Question

Which of the following gating ratio is normally followed for Al alloys:

• A. 1 : 0.75 : 0.5
• B. 2 : 1 : 0.5
• C. 4 : 3 : 1
• D. 1 : 2 : 2

Hint:

For aluminum alloys, a gating ratio of 1:2:2 ensures smooth, non-turbulent metal flow, protecting against oxidation and improving casting quality.

Answer 1

The Correct Option is D

In casting processes, the gating ratio refers to the ratio of the cross-sectional areas of the sprue, runner, and ingate, respectively. It determines how molten metal flows into the mold cavity.
For aluminum (Al) alloys, which are light and prone to oxidation and turbulence, a gating system that provides smooth, non-turbulent flow is essential. A gating ratio of: \[ \text{Sprue : Runner : Ingate} = 1 : 2 : 2 \] is used. This is an unpressurized gating system, meaning the total cross-sectional area increases in the direction of flow.
This setup:
- Minimizes turbulence and oxidation (critical for aluminum),
- Reduces mold erosion,
- Enhances casting quality.
Other gating ratios like \( 4 : 3 : 1 \) are pressurized systems, suited for metals like steel and cast iron where turbulent filling is less harmful.