General Methods of Determining the Thermal Endurance of Glass

JSGT 1936 V20 T475-T497

Experiments on the sudden cooling of glass rods indicated an increased thermal endurance with decreasing diameter of the rods. The difference of temperature at which the first cracks appear is denoted as “technical thermal endurance” and the temperature difference at which the first transverse cracks occur as “true thermal endurance.” The latter is slightly higher and shows a narrower spread of the results. When annealed rods were tested there was not a great deal of difference whether the ends had been fire polished or not. For unannealed rods the “thermal endurance” is about 40° higher, with a much greater dispersion. For ordinary industrial glasses the coefficient of expansion gives a reliable indication of the value of thermal endurance. A method of determining the “thermal endurance” is described, in which the temperature difference is not increased, but the tests repeated until fracture occurs.

H. Schönborn