To a recycler, an object such as an automobile transmission
resembles a piece of candy in which the wrapper is
more desirable than what’s inside. The aluminum of
the casing is more valuable than the steel gears and
other contents it holds. But most recyclers find that
manually separating such transmission cases from their
contents is usually prohibitively costly.
For these recyclers, sweat furnaces offer an effective
and affordable way to separate non-ferrous metals such
as aluminum from less-valuable iron and steel. Sweat
furnaces heat commingled recyclable metals to a temperature
that causes the non-ferrous metals to melt and run
off, leaving behind steel and other materials that
melt at higher temperatures.
At sweat furnace maker EnviroAir, Inc. in Eagle, Wisconsin,
CORECO Product Manager Dean Lesch said modern machines
like those his company makes provide several appealing
features. Compared to traditional sloping hearth sweat
furnaces, recyclers don’t need to manually rake off
iron and other non-melting contaminants. They also
avoid impinging flames directly on molten aluminum,
which creates dross. Other designs may also allow iron
to dissolve into aluminum. Most importantly, up-to-date
equipment meets ever-tougher environmental regulations.
CORECO designs employ a continuous rotary sweat furnace.
“Material is constantly fed into the rotary hearth
while molten aluminum is constantly being sweated out,”
Lesch explained. “Any non-melting metals such as iron,
brass or copper flow out the discharge end of the rotary
hearth clean of any aluminum. The rotating action of
the tube self cleans the tube by constantly creating
a scouring action from the non-melting metal that prevents
a buildup of material on the tube.”
Indirectly heating the CORECO furnace avoids impinging
flame on the materials, reducing the loss of aluminum
and other saleable non-melting metal through oxidation.
“The rotary hearth is heated from the outside thereby
separating the combustion system from the aluminum
sweating process,” Lesch said.
Also, molten aluminum quickly runs down the angled
rotary hearth and into a mold or holding furnace so
that remaining iron won’t dissolve into the aluminum.
“The aluminum does not pool inside the rotary hearth
eliminating the opportunity for the iron to rest in
the molten aluminum and be dissolved,” Lesch said.
CORECO has two standard models. The Model 1231 rotary
sweat furnace handles 2,000 lbs. per hour of input.
The Model 1848 rotary sweat furnace handles 5,000 lbs
per hour of input.
Most customers are scrap processors, foundries, die
casters and part manufacturers, which use the furnaces
for in-plant recovery of mixed metal scrap.
Orders have held up well, Lesch said. “Since our equipment
makes money, lowers operating cost and is good for
the environment, many companies see the value of our
equipment,” he said. “This has allowed us continued
growth and the development of new equipment and processes
to further help our customers.”
At Recycling Services International in Cohoes, New
York, owner David Conway said the ability to satisfy
environmental regulations drives much of his business.
“It’s our pollution controls and the operational controls
for efficiency and pollution control efficiency,” he
said. “We use the latest technology.” Recycling Services
employs solid state controls to help maintain temperature
in furnace oxidizers, while also getting the maximum
That helps his customers rest easy. “With my customers
one of the biggest fears is the Environmental Protection
Agency,” said Conway. “But over the last four years,
we’ve permitted over 35 furnaces and we’ve never been
denied a permit.” Today Conway is designing furnaces
that meet twice the minimum required pollution control
requirements. “The reason we build them that way is,
if EPA does change the regulations, we’re already ahead
of the game,” Conway said.
EPA limits the amount of hazardous air pollutants in
tonnage per year that a furnace can emit. They also
have a minimum requirement of eight tenths of a second
of retention time in the afterburner, at a minimum
temperature of 1,600 degrees in the afterburner chamber.
“Our units have twice that retention time and are capable
of maintaining a temp of 2,000 degrees,” Conway said.
“We overbuild that part of the unit just in case of
something coming down the pike so we’re always a step
Conway’s MAX-4000 aluminum sweat furnace is his most
popular model. These are typically used for melting
aluminum castings, such as transmissions and engines.
The furnaces are large enough to hold approximately
15 transmissions at a time.
After aluminum melts in the MAX-4000, it flows to a
separate holding chamber that is kept at a lower regulated
temperature. “We have that separate holding chamber
because to hold that molten aluminum we only need 1,400
degrees, but we need 1,600 to melt it,” Conway said.
“And the more temperature you have in that holding
chamber, the more metal loss.”
Conway also builds furnaces with special continuously
monitored high-temperature afterburners that run at
2,200 degrees for processing scrap such as electrical
transformers that have been contaminated with PCBs.
He also builds furnaces that reclaim non-ferrous precious
metals such as gold from computer circuit boards.
After a very busy three years, sales slowed almost
to a halt for the last year, Conway said. He is optimistic
about growth in sales of furnaces that employ alternative
fuel sources, such as landfill methane gas. Heat recovery
systems also promise to help spur the market, as furnace
waste heat is redirected to preheating combustion air,
heating existing buildings as other uses. The availability
of government grant money is driving much of that demand,
he said. “It’s really picking up now. We’ve sold two
aluminum furnaces in the last three months and a transformer