What is Gate in Casting?
In Casting, the gate is a small channel or passage which connects the runner with a mold cavity and the molten metal flows through this passage to fill up the mold cavity.
What is Gating System in Sand Casting?
In sand casting process, Gating system is defined as all the channels or passages through which the molten metal is delivered to the mold cavity.
Gating system includes the elements like pouring basin, runner, riser, gate, etc.
Elements of Gating System
The 13 elements of Gating system are mentioned below.
- Pouring basin
- Down sprue
- Sprue base
- Main cavity
- Top risers
- Side risers
- Blind risers
- Open risers
Let’s discuss each of these elements of Gating system one by one.
#1) Pouring basin
Pouring basin is the element of gating system from where the molten metal first enters the gating system.
There should be a radius around the pouring basin to avoid the turbulence of the molten metal when it is poured.
The pouring basin is either made up of core sand or it is cut in the cope portion of the sand mold.
Because of the presence of pouring basin, the ladle operator can easily direct the flow of molten metal from crucible to the pouring basin and sprue.
It also helps in preventing the foreign materials and slag from entering the sprue.
#2) Down sprue
The vertical section through which the molten metal travels downward through the pouring basin is called down sprue.
Down sprue should be tapered (its cross section should decrease as it moves downward) so that molten metal can flow easily through it.
#3) Sprue base
The place where the down sprue ends is known as the sprue base.
From sprue base, the inner cavity of the casting begins.
Ingate (also known as choke area) is the portion in the gating system which is present between the sprue base and mold cavity. The molten metal has to pass through the ingate area in order to enter the inner area of the mold.
#5) Main cavity
The cavity (also known as mold cavity) is the impression of the actual part which is to be casted. This mold cavity is made with the help of casting pattern.
Vents are the small holes in the sand mold which are made for the escape of hot gases from the mold during the solidification process.
Gate is a small channel or passage which connects the runner with a mold cavity and the molten metal flows through this passage to fill up the mold cavity.
Runners are the passages that are made in the sand mold which distributes the molten metal inside the mold cavity.
Risers are the part of gating system which acts as a reservoir for the molten metal. The molten metal from risers enters the mold in order to compensate for the shrinkage due to solidification of casting.
In gating system, the risers are classified into 4 types.
- Top riser: Top riser feeds the metal from the top.
- Side riser: Side riser feeds the metal from the side.
- Blind riser: Blind risers are the risers which are completely contained within the mold.
- Open riser: Open riser is that type of riser which is opened at the top to the outside environment.
Functions of Gating system
In sand casting, the gating system has following functions.
- To distribute the molten metal with least turbulence to prevent the erosion of the mold.
- To ensure that the complete mold cavity is filled with molten metal.
- To fill the mold cavity as quickly as possible in order to avoid the temperature gradient.
- To develop a temperature gradient which leads to directional solidification of casting towards the riser.
- To prevent the oxide formation in the molten metal.
- To prevent the entry of foreign materials and slag into the mold cavity.