Abstract
The accurate measurement of temperature is very important in the material processing. In measuring temperature, it is available to use the radiation thermometer that requires no physical contact with an object, but it is reported that the IR (infrared) radiation thermometer has led to noticeable error in measuring temperature of molten pool where the emissivity is variable.
According to the Planck's law of radiation, it is evident that the luminance temperature (measured by radiation thermometry) approaches the true temperature of an object, when the measuring wavelength is shorter than IR. In the present paper, the molten pool temperature measurement by UV thermal radiation has been discussed. In the experiment, stainless steel (SUS304) and mild steel have been melted with GTA (gas tungsten arc) or laser beam, and the temperature distribution of molten pools has been measured with UV sensor (CCD camera, image intensifier and interference filter).
As a result, the melting point of metals has been measured with a high accuracy by UV sensor, without correcting the emissivity. The maximum temperature in the molten pool melted with GTA has been 90 K-130 K higher than the melting point, but the maximum temperature in the molten pool melted with laser beam has been much higher than the melting point, when the defocal distance is shorter.
