CPT International 02/2019

SIMULATION
Figure 3: Positions of the thermocouples in the real casting trials.
Temperature [°C]
1200
1000
800
600
400
200
Standard deviaon TE1
Standard deviaon TE2
Standard deviaon TE3
Standard deviaon TE4
Standard deviaon TE5
Simulaon TE1
Simulaon TE2
Simulaon TE3
Simulaon TE4
Simulaon TE5
0
350 550 750 950 1150 1350 1550 1750 1950 2150
Time, s
Figure 4: Comparison of measured temperature curves with the simulation results.
Figure 5: Representation of the burning behavior of exothermic feeder sleeves: Left: Start of
the exothermic reaction, Middle: Combustion of the exothermic feeder, Right: ‘Afterglow’ of
the feeder material.
Experimental investigations
GTP Schäfer started by carrying out
measurements of the thermo-physical
properties in order to obtain data on
exothermic feeder materials. Whereby a
sample with a defined energy per time
unit was heated and the material properties
continuously determined. One
difficulty during these measurements
was the high level of dynamism caused
by the exothermic reaction. As soon as
the ignition temperature is reached, the
material burns up autonomously – and
no longer follows the temperature of
the measurement system. So it was only
possible to reliably determine the material
properties in the unburnt state
during these experiments. Therefore
the combustion behavior and material
properties during and after burning
were initially inaccurate or unknown.
So it was necessary to examine the
burning behavior with more precision.
For this purpose, an experimental setup
similar to that in the German Foundrymen’s
Association (VDG) Specification
P81 on the testing of exothermic materials
[2] was selected (Figure 1). Two test
pieces (D = 50 mm, H = 50 mm) were
made for the experiment using exothermic
material, and one was placed on
top of the other. The lower test piece
was ignited and the burning behavior
of the two samples investigated. This
setup allowed good observation and
understanding of the progress of the
combustion process. Then the chronological
and spatial course of the burning
behavior was compared with the simulation
model (Figure 2).
Real casting trials in furan sand
molds were then carried out after the
investigation of the burning behavior
of the test bodies. The effort required
for these experiments turned out to be
considerably greater than anticipated.
But it was shown that the burning
behavior of feeders within sand molds
differs substantially from that in ambient
air. This difference can be explained
by the fact that only a limited amount
of oxygen is available for the exothermic
material within a sand mold. During
the casting experiments, exothermic
feeder sleeve in a furan sand mold were
filled with melt and the temperature
curves were determined. For this purpose,
separate thermocouples were
positioned in the exothermic material,
the molding sand, and the melt in order
to determine the temperature changes.
One thermocouple was placed within
the melt in the feeder. Two more were
located in the sleeve, and two in the
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