Industries | Measuring Temperatures on Metal
Surveillance and Security
In the production as well as in the processing of metal, the monitoring of the temperature with non-contact sensors does not only help in the surveillance and optimization of the procedure, at temperatures of up to 3,000 °C, it also improves workplace security.
Continous temperature monitoring is a key factor in the rolling mill, within the induction hardening or die forming process. For these purposes, Optris has developed infrared measurement devices that are especially suited for high temperatures and rough environment of the metal industry, since non-contact temperature measurement on metal is not quite as easy, as our technicle article Non-contact temperature measurement on metal surfaces via infrared technology demonstrates.
Emissivity and Temperature Measurement of Metals
Emissivity is a major factor in the accurate measurement of temperatures. It must be adjusted according to the application.
Emissivity theoretically depends on the material, its surface quality, the temperature, the wavelength, the measuring angle and, in some cases, even the applied measuring configu-ration. Many non-metallic surfaces to be measured have a constant emissivity with regard to wavelength but emit less radiation than black bodies. They are called gray bodies.
Objects whose emissivity depends, amongst other things, on temperature and wavelength, e.g. metallic surfaces, are called selective radiators.
The Optimal Wave Range
There are several important reasons why the measurement of metals should, if possible, always be done in the short-wave range. Firstly, at high temperatures and short measuring wavelengths (2.3 μm; 1.6 μm; 1.0 μm), metal surfaces do not just have the highest radiation intensity, they also have the highest emissivity.
Secondly, in this range they equal the emissivity of metal oxides so that temperature deviations caused by changing emissivities are minimized.
Temperature Monitoring in the Casting Process
Thanks to improved efficiency the demands on continuous casting lines are also increasing. This necessitates extensive process monitoring measures, especially where temperature measurement is concerned: the technology has become cheaper with increased levels of precision. For the operators the investment is worthwhile, as costly aborted pours can be avoided at the point of origin.
Preventing Aborted Pours Continuous Casting Plants
Within induction hardening processes, the adherence to an optimum temperature-time profile is essential in order to achieve the desired microstructure of the metal. The process temperature lies between 700 and 1100°C and it is recommended to use an online pyrometer for permanent temperature monitoring and/or a handheld for sporadic measurements.
Steel needs to be transported in various vessels including torpedo wagons, slag ladle cars and smelting ladles. Even if the wagons and ladles are equipped with fireproof materials, breaches may result due to the 1500 °C hot steel. This presents a danger to both the stock and personnel which could result in millions of euro in damages.
To prevent any such breaches the vessels are monitored with thermal imaging cameras and protected via recognition of temperature differences.
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