Purpose of Sprue in Casting Process

The purpose of a sprue in the casting process is to feed molten metal from the pouring basin to the gate. The sprue is a channel or passage that connects the pouring basin to the mold cavity. It plays a crucial role in ensuring the successful filling of the mold and the production of a quality casting. Let's explore the reasons why the correct answer is option 'D'.

Feeding the Molten Metal
The primary function of the sprue is to facilitate the flow of molten metal from the pouring basin to the gate. The pouring basin is the reservoir of molten metal, and the gate is the entry point into the mold cavity. By connecting these two points, the sprue allows the molten metal to travel through the system and fill the mold.

Controlling the Flow Rate
The sprue also helps to regulate the flow rate of the molten metal. It ensures that the metal is fed into the mold at a consistent rate, which is essential for proper solidification. If the metal is poured too quickly, it can result in defects such as turbulence, shrinkage, or incomplete filling. On the other hand, if the metal flows too slowly, it may solidify prematurely, leading to incomplete filling or cold shuts.

Reservoir for Molten Metal
While the pouring basin serves as the primary reservoir for molten metal, the sprue also acts as a secondary reservoir. It helps to maintain a constant supply of molten metal to the mold cavity, even as the metal solidifies. This prevents any interruptions in the filling process and ensures that the mold cavity is completely filled.

Feeding the Casting
Once the molten metal enters the mold cavity through the gate, the sprue continues to play a role in feeding the casting until solidification is complete. It helps to direct the flow of metal within the mold, ensuring that all sections of the casting are properly filled. This is particularly important for complex or intricate castings that may have multiple mold cavities or thin sections.

In summary, the sprue in the casting process serves multiple purposes. It feeds the molten metal from the pouring basin to the gate, controls the flow rate, acts as a reservoir for molten metal, and helps feed the casting until solidification takes place.