Glass – Float Glass

Topics Covered

Background

Float glass is manufactured using a melt process whereby recycled glass, silica sand, lime, potash and soda are melted in a furnace and floated onto a bed of molten tin. The molten mass solidifies slowly while flowing over the bed of molten tin, after which it is annealed to remove stresses induced during the cooling process. Annealing also allows the glass to reach a more stable state resulting in a higher density and higher refractive index.

Tinted float glasses are made by adding colouring agents during the melt process. Common colours include grey, green, bronze and blue. While tinting may provide aesthetic alternatives to clear glass, tinted glasses also provide materials with different properties including heat and light transmission (and/or reflectance), ultraviolet transmission and insulation properties.

Reflective glasses are also available for applications where light transmittance is an important design factor. These glasses have a metallic coating applied during manufacture

Typical thicknesses range from 2mm to 19mm for commercial applications.

Key Properties

§ High degree of light transmission

§ Ability to be produced in a range of colours

§ Ability to be produced in a range of opacities

§ Good chmical inertness

§ Attacked by hydrofluoric (HF) acid

Applications

Building industry

Float glass is used for smaller windows in domestic housing. Larger windows are made from toughened glasses. Glass is used for windows for aesthetic and functional reasons, allowing the occupants to see out and at the same time allowing light in.

Commercial glazing

Float glass is becoming more and more popular in commercial applications as it allows structures to be constructed that give the impression of being outside with the benefits of being inside protected from the elements (with the exception of the sun). Glass is also playing an increasing role in buildings where it provides an attractive and easy to maintain exterior surface. It should be noted that most glass used for this application is subject to a post heat treatment toughening process before use.

In this application several design factors are involved apart from aesthetics. Factors such as light and heat transmittance can play a big role in glass selection as they will influence the amount of heating and cooling that will be required inside a building according to the differences in seasons and climates.

Displays

Based on its transparency, hardness and ease of cleaning, glass is often used for display cases in retail outlets and countertops. However, many of these applications are being superseded by toughened glass due to its added strength.