Question

For the design of gating system, the ratio 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:

Remember that gating ratios are typically expressed as Sprue Area : Runner Area : Ingate Area. A ratio like 1:2:4 indicates an unpressurized gating system where the ingate area is the largest, which can lead to faster mold filling but also a risk of aspiration if not managed correctly.

Answer 1

The Correct Option is A

Step 1: Understand the components of a gating system.
A gating system in casting is a channel or network of channels through which molten metal flows into the mold cavity. Key components include:
Pouring Basin: Where molten metal is poured.
Sprue: A vertical channel that connects the pouring basin to the runner.
Sprue Base (or well): The bottom of the sprue, which may be enlarged. Runner: A horizontal channel that distributes metal from the sprue to the gates.
Ingate (or gate): The entry point from the runner into the mold cavity.
Step 2: Understand the concept of gating ratios.
Gating ratios are used to design the cross-sectional areas of different parts of the gating system to control the flow of molten metal and prevent defects. These ratios are expressed as:
Sprue Area (or sprue base area) : Runner Area : Ingate Area. There are two main types of gating systems based on these ratios:
Pressurized Gating System: In this system, the total cross-sectional area of the ingates is less than or equal to the total cross-sectional area of the runner. This creates a back pressure, ensuring the runner and gates are always full of molten metal, which helps prevent aspiration (gas entrapment). Examples of ratios for pressurized systems include 1:0.75:0.5 or 1:0.5:0.25.
Unpressurized (or Open) Gating System: In this system, the total cross-sectional area of the ingates is greater than the total cross-sectional area of the runner. This system fills the mold cavity quickly but can lead to aspiration if not properly designed. Common ratios include 1:2:4, 1:3:3, or 1:1:3.
Step 3: Analyze the given ratio 1:2:4.
The ratio 1:2:4 means that if the sprue base area is 1 unit, the runner area is 2 units, and the ingate area is 4 units.
This specific ratio is characteristic of an unpressurized gating system, where the ingate area is significantly larger than the sprue and runner areas. The components in the ratio are always in the order: Sprue Area : Runner Area : Ingate Area.
Therefore, the ratio 1:2:4 represents sprue base area : runner area : ingate area. The final answer is \( \boxed{\text{1}} \).