Moulding Sand - What is Molding Sand?,Types and Properties

By Mohit Uniyal|Updated : August 3rd, 2022

The history of Moulding Sand is difficult to research because most of the process predates writing. There is no definite historical record to ascribe the earliest metal casting and usage of moulding sand; however, ancient artefacts and literature indicate a period in ancient Mesopotamia about 3200 B.C. The ancient Chinese pioneered the use of moulding sand solely for bronze castings.

The next great breakthrough occurred in India around 500 B.C. when cast-crucible steel was invented. Around 1808, Sir Humphry Davy was the first to do aluminium castings in the United Kingdom. Much of the current metal industry has developed due to the vast improvement in moulding sand quality due to improved tooling, metallurgy, and a better knowledge of metal characteristics.

What is Moulding sand?

Moulding sand, also known as foundries sand, is a kind of sand that is widely used to manufacture all sorts of moulds regardless of whether they are employed for producing casting of ferrous or nonferrous metals. Although silica sand of superior grade is also mined, the natural sand found on the banks and beds of rivers provides a greater source.

Silica sand is utilized in the majority of sand casting procedures. Because of the simplicity of the materials employed, sand casting was one of the earliest kinds of casting undertaken. Because of its simplicity, it is still one of the most affordable metal casting procedures. A combination of water and clay holds the sand required to make a mould for a casting procedure. Engineers frequently compress, heat, and damp moulding sands to produce a particular shape. A typical blend maybe 89 percent sand. 4 percent water, and 7 percent clay.

Types of Moulding Sand

There are various types of moulding sand depending upon the chemical composition of the sand. The main moulding material in the foundry shop is sand. It can withstand hot molten metal. Moulding sand does not chemically react with the moulding sand. This analysis specifically covered the main varieties of moulding sands and their qualities. The different varieties of moulding sands are as follows:

  • Green Sand
  • Dry Sand
  • Loam Sand
  • Facing Sand
  • Backing Sand
  • Parting Sand
  • Core Sand
  • System Sand

Green Sand

Moulding sand or sandstone that is green in colour is known as green sand. It contains silica sand, 18 to 30 per cent clay, and 6 to 8 per cent water overall. It is porous, light, and soft, and the binding between the green sand grains is provided by clay and water. When pressed by hand, it feels slightly moist in green sand. Under pressure, it can retain its shape and impression. The green sand is inexpensive and easily accessible. This moulding sand is used to create a mould that is known as a green sand mould. Castings made of ferrous and non-ferrous metals are frequently produced using it.

Dry Sand

The kind of green sand that has removed moisture is dry sand. In a good oven, the mould created from the green sand is baked or dried to create dry sand. Clay and silica make about 15% to 20% of the dry sand's composition. This Moulding sand is stronger, more thermally stable, and more rigid.

Loam Sand

Loam sand is clay-rich and dries hard. This is specifically used for moulding loam. For large castings like bells, rollers, and pulleys, typically. It has silica, graphite, water, clay, fireclay, and gainster in it. Loams are sandy, wet, and readily absorb water. The texture and richness of loam soil make it easier to work across a large area.

Facing Sand

Sand that forms the mould's face is referred to as facing sand. This sand is known as "facing sand" because manufacturers primarily utilize it to make the face upon which they pour molten metal. Sea coal makes about 5% of the facing sand, and iron makes up 25%. It is positioned as the pattern's next surface to contact the hot, molten metal.

Backing Sand

The Backing sand, also known as the floor sand, supports the face sand. It is ancient and widely used moulding sand that is used for the backing. Due to the addition of coal dust and burning from coming into touch with molten metal, it is occasionally referred to as black sand.

Parting Sand

To create a non-sticky pattern, parting sand (dry sand without the binder) is used. Pure silica makes up parting sand. The parting mould is created using parting sand. Often, the pattern is taken out of the mould. The mould is then used to adhere. Therefore, since the mould does not stick, parting sand is utilized. Such parting sand is used to sprinkle on the mould before connecting it to the pattern. Parting sand is sprinkled over the drag, cope surface, and cheek to prevent sticking.

Core Sand

The sand used to create cores is known as core sand. Since it contains both silica sand and core oil, it is also known as oil sand. Linseed oil, resin, light mineral oil, and other binders are all included in core oil. Mixing pitch, wheat, and water can make large cores economically.

System Sand

The entire flask is filled with system sand in a Mechanical casting where machine moulding is used. This sand mould has a high level of strength, permeability, and refractivity.

Properties of Moulding Sand

Moulding sand is used in the foundry industry for mould preparation during metal casting. The properties of the moulding sand improve the casting metal's quality. When adequate sand is used, casting faults that may occur during the mould preparation and casting process is considerably reduced. Here, we will go over all of the properties that moulding sand must have to prepare an effective mould cavity.

  • Porosity
  • Adhesiveness
  • Collapsibility
  • Flowability
  • Refractoriness
  • Cohesiveness

Porosity

Porosity, often known as permeability, is the most important characteristic of moulding sand. It refers to the moulding sand's capacity to enable gases to pass through. During the pouring of molten metal into the sand hole, gases and steam are produced. This property is affected not only by the form and size of the sand particles but also by the amount of clay, binding substance, and moisture in the combination.

Adhesiveness

The ability of sand particles to adhere to another body is called adhesiveness. Sand's adhesiveness causes sand particles to adhere to the sides of the moulding box. Sand adhesion allows for properly lifting the cope together with the sand.

Collapsibility

Collapsibility refers to the capacity of the moulding sand to collapse after the molten metal has solidified. When the casting is withdrawn from the mould, it should disintegrate into small particles of moulding sand with minimal force.

Flowability

Flowability or plasticity is the ability of sand to adapt to the moulding process by flowing all around the pattern and taking the right mould shape when rammed. Moulding sand must have good plasticity to have a good impression of the pattern in the mould. Fine-grained sand is generally more plastic.

Refractoriness

The moulding sand's capacity to survive the molten metal's high temperature without melting into it is referred to as refractoriness. The moulding sand must have sufficient refractoriness to produce a high-quality, defect-free casting. Sand with low refractoriness melts and fuses in the casting, lowering the quality of the cast metal. The refractoriness of sand is a measure of its sinter point, not its melting point.

Cohesiveness

Cohesiveness refers to the capacity of sand particles to cling together. The sand's strength is determined by how cohesive the sand particles are. The sand should be strong enough to hold its shape throughout carrying, twisting, closing, and pouring. If it is not of sufficient strength, it will be unable to keep its shape, and the mould may be damaged during the pouring of molten metal.

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Moulding Sand FAQs

  • Moulding sand is sand used to create or manufacture moulds. They are also known as foundries sand. Sand is mixed with water and clay in a fixed proportion to produce the mould.

  • Sand can compress naturally and flow fluidly around the edges of the mould as it is pushed. This is a property known as plasticity. This feature is also called flowability since it spreads out throughout the mould like a fluid. The inverse relationship between plasticity and green strength states that as plasticity increases, green strength decreases and vice versa. 

  • The quality that is crucial for moulding sand is refractoriness.  Refractoriness is the ability of a material to withstand extremely high temperatures, which is necessary for the moulding process.  The surface of the moulding sand won't be as smooth after burning if this feature of the sand deteriorates. SiO2, quartz content, particle size, and shape all affect its quality.

  • After adding water to the green sand, the property that emerges is called "green strength." In other words, it can be defined as “Green strength refers to the sand's strength when it is green or damp.” When creating the mould, the water enables the mould to have adequate hardness and strength. Green strength measures the mouldability of the sand mixture.

  • The backing sand is black in color. Backing sand is also referred to as floor sand since it is the primary support for the facing sand. It is ancient and widely used moulding sand that is used for the backing. Due to the addition of coal dust and burning from coming into contact with molten metal, it is occasionally referred to as black sand.

  • The binders can generally be either an organic or an inorganic substance. The inorganic group consists of items like portland cement and clay sodium silicate. Clay is used as a binder in foundries and includes Kaolinite, Ball Clay, Fire Clay, Limonite, Fuller's Earth, and Bentonite. Dextrin, molasses, cereal binders, linseed oil, and resins like phenol formaldehyde and urea formaldehyde are among the binders that fall under the organic category.

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