The chemical binders used to make sand molds and cores thermally decompose and release gas when subjected to the high temperature conditions in sand casting processes. Computational models that predict the evolution of the binder gas are being introduced into casting simulations in order to better predict and eliminate gas defects in metal castings. These models require knowledge of the evolved binder gas mass and molecular weight as a function of temperature, but available gas evolution data are limited. In the present study, the mass and molecular weight of gas evolved from PUNB bonded sand are measured as a function of temperature for use with binder gas models. Thermogravimetric analysis of bonded sand is employed to measure the binder gas mass evolution as a function of temperature for heating rates experienced in molds and cores during casting. The volume and pressure of gas evolved from bonded sand are measured as a function of temperature in a specially designed quartz manometer during heating and cooling in a furnace. The results from these experiments are combined with the ideal gas law to determine the binder gas molecular weight as a function of temperature. Thermogravimetric analysis reveals that the PUNB binder significantly decomposes when heated to elevated temperatures, and the PUNB binder gas mass evolution is not strongly influenced by heating rate. During heating of PUNB bonded sand at a rate of 2°C/min, the binder gas molecular weight rapidly decreases from 375 g/mol at 115°C to 99.8 g/mol at 200°C. The molecular weight is relatively constant until 270°C, after which it decreases to 47.7 g/mol at 550°C. The molecular weight then steeply decreases to 30.3 g/mol at 585°C and then steeply increases to 47.2 g/mol at 630°C, where it remains constant until 750°C. Above 750°C, the binder gas molecular weight gradually decreases to 33.3 g/mol at 898°C. The present measurements are consistent with the molecular weights calculated using the binder gas composition data from previous studies. The binder gas is composed of incondensable gases above 709°C, and the binder gas partially condenses during cooling at 165°C if the bonded sand is previously heated below 507°C.

Foundries today use temporary molds made from silica sand with a resin bonding agent to hold a form until the metal is poured. With the aid of computer simulations, the molds are designed to produce good castings with minimal pattern iterations by calculating cooling and porosity. Stress analysis simulations are being developed using the current software, but the known mechanical properties for the sand mold are minimal and incomplete. This study measures the elastic modulus of bonded sand as a function of temperature to obtain baseline data for the model. Following ASTM standards, a three point bend test is used to measure the elastic modulus of chemically bonded sand as a function of temperature to better understand the complex nature of the mold as it undergoes heating and cooling. Multiple measurements of the elastic modulus of PUNB bonded silica sand are performed from room temperature to 500°C in a nitrogen atmosphere to capture the changes in the elastic modulus under heating. It is found that for an intermediate heating rate of 8°C/min, the elastic modulus decreases steeply from a room temperature value of about 3,600 MPa to 600 MPa at 125°C. Between 125°C and 250°C, the elastic modulus is relatively constant. Above 250°C, it increases to 1,200 MPa at 280°C and then decreases again to 800 MPa at 350°C. Above 350°C, the elastic modulus increases linearly with temperature until it reaches 2,200 MPa at 500°C. At approximately 500°C, the strength of the bonded sand vanishes. At a given temperature above 125°C, the elastic modulus can vary by more than a factor of two depending on the heating rate. Furthermore, the elastic modulus agrees with previous steady state temperature measurement literature when specimens are held at a constant temperature until the elastic modulus reach steady. It is also found that the addition of black iron oxide has no effect on the elastic modulus, whereas solvent removal before a test increases the stiffness of the bonded sand at temperatures below 150°C.