What is Sand Casting Sand, its Properties & Types?

Different types of casting sand are used in sand casting to manufacture most metal components due to their versatility 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, it is a great process for small- or large-volume orders.

The pattern and the types of molding sand used determine the quality of the casting. 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.

Let’s begin!

What is a Sand Casting Sand?

Molding sand, also known as casting sand, is sand that effectively packs and maintains its shape when wet, compressed, greased, or heated. It is employed to prepare the mold cavity during the sand casting process.

Casting sand is a sand mixture used in the sand casting process, a metal fabrication technique where molten metal is poured into a mold made of sand. This sand mold is designed to have a cavity of the desired shape, which the metal solidifies into.

Sand casting is a widely used and versatile process, suitable for various metals and components.

Casting sand is the main raw material used in molding because it offers several important properties that other materials might not be able to deliver. Nature naturally deposits it on the banks and bottoms of rivers and lakes.

Casting sand is a specialized sand mixture, typically made of silica sand, with binders like clay to hold the particles together.

In sand casting, a mold is created using this sand mixture, often around a pattern or model of the desired part. This sand mixture creates a mold for sand casting and solidifies, it takes the shape of the mold cavity.

The process involves creating the mold, pouring in the molten metal, allowing it to cool and solidify, and then breaking apart the mold to extract the cast metal part.

Properties of Casting Sand

The properties of a good sand casting 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:

Cohesiveness is the characteristic of molding sand that enables the sand grain particles to interact and attract together. 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 procedure 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 sand’s ability to compact 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. To do this, the sand grains need to be adhesive, or able to stick to another object.

Sand grains with a high adhesiveness level tend 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, which allows the escape of any air, gases, or moisture present or generated in the mold when molten metal is poured into it.

All these gases 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 ramming level of the sand directly affects the permeability of the mold. Vent rods can further increase the permeability of the mold.

8. Refractoriness

The ability of molding sand to withstand high temperatures without breaking down or fusing is known as refractoriness, and it contributes to the production of good casting. It is a critically important property of molding sands. Enhancing refractoriness can only reach a certain extent.

Types of Sand Casting Sand

Different kinds of sand casting 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 casting sand are naturally occurring minerals that contain sufficient moisture. It contains clay of about 15–30%, 8% water, and silica. The clay and water act as binding materials that give strength to the mold.

It is used only for simple and rough casting. It is used for both ferrous and non-ferrous metals.

2. Dry Sand:

We obtain this casting sand by extracting the moisture from green sand. We use it for large and heavy casting because the molding sand provides the casting with greater strength, rigidity, and thermal stability.

3. Facing Sand:

Sand faces the mold, as its name suggests. Fresh silica sand and clay make up its composition. We do not add any used sand to it. We use it directly next to the pattern’s surface.

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 core 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. The pattern receives a sprinkle of parting sand before the molding sand embeds it. Additionally, the cope, drag, and cheek contact surfaces receive a sprinkle of this casting sand.

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 heavy mechanical castings. It has high strength, permeability, and refractoriness. Machine molding uses system sand to fill the entire flask. Facing sand is not used in this molding because it is cleaned and has special additives.

9. Molasses Sand:

This casting sand is also used for core making and small castings of intricate shapes. It contains molasses as its source of binding.

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