The Flat Glass manufacturing process has three main stages
- Melting – when the raw materials turn to molten glass at a temperature of around 1550°C
- Annealing – where stresses are eliminated from the glass
- Tempering – where glass is heated and quickly cooled so that surface tension is created.
Temperature control is a critical component to each of these processes.
In the melting furnace, raw materials are added to the furnace and heated to about 1550°C / 2800°F. Scum and raw materials that have not yet melted are prevented from exiting the furnace because the exit port is below the level of the melt and the “bridgewall” holds the scum within the furnace.
Infrared thermometers do not measure the temperature of the glass directly because of the scum on the surface. Instead, infrared thermometers are used to measure the refractory temperature – typically at the bridgewall (which is the most critical temperature control point) and next to the burner nozzles (which are protected from overheating by cycling on and off).
Williamson pyrometers are unique in their wavelength selection. Williamson offers the only fiber-optic pyrometers able to view clearly through flames and combustion gasses.
Glass is heated and then cooled very slowly to eliminate stresses. Glass that has not been annealed will break very easily. One or more pyrometers is used to confirm proper annealing temperature distribution throughout the process. For flat glass, as many as 9 or 12 pyrometers may be used. For tumbler, container or pressed and blown glass, only one or two pyrometers may be used, depending upon the configuration of the pieces on the conveyor belt.
The glass is heated and then quickly cooled so that a surface tension is created. This causes the glass to form little pieces when it is broken and is done as a safety measure. The PG wavelength set is recommended for measurements inside the furnace. The PG wavelength set may also be used outside of the furnace; however, the industry tends to use the GL wavelength set. Please note that the Williamson pyrometers have a 60 ms response time which may not be fast enough for some fast-moving tempering processes. If a 10 ms update time is required, then please consider other products.
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