Crucible Melting Furnace

These crucible melting furnace melt the metal without direct contact with a burning fuel mixture. For this reason, they are sometimes called indirect fuel-fired furnaces.

Crucible furnaces are mostly used for melting nonferrous metals and alloys. The metal is melted in a crucible, which is a refractory vessel made of silicon carbide, Graphite, or some other refractory material.

Three types of crucible furnaces are:

1. lift out type

2. Stationary

3. Tilting

They all utilize a container (the crucible) made out of a suitable refractory material (for example, a clay-graphite mixture) or high-temperature steel alloy to hold the charge. In the lift-out crucible furnace, the crucible is placed in a furnace and heated sufficiently to melt the metal charge.

Typical fuels are:

· Oil,

· Gas and

When the metal is melted, the crucible is lifted out of the furnace and used as a pouring ladle. The other two types, sometimes referred to as pot furnaces, have the heating furnace and containers as one integral unit.

In the stationary pot furnace, the furnace is stationary and the molten metal is ladled out of the container. In the tilting pot furnace, the entire assembly can be tilted for pouring. Crucible furnaces are used for nonferrous metals such as bronze, brass, and alloys of zinc and aluminium. Furnace capabilities are generally limited to several hundred pounds.

The metal in the crucible is ordinarily exposed to the furnace atmosphere. It must be mentioned that most non-ferrous metals and alloys absorb gases, oxidize and form dross readily when melted. Steps should be taken to reduce the contamination by fluxing, degassing, and reducing the time in melting. The thermal efficiency of crucible furnaces rarely exceeds 10 percent.

In the stationary pot furnace, the furnace is stationary and the molten metal is ladled out of the container. In the tilting-pot furnace, the entire assembly can be tilted for pouring; crucible furnaces are used for nonferrous metals such as bronze, brass, and alloys of zinc and aluminium. Furnace capacities are generally limited to several hundred pounds.