What is Molding Sand? Properties & Types

Different types of molding sand are used in sand casting to manufacture most metal components, due to its versatile and cost-effective solution in metal production.

Sand casting is a versatile and cost-effective solution for the creation of metal parts. Most metal components can be manufactured using the sand casting method. Sometimes called sand mold casting, sand casting is a great process for small or large-volume orders.

Good casting can be determined by the pattern and the types of molding sand used. One needs to understand the types of molding sand used in casting to perfectly create objects. Well, in this reading, we’ll explore the various kinds of molding sand used in sand casting.

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What is a Molding Sand?

Sand that tends to pack effectively and maintain its shape when wet, compressed, greased, or heated is called molding sand, often referred to as foundry sand. It is employed to prepare the mold cavity during the sand casting process.

Molding sand is the main raw material used in molding because it offers a number of important properties that other materials might not be able to deliver. It can be found in nature on the banks and bottom of rivers and lakes. Depending on where it came from, molding sand is divided into several groups.

Properties of Molding Sand

The properties of a good molding sand are adhesiveness, cohesiveness, collapsibility, flowability, dry strength, green strength, permeability, and refractoriness.

1. Adhesiveness

One of molding sand’s qualities is its adhesiveness, which allows it to attach to or adhere to other objects, as molding sand adhered to the molding box’s inner wall.

2. Cohesiveness

The characteristic of molding sand that allows the sand grain particles to interact and attract together is called cohesiveness. As a result, the molding sand’s binding capacity is improved, increasing the molding and core sand’s green, dry, and hot strength characteristics.

3. Collapsibility

The sand mold needs to be collapsible once the molten metal inside solidifies. This will allow the metal to contract freely and naturally prevent the contracting metal from tearing or cracking. If the metal does not have the collapsibility quality, the mold prevents the metal from contracting, which causes the casting to break and split. This characteristic is crucial for cores.

4. Dry Strength

The moisture in the sand layer next to the hot metal evaporates as soon as the molten metal is poured into the mold; therefore, the mold wall must not be eroded during the flow of molten metal if the dry sand layer has enough strength to maintain its shape.

The metallostatic pressure of the liquid metal causes the mold chamber to increase, but the dry strength stops this from happening.

5. Plasticity or Flowability

The ability of the sand to become compacted and behave like a fluid is known as flowability or plasticity. When rammed, it will flow uniformly to every part of the pattern and disperse the ramming pressure uniformly in every direction.

Sand particles usually don’t like to get around edges or projections. Generally speaking, flowability rises when green strength falls and vice versa. Sand’s flowability rises as its grain size decreases. The amount of moisture and clay in the sand also affects flowability.

6. Green Strength

After adding water, the green sand needs to be strong and durable enough to allow for the creation and manipulation of mold. In order to do this, the sand grains need to be adhesive, or able to stick to another object. Sand grains with a high adhesiveness level intend to adhere to the molding box’s sides.

Additionally, cohesiveness—the capacity of the sand grains to adhere to one another—must be present.

This characteristic allows the pattern to be removed from the mold without shattering it, and it also prevents the molten metal from damaging the mold’s wall surfaces. The amount and kind of clay, as well as the moisture concentration, all affect the green strength.

7. Permeability

Permeability is also known as the porosity of the molding sand to allow the escape of any air, gases or moisture present or generated in the mold when the molten metal is poured into it. All these gaseous produced during the pouring and solidification process must escape otherwise the casting gets defective.

Permeability is an outcome of grain size, grain shape, and moisture and clay contents in the molding sand. The level of ramming of the sand directly affects the permeability of the mold. The permeability of mold can be further increased by venting using vent rods.

8. Refractoriness

Refractoriness is described as the capacity of molding sand to tolerate high temperatures without breaking down or fusing therefore helping to produce good casting. It is a critically important property of molding sands. Refractoriness can only be enhanced to a limited level.

Molding Sand

Types of Molding Sand

Different kinds of molding sand are green sand, dry sand, facing sand, core sand, loam sand, parting sand, backing and floor sand, system sand, and molasses sand.

1. Green Sand: These types of molding sand are natural sand with enough moisture in them. It contains clay of about 15 to 30%, 8% of water, and silica. The clay and water act as binding materials that gives strength to the mold. it is used only for simple and roughcasting. It is used for both ferrous and non-ferrous metals.

2. Dry Sand: This casting sand is obtained when the moisture from green sand is removed. It is used for large and heavy casting because the molding sand offers greater strength, rigidity, and thermal stability to the casting.

3. Facing Sand: as the name implies, facing sand is used for facing the mold. it consists of fresh silica sand and clay. That is, no used sand is added. It is used directly next to the surface of the pattern. Facing casting sand must have high refractoriness and strength because it comes in direct contact with the hot molten metal. These types of molding sand give the mold a very fine grain.

4. Core Sand: Core molding sand types contain silica sand mixed with core oil (linseed oil, resin, and mineral oil) and other binding materials like dextrin, cornflour, and sodium silicate. It is used for cores making and has high compressive strength.

5. Loam Sand: Loam sand is an equal mixture of sand and clay with a sufficient amount of water added to it. It is also used for large and heavy molding like hoppers, turbine parts, etc.

6. Parting Sand: These types of molding sand are pure silica sand poured on the faces of a pattern before molding. Parting sand is sprinkled on the pattern before it is embedded in the molding sand. This casting sand is also sprinkled on the contact surface of cope, drag, and cheek.

7. Backing and Floor Sand: This casting sand is used to back up the facing sand and to fill the volume of the box. It is also known as floor sand.

8. System Sand: This molding sand is applicable to mechanical heavy castings. It has high strength, permeability, and refractoriness. System sand is used for machine molding to fill the whole flask. Facing sand is not used in this molding because cleaned and has special additives.

9. Molasses Sand: This molding sand is also used for core making and small casting of intricate shapes. It contains molasses as its source of binding.

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