Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 94

A process similar to that of Fourcault was developed and introduced by the Pittsburg Plate Glass Company in 1926. In this Pittsburg Pennvernon process, the molten glass was not drawn through a débiteuse but upward from the free surface right above a drawbar, which was a long and thin refractory part immersed below the glass surface. The ribbon width was kept constant because the glass was cooled by edge folks and coolers. After being annealed and cooled in the drawing tower, the glass ribbon was cut off at the top of the tower (Figure 4). The drawbar served to anchor the drawing point and to ensure uniform temperature and glass flow rate across its width. In addition, ell blocks served to homogenize the drawing temperature by keeping the glass melt covered. The operation cycle was much longer than that of the Fourcault process with a better surface quality and without devitrification complications. Typically, the thickness range was 1–8 mm with a width of up to 3.2 m, but the disadvantages were thickness variations resulting from temperature fluctuations and inhomogeneities in chemical composition caused by drawing of the glass directly from its surface [3–6].