improving performance in furnace melt treatment process - Pyrotek

Paul Campbell
Marketing Manager
Metaullics Systems
Division
In-Furnace Melt Treatment Process
The
Metaullics
gas injection
pump is the
product of
choice
where
demagging is
required.
Page 6
DEMAGGING WITH CHLORINE
In order to produce foundry alloys,
secondary smelters often use chlorine gas
to demag, degas, or both. Foundry alloys
for sand, permanent mold, and die casting
require low magnesium levels. Wrought
alloys such as building materials,
extrusions, beverage containers,
and a wide variety of other
commonly recycled consumer
products contain substantially high
levels of magnesium. To the extent
possible, scrap is often blended
based on pricing, availability, and
composition to meet or approach
the magnesium specification for
the material being produced. In
many cases, however, the
specification cannot be met by
blending alone and smelters have
found that gas injection pumps are
an effective tool to achieve the
required result.
Demagging efficiencies are
dependent on thermodynamic and kinetic
considerations. Under favorable
conditions, magnesium can be removed
from molten aluminium alloys by adding
halogen compounds such as chlorine. The
reaction between magnesium and chlorine
occurs because there is a preferred
chemical affinity at normal molten
aluminium operating temperatures.
In accordance with the following reactions,
when gaseous chlorine is introduced into
molten aluminium, aluminium chloride is
produced as a gaseous product (see
equation below). When magnesium is
present, the aluminium chloride reactively
decomposes to form magnesium chloride
which rises to the surface where it can be
removed by skimming. Favorable
thermodynamics alone do not guarantee
efficient magnesium removal. Kinetic
factors such as rate of mixing, contact area,
and concentrations will all have dramatic
effects.
2Al + 3Cl 2AlCl (1)
2 3
2AlCl + 3Mg 3MgCl + 2Al (2)
3 2
The following graph represents typical
demagging results in the production of
foundry ingot in a 75 ton furnace with a 38
ton heel from the previous heat. Scrap
containing high percentages of magnesium
was charged into the furnace while the
pump was operating. The gas injection
pump was able to remove the magnesium
at essentially the same rate that it was
added to the furnace, maintaining the alloy
▲ ▲
PYROTEK
SUPPLEMENT
within the specification limit for the alloy
being produced.
It has always been necessary for chlorination
technology in aluminium recycling to meet
rigorous environmental standards. Current
MACT (Maximum Achievable Control
Technology) standards in the U.S. have
taken this requirement to an even higher
level. Compared to other chlorination
technologies, gas injection pumps provide
the safest and most efficient technology for
accomplishing this aspect of melting and
refining.
When demagging is required, the Metaullics
gas injection pump is the product of choice
due to its proven operating efficiency, low
maintenance, rugged construction and
reliability.
METAULLICS GAS INJECTION
PUMPS
Advanced technology, with the
revolutionary 6-barrel impeller design,
achieves longer life, higher efficiencies,
and reduced maintenance requirements.