/ Copper / Zinc / Lead / Magnesium: Other Melters
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).
and information below illustrate the range of designs available.
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.
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.
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
- 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
uniformity is subject to reduced variance since cold scrap is not introduced into
the molten bath
from 500 to 20,000 pounds per hour
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.
to the Stack Melter vs. Reverb. Furnace Case Study
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:
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.
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.
concept schematic for the VFM is shown right:
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
- Small Footprint.
Very little horizontal area is needed and no moving parts are used.
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.
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.
to the Melting / Holding Area