Heat-strengthened and thermally tempered low emissivity glasses are commonly used architecturally where visual perfection is essential. To create visually perfect glass panes or lites, physical distortion must be avoided and uniform surface temperature profile achieved across the whole lite before entry to the cooling section.
AMETEK Land specialises in infrared measurement for challenging industrial process control applications. Glass measurement solutions normally rely on measurements at 5µm, where the glass becomes opaque with emissivity typically 0.97. However modern low emissivity coatings reduce that emissivity to as little as 0.05. Incorrect estimation of emissivity leads to huge errors in temperature reading.
We propose a solution that uses a 5µm line scanner measuring the low emissivity surface through the narrow gap between the furnace and air blowers, aligned with a 5µm spot thermometer taking measurements of the underside of the glass. The spot thermometer signal is used to compensate for the low emissivity of the upper surface of the glass. A true temperature thermal map of the entire product surface with sub-spot resolution is created in software from successive scan data, which can be used to adjust furnace control parameters and produce visually perfect glass.