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placement boat, which was a quartz tube with the bottom end sealed, was inserted into cylinder 2 such that the boat rested on top of the liquid metal. The displacement boat diameter was 1.15 cm (0.453 in), which allowed for smooth vertical translation of the boat in cylinder 2. The boat’s bottom surface was flat on the exterior and spherical on the interior.


The filled GED was placed on top of a square quartz plate, with 10 cm (3.937 in) sides and 0.3 cm (0.118 in) thickness, inside a Neytech model 85P radiative furnace capable of reaching 1100C (2012F). Three specially made ceramic-in- sulated Type K thermocouples were used to measure the fur- nace temperature (the bead touched the interior of a protec- tive quartz sheath), the glass temperature at the top surface of cylinder 1 (the bead touched the bottom of the glass well), and the interior temperature of the liquid metal in cylinder 1 (the bead touched the bottom of the metal well). A displace- ment probe was threaded through a small hole in a stabilizer plate (attached to the furnace) and then lowered down to rest on the interior spherical surface of the displacement boat. The displacement probe was a thin quartz rod attached to a thin 2.5 cm (0.984 in) square quartz plate that was covered with black spray paint on the top surface. Argon was supplied to cylinder 2 at a rate of 200 cm3 min (12.205 in3


/ /min) in order to prevent the liquid metal from oxidizing during the experiments.


A Micro-Epsilon model optoNCDT 1400 laser optical displacement sensor was mounted to a support rig above the furnace, powered by a Top- ward model 3306D DC power supply, and care- fully calibrated to measure the vertical position of the displacement probe’s square plate. A square steel tube was placed around the probe to reduce displacement measurement noise caused by dis- turbances from the surroundings. A fan forced air over the furnace to keep the laser sensor cool dur- ing tests, and the temperature near the laser sensor was monitored with a fourth Type K thermocouple.


The experimental data was collected using an IO- tech model 3005 Personal DAQ system connected to a laptop via USB. DASYLab®


software28 was


used to control the data acquisition system. Sam- pling was performed at a frequency of 10 Hz for all measurements, and this raw data was averaged and recorded at a frequency of 2 Hz.


In a typical experiment, the initial height of the probe was measured by the laser sensor for five minutes prior to the start of the test. The furnace was heated at a constant rate and the contents of the GED expanded. This caused the metal height in cylinder 2 to rise. The metal displacement moved the position of the displacement probe, and the probe’s vertical translation was detected by the laser sensor. Thus, the total expansion of the


International Journal of Metalcasting/Spring 2012


GED’s contents was measured as a function of temperature. Tests were monitored to ensure that the liquid metal did not overflow in cylinder 2. Cooling data were collected for some tests, and cooling was performed by turning the furnace off and allowing the GED to naturally cool to room tempera- ture. After testing, the GED was removed from the furnace and the GED’s contents were emptied. The liquid metal and GED were cleaned using a solution of low molarity hydro- chloric acid, and any remaining particulate matter was re- moved from the liquid metal. The GED was then washed with acetone, dried, and heated in the furnace to volatize any residual organic matter.


Metal-only expansion tests


It was necessary to determine the expansion behavior of the liquid metal as a function of temperature. The GED was first purged with argon at a rate of 400 cm3


/min (24.410 in3 /min)


for ten minutes prior to filling. The argon flowed into cylin- der 1 of the GED through a flexible plastic tube. The argon tube was then positioned in cylinder 2, and argon flowed into cylinder 2 throughout the remainder of the filling process.


Figure 1. Schematic of gas measurement apparatus and important geometric quantities.


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