Measurement of gas evolution from PUNB bonded sand as a function of temperature

Gas evolved from the thermal decomposition of the binder can greatly deteriorate the quality of sand castings. Binder gas models used in casting simulations require knowledge of the binder gas mass and molecular weight evolution, but available data are limited. In the present study, the mass and molecular weight of gas evolved from phenolic urethane no-bake (PUNB) bonded sand are measured as a function of temperature. Thermogravimetric analysis is used to determine the changes in the binder mass with temperature. The binder is found to be fully pyrolyzed at temperatures above 710C (1310F), with its mass reduced by 82%. Up to 100°C/ min (180°F/min), the binder decomposition does not appear to be a strong function of the heating rate. The evolved volume of the binder gas during heating and cooling is measured using a specially designed quartz manometer with a liquid metal as the working fluid. During heating at 2°C/min (3.6°F/min), the binder gas molecular weight is found to decrease in a complex manner from 375 g/mol at 115C (239F) to 33.3 g/mol at 898C (1648F). When the binder pyrolysis is complete above 710C (1310F), the binder gas is incondensable, but continues to decompose to lower molecular weight compounds until at least 1350C (2462F). If the binder is heated to a temperature not exceeding 510C (950F), the binder gas partially condenses during subsequent cooling; this condensation occurs below 165C (329F).