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

Several additional melter types are utilized by non-ferrous materials processors. These include barrel and rotary melters, shaft, tower, and jet melters, and other design variations. Induction melters (coreless and channel) are also employed. The melter choice generally depends on the type and volume of scrap available and the desired grade of the output aluminum (or other material).

The pictures and information below illustrate the range of designs available.

Barrel melters are usually applied for die casting facilities or plants with smaller but fairly consistent production volume. Prepared scrap and known quality ingot make up the charge. The charge is placed in the well. Molten material is poured into ladles (the melter rotates) and transferred immediately to the die casting machines. A variation on this design is the Rotary type of melter. It typically will utilize lower grade scrap and will be paired with a holding furnace.

Shaft melters have scrap loaded in the top of the furnace and the scrap is continuously dried and preheated by the exhaust gasses passing through the loaded shaft. In this manner, any concerns about explosions of molten metal caused by wet scrap entering a molten bath are eliminated.

Jet and Tower melters (variations of the stack melter in that scrap is continuously fed from the top and the exhaust heats and melts scrap), provide the following benefits:

  • High energy efficiency - 1,000 Btus, or less, to melt & hold per pound
  • Reduced melt loss of 1.5% or less
  • High quality metal due to lower gas inclusion levels
  • Temperature uniformity is subject to reduced variance since cold scrap is not introduced into the molten bath
  • Capacities from 500 to 20,000 pounds per hour

Shaft, Jet and Tower melters are designed to load scrap and ingot continuously and produce a constant stream of molten material into the holding section. The shaft (or tower) is kept full of scrap and ingot during production. Generally, melt losses for these designs are less than traditional reverberatory designs and require lower levels of degassing. These designs are popular in Japan and in USA automotive, and other parts, production facilities operated by offshore owners.

For more information on these furnaces, refer to the case history titled "A Melt Performance Comparison: Stack Melter vs. Reverberatory Furnace". This case history was presented in 1999 and details the experience of a Midwest aluminum foundry with the installation of a 3000 pound per hour stack melter.

Go to the Stack Melter vs. Reverb. Furnace Case Study

Two additional and interesting gas-fired melting equipment designs are emerging and nearing commercial readiness. One is a Continuous Melting and Holding Furnace from Nippon Crucible Company, Ltd. (Tokyo, Japan). The other is a DOE supported project called the Vertical Floatation Melter (VFM) by Energy Research Company (Staten, Island, NY). Summary briefs for these promising gas technology products are as follows:

Continuous Melting and Holding
In this design, the features of both Tower (or shaft) and Crucible melters are combined into a compact continuous melting and holding system. High quality aluminum product, simple operation, and low dross production are three benefits obtained by die casters, and other casting (sand and gravity) operations.

Vertical Flotation Melter
A recent development in gas-fired aluminum melting finished the pilot test stage in 2001 and is ready for full-scale demonstration. A Vertical Floatation Melter (VFM) has been developed (sponsored by DOE) which simultaneously decoats and melts organic laden shredded scrap in a single unit. A 1,000 pound per hour pilot unit has achieved a number of impressive results including:

  • Thermal efficiency about 2 times greater than a conventional melting furnace (nearly 60% efficiency)
  • Energy consumption verified at 850 Btu / Lb when producing at a 1,000 pound per hour melt rate
  • Metals loss is about half those of a traditional melter (dross production is reduced by about half from a traditional melter)
  • Heat transfer coefficients are 10 times higher than that of a conventional furnace allowing rapid melting at a low gas temperature.

A concept schematic for the VFM is shown right:

Scrap aluminum is fed into the top of the VFM where it falls through a cone. Hot gases flow upwards through the cone, creating a drag force on the scrap. When the drag force equals the scrap weight the scrap becomes suspended. The gases strip off and vaporize the organics. Next, the scrap reaches a liquid state, and it falls into a holding furnace. Typical energy use is well under 1,000 Btu/pound.

A picture of VFM Pilot Unit and a list of other advantages are provided below:

  • Can process a wide variety of scrap. This is done by varying the recirculation flow, which allows the floatation of a wide range of scrap sizes and shapes.
  • Rapidly and completely decoats scrap aluminum without oxidizing the underlying metal (de-coating typically occurs in less than two minutes, compared with 10 to 20 minutes for conventional equipment).
  • Small Footprint. Very little horizontal area is needed and no moving parts are used.
  • The VFM can be operated as a combined decoater and melter. It can also be utilized as a preheater (where the organics from the decoater are combusted and provide the desired preheating) resulting in lowered fuel use and increased production. When operated in this manner, the technology is referred to as VFD (Vertical Floatation Dryer). It also can be applied in the glass and steel industries.
  • Meets EPA and Local Emission Regulations

This VFM development was funded by DOE through the Office of Industrial Technologies (OIT). Energy Research Co. has partnered with Stein Atkinson Stordy in Eurpoe and the USA and is actively seeking a full-scale demonstration site. Additional information is available at www.eere.energy.gov/industry.

Electric Induction and Channel Induction Systems:
Induction furnaces use electromagnetic fields to create heat in the metal charge and this rapidly melts the charge. Electric induction systems are either the coreless or channel type. After the material is molten, the electric current results in a stirring action in the melt. This stirring effect produces a homogenized melt. This circulation also quickly submerges chips and other small scrap pieces, resulting in low oxidation losses. Coreless furnaces are generally operated with a "heal" (a pool of molten material kept at the bottom of the unit to assist melting the next load of scrap) or can have oxy-fuel burners applied to assist the scrap melt at the start of a cycle. Coreless furnaces can be emptied and different alloys can be produced from one unit. Channel induction systems are best suited for continuous operation with one material.

Refer to the Basics - Processes Section on Non-Ferrous Melting / Holding for energy use information for induction systems. The general disadvantage of induction systems is their high capital and high operating costs.

Go to the Melting / Holding Area