Misrun Casting Defect

Misrun is a casting defect that occurs when the molten metal fails to completely fill the mold cavity during the casting process. This defect can result in incomplete castings with missing sections or poor surface finish. There are several factors that can contribute to the occurrence of misrun defects, but the most significant factor is the insufficient fluidity of the molten metal.

Factors contributing to misrun defects:

1. Insufficient Fluidity of the Molten Metal: The fluidity of the molten metal refers to its ability to flow and fill the mold cavity properly. If the fluidity is inadequate, the molten metal may solidify before it completely fills the mold, leading to a misrun defect. This can be caused by various factors such as low pouring temperature, improper alloy composition, or incorrect gating system design.

2. Very High Pouring Temperature of the Metal: While it may seem counterintuitive, excessively high pouring temperature can also contribute to misrun defects. When the molten metal is poured at a very high temperature, it can solidify rapidly before completely filling the mold cavity. This can result in incomplete castings and misrun defects.

3. Absorption of Gases by the Liquid Metal: Gases present in the molten metal can affect its fluidity and cause misrun defects. The presence of gases can create voids or bubbles in the solidified casting, preventing the molten metal from properly filling the mold cavity. This can occur due to inadequate degassing of the molten metal or the presence of impurities.

4. Improper Alignment of the Mould Flasks: The alignment of the mold flasks plays a crucial role in ensuring proper filling of the mold cavity. If the mold flasks are not properly aligned, it can result in misrun defects. Misalignment can cause uneven distribution of the molten metal, leading to incomplete castings.

Conclusion:

In conclusion, the correct answer to the question is option 'B' - insufficient fluidity of the molten metal. While factors such as very high pouring temperature, absorption of gases by the liquid metal, and improper alignment of the mold flasks can also contribute to casting defects, the primary cause of misrun defects is the insufficient fluidity of the molten metal. It is important to address this issue by optimizing the pouring temperature, improving the alloy composition, and designing an appropriate gating system to ensure proper filling of the mold cavity and prevent misrun defects.