Abstract
Considering that the appearance of the post-sintering stress localized in the surface layer of the sinter depends greatly on the methods of cooling, investigations were made on thermal changes in the sinter at cooling and thermal expansion curves by experiments with varying conditions:(a)cooling in the furnace, (b)cooling in the cup, (c)natural air cooling and(d)forced air cooling.Also, quantitative analysis of the surface stress induced by them was made, with results as follows:1)In the results of investigation on thermal changes, there was hardly any noticeable difference in the rates of depression between the interior and the surface layer of the sample by cooling in the furnace, a slight difference was observed in the cases by cooling in the cup and natural air cooling, and in the cases by forced air cooling, there was a great difference between the two parts, the thermal difference surpassing 100℃.2)Average coefficients of thermal expansion at 200〜720℃ showed a gradual diminution in the following order cooling in the furnace 1.21%, natural air cooling 1.08%, cooling in the cup 1.05% and forced air cooling 0.95%.3)The velocity of thermal depression and the thermal difference between the interior and the surface layer of the sample gave influence on the generation of stress.4)Whereas the surface stress measurement in the cases of forced air cooling and natural air cooling resulted in 8.5kg/mm2 and 2.5kg/mm2, no value was obtained from the cases by cooling in the cup and cooling in the furnace probably because of the generation of extremely little stress.
