CPT International 01/2019

MOLD AND COREMAKING
Focal point furnace bottom
The quality of the sand is heavily reliant
on the air-gas mixture. The pore burner
system developed by FAT, Niederfischbach,
Germany, ensures an even and
continuous thin layer of sand to flow on
the fluidization bottom of the combustion
chamber.
In the furnace, each individual grain
of sand is continually in the flame and
therefore treated optimally. A „flame
carpet“ on the furnace floor ensures
particularly good combustion of the
binding agents and constant quality of
the sand batches. This means that even
finer grains can be regenerated very
well. In a following unit, the hot sand is
simultaneously cooled and dedusted. In
order to reduce gas consumption, the
thermal energy of the hot sand is partially
recovered during cooling and
returned to the process.
Thermal reclaimed sand
After thermal treatment, the organic
binder shells are nearly completely
burnt. In addition, there is the geometric
change of the individual grains
after the thermal treatment. Above a
temperature of 573 °C, the quartz leap
ensures a reversible change in volume.
Not only residual binders but also corners
and edges flake off the grain. As a
result, thermal reclaimed quartz grains
have a specifically smaller surface area
than many new sands and thus have a
reducing effect on binder consumption.
The thermal reclamation plant leads
to effective waste reduction with moderate
energy consumption and can
therefore be regarded as a contribution
to environmental protection and
resource conservation.
Especially viewed against the background
of economic considerations,
this solution is becoming more and
more interesting for operators. Payback
times of 1.5 to 2.5 years are realistic.
With increasing plant size and sand
throughput, this value decreases
accordingly.
An outlook on future
application possibilities
In addition to the recycling of used
sand, the disposal of filter dusts is also
becoming more and more important in
many companies. The reasons are the
same as for the problem of used sand.
FAT‘s thermal reclamation plant is
also a solution here. Filter dust from
Thermal reclamation plant in France.
no-bake plants can be used as an energy
source for combustion in the furnace.
To analyze the behaviour of the dust
during operation of the reclamation
plant, the FAT test plant was extended
by a dosing unit. A defined amount of
dust was added to the used sand in the
combustion chamber.
Results are promising, because
during the thermal treatment in the
furnace, the loss on ignition of the
dust could be reduced by ~50 % and
the gas consumption could also be
reduced because of the energy of the
residual binder in the dust. Due to the
fine sand content in the dust, which
leaves the plant with the thermal
reclaim, the amount of dust could also
be halved.
Advantage over mechanical
reclamation
The organic load in the resulting filter
dust of the thermal regeneration plant
is as follows: ~1 to 2 % of the sand circulation
volume and therefore explicitly
below the high loaded dust content of
approx. 5 to 15 %, which occurs during
purely mechanical regeneration.
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CASTING PLANT & TECHNOLOGY 1/2019 27