Question

Which one of the following casting defects is caused due to the supply of the molten metal through two gates?

• A. Cold shut
• B. Rat tail
• C. Pin hole
• D. Shift

Hint:

Associate casting defects with their root causes: "Cold" in cold shut refers to the metal streams being too cold to fuse. "Gas" defects (like pin holes, blow holes) are from trapped gases. "Sand" defects (like rat tails, scabs) are from mold sand issues. "Shape" defects (like shift, mismatch) are from mold alignment problems.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify a specific casting defect that is typically caused by having multiple gates for molten metal entry into the mold cavity.
Step 2: Detailed Explanation:
Let's analyze each defect:

• (A) Cold shut: This defect occurs when two streams of molten metal, often flowing from different directions (e.g., from two separate gates), meet within the mold cavity but are too cool to fuse together completely. This results in a discontinuity or a weak spot in the casting that looks like a crack or a seam. This perfectly matches the condition described in the question.
• (B) Rat tail: This is a surface defect characterized by an irregular line on the casting surface. It is caused by the compressive failure of the sand at the mold surface due to the expansion of the sand when heated by the molten metal. It is related to sand properties, not the number of gates.
• (C) Pin hole: These are small gas cavities located on or just below the surface of the casting. They are caused by the evolution of dissolved gases (like hydrogen) from the molten metal as it cools and solidifies. This is related to the melting practice and gas content, not the gating system design.
• (D) Shift: This defect is a mismatch of the top (cope) and bottom (drag) halves of the casting. It is caused by the misalignment of the two halves of the mold, often due to worn-out flask pins or incorrect assembly. It is a molding error, not a flow-related defect.

Step 3: Final Answer:
The defect directly associated with the meeting of two streams of molten metal that have cooled and fail to fuse is a cold shut. Using two gates increases the likelihood of this defect if the pouring temperature and gating design are not optimal.