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. Shift
• C. Pin hole
• D. Rat tail

Hint:

To prevent cold shuts, ensure that the gating system is designed to maintain a uniform flow of molten metal with consistent temperature. Properly positioned gates can help avoid uneven filling and ensure better fusion of metal streams.

Answer 1

The Correct Option is A

In casting processes, molten metal is poured into a mold through gates, and the proper flow of the molten metal into the mold cavity is crucial for preventing defects. If molten metal is supplied through two gates, it is vital that the streams from both gates meet and fuse properly. If the molten metal cools too quickly or the flow from both gates is not coordinated, the metal streams will fail to fuse correctly. This results in a defect known as a cold shut.
A cold shut occurs when two streams of molten metal meet at a junction but do not fully fuse together due to a lack of sufficient temperature or pressure. This leaves a weak joint in the casting, typically resulting in a visible line or separation. The cause of the cold shut can be linked to factors like:
- Insufficient temperature of the molten metal, causing it to solidify prematurely.
- Uneven supply of molten metal from the two gates, causing irregular flow into the mold.
- Inadequate mold or gating design that prevents proper fusion of the two streams.
The cold shut defect typically weakens the casting at the point where the two streams meet and may lead to reduced mechanical properties in the final product. This is especially problematic in critical components where strength and integrity are important.
Why not the other options?
- Option (B) Shift: A shift refers to a misalignment of the mold cavity or mold components during the solidification of the casting. This is not caused by the supply of molten metal through two gates and typically results from issues with mold handling or core movement.
- Option (C) Pin hole: Pin holes are small gas holes formed in castings due to trapped gases during the casting process. These are unrelated to the number of gates used for molten metal supply and are more related to gas entrapment.
- Option (D) Rat tail: Rat tail is a surface defect that occurs when the molten metal solidifies too quickly on the surface, causing a crack or distortion. It is not caused by the use of two gates for supplying molten metal.
Thus, the correct answer is (A) Cold shut because it directly results from the failure of molten metal to properly fuse when supplied through two gates.