JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III FABRICATION PROCESSES Previous Question Paper (August - 2022 - R16)

A crucible furnace is a simple melting unit used for non-ferrous metals like brass, bronze, and aluminum. It consists of a refractory container (the crucible) placed inside a furnace chamber heated by oil, gas, or electricity. The metal is charged into the crucible, and heat is transferred through the walls of the crucible to melt the charge. The furnace is typically designed as a pit or tilting type to facilitate pouring. In a pit furnace, the crucible is lifted out manually, while a tilting furnace allows the entire assembly to pivot for pouring the molten metal directly into ladles.

Applications include melting small quantities of non-ferrous alloys, laboratory research, and producing high-quality castings where contamination from furnace gases must be avoided.

Investment casting, also known as the lost-wax process, is a precision casting technique used to produce complex shapes with high surface finish and dimensional accuracy. The process involves the following steps:

1. A wax pattern is produced by injecting molten wax into a metal die.
2. The wax patterns are attached to a central wax sprue to form a tree assembly.
3. The assembly is coated with a thin layer of refractory slurry (the investment) and then covered with coarser sand particles to build a strong shell.
4. The shell is dried and then heated in an oven to melt and drain the wax, leaving a hollow cavity.
5. The mold is preheated to remove moisture and improve metal flow, then filled with molten metal.
6. After the metal solidifies, the ceramic shell is broken away, and the individual castings are cut from the sprue.

Applications include the manufacturing of turbine blades, jewelry, dental implants, surgical instruments, and intricate components for the aerospace and automotive industries.