JNTU B.Tech III FABRICATION PROCESSES Previous Question Paper (February/March - 2022 - R16)

A crucible furnace is a simple melting unit used for non-ferrous metals and alloys. It consists of a refractory crucible made of graphite or silicon carbide, which holds the metal charge. The crucible is placed inside a furnace chamber lined with refractory bricks and heated by oil, gas, or electricity. The heat is transferred to the metal primarily through the walls of the crucible by conduction and radiation from the furnace walls.

Working: The metal charge is placed inside the crucible. The furnace is fired, and the temperature is raised until the metal reaches its melting point. Once molten, the crucible is removed using tongs, and the molten metal is poured directly into the mold. The furnace is typically of the pit, tilting, or stationary type.

Applications: It is widely used for melting small quantities of non-ferrous alloys like brass, bronze, aluminum, and magnesium in small-scale foundries or for specialized casting requirements.

The gating system is the network of channels that conducts molten metal from the ladle into the mold cavity. Its primary elements include:

1. Pouring Basin: A small funnel-shaped cavity at the top of the mold that receives the molten metal from the ladle and reduces turbulence.
2. Sprue: A vertical passage that connects the pouring basin to the runner. It is usually tapered to prevent air aspiration.
3. Runner: A horizontal channel that distributes the molten metal from the sprue base to the gates.
4. Ingate: The actual entry point where the molten metal enters the mold cavity from the runner.
5. Riser: A reservoir of molten metal provided in the mold to compensate for the liquid shrinkage as the casting cools and solidifies.