The sand casting process also called as sand mold casting. It is a common method for metal casting. Almost 70% of metal casting of product follow by sand casting process. The bonding agent (clay) is mixed with the sand. The mixture is moisturized with water for develop strength and plasticity of clay to make mold. The pattern prepare for required shape of product. which pattern made of wood or metal. First The mold prepared start of process and molten metal is poured into the mold. After cooling process completed, the mold part removed and cleaned. The Various sand casting method such as Green sand , Dry sand, Loam Sand, Facing Sand, Backing or floor sand, System Sand, Parting Sand, Core Sand. The Green Sand is most use method.
Basic of terminology of sand casting process
The pattern is used to produce the mold cavity in mold sand.
The material that is packed around the pattern, sprue etc and to from the cavity. The molten (liquid) metal filled in cavity and forms the casting. Silica sand is the molding material mostly used in foundries.
The top half of flask/ molding box is Known as cope.
It is the bottom half of the flask/mold box called as drag.
The core part is inserted into mold cavity to produce holes , recess in casting process made of sand called core sand.
The region added to the pattern, core, or mold to locate and support the corer. The core print may be of the casting.
The combined open area in the molding material and core, where the liquid metal solidifies to produce the casting.
The network of connected channels that molten material to the mold cavity. This include the riser, sprue, runner and in gates.
Pouring cup or pouring basin:
The part of the gating system which connects the pouring cup and runners. The liguid metal enters into the mold cavity through the sprue.
The vertical part of the gating system which connects the pouring cup and runners. The liquid metal enters into the mold cavity through the sprue.
The horizontal portion of the gating system that connects the sprues to the gates. This is cut in the drag part of the mold.
This is the part of the gating system, normally used to identify the filling position of the liquid metal in the mold. This acts as a reservoir in the mold that is filling the molten metal to compensate of shrinkage during solidification process.
The controlled entrances from the runners into the mold cavities. Properly designed gates admit the liquid metal into the mold cavity without turbulence.
It is a hole that provide passage for escape the gases during pouring and solidification of mold metals. It is a small Hole provide in all parts of mold material.
Parting line or parting surface:
The interface line between the cope and drag halves of the mold, flask.
The taper on the pattern that allows it to be easily withdrawn from the mold.
It is the mold or die used to produce the cores.
The following sand casting process step by step carried out in foundries:
- The suitable flask or molding box selected and space allow ramming the sand.
- The drag is placed on molding board with upside down. Now the pattern lower part is placed on the board inside the flask. The space is left for cutting.
- Now sand is filled in the flask and cover the pattern. Then sand firmly packed by means of hammers. The ramming is properly and the excess sand is leveled off with straight strike off bar.
- The vent holes or vent rod are made in drag to full depth of flask because of gases (or) air removed during pouring and solidification process.
- Then the cope half of pattern is placed over the drag by using locating pins. The cope flask is placed on drag. The sprue pin is provided for sprue passage, it located at a small distance from the pattern. The riser pin also located on the pattern.
- The cope is filled with sand and proper ramming force applied.
- The ramming , filling, venting same as preform.
- The excess sand is cut off from mold surface. The riser pin and sprue
- Molding box is opened, then pattern removed from cope and drag. The dry sand core is mounted in position.
- Now molten metal is poured through riser into mold cavity. After pouring and solidification the part removed with require pattern shape.
Most important of sand casting advantages:
- The intricate shape can be made by this process because of molten metal flow into small section.
- Ferrous, Non-Ferrous and Non-metal can be cast in this process.
- Very simple tools required and inexpensive
- It process produced for lot of small components.
- Size and weight of the product are not limitation.
Disadvantages of Sand Casting:
- Accuracy and surface finish is not properly.
- It is a labor intensive process.