Gating Ratio for Aluminium Alloy Casting

The gating ratio of 1 : 2 : 5 is commonly used in the design of gating systems for aluminium alloy casting. This ratio represents the relationship between the different components of the gating system, which are the sprue base area, runner area, and ingate area. Let's understand the significance of each component and how they are related to each other in the gating system.

1. Sprue Base Area:
The sprue base area is the cross-sectional area of the sprue, which is the vertical channel that connects the pouring basin to the runner system. It serves as the main passage for molten metal to flow from the pouring basin into the runner system. The sprue base area determines the overall flow rate and velocity of the molten metal. It is important to have an appropriate sprue base area to ensure smooth and efficient metal flow.

2. Runner Area:
The runner area is the cross-sectional area of the horizontal channels that distribute the molten metal from the sprue to the individual ingates. The runner system helps to control the flow and pressure of the molten metal, ensuring that it reaches each mold cavity uniformly. The runner area should be designed to minimize turbulence and pressure losses, allowing for a consistent flow of molten metal.

3. Ingate Area:
The ingate area is the cross-sectional area of the channels that connect the runner system to the mold cavity. It controls the flow rate and direction of the molten metal into the mold cavity. The ingate area should be designed to provide a balanced and controlled flow of molten metal to each mold cavity, ensuring proper filling and minimizing defects such as shrinkage and porosity.

Relationship between the Components:
The gating ratio of 1 : 2 : 5 indicates the relative sizes of the sprue base area, runner area, and ingate area. It suggests that the sprue base area is one unit, the runner area is two units, and the ingate area is five units. This ratio ensures a gradual increase in cross-sectional area from the sprue to the ingate, allowing for a smooth and controlled flow of molten metal.

The larger runner area compared to the sprue base area helps to reduce pressure losses and turbulence in the runner system. The larger ingate area compared to the runner area ensures that each mold cavity receives an adequate flow of molten metal. This gating ratio is commonly used in aluminium alloy casting to achieve good metal flow, minimize defects, and promote uniform filling of the mold cavities.

In conclusion, the gating ratio of 1 : 2 : 5 represents the relationship between the sprue base area, runner area, and ingate area in the gating system for aluminium alloy casting. This ratio ensures an appropriate flow of molten metal, minimizing defects and ensuring uniform filling of the mold cavities.

Gating Ratio is defined as the ratio of sprue base area, followed by the total runner area and the total ingate area. The sprue base area is taken as unity.