Advantages of non-contact temperature measurement
A pyrometer detects the infrared radiation emitted by an object’s surface and produces a temperature reading. For temperature detection of molten metal, a non-contact measurement technique offers foundries many advantages over an immersion sensor:
- The temperature of molten metal is measured at a crucial point in the casting process: just as it is poured into the mould. If high/low temperature limits are exceeded, the foundry operator can react immediately and stop the casting process. The foundry can precisely monitor pour stream temperatures and provide documented evidence of strict compliance with process parameters. Because a thermocouple is immersed into the molten metal before it is poured, its temperature reading does not truly represent the metal’s actual temperature at the moment the mould is being filled.
- A pyrometer monitors temperatures continously and saves a reading for each individual mould. In contrast, an immersion thermometer can only be used for spot checks. This is usually done one time for each ladle prior to the pouring process.
- Because a pyrometer detects the temperature of the molten stream just as it enters the mould, which means always at the same point in time, this technique provides much higher accuracy and repeatability. When using a thermocouple, the accuracy of the temperature reading will depend on such factors as the precision of the operator, the point of immersion and the immersion depth.
- A pyrometer has no parts subject to wear and tear, therefore a foundry does not incur any operating costs for expendable parts. The immersion method is subject to wear on parts. Thermocouple tips require frequent replacement.
How the measuring system works
The CellaCast system is based on a two-colour (ratio) pyrometer with high optical resolution. A two-colour pyrometer yields highly reliable measurement results, even when there is a great amount of dust or smoke in the pyrometer’s field of view. The rectangular field of view ensures that the pour is captured every time, even when its position fluctuates, thus producing consistently accurate instream temperature data. CellaCast features an intelligent ATD function (automatic temperature detection) which automatically produces a temperature reading for each mould. Thanks to ATD, the pyrometer starts measuring just as the ladle starts pouring. Interferences such as flames or molten metal drip (as opposed to a pour stream) will not impede the measurement or impair the signal. The temperature reading will remain very accurate despite such disturbances. When the measurement process is finished, CellaCast displays the temperature reading for each poured mould. Data is transmitted via analogue output and serial interface. This value can also be viewed at a large external digital display so that the foundry operator can instantly see the temperature reading. As an option, a visual alarm signal can be connected so that temperature limit violations can be seen. The temperature data can be saved at a PC or recorded via a data acquisition system.
Overview of the CellaCast System
Non-contact temperature monitoring system for molten metal