica sand (SiO2) is used as a moulding sand.
The mould sand is generally mixed with water and clay. This mixture contains around 89% sand, 7% clay and 4% water.
Having said that, let’s discuss the Types of moulding sand used in the metal casting process.
Types of Moulding Sand
There are 8 types of moulding sand for metal casting, which are mentioned below.
Let me tell you a few important things about all these types of foundry sand one by one.
#1) Green sand
- Green sand is a mixture of silica sand which contains 18% to 30% clay and the quantity of water is around 6% to 8%.
- Green sand contains enough water in its natural state which naturally gives it a good bonding properties.
- Before pouring the molten metal in the mould cavity, the green sand is not allowed to dry. In other words, the molten metal is poured in the green sand mould in its wet conditions only.
- As the green sand contains enough moisture, it can be easily moulded with hands.
- Green sand is soft and it will retain its shape when you will squeez it in your hand.
- The moulds prepared by using green sand are used for small to medium casting works and the moulds are known as green sand moulds.
#2) Dry sand
- As the name suggests, dry sand mould is the mould which is obtained by removing the moisture from the green sand mould.
- Dry sand mould is used for making large size castings.
- When the green sand is dried in the mould, it becomes strong and compact, and this sand mould is known as a dry sand mould.
- As dry sand mould possess good strength, it is used for manufacturing the large size metal castings.
#3) Loam sand
- Loam sand contains around 50% of clay.
- Loam sand is used for preparing the moulds for large and rough castings by using sweep pattern, skeleton pattern, etc.
- As the loan sand contains 50% clay, a thin plastic paste can be obtained which can be used to plaster the moulds which harden on drying.
#4) Parting sand
- Parting sand is a fine grained silica sand which is free of clay.
- Parting sand is applied on the surface of the mould cavity made by green sand, so that the green sand does not stick to the pattern and hence it allows the easy separation of pattern from the mould.
- Parting sand includes components like groundnut shell, like stone, charcoal, etc.
#5) Facing sand
- Facing sand is the sand which comes in direct contact with the molten metal.
- As the name suggests, the facing sand covers the pattern from all its surface. In other words, it forms the face of the mould, where molten metal comes in contact with it.
- The facing sand should have high refractoriness and good strength.
- The facing sand is made up of silica sand and clay and it does not contain any previously used sand.
- Around 20 mm to 30 mm thickness is provided by the facing sand in the mould cavity.
#6) Backing sand
- Backing sand is used to back up the facing sand.
- Backing sand is generally the old and repeatedly used sand and this sand is black in color as it gets burnt out due to heat of molten metal as well as it also contains coal dust.
- As the backing sand is black in color, it is also known as black sand.
- The moulding cost can be reduced by using a backing sand.
#7) System sand
- System sand is mainly used in mechanized foundries where machine moulding is done.
- The system sand has higher strength and refractoriness as compared to that of the backing sand.
#8) Core sand
- Just as the name suggests, core sand is used for manufacturing the cores.
- The core sand contains silica which is mixed with core oil. Hence the core sand is sometimes called oil sand.
- The core oil used for preparing the core sand consist of resin, linseed oil, and other light mineral oil along with some binders.