This page contains a Flash digital edition of a book.
percentage (8% of binder mass), and additives (BIO, 3% of total mass) were selected based on feedback from seven steel foundries.

The sand and BIO components were measured using an Ohaus model PA4101 precision balance, and the binder com- ponents were measured using a Denver Instruments model S-403 precision balance. The specimens were prepared by first mixing the BIO into the sand with a KitchenAid®


mixer to ensure uniform particulate distribution. Then, the binder was added according to a procedure recommended by the binder manufacturer. Part 1 (Pep Set® 3 (Pep Set®

X1000) and Part 3500) were combined in a paper cup and sub-

sequently added to the particulate mixture. The batch was mixed for 45 seconds, and then vigorously tossed to bring the coated mixture from the bottom of the mixing bowl to the top. The batch was mixed for another 45 seconds and tossed again. After the second toss, Part 2 (Pep Set®


was added to the batch and mixed for another 45 seconds, which was followed by a third and final toss. The batch was mixed for a final 45 seconds before dumping it into a box with rectangular patterns. The sand-binder mixture was rammed by hand into each pattern, while making sure the specimens were of uniform density, and allowed to set in the box before stripping. The specimens were stripped when the compacted mixture withstood 20 psi of compressive stress without visible deformation.17

The pattern box was capable

of making six bonded sand blocks, each with a 2.54 cm (1 in) square cross-section and a 22.88 cm (9 in) length. The specimens were immediately sealed in plastic bags to mini- mize evaporation of the solvents, and the specimens were allowed to cure for at least 24 hours before testing.

thermogravimetric analysis Gas Measurement apparatus

TGA was performed on the PUNB bonded sand using a PerkinElmer model Pyris 1 thermogravimetric analyzer. The PUNB bonded sand blocks were cut down into smaller piec- es, which were then shaped into small cylinders using a razor blade. The PUNB bonded sand samples for TGA had a mass of approximately 55 mg, and the samples were about 0.45 cm (0.177 in) in diameter and 0.25 cm (0.0984 in) in height. The system was purged with argon gas at a flow rate of 25 cm3 (1.526 in3

/min and 10 cm3

/min), with flow rates of 15 cm3 /min (0.610 in3

/min (0.915 in3 /min) /min) to the balance and furnace

sheath, respectively. The total flow rate was selected in order to minimize non-isothermality in the samples during testing. Argon gas was used in the TGA in order to ensure binder py- rolysis, rather than combustion. The argon gas flow sweeps away the gases evolved from the binder, which can affect the subsequent decomposition of the binder. The magnitude of this effect is not known and requires further investigation where TGA is performed under atmospheres closer in compo- sition to the evolved binder gas.

The samples were heated from room temperature to 1000C (1832F) at rates of 2°C/min (3.6°F/min), 10°C/min (18°F/


A schematic of the gas measurement apparatus is shown in Figure 1. The primary component is the gas evolution device (GED), made by fusing quartz cylinders and discs together. Cylinder 1 was sealed at the top and bottom and had two quartz thermocouple wells attached to the top surface. One thermocouple well extended up from the top of cylinder 1, while the other extended 2 cm (0.787 in) from the top sur- face down into the interior of cylinder 1. Cylinder 1 had an internal diameter of 4 cm (1.575 in) and a height of 3 cm (1.181 in). Cylinder 2 was sealed at the bottom and had an internal diameter of 1.3 cm (0.512 in) and a height of 22 cm (8.661 in). Cylinders 1 and 2 were joined by a third quartz tube, creating a container with a “J-shaped” cavity that acted as a manometer.

A sample of interest was loaded into cylinder 1 of the GED, and the GED was filled with a near-eutectic alloy of gallium (75% by mass) and indium (25% by mass) to a specified ini- tial height in cylinder 2. Specific filling procedures will be described later. The metal alloy is liquid at room temperature and has low vapor pressures at high temperatures. A dis-

International Journal of Metalcasting/Spring 2012 Eqn. 1

Where: ms is the sample mass measured by the TGA ma- chine at both the initial temperature T0

ature T, and varying temper- is the initial sample mass measured separately

with an analytical balance, and χ is the binder content of the bonded sand sample based on total weight percentage. The fraction of original binder mass remaining in bonded sand during heating was interpolated at intervals of 0.1°C (0.18°F) from the corresponding fractions obtained from the TGA measurements. This allowed the measurements of the binder gas mass evolution to be matched with the binder gas volume and pressure measurements (obtained from later gas evolution experiments) at discrete temperature points.

min), and 100°C/min (180°F/min). The heating rates for TGA were selected to reflect those experienced in molds and cores during casting processes. The high TGA heating rate of 100°C/min (180°F/min) simulated mold heating rates at a close distance [i.e., about 1.3 cm (0.5 in) for steel casting] from the mold-metal interface, and the 10°C/min (18°F/min) and 2°C/min (3.6°F/min) TGA heating rates simulated mold heating rates at distances further away from the mold-metal interface. Multiple tests were performed at each heating rate to verify repeatability of the experiments. The TGA machine was allowed to self-clean periodically between tests, and the sample pans were cleaned according to the recommenda- tions of the manufacturer.

The fraction of original binder mass remaining, f, in a PUNB bonded sand sample as a function of temperature during heating is calculated from

Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91