Aluminum / Copper / Zinc / Lead / Magnesium: Crucible Melters

Equipment Overview:
Crucible melting equipment (sometimes referred to as "pot" melters) consists of a cast iron, steel or other alloy, or clay bonded graphite crucible that usually holds between 200 and 3000 pounds of molten material. Many crucibles are sized in the 500 to 1000 pound melt size. The crucible is surrounded by a structure where natural gas, or other fuels, is fired into the space between the crucible and the structure. Electrical elements are also used in this space to heat (indirectly) and melt the materials in the crucible.

In addition to varying melt capacities, crucibles are produced with several design features suited for the end-use need. They can be stationary or can be fitted with quick disconnect devices to allow melting in one location and transport to another for pouring (most are stationary). They can also tilt to more easily facilitate pouring into transport ladles to the casting area. Gas fired designs that separate the flue gas exhaust from coming in contact with the surface of the molten bath and that utilize covers will result in reduced metal losses and the lowest operating cost.

Besides aluminum, crucible furnaces are also used for melting copper bearing alloys (brass, bronze, copper alloys), magnesium, and zinc. Only the pot (or crucible) materials change. Gas and electric designs exist for all materials. The following series of pictures illustrate the basic look and design of crucible furnaces.

Gas-fired crucibles have historically been perceived as a low-cost but higher metal loss melting option. Newer designs keep the products of combustion away from the melted materials. The next two images illustrate available exhaust discharge options:

Also a more recent development is a "Non-Crucible" furnace. A series of pictures illustrates features that include:

• Metal is charged into a dry hearth charging chamber. This eliminates any safety issues associated with placing cold or moisture bearing charge materials into a molten bath of aluminum.
• Captures exhaust energy (to preheat and help melt the new charge)
• Improves metal quality by leaving slag, dross, and other residuals on the dry hearth where they can be removed.
• Uses gate filters and inert gas degassing to assure that only clean filtered aluminum is available for tapping.