VISCOSITY OF GLASS BETWEEN THE STRAIN POINT AND MELTING TEMPERATURE ¹

Abstract

ABSTRACT An apparatus is described which employs the elongation of a glass fiber under load for the determination of annealing and strain points. The same apparatus is also used by varying the suspended load for the determination of the temperature‐viscosity curve between the annealing range and the softening point of the glass. A description is given of measurements made in this manner on a series of three simple soda‐lime‐silica glasses at theses low temperatures, as well as measurements made in a rotating cylinder viscomcter between the softening point and the melting temperature. Curves are shown for the viscosities of the three glasses in the two temperature ranges and a complete viscosity curve from 500 to 1400°C is given for one of them. It is found that the two methods yield results that fit a smooth curve between these limits of temperature.