熱放射を利用した溶射粒子の温度と速度の測定

Abstract

Methods to measure the surface temperature and the velocity of thermally sprayed particles were developed and applied to plasma-sprayed Mo, Ni-Cr alloy, and alumina particles in the air.In the temperature measurement, radiation from particles within a cylindrical measurement volume is measured and its spectrum is analyzed by a monochromator. Then the spectrum is compared with the spectra of blackbody radiation to determine the surface temperature of the particles through the least squares method.Spatial filtering technique using a mask with four thin parallel slits was adopted in the velocity measurement. When a single particle travels in front of the plates, radiation passing through the spacings between the plates is detected by a photo-multiplier, which gives a signal with four peaks. Then the velocity v of the particle is given by υ=d/t, where d is the distance between the neighboring slits and t the period between the peaks. It was also found that the mean velocity of a high-density particle stream can be determined by analyzing the power spectrum of the signal by a method such as FFT.As the results of those measurements, the change in the temperature and the velocity of sprayed particles with the distance from the exit of a plasma-torch was obtained. Where as the metal powders exhibited similar history of cooling and deceleration with the distance, alumina particles were found to be accelerated to a much higher velocity close to 300 m/s but decelerated at a much faster rate. The temperature of alumina particles could be measured for only a limited region due to the weak radiation. Also the effects of particle size on the distribution of both the temperature and the velocity of sprayed Mo particles were examined.