Many firing cycles were examined: these comprised two with multiple dwells during ramping to the burnout temperature, five with one dwell to dry and dewax the flasks before ramping to the burnout temperature, and two with only a burnout dwell. A 3.8KW electric furnace was used to fire six flasks using each firing cycle. Thermocouples were embedded in some flasks and positioned in the furnace to record the air and investment temperatures during firing. The optimum firing cycles were ones with a single drying/dewaxing dwell between 190° and 270°C. Fifteen flasks were fired using three of the cycles. In this case, the cycle with a 270°C drying/dewaxing dwell was the only one that permitted complete burnout of all the flasks.

Author: Dr. Ian McKeer