Temperature Measurements During Chill-Block Melt Spinning

In this work we have used two methods for direct measurement of the cooling rate during chill-block melt spinning. In order to make a comparison of the cooling rates during and just after solidification, the length of the melt puddle was measured and a photo calorimetric technique was used, respectively. The material that was cast in these experiments was Mm(NiCoMnAl)5 which is a suitable alloy for hydrogen storage. The length of the melt puddle is related to the quenching time, as has been proposed by H. Hillmann and H.R. Hiltzinger. In our experiments, several photographs were taken of the melt puddle during casting at different wheel speeds. From the surface velocity, the melt temperature and the solidus temperature the cooling rate during solidification was calculated. Since the metal was incandescent after solidification, the surface temperature of the ribbon could be measured by a photo calorimetric technique, as proposed by A.G. Gillen and B. Cantor. In order to increase the accuracy in the temperature measurement localisation, and thereby obtain a more accurate cooling rate, a slightly modified version of this technique was used. Photographs of the ribbon were taken during casting and these photographs were subsequently digitised. Instead of using a colour transmission densitometer to quantify a particular colour hue at specific positions in the pictures, digital pictures were used, and the digital red (R) and green (G) values were measured in several positions. The digital measurements were converted to temperatures by a comparison with corresponding digitised photographs taken from a specimen at known temperatures. The experimental results showed that both techniques seem to give good and consistent estimates of the cooling rate during chill-block melt spinning.