Producing thin glass by thermal polishing on molten metal (survey)

Various patented methods for producing sheet glass by thermal polishing on molten metals are reviewed. Tin, tin- copper alloys, or other metals with melting points below the softening point of glass can be used. Research by Pilkington Brothers led to the first commercial line for making polished sheet glass by the float method in 1957. High-speed float glass drawing is necessary for producing thin sheet; however, the strip quality deteriorates as the pulling speed is increased, particularly on the lower surface, due to forced convection in the tin. Temperature gradients across the bath and rapid reverse flows of chilled tin adversely affect the glass quality. Barriers are traditionally used to deal with these effects, and the main types are considered in more detail. Optimisation of glass quality involves joint consideration of the thermal and hydrodynamic aspects by means of numerical models.