Infrared Thermometry and Its Applications in the Glass Industry
In the production process of the glass industry, temperature measurement and control is one of the very important and necessary means. Infrared temperature measurement is highly valued due to its simple operation, fast response speed, no aging, small drift, flexible configuration, and no pollution of the glass solution.
In the glass industry, it is necessary to measure the temperature of transparent and opaque objects. Opaque objects include molds, domes, and sidewalls of glass melting furnaces. As a non-contact temperature measurement object, glass is a transparent visible substance with a spectrum in the near-infrared range. Its emissivity is related to wavelength and glass thickness. When the spectral range is between 5 and 8 μ m, its emissivity * is high, so the temperature of the glass can be reliably measured in this range. The measured value is consistent with the surface temperature of the glass, independent of the thickness of the glass, and within this range, there is basically no radiation present. In order to avoid measurement being affected by the surrounding air, the thermometer only uses a very narrow infrared spectral band. High quality thermometers only operate within the spectral range of this so-called environmental window, as there is no absorption of infrared radiation due to air humidity or carbon oxides, thus avoiding temperature measurement errors caused by changes in air humidity or measurement distance. Narrowband range of 5 (approximately 5 μ m) is used to measure surface temperature.
Infrared thermometers generally operate within a spectral range of 5.14 μ m, as the hot exhaust gas from the burning flame in this area does not affect the measured values. For other application areas, it is necessary to measure the temperature inside the glass, as the glass layer near the surface is greatly affected by convection. What needs to be measured here is the melted glass, which requires the use of a thermometer in the near-infrared range. Because the penetration depth achieved at different wavelengths also varies, the choice of thermometer depends on the thickness of the glass layer. Non contact temperature measurement technology for glass melting furnaces, tin baths, and annealing kilns is increasingly replacing traditional thermocouple temperature measurement in glass melting furnaces.
Compared with thermometers, thermocouples quickly age and drift under high operating temperatures and corrosive environmental conditions. In order to protect thermocouples, platinum metal is needed as a protective shell in some places, which increases the cost significantly. Specially designed for this field, it can work even at an ambient temperature of 250 ℃ without the need for a cooling system. By using a fiber optic pyrometer, installation and operating costs can be significantly reduced. The fiber optic can be protected by a sturdy stainless steel casing and can reach a length of up to 30 meters. The required installation accessories include installation brackets, air cleaners, and sight pipes (which can be used up to 1200 ℃).
