What is gating system? It is nothing but the basic design, which is needed to construct a smooth and proper filling of the mold cavity of the casting without any discontinuity, voids or solid inclusions. A proper method of gating system is that it leads the pure molten metal to flow through a ladle to the casting cavity, which ensures proper and smooth filling of the cavity. This depends on the layout of the gating channels too, such as the direction and the position of the runner, sprue and ingates.Objective of the Gating System :
The four main points, which enables a proper gating system, are:
- Clean molten metal.
- Smooth filling of the casting cavity.
- Uniform filling of the casting cavity.
- Complete filling of the casting cavity.
The mold cavity must be filled with a clean metal so that it prevents the entry of slag and inclusions into the mold cavity, which in turn minimizes the surface instability. If the mold has smooth filling then it helps to reduce the bulk turbulence. If it has a uniform filling it means that the casting fill is in a controlled manner. Complete filling of the cavity makes the metal thin with minimum resistance at the end sections.Procedure :
The main elements needed for the gating system are as follows:
- Pouring basin or bush.
- Sprue or downspure.
- Sprue Well
- Slag trap or filter.
The characteristics of each element are mentioned below:
- Pouring basin : This is otherwise called as bush or cup. It is circular or rectangular in shape. It collects the molten metal, which is poured, from the ladle.
- Sprue : It is circular in cross section. It leads the molten metal from the pouring basin to the sprue well.
- Sprue Well : It changes the direction of flow of the molten metal to right angle and passes it to the runner.
- Runner : The runner takes the molten metal from sprue to the casting. Ingate: This is the final stage where the molten metal moves from the runner to the mold cavity.
- Slag trap : It filters the slag when the molten metal moves from the runner and ingate. It is also placed in the runner.
The gating system also depends on the direction of the parting plane, which contains the sprue, runner and the ingate. They are as follows:
Horizontal Gating System : This is used most widely. This type is normally applied in ferrous metal's sand casting and gravity die-casting of non-ferrous metals. They are used for flat casting, which are filled under gravity.
Vertical Gating System : This is applied in tall castings were high-pressure sand mold, shell mold and die-casting processes are done. Top Gating System : this is applied in places where the hot metal is poured form the top of the casting. It helps directional solidification of the casting from top to bottom. It suits only flat castings to limit the damage of the metal during the initial filling.
Bottom Gating System : it is used in tall castings where the molten metal enters the casting through the bottom.
Middle Gating System : It has the characteristics of both the top and bottom.