What is Green Sand Casting?
Green sand casting is a metal casting process in which castings are prepared using sand molds which are wet and contain moisture in it.
The fact is that the Green sand is not green in color, but it is wet and it contains more moisture. Hence it is named “green sand”.
How to make Green Sand Molding?
The main constituents in green sand are silica, 10 % to 15 % clay and 6 % to 7 % is water.
All these ingredients are properly mixed and then the molding of sand is done.
There are 3 main methods for green sand moulding.
- Open sand method
- Bedded in method
- Turn over method
Let me tell you a few things about these Green Sand Molding processes.
#1) Open sand method
- Out of the three methods of green sand molding, this is the simplest method and it is more suitable for solid type of patterns.
- In the open sand molding process, the sand mould is prepared on the floor.
- The green sand is rammed on the floor such that it can support the weight of the molten metal when it is poured.
- After the ramming and levelling of the sand, the pattern is pressed down in the sand to make the mould cavity.
- Open sand casting method is mainly used for manufacturing simple castings like grills, railings, floor plates, etc.
#2) Bedded in method
- Bedded in method for green sand casting is a method which is used when the upper surface of casting is not flat, and it requires a smoother surface.
- First of all, the molding sand is partially filled in the drag and the pattern is pressed down in the sand mold, which forms a mould cavity.
- After this, the pattern is again pressed downward until a properly rammed mold cavity is obtained.
- The cope is placed over the pattern and it is rammed properly.
- As the final mold cavity is prepared, the molten metal is poured into the mold cavity and it is allowed to solidify.
- In this way, the castings are prepared using bedded in method.
#3) Turn over method
- Turn over method is a method of making green sand mold, which is most suitable for split patterns and solid type patterns.
- By using a turn over method, the small and medium size castings are made. The castings of non-ferrous metals are made by using this method.
- First of all, the half part of the pattern is placed in the moulding box such that its flat surface rests on the bottom side.
- The drag part is filled with the green moulding sand and then it is rammed properly.
- Excess molding sand is removed from the top of the drag, by using a foundry tool called strike off bar.
- After this, the box is turned over as shown in the image below.
- The other half part of the pattern is assembled with the previous half part of the pattern as shown in the above image.
- This attachment of both the half parts of patterns is done by using a dowel pin, which helps in proper alignment of the pattern.
- The parting sand is sprinkled at the parting line of cope and drag. This is done to avoid the adhering of cope sand and drag sand when they are separated.
- The runners are risers are set in the mould for the flow of molten metal in the mould cavity.
- The cope is filled with the moulding sand and it is rammed properly.
- Excess sand present on the top of the cope is then removed using a strike-off-bar.
- Vent holes are provided in the mould by using a vent wire, which helps in escaping the hot gases from the mold.
- The pattern is removed from the mould by rolling down the cope.
- Dry sand core can also be placed in the mold cavity as per the required castings.
- The molten metal is then poured into the mold cavity from the runner and then it is allowed to solidify.
- In this way, the turn over method is used for green sand molding.