In a casting process, a vertical channel through which molten metal flows downward from pouring basin to runner for reaching the mold cavity is called

The correct answer is sprue.

In a sand casting gating system, the molten metal travels through several components designed to regulate its flow, reduce turbulence, and prevent defects. Let's break down the functions of these components step-by-step:

1. Pouring Basin: This is the small reservoir at the top of the mold where the molten metal is directly poured from the ladle. It helps in maintaining a continuous flow and reducing turbulence.

2. Sprue (Vertical Channel): The molten metal flows downwards from the pouring basin through a vertical passage called the sprue. The sprue is typically tapered downwards to prevent air aspiration (drawing in of atmospheric gases) by keeping the channel completely full of liquid metal.

3. Runner: From the bottom of the sprue, the molten metal enters a horizontal channel called the runner, which distributes the metal to the gates leading into the mold cavity.

4. Riser: A riser is an extra reservoir of liquid metal placed in the mold to feed the casting as it shrinks during solidification, preventing shrinkage cavities.

5. Defects (Blister and Pin Hole): A blister and a pin hole are casting defects caused by trapped gases or moisture, rather than channels in the gating system.

Therefore, the vertical channel through which molten metal flows downward from the pouring basin to the runner is called the sprue.