Moulding Sand: Types and Properties
Types of Moulding Sand:
According to the use, moulding sand may be classified as below:
1. Green Sand:
The green sand is the natural sand that contains enough moisture. It is a combination of silica and clay of 15 to 30% with water of about 8%. Clay and water function to offer power as a binding substance. Molds of this sand are regarded as moulds of green sand.
The green sand is only used for products with easy and hard casting. It is used for ferrous as well as non-ferrous metals.
2. Dry Sand:
It is regarded as dry sand when the moisture is taken from the green sand. The dry sand mould has higher power, stiffness and thermal stability. For big and strong casts, this sand is used.
3. Loam Sand:
Loam sand is a 50% sand and 50% clay combination. A adequate quantity of water is introduced. It is used for heavy and big moulds, such as turbine components, hoppers, etc.
4. Facing Sand:
A sand used for mould facing is regarded as sand facing. It is made up of silica sand and concrete, without adding the sand used. It is used right next to the model ground. Facing sand falls in direct contact with the warm molten metal, so it must be highly refractory and strong. It's got good grains.
5. Parting Sand:
A plain silica sand used before moulding on the heads of the structure is regarded as dividing sand. The moulding sand sticks to it when the model is removed from the mould.
Separating sand is sprinkled on the structure before it is integrated in the moulding sand in order to prevent sticking. Parting sand is also sprinkled on cope, drag and face contact surfaces.
6. Backing or Floor Sand:
The supporting sand is black sand that is ancient and constantly used. It is used to back up the sand facing and fill the box's entire quantity. After casting, this sand accumulates on the ground and is therefore also known as ground sand.
7. System Sand:
The sand used in mechanical light castings is regarded as unit sand and has elevated power, permeability and refractory. It is used to supply the entire flask with machine moulding. No face sand is used in factory moulding. The system sand has special additives and is cleaned.
8. Core Sand:
Core sand is known as a sand used to make cores. It is silica sand mixed with core oil and other binding materials (dextrine, corn flour, sodium silicate). It has remarkable strength of compression.
9. Molasses Sand:
A sand that holds molasses as a binder is referred to as sand molasses. It is used for the production of nucleus and tiny casts of complex forms.
Properties of Moulding Sand
Following are the important properties of moulding sand:
1. Porosity:
The most significant characteristic of the moulding sand is porosity also recognized as permeability. It is the moulding sand's capacity to allow the passage of gasses. During the passing of molten metal into the sand cavity, gas and steam are produced. This property relies not only on the form and size of the sand droplets, but also on the quantity of the mixture's clay, binding material, and moisture content.
2. Cohesiveness:
Cohesiveness is sand's property of holding together its particles. It can be described as the moulding sand's force. This estate performs a crucial part in keeping the mould's complicated forms.
During processing, rotating, or closing, insufficient resistance can contribute to a fall of the mould particles. Cohesiveness is enhanced by clay and bentonite.
3. Adhesiveness:
Adhesivity is the property of sand, which causes the sand droplets to stick to the bottom of the moulding container. Sand adhesivity allows stress to be properly lifted along with the sand.
4. Plasticity:
Plasticity is the property of the moulding sand by virtue of which, when rammed, it flows into all corners around the mould, thus providing no possibility of spaces being left out and acquiring a predetermined shape under ramming pressure.
5. Flow-Ability:
The capacity of moulding sand to flow freely and fill the recesses and nice information in the model is flow-ability. It differs with the content of moisture.
6. Collapsibility:
Collapsibility is the property of sand which causes the sand mould to automatically fall after the mold has been solidified. The mould should disintegrate with minimal force into tiny droplets of moulding sand after removal of the mold.
7. Refractoriness:
Refractory is the property of sand that can resist elevated molten metal temperatures without fusion or softening. If the molten metal is poured into the mould, molding sands with poor refractoriness may burn. Sand moulds should normally be able to resist up to 1650 ° C.
