Question

While designing the gating system, the ratio of 1 : 2 : 4 represents:

• A. Sprue base area : runner area : ingate area
• B. Pouring basin area : ingate area : runner area
• C. Sprue base area : ingate area : casting area
• D. Runner area : ingate area : casting area

Hint:

The gating ratio order is fixed by convention: Sprue Base Area : Runner Area : Ingate Area. Remember the acronym S-R-I to avoid mixing up the sequence.

Answer 1

The Correct Option is A

Concept: A gating ratio defines the relative cross-sectional areas of the key channels within a casting's delivery system. The standard reporting sequence for a gating ratio is consistently defined as: \[ \text{Gating Ratio} = A_s : A_r : A_g \] Where:
• \( A_s \) = Cross-sectional area of the sprue base choke section.
• \( A_r \) = Total cross-sectional area of the runner channel(s).
• \( A_g \) = Total cross-sectional area of the ingate channel(s). Gating systems are categorized into two primary styles:
• Pressurized Gating System: Where the choke area is at the ingate (e.g., $1 : 0.75 : 0.5$). The metal enters the mold cavity at high velocity.
• Unpressurized Gating System: Where the choke area is at the base of the sprue (e.g., $1 : 2 : 2$ or $1 : 2 : 4$). The flow expands into larger runner and gate areas, decreasing its kinetic energy.

Step 1: Identify the components from the ratio $1 : 2 : 4$. The ratio indicates a sequential widening of the passages ($1 \rightarrow 2 \rightarrow 4$). Following the standard convention: - First component ($1$) correspond to the Sprue base area. - Second component ($2$) corresponds to the Runner area. - Third component ($4$) corresponds to the Ingate area. This expanding unpressurized design reduces flow velocity and minimizes turbulence and sand erosion inside the cavity.