Effect of the Temperature of Firing the Grog and the Green Body on the Physical Properties of the Pot for Melting Optical Glasses : Studies on the Pot used for Melting Optical Glasses, V

The author's papers (J. Ceram. Assn. Japan, 63 [715] 566 (1955); J. Ceram. Assn. Japan, 64 [723] 110 (1956); 65 [733] 45 (1957); 65 [737] 104 (1957)) concerned the effects of the body composition etc. on the physical properties of the pot for melting optical glass which, however, did not cover the problems of the effects of firing temperatures of grog and green body.In order to summarize and reexamine the data a series of investigations on the spalling and load deformation properties of the pot materials containing the grog fired at the temperatures 1280°-1525°C and matured at the temperatures ranging from 1290° to 1545°C, have been carried out.The important results are as follows:(a) As far as the present test is concerned the strength of clay-grog bodies showed an increase with increasing firing temperature, while the elevation of the firing temperature of grog did not necessary show the same effect.(b) The total linear shrinkage from greeen to fired specimen increased with increasing firing temperature, but the same result could not always be expected with the grog.(c) The increase of bulk density with the firing temperature was observed with the body, but the same trend did not hold with the grog.(d) The strength of the body decreased with raising quenching temperature.(e) The quenched specimen subjected to the firing at higher temperature proved to be stronger so long as the quenching temperature was low, but when it was raised the difference became neglible.(f) The resistance to spalling decreased with the raise of quenching temperature.(g) Irrespective of the firing temperature of grog the body fired at higher temperature showed positively the poorer spalling resistance when it was quenched from higher temperature, but for lower quenching temperature this relation did not hold so that it is highly probable that the specimen fired at some intermediate temperature would show the lowest spalling resistance.(h) In the specimen fired at a higher temperature cracks in the intermediate layer between the grog and the bonding clay were observed, while it was impossible to locate such cracks in the body fired at lower temperature.(i) By quenching, cracks came into existence in the intermediate layer, and also the grow up of the existing cracks was observed. This phenomenon was most remarkable with the bodies composed of the grogs fired at higher temperature, as long as the green was fired at comparatively lower temperature.(j) The adhesion between the grog and the bonding clay seems to play the most important roll to the resistance to spalling of fire-clay pots.(k) The firing temperature of the body was found to be the most influential, whereas the influence of the firing temperature of grog seemed to be not so remarkable as the former.(l) Comparing the specimens prepared by high temperature with those by low temperature firing a marked difference was seen in the initial stage of load test, the latter being deformed much slower than the former. And up to 20% deformation, these values came closer more and more with the elevation of temperature.(m) It was found thatthe body containing the grog fired at higher temperatures did not always give a higher softening temperature.