Sand Casting Types
 |
| Sand Castig Types |
What are the types of sand casting processes?
There are 9 types of sand casting explained below based on different mould materials and they are as follows.
- Green sand moulding.
- Dry sand moulding.
- Skin-dry moulding.
- Co2 sand casting process.
- Sodium silicate sand casting.
- Cement sand casting.
- Dicalcium silicate moulding.
- Ferro-silicon moulding process.
- Shell moulding process.
Green Sand Moulding
Dry Sand Moulding
Skin-Dry Moulding
Carbon Dioxide Moulding (`CO_{2}` Sand Casting )
This process is called carbon dioxide moulding or `CO_{2}` sand casting because of the use of carbon dioxide to create a strong bond between fine sand and water glass to make a strong mould without the use of clay.
GFN (grain fineness number) for dry sand in this process is higher allowing the process to produce higher surface finish casting.
The process of making `CO_{2}` sand moulding process starts with mixing fine sand, sodium silicate (up to 5%), a little moisture, adding additives (coal dust, saw flour, dextrin, molasses and husk) and curing the mixture under `CO_{2}` gas until sodium silicate gel gets hard and binds fine dry sand together.
The process of making a `CO_{2}` sand core is similar to the sand mould described above. The bench life and strength of core and mould are limited for a longer time, bonds do not stay strong between sand and sodium silicate.
The disadvantages of the `CO_{2}` sand moulding process are that moulds have difficulty in shakeout property during pattern removal and collapsibility after casting is solidified.
Sand cannot be reused again and the process becomes costly because of `CO_{2}` gas consumption and sodium silicate as compared to us of clay and water to bind sand particles.
The advantage of using this process is the process of making `CO_{2}` sand moulds requires the same equipment, mould-making hand tools, floor space and labour except `CO_{2}` gas equipment.
This process is faster than the traditional way of making a sand mold, eliminating baking core and mould in ovens. Reducing labour cost and time for mould production but giving better surface finish and dimensional accuracy output.
Cement Sand Moulding
The cement sand moulding process is done by a slurry mixture of fine sodium silicate (2.5 to 4.5%) sand and cement to form a mould where molten metal is poured into the mould cavity to produce casting products.
Other binding agents such as sawdust, cereals, molasses and husk are added to the mould to improve the strength of the cement mould.
The advantage of cement sand moulding is that a better surface finish is obtained at the end of the casting process. The flowability of cement sand mixture is better than traditional sand, clay and moisture reducing ramming and mould-making operations.
Cement sand casting has fewer surface defects, fewer mould defects and better dimensional accuracy as there is better permeability. This process is best suited for brass and bronze casting.
The disadvantage of cement sand mould compared to traditional sand casting mould is that removing the final casting from the mould becomes difficult as a hard mixture of cement and sand needs to be broken. This mould has lower collapsibility properties as compared to dicalcium silicate mould.
If the same process was carried out with dry sand moulding, dry sand moulds had to be dried completely before which was more time-consuming.
Dicalcium Silicate Moulding
The dicalcium silicate moulding process starts with mixing sand with dicalcium silicate (2-3.5%), sodium silicate (5-6%) and additives to the moulding sand mixture's improving surface finish, hardness and flowability.
Dicalcium silicate, sodium silicate and binding chemical agents mixture is directly poured into the flask to form a sand mould. There is no need for ramming and compacting required for this mould. Chemicals create a strong bond between sand making a solid mould.
Dicalcium silicate moulds have better collapsable properties as compared to cement sand moulds. This process can produce small to large casting porosity defect-free casting for ferrous metals such as steel, grey cast iron and cast iron.
Ferro-Silicon Moulding Process
This process starts with mixing sodium silicate and ferro-silica con together in a 2:1 ratio and mixing it with silica sand. This mixture forms an exothermic reaction between these chemicals at room temperature forming a strong bond between them making sand mould stronger and having high GFN.
The process takes place without baking, external heating elements for curing mould sand or any `CO_{2}` gas.
Suction Moulding
The suction moulding process is where negative pressure is created around moulding sand sucking all sand towards the flask producing a cavity where molten metal is poured for producing sand casting.
This process starts with pouring sand on the pattern and creating pressure in the moulding sand for the ramming and compacting operation. The suction moulding process is suitable for large ferrous and non-ferrous castings for creating an accurate mould cavity producing high dimensional tolerance casting.
Shell Moulding Or Shell Casting
The shell moulding process consists of making a sand mould by heating a metal pattern and forming a mould made from a mixture of thermosetting resin and fine sand.
In the shell moulding process a shell mould is created in which molten metal is poured to make highly dimensional accuracy and surface finished casting because of fine grain sand (Sand used in this process has GFN up to 150).
The shell mould mould-making process starts with pouring the mixture on metal and curing it for up to 60 seconds up to 150℃.