In castings, the temperature of liquid melts is typically measured by immersion thermometers. The high consumption costs of the thermocouples are problematic. As an alternative, special short-wave measuring spectral pyrometers have been offered as portable devices for a long time. A special feature and advantage, compared to standard pyrometers, is the lower sensitivity to interference, based on the degree of emission, in other words the radiation properties of the surface for these devices. The actual measuring problem of the non-contact temperature measurement, however, is the slag and oxide layer on the surface of the melt. Clean melt has an emissivity of approx. 35-45 %.
Whereas the emissivity of the oxide layer with approx. 80 % is significantly higher. With reference to a temperature of e.g. 1350 °C of the melt and with the same parameter setting, the device displays a temperature of approx. 1460 °C. The operating instruction that the oxide and slag layer has to be removed for measurement in the melting furnace or transport ladle is not really practical, since the layer is formed again within milliseconds. When measuring on a pour stream, the removal of the oxide is not possible at all. This leads to strongly varying measuring results. This probably is the reason why the alleged special portable pyrometers for liquid metals could not be established on the market so far.
With the CellaCast PT 183, KELLER ITS (Infrared Thermometer Solutions) has developed a new pyrometric measuring method, which is able to distinguish between a clean and oxide-bearing surface.This CSD (Clean Surface Detection) function detects the temperature of the clean melt. The only precondition is, that a clean melt is seen from the device at least for a few milliseconds during the measurement. In practice this is ensured by a flowing melt during casting into a transport ladle or into the mold as well as into the runner of a melting or cupola furnace.
However, a non-contact temperature measurement on the smooth surface in the holding furnace or ladle doesn’t submit reliable measurements, because of the permanent oxide layer.
Conclusion: With state-of-the art pyrometers, in contrast to immersion thermometers, the actual process-relevant temperature of the metal can be controlled safely, wear-free and from a considerable distance, when filling the molds. The temperature in the melting furnace or ladle can be determined with an immersion thermometer only before casting. Though the melt loses about 10 °C/ min of temperature in the meantime. The proof required by the automobile industry, with which temperature each individual component was cast, is therefore only possible with a pyrometer.
The portable device CellaCast PT 183 is equipped with an ATD (Automatic Temperature Detection) function. The operator only needs to aim at the pour stream with the device and the measurement starts automatically. An acoustic alarm signals the end of the measurement. Depending on the width of the pouring stream, a traffic light indicator indicates the maximum measuring distance in the through-the-lens sighting.
Another technological innovation of CellaCast is the rectangular measurement area. Capturing the molten pour within the rectangular area greatly facilitates targeting from a distance. This also ensures that the molten stream is captured every time even when its position varies, such as when the angle of the pour changes.
The dual wavelength measurement method in the CellaCast yields accurate readings even in the extreme environmental conditions due to by strong dust, steam and smoke in the field of view in foundries or steel plants.