Verfahren zur Herstellung von Tafelglas

摘要

In the production of sheet glass in the form of a layer using the "float" technique the width and thickness of the layer are substantially stabilized at the dimensions attained during contact with side walls of the bath. The apparatus is the same as that disclosed in Specifications 1,019,752 and 1,019,753. A layer of molten glass is delivered from a spout on to a bath of molten tin or tin alloy and is allowed to spread out into wetted contact with diverging side walls 19a, 19b of the bath. Whilst in contact with the side walls 19a, 19b the molten layer passes beneath the front depending wall of the bath roof into tank 18. This is divided into two zones 25c and 28b by a circumferential wall 40 depending from the roof. Inert gas under pressure is fed to each zone between which a pressure differential may be maintained. Non-wetting inserts, e.g. graphite, 21a, 21b are placed at the downstream terminal end of the side walls to facilitate freeing of the molten layer from contact with the side walls at its predetermined width and thickness. The layer then passes along the length of the bath and is cooled progressively so as to be removed unburned. The gaseous pressures above the layer in zones 28c and 28b is adjusted so as to maintain the width and thickness of the layer. In an alternative embodiment the pressure zones are replaced by a bi-level bath, the central bath 214a (Fig. 13) being separated from side baths 214b by upstanding graphite walls 224, 225. The traction on the cold end of the formed sheet may be controlled with the rate of flow on to the bath to control the sheet thickness at, above, or below equilibrium thickness. Various modifications of the divergent side walls are given particularly with reference to Figs. 8 to 11 (not shown) in which the length and shape of the side walls is modified; and the graphite inserts may be omitted. When the glass layer leaves contact with the side walls 19a, 19b its temperature is still above 1500 DEG F. An inert atmosphere is maintained above the molten metal bath. After leaving contact with the side walls the width or thickness of the sheet may be altered slightly, such as by the application of a tractive force or by supporting the central portion at a higher level or applying a greater pressure to that portion than the surrounding portions. The composition of the glass may be, in weight per cent, SiO2, 71.38, Na2O + K2O 13.36, CaO 11.76, MgO 2.54, Na2SO4 0.75, Al2O3 0.15, Fe2O3 0.11, NaCl 0.06.