Fabrication of a Low-Cost Lab-Scale Furnace for Glass Chemical Tempering Using Molten KNO₃ Salt Bath

In this study, a low-cost lab-scale furnace was fabricated for chemical glass tempering such as soda-lime-silica glasses, through a molten KNO₃ salt bath. It was constructed from stainless-steel casing, refractory firebricks, ceramic insulation, and the resistance heating elements designed according to International Electrical Engineering (IEE) standards. A K-type thermocouple was used in conjunction with a PID controller for accurate temperature monitoring and control. The 3D model of the furnace was designed to optimize the furnace chamber, heating element arrangement, and thermal insulation to increase temperature uniformity and decrease heat loss. The total cost of the furnace, including mechanical system installation and the control system integration was fabricated to be about USD 1,881. The pre-heat chamber temperature can be increased from 30°C to 300°C in 35 minutes using 1.2 kWh of electricity. In contrast, the temperature setpoint of main heating chamber can be raised to 600°C using an energy consumption of 55.1 kWh in less than six hours. Results indicated that a new fabricated furnace could increase compressive stress of soda-lime-silica glasses (amount: 12 glasses, size: 300 mm × 150 mm × t: 5.6 mm) from 90 to 450 MPa within 12 hours of heating time. This fabricated furnace is a reliable and inexpensive for lab-scale studies and for further research on glass strengthening processes.