Strong composite glasses

Abstract Glass strength can be enhanced by several methods including thermal tempering and ion exchange which put the surface in compression. Overlaying a higher expansion core with a lower expansion surface cladding to achieve a compressive surface is also known. A new modification of the overlay technique involves pairs of glasses which are melted separately and delivered to a single compound orifice that overlays one glass on the other as they leave the orifice. This is in contrast to most of the previous overlay methods in that the surfaces of the two glasses which form the interface are fluid and flaw-free. Physical property and composition constraints are presented for glasses which achieve a modulus of rupture as high as 42 kg/mm 2 . Stress relationships and profiles are also shown.